Nrdc v. Winter ( 2008 )


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  •                                                Volume 1 of 2
    FOR PUBLICATION
    UNITED STATES COURT OF APPEALS
    FOR THE NINTH CIRCUIT
    NATURAL RESOURCES DEFENSE               
    COUNCIL, INC.; THE INTERNATIONAL
    FUND FOR ANIMAL WELFARE;
    CETACEAN SOCIETY INTERNATIONAL;
    LEAGUE FOR COASTAL PROTECTION;
    OCEAN FUTURES SOCIETY; JEAN-
    MICHEL COUSTEAU,
    Plaintiffs-Appellees,
    CALIFORNIA COASTAL COMMISSION,
    Intervenor-Appellee,
    v.                          No. 08-55054
    DONALD C. WINTER, Secretary of
    the Navy; UNITED STATES                        D.C. No.
    CV-07-00335-FMC
    DEPARTMENT OF THE NAVY; CARLOS
    M. GUTIERREZ, Secretary of the                 OPINION
    Department of Commerce;
    NATIONAL MARINE FISHERIES
    SERVICES; WILLIAM HOGARTH,
    Assistant Administrator for
    Fisheries of the National
    Oceanographic and Atmospheric
    Administration; CONRAD C.
    LAUTENBACHER, JR., Administrator
    of the National Oceanographic and
    Atmospheric Administration,
    Defendants-Appellants.
    
    Appeal from the United States District Court
    for the Central District of California
    Florence Marie Cooper, District Judge, Presiding
    2079
    2080                   NRDC v. WINTER
    Argued and Submitted
    February 27, 2008—Pasadena, California
    Filed February 29, 2008
    Before: Betty B. Fletcher, Dorothy W. Nelson, and
    Stephen Reinhardt, Circuit Judges.
    Opinion by Judge B. Fletcher
    2084                  NRDC v. WINTER
    COUNSEL
    Ronald J. Tenpas (argued), Acting Assistant Attorney Gen-
    eral; Michael R. Eitel, Luther L. Hajek, and Allen M. Bra-
    bender, Appellate Section, U.S. Department of Justice,
    Environment & Natural Resources Division, Washington,
    D.C.; Craig D. Jensen and J. Page Turney, Office of General
    Counsel, Department of the Navy, for the federal defendants-
    appellants.
    Joel R. Reynolds, Cara A. Horowitz, Stephen Zak Smith, Nat-
    ural Resources Defense Council, Inc., Santa Monica, Califor-
    nia; Richard B. Kendall (argued), Gregory A. Fayer, and Josh
    B. Gordon, Irell and Manella LLP, Los Angeles, California,
    for the plaintiffs-appellees.
    Edmund G. Brown, Jr., Janet Gaard, J. Matthew Rodriguez,
    Jamee Jordan Patterson (argued), Office of the Attorney Gen-
    NRDC v. WINTER                             2085
    eral of California, for intervenor-appellee California Coastal
    Commission.
    OPINION
    B. FLETCHER, Circuit Judge:
    Defendants Secretary of the Navy, Department of the Navy,
    Secretary of the Department of Commerce, National Marine
    Fisheries Service (NMFS),1 and two Administrators of the
    National Oceanographic and Atmospheric Administration
    (NOAA) appeal the district court’s January 3, 2008 order, as
    modified on January 10, 2008, granting a motion for a prelim-
    inary injunction and imposing certain conditions on the com-
    pletion of the remaining eight of fourteen large training
    exercises scheduled to be conducted by the Navy’s Third
    Fleet in the waters off the coast of southern California
    between February 2007 and January 2009 (the “SOCAL exer-
    cises”).2 The motion was filed by plaintiffs Natural Resources
    Defense Council, Inc., International Fund for Animal Wel-
    fare, Cetacean Society International, League for Coastal Pro-
    tection, Ocean Futures Society, and Jean-Michel Cousteau
    (collectively “NRDC” or “plaintiffs”), who are concerned that
    the Navy’s use of high-intensity, mid-frequency active sonar
    (“MFA sonar”) in the SOCAL exercises will cause serious
    harm to various species of marine mammal present in the
    southern California waters, and by extension, to plaintiffs
    themselves.
    1
    The National Marine Fisheries Service has now been renamed “NOAA
    Fisheries.” Because many of the documents refer to the agency by its for-
    mer name, it shall be referred to as “the NMFS” throughout this opinion.
    2
    While the district court imposed the injunction when the Navy had yet
    to conduct nine training exercises, it issued a temporary partial stay of its
    injunction on January 17, 2008, after which the Navy conducted its sixth
    exercise. Accordingly, only eight of the fourteen scheduled exercises have
    not yet been conducted.
    2086                   NRDC v. WINTER
    In granting NRDC’s motion for a preliminary injunction,
    the district court found that NRDC had demonstrated probable
    success on the merits of its claim that the Navy violated the
    National Environmental Policy Act (“NEPA”), 42 U.S.C.
    § 4321 et seq., by failing to prepare an Environmental Impact
    Statement (“EIS”). The district court also found that NRDC
    had demonstrated probable success on the merits of its claim
    that the Navy violated the Coastal Zone Management Act
    (“CZMA”), 16 U.S.C. § 1451 et seq., by submitting a consis-
    tency determination to the California Coastal Commission
    (“CCC”) that did not take into account the planned use of
    MFA sonar and by failing to adopt the mitigation measures
    the CCC determined were necessary for the SOCAL exercises
    to be consistent with the California Coastal Management Pro-
    gram (“CCMP”).
    On January 15, 2008, the Council on Environmental Qual-
    ity (“CEQ”) purported to approve “alternative arrangements,”
    pursuant to 40 C.F.R. § 1506.11, that would permit the Navy
    to continue its exercise without first completing an EIS. On
    the same day, President George W. Bush, pursuant to 16
    U.S.C. § 1456(c)(1)(B), exempted from the requirements of
    the CZMA the Navy’s use of MFA sonar in the SOCAL exer-
    cises.
    On February 4, 2008, the district court upheld its injunction
    on the basis of plaintiffs’ NEPA claim, concluding CEQ’s
    action was invalid and therefore not entitled to deference. The
    district court also expressed concerns about the constitutional-
    ity of the President’s CZMA exemption on the ground that it
    appeared to amount to an executive revision of a judicial deci-
    sion and thus violated the principle, recognized in Hayburn’s
    Case, 2 U.S. (2 Dall.) 408 (1792), that Congress cannot vest
    review of the decisions of Article III courts in officials of the
    Executive Branch. However, the court declined to decide the
    constitutionality of the CZMA exemption because it con-
    cluded the preliminary injunction was firmly supported on
    NRDC v. WINTER                             2087
    NEPA grounds.3 The district court also found that plaintiffs
    had demonstrated a possibility of irreparable harm and that
    the balance of hardships tipped in plaintiffs’ favor. Natural
    Res. Def. Council v. Winter, ___ F.Supp. 2d ___, 
    2008 WL 314192
    (C.D. Cal. Feb. 4, 2008) (“Feb. 4, 2008 Dist. Ct.
    Order”).
    For the reasons stated below, we uphold the district court’s
    preliminary injunction.
    I.   Procedural History
    Plaintiffs commenced this action on March 22, 2007. On
    August 7, 2007, the district court granted in part NRDC’s
    motion for a preliminary injunction and enjoined the Navy
    from conducting the then remaining eleven SOCAL exercises.4
    After appealing the district court’s preliminary injunction
    order,5 the Navy filed an emergency motion with this court for
    a stay of the order while its appeal was pending. On August
    31, 2007, a divided motions panel granted the Navy’s motion
    on the grounds that the district court had failed to consider the
    “public interest” in having a trained and effective Navy and
    had failed to explain why an unconditional injunction on the
    SOCAL exercises, rather than an injunction conditioning the
    conduct of those exercises on the adoption of additional miti-
    gation measures, was appropriate. NRDC v. Winter, 
    502 F.3d 859
    (9th Cir. 2007).
    3
    Because the district court did not rule on the likelihood of success of
    plaintiffs’ CZMA claim in light of the President’s exemption, we decline
    to reach that issue.
    4
    The district court granted NRDC’s motion only in part because it found
    that NRDC had not demonstrated probable success on the merits of its
    additional claim that the NMFS and the other non-Navy defendants had
    failed to prepare an adequate Biological Opinion and Incidental Take
    Statement in violation of the Endangered Species Act and the Administra-
    tive Procedure Act. NRDC has not appealed that portion of the district
    court’s ruling.
    5
    The CCC has intervened as appellee in this action.
    2088                   NRDC v. WINTER
    On November 13, 2007, after hearing oral argument, we
    filed an order concluding that NRDC had met the necessary
    burden of proof to demonstrate that some form of preliminary
    injunctive relief was appropriate. Accordingly, we vacated the
    stay of the preliminary injunction order effective upon the
    Navy’s completion of its fifth SOCAL exercise, which was in
    progress at the time of oral argument. However, we also con-
    cluded that an injunction conditioning continuation of the
    exercises on the Navy’s adoption of narrowly tailored mitiga-
    tion measures would be more appropriate than a total injunc-
    tion. Accordingly, we remanded the case for the district court
    to enter a modified preliminary injunction containing appro-
    priate mitigating measures. NRDC v. Winter, 
    508 F.3d 885
    (9th Cir. 2007).
    On January 3, 2008, the district court, after having received
    briefing from the parties and having toured the destroyer USS
    Milius at the naval base in San Diego, California, to improve
    its understanding of the Navy’s sonar training procedures and
    the feasibility of the parties’ proposed mitigation measures,
    issued a new preliminary injunction that allowed the Navy to
    conduct the remaining SOCAL exercises provided that it
    employ certain measures intended to mitigate the impact of
    the Navy’s use of MFA sonar on the environment. On January
    9, 2008, the Navy applied for a stay pending appeal and
    requested relief from the district court by January 14, 2008.
    On January 10, 2008, in response to arguments raised in the
    Navy’s stay application, the district court modified the pre-
    liminary injunction by narrowing the mitigation measures
    contained in the January 3, 2008 order. The Navy filed a
    notice of appeal the following day. The district court denied
    the Navy’s stay application on January 14, 2008.
    On the evening of January 15, 2008, the Navy filed an
    emergency motion with this court requesting vacatur of the
    preliminary injunction or, alternatively, a partial stay of the
    preliminary injunction pending a decision on its appeal by our
    NRDC v. WINTER                      2089
    court. The Navy’s motion was based in part on two develop-
    ments that occurred on the same day that the motion was
    filed. First, the President of the United States, pursuant to 16
    U.S.C. § 1456(c)(1)(B), exempted from the provisions of the
    CZMA the Navy’s use of MFA sonar during the SOCAL
    exercises, finding that such use of MFA sonar is “essential to
    national security” and in the “paramount interest of the United
    States.” Second, the CEQ, finding “emergency circum-
    stances,” purported to approve “alternative arrangements” to
    accommodate those emergency circumstances, pursuant to 40
    C.F.R. § 1506.11. It permitted the Navy to follow the pre-
    scribed arrangements to continue its exercises pending com-
    pletion of the Navy’s EIS. The Navy subsequently adopted
    the alternative arrangements and determined that it would
    comply with them. See Decision Memorandum Accepting
    Alternative Arrangements for the U.S. Navy’s Southern Cali-
    fornia Operating Area Composite Training Unit Exercises and
    Joint Task Force Exercises Scheduled To Occur Between
    Today and January 2009, 73 Fed. Reg. 4189 (Jan. 24, 2008).
    On January 16, 2008, we remanded the matter to the district
    court to consider in the first instance the effect, if any, of
    these developments on its preliminary injunction order. On
    January 17, 2008, the district court issued a temporary partial
    stay of its preliminary injunction order pending the court’s
    consideration of the Navy’s ex parte application to vacate the
    preliminary injunction. The Navy subsequently conducted its
    sixth SOCAL exercise.
    On February 4, 2008, following briefing by the parties and
    oral argument, the district court denied the Navy’s application
    to vacate the preliminary injunction and lifted the temporary
    partial stay. In its published order, the district court held in
    relevant part that CEQ’s approval of “alternative arrange-
    ments” was invalid because there are no “emergency circum-
    stances” within the meaning of 40 C.F.R. § 1506.11. Feb. 4,
    2008 Dist. Ct. Order at 13-25. Thus, the district court left in
    2090                        NRDC v. WINTER
    place the original preliminary injunction. The Navy filed a
    notice of appeal two days later.
    On February 8, 2008, we issued a sua sponte order expedit-
    ing the appeal of the district court’s order imposing the pre-
    liminary injunction. On February 15, 2008, the Navy filed an
    emergency motion for a partial stay of the preliminary injunc-
    tion pending our consideration of the appeal on the ground
    that the injunction would interfere with the Navy’s conduct of
    two exercises in March, 2008. On February 19, 2008, we
    denied the Navy’s motion for a partial stay in light of our
    order expediting the appeal, which set oral argument for
    Wednesday, February 27, 2008. We now affirm the district
    court’s order imposing the preliminary injunction.
    II.   Factual Background
    A.   The SOCAL Exercises and the Effect of MFA
    Sonar on Marine Mammals
    The scheduled SOCAL exercises consist of seven Compos-
    ite Training Unit Exercises (“COMPTUEX”), which last three
    to four weeks each, and seven Joint Tactical Force Exercises
    (“JTFEX”), which last approximately ten days each. The
    exercises, which involve the use of multiple surface ships, air-
    craft and submarines, are part of the “integrated” training
    phase of the Navy’s Fleet Response Training Plan, in which
    individual naval units — ships, submarines and aviation
    squadrons — learn and demonstrate skills as members of a
    strike group.6 Declaration of Captain Martin N. May (“May
    6
    The Navy employs two types of strike groups. A carrier strike group
    generally consists of an aircraft carrier and five surface combatant ships.
    May decl. ¶ 5. An expeditionary strike group includes surface combatant
    ships and an amphibious ready group. 
    Id. A strike
    group starts developing skill sets at the individual ship, subma-
    rine, or aviation squadron level by conducting unit-level training. 
    Id. ¶ 6.
    As skill levels increase, units coordinate training with other units. 
    Id. Prior NRDC
    v. WINTER                             2091
    decl.) ¶ 6. In a COMPTUEX exercise a strike group must
    demonstrate that it is capable of operating in a “complicated
    threat-based scenario environment that simulates real world
    situations.” 
    Id. In a
    JTFEX exercise, which follows the
    COMPTUEX exercise and typically includes other Depart-
    ment of Defense services and Allied Forces, the focus is on
    “mission planning and strategy and on the orchestration of
    integrated maneuvers, communication and coordination.” 
    Id. ¶ 7.
    Upon completion of the integrated training phase the
    Fleet Commander is able to certify that a strike group is ready
    for deployment. 
    Id. According to
    the Navy, the ability to execute anti-
    submarine warfare (“ASW”) is critical to a Commander’s cer-
    tification of a strike group. 
    Id. Improving ASW
    is the Pacific
    Fleet’s top “war-fighting” priority because of the proliferation
    of extremely quiet diesel electric submarines throughout the
    world.7 
    Id. ¶ 11;
    Dec. 14, 2007 Declaration of Rear Admiral
    John M. Bird (“Bird. Decl”) ¶ 16. In turn, an important part
    of ASW is the use of active sonar, a technology which the
    Navy deems absolutely necessary to detect today’s extremely
    quiet submarines. The type of active sonar, the use of which
    to commencing the “integrated” phase of the Navy’s training plan, the
    individual units comprising a strike group must be trained and attain profi-
    ciency in the “basic” phase of the training plan. 
    Id. ¶ 25.
    During the “inte-
    grated” training phase, an individual unit learns and demonstrates skills as
    a team member of the strike group. Following completion of the “integrat-
    ed” phase, strike groups enter the “sustainment” phase of the training plan.
    
    Id. This phase
    continues through the strike group’s scheduled deployment
    and post-deployment periods and ends with the commencement of the
    “maintenance” phase, during which the ships comprising the strike group
    undergo maintenance and modernization. 
    Id. ¶¶ 24,
    25.
    7
    We note that neither quiet submarines, nor the use of active sonar to
    detect them, are new technologies. According to the Navy’s Environmen-
    tal Assessment (“EA”), active sonar was used effectively against German
    U-boats during World War II, and during the Cold War technological
    developments in active sonar were “critical” for tracking sophisticated
    Soviet submarines.
    2092                       NRDC v. WINTER
    NRDC challenges, is mid frequency active sonar; other cate-
    gories of active sonar are low-frequency active sonar and
    high-frequency active sonar.8
    Active sonar involves a vessel or other sonar source emit-
    ting a loud noise underwater and then listening for whether
    the noise comes back to the source, indicating that the noise
    may have bounced off the hull of a previously undetected sub-
    marine. According to the Navy, active sonar has two impor-
    tant advantages over passive sonar, which merely involves
    listening for noise made by submarines themselves: active
    sonar gives both the bearing and the distance of the target
    submarine, while passive sonar gives only the bearing;9 and
    active sonar allows the Navy to target submarines that emit
    sound at levels below those of the surrounding marine envi-
    ronment. Bird decl. ¶ 9. Accordingly, the Navy has concluded
    that in certain environments, including shallow coastal waters
    where ambient noise levels are high, MFA sonar allows better
    detection of quiet submarines than passive sonar. May decl.
    ¶¶ 9, 14.
    According to the Navy, personnel using MFA sonar must
    train with it regularly, under realistic conditions, and in a vari-
    ety of situations. May decl. ¶ 10. The Navy therefore trains
    with MFA sonar in the ASW exercises that constitute an
    important component of the SOCAL exercises.
    The SOCAL exercises are conducted in the Navy’s training
    ranges off the coast of southern California (“the Southern Cal-
    ifornia Operating Area”). This area is located in biologically
    8
    According to the Navy, low-frequency active sonar is transmitted at
    frequencies between 0.1 kHz and 1.0 kHz; mid-frequency active sonar at
    frequencies between 1.0 kHz and 10.0 kHz; and high-frequency active
    sonar at frequencies greater than 10.0 kHz. Bird decl. ¶ 12; May decl. ¶ 9.
    9
    Active sonar allows a calculation of the distance of a target submarine
    by considering the speed at which the sonar sound moves through water
    and the time it takes for emitted sonar sound to travel to the target and
    back. Bird decl. ¶ 12.
    NRDC v. WINTER                           2093
    diverse waters. At least thirty-seven species of marine mam-
    mals are found there, with the most common being various
    species of dolphin and whale, as well as the California sea
    lion. Nine of those species are listed as threatened or endan-
    gered under the Endangered Species Act (“ESA”), 16 U.S.C.
    § 1531 et seq.: the blue whale, fin whale, humpback whale,
    Northern Pacific right whale, sei whale, sperm whale, sea
    otter, Stellar sea lion, and Guadalupe fur seal. In addition, up
    to eight species of beaked whale are found in the Southern
    California Operating Area. A study submitted by NRDC clas-
    sifies the California coastal waters as a “key area” for beaked
    whales because over 25% of all beaked whale species are
    found there.10
    The Navy acknowledges in its EA that MFA sonar may
    affect both the physiology and behavior of marine mammals.
    Exposure to “very high” acoustic energy levels may impair
    the functioning of marine mammals’ visual system, vestibular
    system and internal organs, and may cause injury to their
    lungs and intestines. However, the primary physiological
    effects of MFA sonar are on marine mammals’ auditory sys-
    tem: very high sound levels may rupture the eardrum or dam-
    age small bones in the middle ear, but even exposure to lower
    levels of sound may cause permanent or temporary hearing
    loss.
    Several studies suggest that active sonar may also cause a
    form of decompression sickness (or the “bends”) in marine
    mammals by inducing growth of gas bubbles in their blood
    stream or tissues, potentially leading to fatal hemorrhaging,
    lesions and emboli in the organs. However, the Navy disputes
    the conclusions of these studies and it has submitted a decla-
    10
    According to the study, the “key area” in southern California com-
    prises the California shelf margins, which the study defines as the area
    west of the Californian coast up until the 125.0 degree longitude. Navy
    maps in the record show that the Southern California Operating Area falls
    largely within this area.
    2094                      NRDC v. WINTER
    ration by an expert on marine mammal auditory systems stat-
    ing that decompression sickness requires super-saturation of
    tissue with gas and that such super-saturation has not been
    shown to occur in marine mammals. See Declaration of Dr.
    Darlene R. Ketten (“Ketten decl.”) ¶¶ 12-16.
    The Navy also acknowledges that the use of MFA sonar
    may overtly disrupt the normal behavior of marine mammals
    even if it does not affect their physiology. While the Navy
    acknowledges that active sonar may cause behavioral
    responses such as attempting to avoid the site of sound expo-
    sure, swimming erratically, sluggish behavior, tail slapping,
    “jaw popping,” and aggressive behavior, those responses were
    observed in studies using trained animals held in captivity.11
    NOAA concluded in 2006 that studies of marine mammals in
    the wild “strongly suggest” that the use of sonar at levels
    lower than those found to produce behavioral effects in the
    tests of captive animals can result in “profound” behavioral
    alterations, including changes in feeding, diving, and social
    behavior. In a February 9, 2007 Biological Opinion concern-
    ing the SOCAL exercises,12 the NMFS found that acoustic
    exposures can impair marine mammals’ foraging ability and
    their ability to detect predators or communicate. The NMFS
    cited studies finding that noise has caused whales to move
    away from their feeding and mating grounds and migration
    routes, and to change their calls.
    11
    These behavioral responses were observed in a study to which the EA
    cites for the effects of MFA sonar on marine mammals. See J.J. Finneran
    and C.E. Schlundt, Effects of Intense Pure Tones on the Behavior of
    Trained Odontocetes, Space and Naval Warfare Systems Center, San
    Diego, Technical Document (September 2004).
    12
    The NMFS issued the Biological Opinion pursuant to section 7(a)(2)
    of the Endangered Species Act (“ESA”), 16 U.S.C. § 1536(a)(2), which
    concluded that while the SOCAL exercises might “adversely affect” cer-
    tain threatened and endangered species, the exercises were not “likely to
    jeopardize the [species’] continued existence.” The NMFS also issued an
    Incidental Take Statement under which harm done to animals of the
    threatened or endangered species would be excused under the ESA as inci-
    dental.
    NRDC v. WINTER                             2095
    As the record demonstrates, substantial evidence suggests
    that beaked whales are particularly vulnerable to MFA sonar.
    While it is not settled what causes this vulnerability,13 it is
    clear that use of MFA sonar may lead to the stranding of
    beaked whales. A 2004 Navy-sponsored study concluded that
    “the evidence of sonar causation is . . . completely convincing
    and that therefore there is a serious issue of how best to avoid/
    minimize future beaching events.” Likewise, the Standing
    Working Group on Environmental Concerns of the Interna-
    tional Whaling Commission’s Scientific Committee con-
    cluded in 2004 that “[t]he weight of accumulated evidence
    now associates mid-frequency, military sonar with atypical
    beaked whale mass strandings,” and found that “[t]his evi-
    dence is very convincing and appears overwhelming.”
    A 2006 study cited as possible explanations for the associa-
    tion between MFA sonar and strandings of beaked whales that
    (1) beaked whales may swim into shallow waters to avoid the
    sonar sound and strand if they are unable to navigate back to
    deeper waters, and (2) that behavioral responses to sonar may
    lead to tissue damage that in turn leads to stranding. The study
    explains that while a stranding need not be fatal, stranded
    marine mammals have died from cardiovascular collapse due
    to hyperthermia or from the stress associated with the strand-
    ing. Several mass strandings of marine mammals—mostly,
    though not exclusively, beaked whales—have been associated
    with the use of active sonar. Another 2006 study describes a
    stranding of twelve beaked whales in Greece in 1996, a
    stranding of seventeen marine mammals (including fourteen
    beaked whales) in the Bahamas in 2000, and a stranding of
    13
    A 2004 Navy-sponsored study investigated several possible explana-
    tions for beaked whales’ vulnerability to MFA sonar, including that
    beaked whales have a specialized anatomy, possibly due to their deep div-
    ing, which renders them especially sensitive to sound, and that beaked
    whales are “especially skittish” such that loud, reverberant acoustic fields
    cause “uncontrolled attempts to escape.” The study concluded that the lat-
    ter explanation was the most likely to be correct, but that this conclusion
    could change “as more research is done on this problem.”
    2096                        NRDC v. WINTER
    fourteen beaked whales in the Canary Islands in 2002,14 all of
    which occurred at the same time and place as the naval use
    of MFA sonar. The study also recounts a stranding of three
    beaked whales in the Madeira Islands in 2000, which coin-
    cided with NATO’s conduct of naval exercises,15 as well as a
    stranding of two beaked whales in the Gulf of California,
    Mexico, in 2002, which coincided with the conduct of seismic
    surveys involving, among other acoustic sources, a multi-
    beam, high-frequency sonar. In addition, a 2006 report by the
    NMFS recounts that 150 to 200 melon-head whales stranded
    in a Hawaiian bay in 2004, at the same time and place as the
    Navy’s use of active sonar as part of its biennial Rim of the
    Pacific (RIMPAC) exercise.16
    Necropsies of the dead whales involved in the Bahamas,
    Canary Islands and Madeira Islands strandings revealed hem-
    orrhages in and around the ears, in the cranial spaces, and in
    other parts of the body such as the jaw fat, lungs and kidneys.
    In a joint report, the Navy and NOAA concluded that the inju-
    ries to the whales that stranded in the Bahamas constituted
    “some sort of acoustic or impulse trauma,” and that the
    Navy’s use of MFA sonar was the “most plausible” source of
    that trauma. The International Whaling Commission agreed
    14
    Notably, the study states that after the stranding in the Canary Islands,
    local researchers examined past stranding records and found reports of
    eight other strandings of beaked whales in the Canaries since 1985, at least
    five of which coincided with naval activities offshore.
    15
    According to the study, NATO has been unwilling to provide informa-
    tion on its sonar activity during the Madeira Island exercises.
    16
    The RIMPAC exercises have been conducted biennially since 1968 in
    the “Hawaiian operating area” and are intended to enhance the communi-
    cation and coordination between Pacific Rim armed forces “as a means of
    promoting stability in the region to the benefit of all participating nations.”
    Bird decl. ¶ 34. Unlike the JTFEX and COMPTUEX exercises, the RIM-
    PAC exercises are not part of the “integrated” phase of the Fleet Response
    Training Plan; they are focused on command and control among the
    nations involved, and not focused on certifying strike groups for deploy-
    ment. 
    Id. However, like
    the JTFEX and COMPTUEX exercises, the RIM-
    PAC exercises include ASW training that involves the use of MFA sonar.
    NRDC v. WINTER                     2097
    that the hemorrhages in the inner ears and cranial spaces were
    consistent with “direct acoustic effects.”
    According to a biologist on whose declaration NRDC
    relies, the use of MFA sonar in the Bahamas may also have
    had a serious effect on the local population of beaked whales.
    See Declaration of Dr. Hal Whitehead. The biologist cites a
    study showing that no Cuvier’s beaked whales were sighted
    for twenty months following the stranding in the Bahamas,
    despite an increased survey effort. 
    Id. ¶ 8.
    He also cited
    studies showing that of the Cuvier’s beaked whales that had
    been photo-identified over a nine-year period, only a few have
    been sighted since the stranding in 2000. 
    Id. With respect
    to the stranding of the melon-head whales in
    Hawaii, the NMFS issued a report concluding that “[w]hile
    causation of this stranding event may never be unequivocally
    determined, we consider the active sonar transmissions . . . a
    plausible, if not likely, contributing factor in what may have
    been a confluence of events.”
    Undoubtedly, many training exercises involving the use of
    active sonar occur around the world without marine mammal
    strandings being observed or reported. However, a declaration
    by a NOAA scientist submitted by the Navy acknowledges
    that it is generally poorly understood in which combinations
    of physical and biological circumstances such strandings are
    likely to occur. Declaration of Brandon L. Southall ¶ 19. The
    declaration also acknowledges that whether marine mammal
    strandings are observed depends on the extent to which peo-
    ple are looking for them. 
    Id. B. The
    Navy’s EA and the Predicted Harm to Marine
    Mammals in the Southern California Waters
    In February 2007, the Navy issued an Environmental
    Assessment (“EA”) for the SOCAL exercises pursuant to
    NEPA. See 40 C.F.R. § 1501.3. The EA set forth the Navy’s
    2098                   NRDC v. WINTER
    estimate of how much harm the use of MFA sonar would
    inflict on marine mammals, classifying the harm as either
    “Level A harassment” or “Level B harassment.”
    Level A harassment is an act that physically injures the
    marine mammal. Level A harassment refers to an exposure to
    MFA sonar that “injures or has the significant potential to
    injure a marine mammal or marine mammal stock in the
    wild.” Injury is defined as any destruction or loss of any bio-
    logical tissues, and includes permanent hearing loss.
    Level B harassment is an act that disrupts the behavior of
    a marine mammal. Level B harassment refers to an exposure
    to MFA sonar that “disturbs or is likely to disturb a marine
    mammal or marine mammal stock by causing disruption of
    natural behavioral patterns including, but not limited to,
    migration, surfacing, nursing, feeding, or sheltering to a point
    where such behaviors are abandoned or significantly altered.”
    Notably, Level B harassment may also, though it need not,
    include temporary hearing loss.
    The behavioral effects that result from Level B harassment
    may have severe consequences. According to the Biological
    Opinion of the NMFS, acoustic exposures can result in the
    death of a marine mammal by impairing its foraging or its
    ability to detect predators or communicate by increasing stress
    or by disrupting important physiological events.
    In its EA, the Navy classified predicted sonar exposures as
    either Level A harassments or Level B harassments based on
    the sound intensity to which a marine mammal would be
    exposed. For cetaceans—which include whales and dolphins
    and which are the focus of NRDC’s challenge to the SOCAL
    exercises—the Navy applied the following “impact thresh-
    olds”: it classified as Level A harassments exposures to sonar
    levels of 215 decibels (dB) or greater, as Level B harassments
    including temporary hearing loss exposures to sonar levels
    between 195 dB and 215 dB, and as Level B harassments not
    NRDC v. WINTER                             2099
    including temporary hearing loss exposures to sonar levels
    between 173 dB and 195 dB.17
    Significantly, the Navy acknowledged in the EA that it
    does not know whether the above impact thresholds apply to
    beaked whales. Recognizing the recent beaked whale strand-
    ings and the fact that the exact causes of those strandings are
    unknown, the Navy concluded that “separate, meaningful
    impact thresholds cannot be derived specifically for beaked
    whales.” Put simply, the Navy did not know whether expo-
    sure of a beaked whale to an acoustic energy of less than 215
    dB might nevertheless cause permanent injury to the whale.
    Accordingly, the Navy took a “conservative approach” and
    counted all predicted Level B exposures of beaked whales as
    non-lethal Level A exposures. Thus, the Navy treated every
    predicted exposure of a beaked whale to a sonar level of 173
    dB or greater as causing physical injury including permanent
    hearing loss.
    In its EA, the Navy estimated that over the course of the
    SOCAL exercises, the use of MFA sonar would result in 564
    instances of Level A harassment to marine mammals, 548 of
    which would be to beaked whales.18 Specifically, the follow-
    17
    The EA expressed the impact thresholds in terms of “energy flux den-
    sity level,” which is a measure of the flow of sound energy through an
    area, or, more formally, the time integral of the squared pressure divided
    by the impedance. Energy flux density is expressed in units of decibels
    referenced to the pressure and duration of the sound, e.g., 215 dB re 1 µPa2
    -s. For convenience, we express the impact thresholds, and exposures to
    MFA sonar generally, only in units of decibels.
    18
    The statements in the EA that “[t]he modeling efforts and harassment
    analysis for mid-frequency active sonar estimate that no Level A harass-
    ment” of beaked whales will occur is not to the contrary. As explained
    above, the Navy acknowledged in the EA that it did not know whether the
    impact thresholds it established for cetaceans generally also applied to
    beaked whales. Accordingly, the Navy decided that although its harass-
    ment model using those impact thresholds did not predict any Level A
    harassments to beaked whales, it would nevertheless treat all predicted
    Level B harassments to beaked whales as Level A harassments.
    2100                       NRDC v. WINTER
    ing species would be subjected to Level A harassments:
    Cuvier’s beaked whales in 436 instances; Ziphiid beaked
    whales in 104 instances; common dolphins in 16 instances;
    and Baird’s beaked whales in 8 instances.19
    The Navy also estimated that the use of MFA sonar would
    result in 8,160 exposures to Level B harassment with tempo-
    rary hearing loss and 161,368 exposures to Level B harass-
    ment without hearing loss. Eight marine mammal species,
    including one endangered species, would be exposed to over
    1,000 incidents of Level B harassment: 145,444 exposures to
    common dolphins; 6,460 exposures to Northern Pacific right
    whale dolphins; 4,292 exposures to Risso’s dolphins; 4,100
    exposures to Pacific white-sided dolphins, 3,252 exposures to
    striped dolphins; 1,830 exposures to pygmy sperm whales
    (endangered); 1,094 exposures to Pantropical spotted dol-
    phins; and 1,092 exposures to bottlenose dolphins.
    In light of the harm that marine mammals are expected to
    suffer as a result of the SOCAL exercises, plaintiffs contend
    that they and their members living in southern California will
    be harmed. For example, plaintiff Jean-Michel Cousteau
    alleges that as an environmental enthusiast and film-maker his
    ability to enjoy and educate others about the marine environ-
    ment in southern California will be impaired if the harmful
    effects of MFA sonar on marine mammals are not sufficiently
    mitigated. Other plaintiffs make similar allegations.
    The Navy stated in the EA that it “assumed” that its meth-
    odology for estimating harm overestimated the effects of
    MFA sonar on marine mammals, citing the lack of observed
    effects during several past major exercises. However, the EA
    also maintained that the methodology used was based on the
    19
    These figures appear in the EA’s Appendix A; the slightly different
    figures cited by the parties and the district court appear to be incorrect
    because they fail to account for 98 instances of Level A harassment to
    Ziphiid whales.
    NRDC v. WINTER                           2101
    “best available science,” and it provided no indication of the
    extent to which its methodology overestimated the effects of
    MFA sonar. In fact, there is at least some evidence that the
    Navy’s methodology may have underestimated the effects of
    MFA sonar on marine mammals. NRDC has submitted decla-
    rations of several scientists who cite evidence that extraordi-
    nary behavior in marine mammals, including stranding by
    beaked whales, may be caused by acoustic energy levels
    below the Navy’s bottom impact threshold of 173 dB. See
    Declaration of Dr. David E. Bain ¶¶ 6-11; Declaration of Dr.
    Edward C.M. Parsons ¶ 4; Declaration of Dr. Linda Weilgart
    (“Weilgart decl.”) ¶ 9.
    While NRDC has presented no evidence that marine mam-
    mals have actually been harmed by the Navy’s use of MFA
    sonar in the Southern California Operating Area over the past
    forty years,20 the record indicates that because harm to marine
    mammals is difficult to detect, except in cases of stranding,
    marine mammals may nonetheless be harmed by the Navy’s
    use of MFA sonar in the Southern California Operating Area.
    In the Navy’s January 2007 “after action report” following
    the completion of the first three SOCAL exercises, the Navy
    acknowledged that “it is difficult to assess the potential expo-
    20
    The “after action reports” compiled by the Navy following completion
    of COMPTUEX and JTFEX exercises in the Southern California Operat-
    ing Area do catalogue a number of marine mammal deaths. For example,
    the Navy’s June 2007 “after action report” following the first three
    SOCAL exercises notes that during one of the exercises the Navy
    observed a floating, badly decomposed whale carcass, and that during two
    of the exercises it observed floating pinniped and dolphin carcasses. The
    report does not disclose whether necropsies were performed on the car-
    casses and it does not discuss whether the deaths might be related to the
    use of MFA sonar. Instead, the report proffers only the tentative explana-
    tion that “circumstantial evidence” of a link between “potential” algal
    toxin in California ocean waters and increased marine mammal mortality
    “is not unexpected” and “may” have “contributed” to the fact that pinni-
    ped and dolphin carcasses were observed. June 28, 2007 COMPTUEX/
    JTFEX Combined After Action Report at 13-14.
    2102                      NRDC v. WINTER
    sure to sonar for species not observed.” Indeed, the “after
    action reports” for the last eight COMPTUEX and JTFEX
    exercises in the Southern California Operating Area reveal
    that in less than 15% of the instances in which marine mam-
    mals were observed, MFA sonar was in fact being used.21
    Thus, the Navy’s reports show that relatively few marine
    mammals have been observed while MFA sonar was being
    used.
    Beaked whales are particularly difficult to observe. Accord-
    ing to a 2004 Navy-sponsored report, “[t]heir very low
    broaching profile and the limited time they spend at the sur-
    face have conspired to make them resistant to easy survey-
    ing.” The report notes that beaked whales are “very deep
    divers” and spend an estimated 80% of their time at consider-
    able depths. According to the EA, Cuvier’s and Mesoplodont
    beaked whales make dives of up to 87 minutes.22 An interna-
    tional workshop on beaked whales organized by the U.S.
    Marine Mammal Commission noted that only 1 in 50 beaked
    whales would be detected in naval mitigation surveys using
    shipboard visual observation, even assuming ideal observa-
    tion conditions.
    Correspondingly, injuries to beaked whales are also diffi-
    cult to observe. In a January 2007 memorandum, the NMFS
    concluded that “injuries or mortalities . . . would rarely be
    documented, due to the remote nature of many [naval activi-
    ties] and the low probability that an injured or dead beaked
    whale would strand.” While the parties have presented con-
    flicting declarations on the issue whether whale carcasses
    resurface for some time after they initially sink, compare
    21
    The data in the “after action reports” for the eight COMPTUEX and
    JTFEX exercises in the Southern California Operating Area show that of
    345 instances of marine mammal sighting, MFA sonar was being used
    only in 51 instances, or 14.8% of the time.
    22
    The EA provides no information on the length of the dives of Baird’s
    and Ziphiid beaked whales.
    NRDC v. WINTER                      2103
    Weilgart decl. ¶ 7 with Ketten decl. ¶ 17, the likelihood that
    a whale carcass would be detected if it does not strand logi-
    cally depends on how well the waters are searched for such
    carcasses. A 2007 study by NMFS researchers suggests that
    the likelihood of detecting dead beaked whales is low, as it
    concluded that, given current biological survey efforts, in
    90% of beaked whale stocks a decline in population of 50%
    over a 15-year period would go undetected as a decline at all.
    Non-fatal injuries not leading to stranding would be even
    more difficult to detect because no beaked whale carcass
    would surface.
    Moreover, it is not clear from the record whether in the past
    forty years the waters of southern California have been
    exposed to MFA sonar at the same power level and frequency
    and for the same duration as they are now. First, the Navy has
    provided no information about the frequency with which exer-
    cises involving the use of MFA sonar were conducted prior to
    1992.
    Second, while the Navy states that “Navy data going back
    to 1992 shows that the number of yearly exercises in the last
    15 years and amount of [MFA sonar] use in SOCAL waters
    was greater in the past than it is now, showing a slight reduc-
    tion trend,” Bird decl. ¶ 18, that statement is too vague to
    allow conclusions to be drawn from it. The statement says
    nothing about the type of exercises or their duration over the
    years, and it does not make clear whether “in SOCAL waters”
    refers only to sonar use or also to the number of yearly exer-
    cises. Further, the statement does not specify whether
    “amount of [MFA sonar] use” refers to sonar use in each
    exercise or to total sonar use in a year, nor does it make clear
    whether that phrase refers to the number of times sonar was
    employed or to the aggregate duration of sonar transmission.
    The Navy produces no data in the record to clarify its state-
    ment.
    Third, while the EA states that an average of seven JTFEX
    or COMPTUEX exercises are conducted each year, which is
    2104                        NRDC v. WINTER
    consistent with fourteen SOCAL exercises to be conducted
    over two years, the EA does not state the starting date after
    which that average has been maintained.
    Fourth, while the Navy points out that its currently-used
    SQS-53 sonar system transmits sonar at the same power
    levels and frequencies as the SQS-26 system that the Navy
    used in earlier years, it acknowledges that in a new class of
    destroyers the SQS-53 system has replaced the SQS-56 sys-
    tem. Bird. decl. ¶ 18. As the Biological Opinion of the NMFS
    makes clear, the SQS-56 system transmits MFA sonar at a
    lower power level and at different frequencies than the SQS-
    53 system.23 Thus, the record suggests that with the new class
    of destroyers the average MFA sonar transmission may have
    increased in power level and changed in frequency. The Navy
    does not cite evidence to the contrary.
    Finally, we can draw no conclusion from the statement in
    the EA that “output from active sonar systems used in [the
    Southern California Operating Area] and throughout the Navy
    has remained largely the same for the past 30 years.” The EA
    does not explain whether “output” refers to frequency, sound
    intensity level, amount of time used during an exercise, or
    amount of time used per year.24 Even assuming the statement
    23
    Moreover, the NMFS’ Biological Opinion states that two low-
    frequency sonar systems are likely to be employed in the SOCAL exer-
    cises, but it does not state in what proportion they have been used in the
    past or will be used now. The fact that one of those systems has the same
    acoustic capabilities as, but improved processing capabilities over, the
    other system—a fact to which the Navy refers in its November 13, 2007
    letter to the court—is irrelevant.
    24
    The same lack of clarity afflicts the statement in a Navy declaration
    that the Navy’s training activities involving sonar during World War II
    “were similar in nature and intensity to those currently analyzed in the
    [EA for the SOCAL exercises].” Declaration of Conrad Erkelens ¶ 16. The
    statement does not make clear whether “intensity” refers generally to the
    frequency or size of the exercises or more specifically to the length of time
    during which sonar was used. Even if it refers to the latter, it appears to
    refer to the use of sonar per training activity, not per year.
    NRDC v. WINTER                           2105
    refers to the use of the sonar systems during an exercise or
    during the year, it is unclear whether it refers to total use in
    the Southern California Operating Area or rather to total use
    by the Navy in all its training areas combined.
    In any event, the Navy’s estimate that its use of MFA sonar
    in the SOCAL exercises will expose marine mammals to 564
    instances of Level A harassment and nearly 170,000 instances
    of Level B harassment clearly indicates that at least some sub-
    stantial harm will likely occur in the Southern California
    Operating Area.
    C.    The Mitigation Measures Employed by the Navy
    and Those Imposed by the District Court
    While the Navy adopted a number of mitigation measures
    intended to reduce the harm caused by the use of MFA sonar
    in the SOCAL exercises, the district court concluded that
    those measures were inadequate both to cure the Navy’s
    likely NEPA violation and to avoid the possibility of irrepara-
    ble harm to NRDC. Accordingly, following our November
    13, 2007 remand order, the district court established addi-
    tional, narrowly-tailored mitigation measures which the Navy
    would have to employ during the remaining SOCAL exer-
    cises. To place these mitigation measures in context, we
    explain what mitigation measures the Navy has previously
    employed and is currently employing in the SOCAL exer-
    cises.
    In June 2006, shortly before the Navy was to conduct that
    year’s “Rim of the Pacific” exercise off the coast of Hawaii
    (the “2006 RIMPAC exercise”), plaintiffs sued the Navy and
    the same co-defendants here,25 seeking to enjoin the Navy
    from using MFA sonar in that exercise. Following the district
    court’s grant of NRDC’s motion for a temporary restraining
    25
    Only the League for Coastal Protection was not a plaintiff in the 2006
    action.
    2106                       NRDC v. WINTER
    order, the parties entered into a settlement agreement that
    allowed the Navy to use MFA sonar in the 2006 RIMPAC
    exercise but only if it employed certain mitigation measures
    in addition to those already imposed by the NMFS in its June
    27, 2006 Incidental Harassment Authorization and by the
    Department of Defense in its June 30, 2006 National Defense
    Exemption (“NDE I”).26
    The mitigation measures the Navy adopted for the 2006
    RIMPAC exercise include operating MFA sonar at the lowest
    practicable level not to exceed 235 dB except for short peri-
    ods to meet tactical training objectives, and using at least one
    lookout dedicated to the detection of marine mammals, as
    well as three non-dedicated lookouts, on each ship operating
    MFA sonar and requiring them to report sightings of marine
    mammals.
    The following mitigation measures employed during the
    2006 RIMPAC exercise are of particular importance here:
    •   The designation of “safety zones” in which:
    -   the MFA sonar level is reduced by 6 dB
    if a marine mammal is detected within
    1,000 meters of the sonar dome (located
    in the bow of the vessel);27
    26
    The NMFS’s Incidental Harassment Authorization (IHA), issued pur-
    suant to 16 U.S.C. § 1371(a)(5), authorized the incidental “taking” of a
    small number of marine mammals under the Marine Mammal Protection
    Act (MMPA), 16 U.S.C. § 1361 et seq. The Deputy Secretary of Defense
    incorporated the mitigation measures imposed by the NMFS into NDE I
    issued pursuant to 16 U.S.C. § 1371(f), which exempted from the MMPA
    for a period of six months all military readiness activities employing MFA
    sonar, including the 2006 RIMPAC exercise. The NDE I imposed differ-
    ent mitigation measures for non-RIMPAC exercises during the six month
    period, including the prohibition on use of MFA sonar within 12 nautical
    miles of a coast.
    27
    Because the decibel is a logarithmic unit of acoustic power (using the
    base-10 logarithm), a reduction in sonar level of 6 dB corresponds to a
    reduction in sound intensity of approximately 75%, and a reduction in
    sonar level of 10 dB corresponds to a reduction in sound intensity of 90%.
    See Bird decl. ¶ 29.
    NRDC v. WINTER                           2107
    -   the MFA sonar level is reduced by 10
    dB if a marine mammal is detected
    within 500 meters of the sonar dome;
    and
    -   the use of MFA sonar is stopped if a
    marine mammal is detected within 200
    meters of the sonar dome.28
    •   In conditions of strong surface ducting—where
    sonar sound carries over a greater distance than
    would otherwise be the case—the safety zones
    will be expanded such that the MFA sonar level
    is reduced by 6 dB if a marine mammal is
    detected within 2,000 meters of the sonar dome
    and by 10 dB if one is detected within 1,000
    meters of the dome, and that the use of MFA
    sonar is stopped if a marine mammal is detected
    within 500 meters of the sonar dome.
    •   In conditions of low visibility—i.e., whenever a
    safety zone is not fully visible—additional detec-
    tion measures will be used, such as infrared or
    enhanced passive acoustic detection. If detection
    of marine mammals is not possible out to the lim-
    its of the safety zone, the sonar level will be
    reduced as if a marine mammal is present imme-
    diately beyond the extent of detection.
    •   With the exception of three specific “choke
    point” exercises, MFA sonar will not be operated
    in constricted channels or canyon-like areas or
    within 25 kilometers of the 200 meter isobath.29
    28
    As one meter equals 1.094 yards, the sizes of the three safety zones
    correspond to approximately 1,100 yards, 550 yards, and 220 yards,
    respectively.
    29
    An isobath is a line (either imaginary or on a map) joining places
    where water has equal depth.
    2108                        NRDC v. WINTER
    •   During the three choke point exercises, additional
    mitigation measures will be employed, including
    two hours of pre-exercise monitoring for marine
    mammals.
    Following the 2006 RIMPAC exercise, the Navy issued an
    “after action report” in which it reported that it had used MFA
    sonar for a total of 472 hours during the 2006 RIMPAC exer-
    cise and that the mitigation measures resulted in a loss of 8
    hours of MFA sonar use.30 Dec. 7, 2006 Rim of the Pacific
    After Action Report at 9. Although no unusual behavior of
    marine mammals had been observed, the Navy reported that
    of the estimated 256 marine mammals potentially affected by
    the 472 hours of MFA sonar use, approximately 100 of them
    had been precluded from exposure to MFA sonar as a result
    of the mitigation measures.
    In October 2006, in anticipation of the SOCAL exercises,
    the Navy submitted a consistency determination to the CCC,
    seeking the CCC’s concurrence in the Navy’s determination
    that the SOCAL exercises were consistent to the maximum
    extent possible with the enforceable policies of the CCMP,
    which, for purposes of the CZMA, are contained in the Cali-
    fornia Coastal Act. See Cal. Pub. Res. Code § 30008.31 The
    CCC disagreed with the Navy that the use of MFA sonar in
    the SOCAL exercises would not affect California’s coastal
    resources. Accordingly, the CCC conditioned its concurrence
    in the Navy’s consistency determination on the Navy adopting
    30
    The Navy asserted in its “after action report” that 8 hours of lost MFA
    sonar use translated into a somewhat greater amount of lost exercise time
    because once the sonar is turned off, simply turning it back on does not
    usually allow the Navy Commander to continue the exercise where it left
    off.
    31
    The CZMA requires that a federal agency planning to conduct activi-
    ties that may have reasonably foreseeable effects on California’s coastal
    resources must apply to the CCC for a determination that those activities
    are consistent to the maximum extent practicable with the enforceable pol-
    icies of the CCMP. See 16 U.S.C. § 1456(c)(1)(C); 15 C.F.R. § 930.36.
    NRDC v. WINTER                          2109
    fourteen mitigation measures, several of which the Navy had
    already employed in the 2006 RIMPAC exercise. The Navy
    agreed to adopt only four of the CCC’s measures—all but one
    of which do not actually prevent the use of MFA sonar from
    harming marine mammals32 —and it refused to adopt the
    remaining ten measures:
    •   The measures used in the 2006 RIMPAC exercise
    for reducing sonar levels during conditions of
    low visibility;
    •   The measures used in the 2006 RIMPAC exercise
    in “choke points;”
    •   Increasing the outer safety zone to 2 kilometers
    even in conditions not involving strong surface
    ducting;33
    •   Reducing sonar level by 6 dB during strong sur-
    face ducting conditions;
    32
    Following the CCC’s conditional concurrence, the Navy agreed to
    adopt two of the CCC’s mitigation measures: retrieving inert dropped
    mine shapes from the water and submitting to the CCC all monitoring
    results provided to the NMFS. The mitigation measures set forth in the
    EA, which have been standard operating procedure since 2004, appear to
    include two other measures proposed by the CCC: requiring passive sonar
    operators to monitor for marine mammals and report the detection of any
    such mammals; and providing a report to the NMFS following a major
    exercise that includes the results of marine mammal monitoring (a mea-
    sure already employed in the 2006 RIMPAC exercise). The Navy con-
    cedes that the measure concerning dropped mine shapes “has nothing to
    do with MFA sonar usage,” Dec. 20, 2007 Declaration of Rear Admiral
    John M. Bird ¶ 13, and the two reporting requirements do not mitigate
    actual harm to marine mammals but instead assist in the determination of
    the impacts of the SOCAL exercises. See Feb. 4, 2008 Dist. Ct. Order at
    6 n.7. Only the use of passive sonar to monitor for marine mammals miti-
    gates the harm caused by the use of MFA sonar.
    33
    As stated above, the Navy had agreed to employ in the 2006 RIMPAC
    exercise a 2,000 meter safety zone in strong surface ducting conditions.
    2110                       NRDC v. WINTER
    •   Using two marine mammal observers who have
    received NOAA-approved training for surveil-
    lance during use of MFA sonar;
    •   Requiring aerial monitoring off San Clemente
    Island throughout exercises involving MFA
    sonar;
    •   Monitoring for marine mammals for 30 minutes
    prior to commencing use of MFA sonar;
    •   Avoiding training in areas with known high con-
    centrations of marine mammals; and
    •   Locating and scheduling training outside the
    migration season for the grey whale.34
    In January 2007, the Deputy Secretary of Defense issued,
    pursuant to 17 U.S.C. § 1371(f), a second National Defense
    Exemption (“NDE II”), which exempted from the require-
    ments of the MMPA all the Navy’s military readiness activi-
    ties employing MFA sonar for the duration of the SOCAL
    exercises. The Deputy Secretary of Defense conditioned the
    exemption on the Navy adopting a number of mitigation mea-
    sures, which already had been standard operating procedure in
    the Navy’s ASW exercises since 2004. As the EA makes
    clear, it is those mitigation measures, and only those mea-
    sures, which the Navy adopted for the SOCAL exercises.
    While the Navy describes the adopted mitigation measures
    as consisting of 29 separate measures, the district court found
    that, in effect, they consist of only four basic measures: “(1)
    personnel training (providing approved Marine Species
    Awareness Training materials for lookouts and commanding
    34
    The nine bullet points reflect the substance of the ten mitigation mea-
    sures the Navy refused to adopt; two of the conditions have been consoli-
    dated in the fifth bullet point.
    NRDC v. WINTER                              2111
    officers), (2) on-deck lookouts, armed with binoculars or
    night vision goggles, to watch for marine mammals, (3) oper-
    ating procedures to ensure that any sightings of marine mam-
    mals are communicated up the chain of command, so that
    MFA sonar is powered down [(i.e., sonar power is reduced)]
    when a marine mammal approaches within 1,000 yards, 500
    yards, and ‘secured’ (shut-down) at 200 yards,35 and (4) coor-
    dination and reporting procedures.” Feb. 4, 2008 Dist. Ct.
    Order at 6 n.7. Our review of the EA reveals at most two
    additional basic measures: that passive sonar will be used to
    detect marine mammals and that Navy aircraft participating in
    exercises will conduct surveillance when doing so does not
    interfere with safety or the “accomplishment of primary oper-
    ational duties.”36 Notably, the measures adopted by the Navy
    35
    We note that the Navy has recently agreed to slightly enlarge its safety
    zones by applying safety zones of 1,000, 500 and 200 meters instead of
    1,000, 500 and 200 yards. Bird decl. ¶ 58. As a result, those safety zones
    are now of equal size as those employed in the 2006 RIMPAC exercise.
    However, the Navy has not agreed to employ expanded safety zones in
    strong surface ducting conditions.
    36
    The Navy also adopted a mitigation measure requiring “increased vig-
    ilance” during major ASW exercises using MFA sonar when “critical con-
    ditions” are present: a rapid change in bathymetry in areas of a certain
    depth; where three or more vessels are operating MFA sonar in the same
    area for six hours or more; where MFA sonar may “cut off” the exit route
    for marine mammals from a bay or channel; and the historical presence of
    a significant surface duct. However, in its June 2007 “after action report”
    the Navy explained that it had assessed the conditions of the Southern Cal-
    ifornia Operating Area and concluded that “the requirements stated in [the
    aforementioned mitigation measure] do not apply to the physical condi-
    tions found in Southern California.” Accordingly, this mitigation measure
    is not being employed in the SOCAL exercises and therefore does not, in
    fact, mitigate the impact of MFA sonar on marine mammals during those
    exercises.
    Similarly, the Navy adopted as a mitigation measure the requirement
    that MFA sonar be operated “at the lowest practical level, not to exceed
    235 dB, except as required to meet tactical training objectives.” However,
    that requirement, also adopted for the 2006 RIMPAC exercise, has no
    apparent mitigating effect because (1) it is not clear whether the Navy ever
    2112                       NRDC v. WINTER
    do not include the ten aforementioned mitigation measures
    recommended by the CCC, such as increasing the outer safety
    zone to 2 kilometers, monitoring for marine mammals at least
    30 minutes before commencing MFA sonar use, and conduct-
    ing the SOCAL exercises outside the grey whale’s migratory
    season and outside areas with high concentrations of marine
    mammals. Moreover, the adopted measures do not include the
    2006 RIMPAC measures requiring that MFA sonar not be
    used in constricted channels and canyon-like areas or within
    25 kilometers of the 200 meter isobath. Nor do they include
    the requirement, imposed by NDE I for non-RIMPAC exer-
    cises in 2006, that MFA sonar not be used within 12 nautical
    miles from the coastline.
    Following our November 13, 2007 remand order, the dis-
    trict court set out to determine what narrowly-tailored mitiga-
    tion measures should be imposed for the remaining SOCAL
    exercises. In the words of the district court, NRDC proposed
    “sweeping geographic exclusions” to the Navy’s use of MFA
    sonar, including a 25 nautical mile coastal exclusion, locating
    exercises to the maximum extent possible in waters deeper
    than 1,500 meters, and an exclusion in the Catalina Basin, the
    Westfall seamount, and the Cortez and Tanner Banks. Jan. 3,
    2008 Dist. Ct. Order at 13 n.6. The Navy also proposed sev-
    eral mitigation measures. See 
    id. After reviewing
    the parties’ briefs and taking a Navy-
    guided tour of the USS Milius, the district court imposed six
    mitigation measures in addition to those already required by
    assumed higher sonar levels when using its harassment model to predict
    harm to marine mammals, (2) the Navy’s interim report on the Bahamas
    stranding indicates that sonar levels during the Bahamas exercise did not
    exceed 235 dB even without the mitigation measure, and (3) the exception
    that the Navy may exceed the 235 dB limit “as required to meet tactical
    training objectives” swallows the rule, as tactical training objectives are
    the only reason for using MFA sonar to begin with, thus allowing the
    Navy to exceed the 235 dB limit whenever it in fact uses MFA sonar.
    NRDC v. WINTER                             2113
    NDE II: (1) the Navy shall suspend use of MFA sonar when
    a marine mammal is detected within 2,200 yards from the
    sonar source, except where the marine mammal is a dolphin
    or a porpoise and it appears that the mammal is intentionally
    following the sonar-emitting naval vessel in order to play in
    or ride the vessel’s bow wave; (2) the Navy shall reduce the
    MFA sonar level by 6 dB when significant surface ducting
    conditions are detected;37 (3) the Navy shall not use MFA
    sonar within 12 nautical miles from the California coastline;
    (4) the Navy shall monitor, including by aircraft, for the pres-
    ence of marine mammals for 60 minutes before employing
    MFA sonar, shall utilize two dedicated, NOAA- and NMFS-
    trained lookouts at all times when MFA sonar is being used,
    shall employ passive acoustic monitoring to supplement
    visual detection of the presence of marine mammals, and shall
    use aircraft participating in the training exercises to monitor
    for marine mammals for the duration of the exercises when
    MFA sonar is being used; (5) Navy helicopters shall monitor
    for marine mammals for 10 minutes before employing active
    dipping sonar; and (6) the Navy shall refrain from using MFA
    sonar in the Catalina Basin between the Santa Catalina and
    San Clemente Islands because ingress and egress to the basin
    are restricted and the basin has a high density of marine mam-
    mals. See Jan. 10, 2008 Dist. Ct. Order at 1-5.
    The district court rejected many of the geographic exclu-
    sions proposed by NRDC in favor of a 2,200-yard safety
    zone, accepted the Navy’s representations that the bathymetry
    off the shores of southern California presents unique training
    opportunities, see Feb. 4, 2008 Dist. Ct. Order at 7, and
    declined to limit the use of sonar at night or in conditions of
    low visibility despite the Navy’s voluntarily adoption of such
    limitations for the 2006 RIMPAC exercise, see Jan. 3, 2008
    Dist. Ct. Order at 7-8.
    37
    The parties clarified at oral argument on February 27, 2008, that “sig-
    nificant” is the same as “strong,” the term used to modify surface ducting
    conditions in the mitigation measures for the 2006 RIMPAC exercise.
    2114                     NRDC v. WINTER
    The Navy takes issue only with the first two of the mitiga-
    tion measures imposed by the district court, namely the 2,200
    yard “shutdown zone” and the “power-down” requirement
    during significant surface ducting conditions. Specifically, the
    Navy argues that those two mitigation measures tip the bal-
    ance of hardships in its favor and are contrary to the public
    interest.
    In support of its argument the Navy has submitted declara-
    tions by high-ranking officers attesting to the adverse conse-
    quences that those measures will have on the Navy’s military
    readiness. For example, Vice Admiral Locklear, Commander
    of the U.S. Third Fleet, opines that “imposing a 2200-yard
    shutdown zone will have crippling implications on Navy’s
    ability to conduct realistic pre-deployment ASW training
    employing MFA sonar” and will “jeopardize the training and
    readiness of U.S. THIRD Fleet [strike groups].” Declaration
    of Vice Admiral Samuel J. Locklear. ¶¶ 9, 13. Likewise, Rear
    Admiral Bird opines that “[t]raining in surface ducting condi-
    tions is critical to effective training.” Bird decl. ¶ 52. In their
    classified declarations, Admiral Gary Roughead and Rear
    Admiral Ted N. Branch opine that both the 2200-yard shut-
    down zone and the power-down requirement in significant
    surface ducting conditions will create an unacceptable risk
    with respect to the Navy’s ability to certify its strike groups
    as combat ready and will thus profoundly affect national
    security.
    III.   Standards of Review
    Our review of a district court’s grant of a preliminary
    injunction is “very deferential.” Nat’l Wildlife Fed’n v. Nat’I
    Marine Fisheries Serv., 
    422 F.3d 782
    , 794 (9th Cir. 2005).
    We do not reverse the district court unless it “relie[s] on an
    erroneous legal premise or abuse[s] its discretion.” Sports
    Form, Inc. v. United Press Int’l, Inc., 
    686 F.2d 750
    , 752 (9th
    Cir. 1982) (internal citations omitted). A court abuses its dis-
    cretion if it bases its decision on an erroneous legal standard
    NRDC v. WINTER                        2115
    or clearly erroneous findings of fact. Earth Island Inst. v. U.S.
    Forest Serv., 
    442 F.3d 1147
    , 1156 (9th Cir. 2006) (“Earth
    Island II”).
    A district court may grant a preliminary injunction if one
    of two sets of criteria are met. “Under the ‘traditional’ criteria,
    a plaintiff must show (1) a strong likelihood of success on the
    merits, (2) the possibility of irreparable injury to plaintiff if
    preliminary relief is not granted, (3) a balance of hardships
    favoring the plaintiff, and (4) advancement of the public inter-
    est (in certain cases). Alternatively, a court may grant the
    injunction if the plaintiff demonstrates either a combination of
    probable success on the merits and the possibility of irrepara-
    ble injury or that serious questions are raised and the balance
    of hardships tips sharply in his favor.” Freecycle Network,
    Inc. v. Oey, 
    505 F.3d 898
    , 902 (9th Cir. 2007); see also Earth
    Island 
    II, 442 F.3d at 1158
    .
    IV.   Discussion
    A.    Likelihood of Success on the Merits
    1.   Effect of CEQ’s Alternative Arrangements for
    NEPA Compliance
    On January 15, 2008 CEQ purported to approve “alterna-
    tive arrangements” for the Navy to continue its use of MFA
    sonar while complying with NEPA, reasoning that “emer-
    gency circumstances” prevented normal compliance. CEQ’s
    authority to grant such relief derives from 40 C.F.R.
    § 1506.11, which provides in full:
    Where emergency circumstances make it necessary
    to take an action with significant environmental
    impact without observing the provisions of these
    regulations, the Federal agency taking the action
    should consult with the Council about alternative
    arrangements. Agencies and the Council will limit
    2116                   NRDC v. WINTER
    such arrangements to actions necessary to control the
    immediate impacts of the emergency. Other actions
    remain subject to NEPA review.
    40 C.F.R. § 1506.11. CEQ’s letter of explanation to the Navy
    stated that the district court’s modified injunction “imposes
    training restrictions . . . that continue to create a significant
    and unreasonable risk that Strike Groups will not be able to
    train and be certified as fully mission capable.” CEQ Letter
    to Donald C. Winter at 3. CEQ also stated that “the inability
    to train effectively with MFA sonar puts the lives of thou-
    sands of Americans directly at risk. . . . Therefore, there are
    urgent national security reasons for providing alternative
    arrangements under the CEQ regulations.” 
    Id. at 3-4.
    The Navy then petitioned this court to vacate the district
    court’s preliminary injunction, arguing that CEQ’s approval
    of “alternative arrangements” deprived NRDC of the “likeli-
    hood of success on the merits” of its NEPA claims, thus elim-
    inating the legal basis for the injunction. We remanded to the
    district court to allow it to consider in the first instance
    whether this legal development merited vacatur or a partial
    stay of the injunction.
    On remand, the Navy maintained that the CEQ’s “emer-
    gency circumstances” determination relieved it of the require-
    ment to prepare an EIS prior to commencing the remaining
    SOCAL exercises. NRDC argued that CEQ’s action was
    beyond the scope of the regulation and otherwise invalid, and
    that the preliminary injunction should remain in place. The
    district court considered these arguments and concluded that
    its preliminary injunction was “not affected by [CEQ’s]
    approval of emergency alternative arrangements because there
    is no emergency.” Feb. 4, 2008 Dist. Ct. Order at 2. Accord-
    ingly, it held that “CEQ’s action is beyond the scope of the
    regulation and is invalid[ ]” and that “[t]he Navy is not, there-
    fore exempted from compliance” with NEPA and the prelimi-
    nary injunction. 
    Id. The district
    court found that CEQ’s
    NRDC v. WINTER                             2117
    interpretation of “emergency circumstances” to include a
    court order entered in the course of pending litigation was not
    authorized by 40 C.F.R. §1506.11, because it was contrary to
    both the plain meaning of “emergency circumstances” and the
    drafters’ original intent. It also found that CEQ’s action was
    contrary to the governing statute, NEPA.38
    The Navy makes two basic arguments as to why the district
    court erred by failing to vacate the preliminary injunction in
    light of CEQ’s approval of “alternative arrangements.” First,
    the Navy argues that the district court lacked subject matter
    jurisdiction to review CEQ’s approval of alternative arrange-
    ments because such approval constitutes a superseding agency
    action that removes as moot any basis for an injunction predi-
    cated on plaintiffs’ original claims concerning the Navy’s EA.
    Second, the Navy argues that, even if the district court could
    review CEQ’s action, the court erred by not deferring to
    CEQ’s and the Navy’s assessment that “emergency circum-
    stances” exist within the meaning of 40 C.F.R. § 1506.11. We
    address the Navy’s arguments in turn.
    a.     Subject Matter Jurisdiction over NRDC’s Challenge
    to CEQ’s Action
    [1] The Navy argues that the district court lacked subject
    matter jurisdiction to consider the validity of CEQ’s action
    because that action allegedly moots the plaintiffs’ original
    claims. Specifically, the Navy contends that the adoption of
    CEQ’s “alternative arrangements” in a superseding Decision
    Memorandum constitutes a new administrative action, which
    can only be challenged by a new claim on the merits. See Rat-
    38
    The district court also noted that CEQ had essentially crafted its own,
    alternative injunction, which suggested that CEQ, as an executive body,
    was effectively “sitting in review of a decision of the judicial branch.” The
    district court observed that CEQ’s actions raised “serious constitutional
    concerns under the Separation of Powers doctrine,” but it declined, pursu-
    ant to the doctrine of constitutional avoidance, to make a finding as to the
    constitutionality of its action. See Feb. 4, 2008 Dist. Ct. Order at 24.
    2118                       NRDC v. WINTER
    tlesnake Coalition v. EPA, 
    509 F.3d 1095
    , 1103-04 (holding
    that the district court lacked subject matter jurisdiction over
    new final agency action).39 The district court implicitly
    rejected this argument by continuing to exercise jurisdiction
    over the plaintiffs’ NEPA claim. Its decision to do so is firmly
    grounded in the familiar principle that only a valid subsequent
    action can render a legal claim moot. See Adarand Construc-
    tors, Inc. v. Slater, 
    528 U.S. 216
    , 222-23 (2000); United
    States v. Larson, 
    302 F.3d 1016
    , 1020 (9th Cir. 2002) (“The
    stipulation moots [plaintiff’s] challenge to the suppression
    ruling only if it is valid.”). Accordingly, the district court did
    not rely on an erroneous legal premise or abuse its discretion
    in concluding that it had jurisdiction to assess the validity of
    the new action in order to determine whether plaintiffs’ origi-
    nal claims could survive. See 
    Adarand, 528 U.S. at 222-23
    .
    [2] Nor did the district court abuse its discretion by leaving
    in place the preliminary injunction after determining that
    CEQ’s action did not require its vacatur. The Navy’s conten-
    tion that the district court issued “an entirely new injunction
    . . . based on new, ancillary claims” mischaracterizes the pos-
    ture of this case. The Navy challenged the injunction based on
    39
    Notably, none of the cases that the Navy cites in support of this argu-
    ment involve a plaintiff’s challenge to the validity of a new agency action.
    For example, in Forest Guardians v. U.S. Forest Serv., 
    329 F.3d 1089
    ,
    1096 (9th Cir. 2003), plaintiffs’ claims were rendered moot because the
    superseding and controlling environmental documentation that displaced
    the earlier agency action did not rely on the challenged assumptions that
    formed the basis of plaintiffs’ claims. In W. Radio Serv. Co. Inc. v. Glick-
    man, 
    113 F.3d 966
    , 974 (9th Cir. 1997), a challenge to a letter postponing
    the issuance of certain permits until a fee structure was established was
    rendered moot by the subsequent issuance of a fee structure. In Aluminum
    Co. of Am. v. Bonneville Power Admin., 
    56 F.3d 1075
    (9th Cir. 1995),
    challenges to a 1993 Rule of Decision were moot because augmentations
    were being issued under a subsequent Rule of Decision. Finally, in Ore-
    gon Natural Res. Council v. Harrell, 
    52 F.3d 1499
    , 1501-02, 1508 (9th
    Cir. 1995), the district court ordered a challenged ROD withdrawn
    because it was incomplete, and a subsequent challenge to that non-
    operative ROD was thus held to be moot.
    NRDC v. WINTER                       2119
    CEQ’s action; NRDC argued only that CEQ’s action did not
    change the merits of its NEPA claims. Thus, the district court
    here did not “[g]rant[ ] a preliminary injunction based on a
    showing that the plaintiffs were likely to succeed in establish-
    ing a violation of an ancillary court order, rather than a show-
    ing that they were likely to succeed on the merits of any of
    their claims.” Alabama v. U.S. Army Corps of Engineers, 
    424 F.3d 1117
    , 1135 (11th Cir. 2005).
    b.   The District Court’s Assessment of Whether
    “Emergency Circumstances” Existed
    (1)   Deference
    The district court concluded that CEQ’s interpretation of 40
    C.F.R. § 1506.11 is not entitled to deference. It reasoned that
    under the Administrative Procedure Act (“APA”), 5 U.S.C.
    § 551 et seq., the courts traditionally afford deference to (1)
    an agency’s reasonable interpretation of a statute it adminis-
    ters “if the statute is silent or ambiguous with respect to the
    specific issue . . . ,” citing Chevron, U.S.A., Inc. v. NRDC, 
    467 U.S. 837
    , 843 (1984), and (2) an agency’s interpretation of its
    own regulations unless “an alternative reading is compelled
    by the regulation’s plain language or by other indications of
    the [agency’s] intent at the time of the regulation’s promulga-
    tion,” citing Thomas Jefferson Univ. v. Shalala, 
    512 U.S. 504
    ,
    512 (1994), and Bowles v. Seminole Rock & Sand Co., 
    325 U.S. 410
    , 414 (1945). See Feb. 4, 2008 Dist. Ct. Order at 13-
    14.
    NRDC challenged neither the propriety of CEQ’s original
    promulgation of 40 C.F.R. § 1506.11 nor the fact that
    § 1506.11 allows alternative arrangements for compliance
    with NEPA under genuine emergency circumstances. Instead,
    NRDC limited its challenge to CEQ’s application of the regu-
    lation to the facts of this case. Accordingly, the district court
    considered whether the term “emergency circumstances”
    could be afforded so broad an interpretation as to encompass
    2120                        NRDC v. WINTER
    the Navy’s need to continue its long-planned, routine sonar
    training exercises without the mitigation measures imposed
    by the district court. The district court concluded that the
    plain language of the regulation and the limited indicia of the
    agency’s original intent compelled a narrower interpretation
    of “emergency circumstances” than the one afforded it by
    CEQ. Accordingly, the district court concluded that it did not
    owe deference to CEQ’s interpretation of § 1506.11 under
    Thomas Jefferson and Seminole Rock. We review that conclu-
    sion to determine whether in so doing it relied on an errone-
    ous legal premise or abused its discretion; we conclude that
    it did neither.
    [3] The district court followed established Supreme Court
    precedent in finding that an agency’s interpretation of its own
    regulation is not entitled to deference when it is inconsistent
    with the regulation itself, conflicts with agency intent at the
    time of promulgation, and reaches beyond “the limits imposed
    by the statute,” NEPA. See Auer v. Robbins, 
    519 U.S. 452
    ,
    461-63 (1997). Next, the district court, after concluding that
    the meaning of “emergency circumstances” was clear, applied
    the appropriate legal principles that an agency’s interpretation
    of its own regulation is entitled to deference “only when the
    language of the regulation is ambiguous.” See Christensen v.
    Harris County, 
    529 U.S. 576
    , 588 (2000). Accordingly, the
    district court did not abuse its discretion when it determined
    not to give deference to CEQ’s overly broad interpretation of
    “emergency circumstances.”40
    40
    The district court also held that Skidmore deference is inapplicable
    because this case involves an agency’s interpretation of a regulation, not
    its informal interpretation of a statute it administers. See Feb. 4, 2008 Dist.
    Ct. Order at 19 n.13 (rejecting plaintiffs’ argument that because it does not
    arise out of formal rulemaking, CEQ’s interpretation is entitled to little or
    no deference under Skidmore v. Swift & Co., 
    323 U.S. 134
    , 140 (1944)).
    While this holding is correct as a matter of law, our determination that the
    district court neither abused its discretion nor relied on an erroneous legal
    premise in concluding that no deference is owed CEQ’s overly broad
    interpretation of “emergency circumstances” renders this issue moot.
    NRDC v. WINTER                       2121
    (2)   Plain Meaning and Intent of CEQ Regulation
    In finding that no emergency circumstances existed, the
    district court reasoned that the “Navy’s current ‘emergency’
    is simply a creature of its own making, i.e., its failure to pre-
    pare adequate environmental documentation in a timely fash-
    ion, via the traditional EIS process or otherwise.” Feb. 4, 2008
    Dist. Ct. Order at 17. In short, it was not a sudden unantici-
    pated event. The district court supported its conclusion by
    noting that the CEQ letter does not specify an “emergency”
    other than the district court’s mitigation order itself, which, in
    CEQ’s view, creates a “significant and unreasonable risk” that
    strike groups will not be able to train and be certified as fully
    mission capable. 
    Id. at 16-17.
    [4] On appeal, the Navy argues that “no matter its gene-
    sis[,] . . . the inability to certify its west coast-based strike
    groups for deployment to hostile areas overseas during a time
    of war” is a pressing national emergency. The Navy cites to
    declarations, including one of the Chief of Naval Operations,
    that attests to the national security impacts of such a failure
    at a time when the United States is currently engaged in war
    in two countries. The Navy contends that the district court’s
    view that the term “emergency circumstances” as used in the
    regulation per se excludes the circumstances presented here is
    an impermissible substitution of its judgment for that of mul-
    tiple federal agencies (citing Ass’n of Pac. Fisheries v. EPA,
    
    615 F.2d 794
    , 810-11 (9th Cir. 1980)). We reject this argu-
    ment and hold, for the reasons explained above, that the dis-
    trict court did not abuse its discretion in determining that the
    plain meaning of “emergency circumstances” precludes an
    interpretation so broad as to encompass the Navy’s need to
    continue long-planned, routine training exercises without mit-
    igation measures ordered by the court.
    [5] There is ample support for the manner in which the dis-
    trict court exercised its discretion. The district court properly
    relied on dictionary definitions of “emergency” and “emer-
    2122                        NRDC v. WINTER
    gency circumstances” to support its conclusion that CEQ’s
    interpretation is not entitled to deference. See Watson v.
    United States, 
    128 S. Ct. 579
    , 583 (2007) (noting that terms
    are construed consistently with their everyday meaning,
    including by reference to the dictionary absent statutory defi-
    nition or definitive clue). As the district court observed, the
    Oxford English Online Dictionary defines “emergency” as
    “[t]he arising, sudden or unexpected occurrence (of a state of
    things, an event, etc.).” Oxford English Online Dictionary,
    available at http://dictionary.oed.com. Black’s Law Dictio-
    nary defines the term “emergency circumstances,” through a
    cross-reference to “exigent circumstances,” as “[a] situation
    that demands unusual or immediate action and that may allow
    people to circumvent usual procedures, as when a neighbor
    breaks through a window of a burning house to save someone
    inside.” Blacks Law Dictionary 260, 562 (8th ed. 2004)
    (emphasis added). The district court did not abuse its discre-
    tion in concluding that the circumstances in the present case
    fall outside the scope of these definitions because its prelimi-
    nary injunction was entirely predictable given the parties’ liti-
    gation history. Feb. 4, 2008 Dist. Ct. Order at 15.41
    The Navy urges that the risk to national security created by
    the preliminary injunction falls squarely within the legal defi-
    nition of “emergency circumstances.” However, the Navy has
    been on notice of its possible legal obligations to prepare an
    EIS for the SOCAL exercises from the moment it first
    41
    NRDC provides several more dictionary definitions of “emergency,”
    all of which include the terms “unexpected” or “unforseen.” The Navy
    refers us to another source that defines “emergency” as “a situation
    demanding immediate attention.” Random House Dict. of the English
    Lang. 636 (2d ed. 1987). We do not adjudicate the meaning of the word
    “emergency” here. Rather, we need conclude only that the district court
    did not rely on erroneous legal principles or abuse its discretion in reach-
    ing its determination as to that term’s plain meaning. Because we are not
    “left with the definite and firm conviction that a mistake has been commit-
    ted[,]” we leave the district court’s determination intact. Sports Form, 
    Inc., 686 F.2d at 752
    .
    NRDC v. WINTER                       2123
    planned those exercises. In addition, NRDC filed its com-
    plaint almost a year ago, and on August 7, 2007, the district
    court held that the Navy was likely to lose on the merits of
    NRDC’s claims. We affirmed that ruling in November of
    2007. Still, the Navy waited until January 10, 2008, to raise
    a cry of “emergency” and request the NEPA and CZMA
    waivers it relies on here, in order to continue its routine,
    planned training exercises. We find no abuse of discretion in
    the district court’s determination that such a series of events
    gives rise to a predictable outcome, not an unforeseeable one
    demanding “unusual or immediate action.”
    Moreover, the district court’s conclusion finds support in
    CEQ’s recent response to Hurricane Katrina. In March 2006,
    CEQ approved alternative arrangements to allow the Federal
    Emergency Management Agency to respond on an emergency
    basis to “[d]amages to the critical physical infrastructure in
    the New Orleans Metropolitan Area from the impact of Hurri-
    canes Katrina and Rita [that] rendered parts of the city inoper-
    able and uninhabitable.” NEPA Alternative Arrangements for
    Critical Physical Infrastructure in New Orleans, 71 Fed. Reg.
    14712, 14713 (March 23, 2006). The alternative arrangements
    explain that generally, such arrangements are made when
    “emergency circumstances require taking actions with signifi-
    cant environmental impacts and there is not sufficient time to
    follow the regular [EIS] process.” 
    Id. (emphasis added).
    This
    language supports the district court’s view that the words
    “emergency circumstances” in 40 C.F.R. § 1506.11 refer to
    unexpected, suddenly arising situations that require agency
    action in a shorter time frame than would be required to pre-
    pare an EIS. By contrast, the Navy’s routine SOCAL exer-
    cises were planned well in advance and with “sufficient time
    to follow the regular [EIS] process.”
    In concluding that the Navy’s failure to comply timely with
    NEPA does not constitute an “emergency circumstance”
    within the meaning of 40 C.F.R. § 1506.11, the district court
    also relied on the limited drafting history of the regulation. As
    2124                        NRDC v. WINTER
    the district court pointed out, the initial proposed version of
    the regulation required an agency “proposing to take” an
    emergency action to consult with CEQ regarding alternative
    arrangements.42 See Proposed Implementation of Procedural
    Provisions, 43 Fed. Reg. 25230, 25243 (June 9, 1978)
    (emphasis added). However, the drafters changed “proposing
    to take” to “taking” in order to remove the inference that con-
    sultation must necessarily precede agency action because
    “such a requirement might be impractical in emergency cir-
    cumstances and could defeat the purpose of the section.”
    Implementation of Procedural Provisions; Final Regulations,
    43 Fed. Reg. 55978, 55988 (Nov. 29, 1978). While the Navy
    dismisses this drafting history as reflecting only that “the pro-
    posed regulation was broadened to allow actions to be taken
    prior to consultation with CEQ,” we find no abuse of discre-
    tion in the district court’s contrary conclusion that the regula-
    tory history “supports a narrow, rather than a broad
    interpretation of the phrase ‘emergency circumstances’ ” and
    that the regulatory history reflects CEQ’s intent to use the reg-
    ulation to accommodate “sudden unanticipated events” but
    not more predictable events such as provisionally unfavorable
    litigation results. Feb. 4, 2008 Dist. Ct. Order at 19.
    Accordingly, we conclude that the district court did not rely
    on an erroneous legal premise or abuse its discretion in find-
    ing that the Navy’s attempt to characterize a federal court
    injunction as an “emergency circumstance” is contrary to the
    plain meaning of the language and to the intended purpose of
    CEQ’s emergency circumstances regulation.43
    42
    In its analysis of the agency’s intent, the district court appropriately
    declined to consider the declaration of Nicholas C. Yost, CEQ general
    counsel at the time the regulation was drafted, as “an unreliable guide” to
    CEQ’s intent, comparing the declaration to “subsequent legislative histo-
    ry.” Feb. 4, 2008 Dist. Ct. Order at 18-19 (quoting Chapman v. United
    States, 
    500 U.S. 453
    , 464 n.4 (1991) (internal citations omitted)).
    43
    NRDC makes the additional argument that CEQ’s order goes beyond
    the scope of the regulation because the “alternative arrangements,” pre-
    NRDC v. WINTER                           2125
    (3)    Prior Decisions
    [6] Prior judicial decisions also support our conclusion that
    the district court did not rely on erroneous legal premises or
    abuse its discretion in concluding that CEQ’s action is invalid.
    In each of the cases sustaining an application of 40 C.F.R.
    § 1506.11, CEQ allowed “alternative arrangements” in
    response to unanticipated emergencies that required federal
    agencies to respond quickly to new and changing events.
    For example, in Valley Citizens for a Safe Environment v.
    Vest, the court upheld “alternative arrangements” which per-
    mitted the Air Force to fly C-5A transport planes into and out
    of Westover Air Force Base on a twenty-four hour schedule,
    despite a previously prepared EIS’s prohibition of such
    flights. 
    1991 WL 330963
    (D. Mass. May 30, 1991). The court
    in Valley Citizens denied the plaintiffs’ request for an injunc-
    tion until a supplemental EIS was completed because it con-
    cluded that the modified flight schedule was essential to
    supply military equipment and personnel for Operation Desert
    Storm, an emergency response to Iraq’s sudden invasion of
    Kuwait that same month. 
    Id. at *5-6.
    The court agreed with
    the determination of CEQ and the Air Force that Iraq’s inva-
    sion of Kuwait reasonably constituted an emergency “given
    the military’s operational and scheduling difficulties and the
    hostile and unpredictable nature of the Persian Gulf region.”
    
    Id. at *5.
    Other cases sustaining CEQ’s application of 40 C.F.R.
    § 1506.11 also support the district court’s narrow interpreta-
    tion of the phrase “emergency circumstances.” Courts have
    scribed prospectively through January 2009, go beyond those “actions
    necessary to control the immediate impacts of the emergency,” even if
    there were an emergency. Because we hold that there is no basis for
    reversing the district court’s determination that there were no “emergency
    circumstances” under 40 C.F.R. § 1506.11, and therefore no basis for
    CEQ’s order, we do not reach the merits of this argument.
    2126                      NRDC v. WINTER
    routinely given deference to CEQ’s finding of “emergency
    circumstances” in situations where that finding has been used
    to “avert imminent crises outside the agency’s control.” 
    Id. at 17;
    see, e.g., Nat’l Audobon Society v. Hester, 
    801 F.2d 405
    ,
    405-7 (D.C. Cir. 1986) (giving deference where immediate
    action was necessary to prevent the extinction of the Califor-
    nia condor); Miccousukee Tribe of Indians of Fla. v. United
    States, 
    509 F. Supp. 2d 1288
    , 1290-91 (S.D. Fla. 2007) (giving
    deference where immediate deviation from a water delivery
    method was necessary to avoid pending extinction of the
    Cape Sable seaside sparrow in the Everglades); NRDC v.
    Pena, 
    20 F. Supp. 2d 45
    , 50 (D.D.C. 1998) (giving deference
    where immediate action was necessary to secure storage of
    nuclear materials); Crosby v. Young, 
    512 F. Supp. 1363
    , 1380,
    1386 (E.D. Mich. 1981) (where an immediate response was
    required for a city to meet a federal funding deadline for a
    development project to counteract potentially dire economic
    effects of the closure of a General Motors plant). In looking
    to prior decisions, the district court certainly did not apply an
    erroneous legal principle. Rather, it found legal authority that
    supported its view.
    (4)   CEQ’s Broad Reading of “Emergency
    Circumstances” and NEPA
    The district court also held that CEQ’s broad reading of
    “emergency circumstances” here is ultra vires because it sub-
    verts NEPA’s directive that agencies perform their NEPA
    duties “to the fullest extent possible.”44 See 42 U.S.C. § 4332.
    The existence of specific Congressional exemptions to NEPA
    informed the district court’s decision not to read the regula-
    tion “so broadly as to independently authorize CEQ to do the
    same, in the absence of a legitimate ‘emergency.’ ” Feb. 4,
    2008 Dist. Ct. Order at 21. Moreover, the court noted that
    44
    Moreover, NEPA also requires agencies to use “all practicable means
    and measures” to fulfill their duties under it. 42 U.S.C. § 4331(b).
    NRDC v. WINTER                            2127
    many of the exemptions granted in other cases involved agen-
    cies faced with conflicting Congressional mandates. 
    Id. at 22.
    NEPA, the statute authorizing 40 C.F.R. § 1506.11,
    requires federal agencies to prepare an EIS for a major federal
    action “significantly affecting the quality of the human envi-
    ronment,” 42 U.S.C. § 4332(2)(C), or, in the alternative, to
    implement mitigation measures to minimize impacts to the
    point where an EIS in not required. See, e.g., Nat’l Parks &
    Conservation Ass’n v. Babbitt, 
    241 F.3d 722
    , 734 (9th Cir.
    2001). Although CEQ justified its approval of “alternative
    arrangements” to satisfy NEPA as grounded in “urgent
    national security” concerns, see Jan. 15, 2008 CEQ Letter at
    4, the district court noted that, in the absence of a bona fide
    emergency, the “alternative arrangements” “operate[ ] to
    exempt [the Navy] from the ususal rigors involved in the
    preparation of an EIS, which forms the ‘heart’ of NEPA.”
    Feb. 4, 2008 Dist. Ct. Order at 21 n.14 (quoting Envtl. Def.
    Fund, Inc. v. Andrus, 
    619 F.2d 1368
    , 1374-5 (10th Cir.
    1980)).
    Reviewing CEQ’s justification in this light, the district
    court concluded that CEQ’s broad reading of “emergency cir-
    cumstances” has the effect of reading a “national security” or
    “defense” exemption into NEPA, where none exists.45 As the
    45
    Moreover, the district court’s conclusion was grounded in the well-
    established fact that there is no “national defense” exception to NEPA. See
    San Luis Obispo Mothers for Peace v. Nuclear Regulatory Comm’n, 
    449 F.3d 1016
    , 1035 (9th Cir. 2006); No GWEN Alliance of Lane County, Inc.
    v. Aldridge, 
    855 F.2d 1380
    , 1384 (9th Cir. 1988). “ ‘The Navy, just like
    any federal agency, must carry out its NEPA mandate to the fullest extent
    possible and this mandate includes weighing the environmental costs of
    the [project] even though the project has serious security implications.’ ”
    San Luis 
    Obispo, 449 F.3d at 1035
    (quoting No 
    GWEN, 855 F.2d at 1384
    ).
    Indeed, Congress has included exemptions for “paramount” national
    security concerns in many environmental statutes, but not in NEPA. See,
    e.g., Toxic Substances Control Act, 15 U.S.C. § 2621 (compliance waived
    if the President determines a requested waiver to be necessary “in the
    2128                       NRDC v. WINTER
    district court pointed out, Congress knows well how to
    exempt planned Defense Department activities from the
    requirements of NEPA. See, e.g., Nat’l Defense Auth. Act,
    Pub. L. No. 106-398, § 317, 114 Stat. 1654, 1654A-57 (2000)
    (specifically exempting Defense Department from preparing
    nationwide EIS for low-level flight training). The fact that
    Congress has not so exempted the Navy’s exercises in the
    Southern California Operating Area further supports the dis-
    trict court’s conclusion that 40 C.F.R. § 1506.11 should not be
    read to exempt the routine SOCAL exercises from NEPA’s
    requirements.
    The district court’s interpretation also comports with well-
    established Supreme Court precedent that narrowly interprets
    NEPA’s requirement that agencies comply with its provisions
    “to the fullest extent possible.” The Supreme Court has made
    clear that the “to the fullest extent possible” language was
    intended to address only cases in which there is an “irrecon-
    cilable and fundamental conflict” between NEPA’s require-
    interest of national defense”); Coastal Zone Management Act, 16 U.S.C.
    § 1456(c)(1)(b) (under certain circumstances the President may exempt an
    activity that is in the “paramount interest of the United States”); Endan-
    gered Species Act, 16 U.S.C. § 1536(j) (exemption granted if the Secre-
    tary of Defense finds such exemption necessary “for reasons of national
    security”); Clean Water Act, 33 U.S.C. § 1323(a) (the President may
    exempt federal effluent source for up to one year if in the “paramount
    interest of the United States”); Safe Drinking Water Act, 42 U.S.C. § 300j-
    6(a) (the President may exempt federal facility for up to one year if in the
    “paramount interest of the United States”); Resource Conservation and
    Recovery Act, 42 U.S.C. § 6961(a) (the President may exempt federal
    solid waste management facility for up to one year if in the “paramount
    interest of the United States”); Clean Air Act, 42 U.S.C. § 7417(b) (the
    President may exempt federal emission source for up to one year if in the
    “paramount interest of the United States”); Comprehensive Environmental
    Response, Compensation and Liability Act, 42 U.S.C. § 9620(j) (the Presi-
    dent may issue orders to exempt facilities of the Department of Energy
    and the Department of Defense “as may be necessary to protect the
    national security interests of the United States . . .”). See Oct. 1, 2007
    Brief of Amicus Curiae Law Professors Hope Babcock, et al. at 16 & n.4.
    NRDC v. WINTER                     2129
    ments and the requirements of another statute. See Flint Ridge
    Dev. Co. v. Scenic Rivers Ass’n. of OK, 
    426 U.S. 776
    , 787-88
    (1976). Here, as the district court noted, the Navy has never
    contended that it could not reconcile the district court’s
    injunction with the requirements of NEPA.
    Similarly, NEPA regulations interpret the language “to the
    fullest extent possible” to mean that “each agency of the Fed-
    eral Government shall comply with that section unless exist-
    ing law . . . expressly prohibits or makes compliance
    impossible.” 40 C.F.R. § 1500.6. The legislative history of
    § 1500.6 explains that this language “shall not be used by any
    Federal agency as a means of avoiding compliance with
    [NEPA’s] directives . . . .” 115 Cong. Rec. (Part 29) 39702-
    39703 (1969); see also Calvert Cliffs’ Coordinating Comm.
    Inc. v. U.S. Atomic Energy Comm’n, 
    449 F.2d 1109
    , 1114
    (D.C. Cir. 1971) (“We must stress as forcefully as possible
    that this language does not provide an escape hatch for foot-
    dragging agencies; it does not make NEPA’s procedural
    requirements somehow ‘discretionary.’ . . . Indeed, [the lan-
    guage] sets a high standard for the agencies, a standard which
    must be rigorously enforced by the reviewing courts.”).
    The Navy asserts that national policy requires that it must
    be confident that its west coast-based strike groups are pre-
    pared and certified for deployment to hostile areas overseas
    during a time of war. However, as the district court noted,
    nothing prevented the Navy from preparing an EIS prior to
    commencing the SOCAL exercises; indeed, the fact that the
    Navy is currently developing an EIS for exercises in the
    Southern California Operating Area confirms that it is fully
    capable of meeting NEPA’s requirements. See Notice of
    Intent To Prepare an Environmental Impact Statement/
    Overseas Environmental Impact Statement for the Southern
    California Range Complex, 71 Fed. Reg. 76,639 (Dec. 21,
    2006).
    2130                       NRDC v. WINTER
    Although the Navy argues that “NEPA must give way” so
    that it may proceed with its training and certification unhin-
    dered by environmental rules, quoting Flint 
    Ridge, 426 U.S. at 788
    , Flint Ridge itself holds that NEPA’s procedural
    requirements are not discretionary and do not give way unless
    a “clear and unavoidable conflict in statutory authority
    exists,” id, here, the district court carefully examined the
    record, with which it has longstanding familiarity, and deter-
    mined that there was no such conflict in statutory authority,
    concluding that conditioning phrases like “consistent with
    other essential considerations of national policy,” 42 U.S.C.
    §4331(b), and “to the fullest extent possible,” 
    id. §4332, do
    not indicate Congressional intent to create a statutory escape
    hatch. Nor does any intent appear in the implementing regula-
    tions, that would allow the Navy to conduct its exercises
    before completing an EIS.46 Feb. 4, 2008 Dist. Ct. Order at
    22-23.
    In reaching these conclusions, the district court examined
    the various legal rules and applied those that were relevant to
    this proceeding. Having done so, it acted well within its dis-
    cretion in determining that CEQ’s broad interpretation of
    “emergency circumstances” is contrary to the dictates of
    NEPA.
    (5)   Additional Considerations
    We also note that NRDC has raised a serious question as
    to whether CEQ acted arbitrarily and capriciously in the pro-
    cedure it used to reach its “emergency circumstances” deter-
    mination pursuant to 40 C.F.R. § 1506.11. The Navy, arguing
    46
    The Navy argues, in the alternative, that CEQ’s action comports with
    NEPA because it actually gives effect to the district court’s conclusion
    that an EIS is likely required and provides “alternative arrangements” as
    a bridge until the agency completes this EIS. Because we have concluded
    that the district court did not abuse its discretion in determining that no
    emergency existed and that CEQ had no authority to issue its order, we
    need not reach this argument.
    NRDC v. WINTER                           2131
    that the district court’s order created an emergency by com-
    promising its ability to effectively train and certify its strike
    groups, requested alternative arrangements on January 10,
    2008, and submitted evidence supporting that request the fol-
    lowing day. Jan. 15, 2008 CEQ Letter at 1. CEQ approved the
    Navy’s request four days later, on January 15, 2008. 
    Id. In the
    intervening time, CEQ held discussions with, and received
    briefings from, the Navy and NMFS and reviewed the Navy’s
    supporting documents. 
    Id. at 4.
    At no point did CEQ request,
    nor did the Navy provide it, any of the evidence in the district
    court record contrary to the Navy’s position that the chal-
    lenged mitigation measures would compromise its ability to
    train and certify its strike groups. Thus, CEQ reached its
    “emergency circumstances” determination without consider-
    ing any of the substantial evidence on which the district court
    relied in concluding that the mitigation measures it imposed
    would not render the Navy unable to train and certify its strike
    groups. Where, as here, the basis for an emergency is alleged
    to be the effect of a district court order, entered after careful
    review of a full record submitted by both parties, a substantial
    question exists as to whether CEQ acted arbitrarily and capri-
    ciously when it failed to review the full record, and instead
    considered only one side’s views, and on that basis deter-
    mined that the court’s order gave rise to “emergency circum-
    stances.”47
    47
    CEQ’s action raises a serious question not only under the APA, but
    also under the Constitution. The separation of powers doctrine prevents
    Congress from vesting review of the decisions of Article III courts in the
    Executive Branch. See Plaut v. Spendthrift Farm, Inc., 
    514 U.S. 211
    , 218-
    19 (1995) (explaining that Article III “gives the Federal Judiciary the
    power, not merely to rule on cases, but to decide them, subject to review
    only by superior courts in the Article III hierarchy”); see also Hayburn’s
    Case, 2 U.S. (2 Dall.) 409, 410 (1792). Here, the Navy represented, and
    CEQ determined, that “emergency circumstances” existed because the dis-
    trict court’s preliminary injunction prevented the Navy from effectively
    training and certifying its strike groups for deployment. In making this
    determination, CEQ presumably reviewed the same evidence that the
    Navy presented to the district court (without, as noted above, the benefit
    of NRDC’s evidence) and concluded, despite the district court’s explicit
    2132                       NRDC v. WINTER
    (6)   Conclusion
    [7] For the foregoing reasons, we hold that the district court
    did not abuse its discretion or rely on an erroneous legal
    premise in determining that CEQ’s broad interpretation of
    “emergency circumstances” was not authorized by 40 C.F.R.
    § 1506.11 because it was contrary to the plain meaning of the
    regulation and contrary to NEPA and, accordingly, that the
    Navy remains subject to the traditional requirements of
    NEPA.
    factual finding to the contrary, that the imposed mitigation measures
    would compromise the Navy’s ability to train and certify its forces. We
    find substantial merit in NRDC’s argument that even if the district court’s
    factual findings with respect to the effect of its mitigation measures were
    erroneous, it was the job of the appellate court—and not the Executive
    Branch—to so conclude. However, because the district court declined to
    reach this question, we, too, do not consider the constitutional argument
    in determining that the district court did not rely on an erroneous legal
    premise or abuse its discretion when it held that CEQ’s action was invalid.
    NRDC v. WINTER            2133
    Volume 2 of 2
    2134                  NRDC v. WINTER
    2.   NRDC’s NEPA Claim
    We next address the district court’s conclusion that NRDC
    has shown probable success on the merits of its claim that the
    Navy violated NEPA by failing to prepare an EIS for the
    SOCAL exercises.
    In our November 13, 2007 order we concluded that “Plain-
    tiffs have shown a strong likelihood of success on the merits
    of their claims under [NEPA].” 
    NRDC, 508 F.3d at 886
    .
    While that conclusion was based on our review of the record
    underlying the district court’s August 7, 2007 preliminary
    injunction order, the only subsequent developments are
    CEQ’s approval of “alternative arrangements” pursuant to 40
    C.F.R. § 1506.11 and the Navy’s concession, by virtue of
    seeking such approval, that the SOCAL exercises will have a
    “significant environmental impact.” See 40 C.F.R. § 1506.11
    (“Where emergency circumstances make it necessary to take
    an action with significant environmental impact without
    observing the provisions of these regulations, the Federal
    agency taking the action should consult with the Council
    about alternative arrangements.”) (emphasis added). Although
    we elaborate on our reasons, our original conclusion remains
    unchanged.
    NRDC v. WINTER                       2135
    a.   Statutory Background
    As discussed earlier, NEPA requires a federal agency such
    as the Navy to prepare a detailed EIS for all “major Federal
    actions significantly affecting the quality of the human envi-
    ronment.” 42 U.S.C. § 4332(2)(C). However, if, as here, an
    agency’s regulations do not categorically require the prepara-
    tion of an EIS, then the agency must first prepare an EA to
    determine whether the action will have a significant effect on
    the environment. Nat’l Parks & Conservation Ass’n v. Bab-
    bitt, 
    241 F.3d 722
    , 730 (9th Cir. 2001); see 40 C.F.R.
    § 1501.4. If the action will significantly affect the environ-
    ment, an EIS must be prepared, while if the project will have
    only an insignificant effect, the agency issues a Finding of No
    Significant Impact (FONSI). Ocean Advocates v. U.S. Army
    Corps of Eng’rs, 
    402 F.3d 846
    , 864 (9th Cir. 2005); see 40
    C.F.R. §§ 1501.3, 1501.4.
    [8] “An EIS must be prepared ‘if substantial questions are
    raised as to whether a project . . . may cause significant degra-
    dation of some human environmental factor.’ ” Blue Moun-
    tains Biodiversity Project v. Blackwood, 
    161 F.3d 1208
    , 1212
    (9th Cir. 1998) (quoting Idaho Sporting Congress v. Thomas,
    
    137 F.3d 1146
    , 1149 (9th Cir. 1998)). Thus, a plaintiff need
    not show that significant effects on the environment will in
    fact occur; raising “substantial questions whether a project
    may have a significant effect” on the environment is enough.
    Id.; Idaho 
    Sporting, 137 F.3d at 1150
    .
    NEPA’s procedural requirements mandate that an agency
    take a “hard look” at the environmental consequences of its
    actions. Earth Island 
    II, 442 F.3d at 1159
    . NEPA is unique in
    that it does not direct or require any particular substantive
    action on the part of an agency. Its sole purpose is to require
    that the agency be fully informed as to the environmental con-
    sequences of its actions, the mitigation measures available,
    and the alternatives to its proposed action. Once fully
    informed, the agency may make its own final rule or decision.
    2136                   NRDC v. WINTER
    However, an agency may not avoid preparing an EIS by mak-
    ing conclusory assertions that an activity will have only an
    insignificant impact on the environment. Ocean 
    Advocates, 402 F.3d at 864
    . If an agency opts not to prepare an EIS, it
    must put forth a “convincing statement of reasons” to explain
    why a project’s impacts are insignificant. Blue 
    Mountains, 161 F.3d at 1212
    (quoting Save the Yaak Comm. v. Block, 
    840 F.2d 714
    , 717 (9th Cir. 1988)).
    [9] NEPA challenges are reviewed under the APA, which
    provides that an agency action may be set aside if it is “arbi-
    trary, capricious, an abuse of discretion, or otherwise not in
    accordance with law[.]” 5 U.S.C. § 706(2)(A). The agency’s
    decisions are “entitled to a presumption of regularity. But that
    presumption is not to shield [the agency’s] action from a thor-
    ough, probing, in-depth review.” Citizens to Preserve Overton
    Park, Inc. v. Volpe, 
    401 U.S. 402
    , 415 (1971) (citations omit-
    ted). Thus, in reviewing an agency’s decision not to prepare
    an EIS, a court must “determine whether the agency has taken
    a ‘hard look’ at the consequences of its actions, ‘based [its
    decision] on a consideration of the relevant factors,’ and pro-
    vided a ‘convincing statement of reasons to explain why a
    project’s impacts are insignificant.’ ” Native Ecosystems
    Council v. U.S. Forest Serv., 
    428 F.3d 1233
    , 1239 (9th Cir.
    2005) (quoting Nat’l Parks & Conservation 
    Ass’n, 241 F.3d at 730
    ).
    Agencies have wide discretion in assessing scientific evi-
    dence, but they “must ‘take a hard look at the issues and
    respond[ ] to reasonable opposing viewpoints.’ ” Earth Island
    
    II, 442 F.3d at 1160
    (internal quotation omitted, brackets in
    original). “ ‘When specialists express conflicting views, an
    agency must have discretion to rely on the reasonable opin-
    ions of its own experts, even if a court may find contrary
    views more persuasive. At the same time, courts must inde-
    pendently review the record in order to satisfy themselves that
    the agency has made a reasoned decision based on its evalua-
    tion of the evidence.’ ” 
    Id. (quoting Marsh
    v. Or. Nat. Res.
    NRDC v. WINTER                     2137
    Council, 
    490 U.S. 360
    , 378 (1989)). “If an agency has failed
    to make a reasoned decision based on an evaluation of the
    evidence, we may properly conclude that an agency has acted
    arbitrarily and capriciously.” 
    Id. b. Substantial
    Questions about the Environmental
    Impact of the Exercises
    The district court found that NRDC had raised substantial
    questions as to whether the SOCAL exercises would have a
    significant impact on the environment. Jan. 3, 2008 Dist. Ct.
    Order at 6-7. Accordingly, the court concluded that NRDC
    had demonstrated probable success on the merits of its claim
    that the Navy’s failure to prepare an EIS was arbitrary and
    capricious and in violation of NEPA and the APA. 
    Id. at 7.
    The district court did not rely on an erroneous legal premise
    or abuse its discretion in so concluding.
    [10] Initially, we repeat our observation that the Navy, by
    seeking approval by CEQ of “alternative arrangements” pur-
    suant to 40 C.F.R. § 1506.11, has effectively conceded that
    the SOCAL exercises will have a significant impact on the
    environment. See 40 C.F.R. § 1506.11. As the text of
    § 1506.11 indicates, the very purpose of the regulation is to
    provide for the possibility of alternative arrangements where
    emergency circumstances require the taking of an action
    “with significant environmental impact” without observing
    the requirements of NEPA. See 
    id. The fact
    that the Navy
    sought relief under § 1506.11 is evidence that the Navy recog-
    nizes that the SOCAL exercises have a “significant environ-
    mental impact.”
    Moreover, the fact that “[t]he Navy is currently evaluating
    the environmental impact of MFA sonar training exercises
    through its development of the SOCAL Range Complex Envi-
    ronmental Impact Statement,” Jan. 15, 2008 CEQ Letter at 2,
    confirms that, at the very least, the Navy acknowledges that
    substantial questions have been raised as to whether the
    2138                       NRDC v. WINTER
    SOCAL exercises will have a significant impact on the envi-
    ronment. Accordingly, were we not to review the Navy’s EA,
    we would have little difficulty concluding that the district
    court did not rely on an erroneous legal premise or abuse its
    discretion in determining that NRDC has demonstrated proba-
    ble success on the merits of its NEPA claim. Our own review
    of the EA leads us to the same conclusion.48
    The Navy argues that the district court made a clearly erro-
    neous assessment of the evidence of the effect of MFA sonar
    on marine mammals in the waters of southern California. Spe-
    cifically, the Navy asserts that the court misunderstood the
    significance of the EA’s reference to the 548 predicted
    instances of Level A harassments of beaked whales. The
    Navy explains that it categorized predicted sonar exposures to
    beaked whales as Level A harassments not because beaked
    whales were expected to suffer such harassments but rather
    because such categorization would allow the Navy to analyze
    the potential impacts of MFA sonar on each beaked whale
    species in greater detail than it would otherwise.
    We find no abuse of discretion in the district court’s rejec-
    tion of the Navy’s argument. The Navy’s explanation for its
    categorization of predicted sonar exposures to beaked whales
    as Level A harassments finds no support in the EA, and coun-
    sel for the Navy was unable to explain at oral argument on
    November 8, 2007, how classifying exposures as Level A
    harassments would allow the Navy to better analyze the
    impacts of MFA sonar on various species of beaked whales.
    Rather, the EA makes clear that the Navy categorized the
    expected exposures to beaked whales as Level A harassments
    because it concluded, in light of recent beaked whale strand-
    ings linked to the use of MFA sonar, that beaked whales may
    48
    The Navy does not reargue the merits of NRDC’s NEPA claim in its
    current appeal brief. We therefore assume that the Navy’s current position
    is the same as set forth in its brief filed with our court on September 14,
    2007.
    NRDC v. WINTER                            2139
    be more sensitive to sonar exposures than other cetaceans.
    Because the lack of data precluded the Navy from establish-
    ing separate impact thresholds for beaked whales, the Navy
    decided that for beaked whales it would categorize exposures
    as Level A harassments that would constitute Level B harass-
    ments for other cetaceans.
    The Navy’s decision to do so is supported by ample evi-
    dence indicating that beaked whales are particularly vulnera-
    ble to MFA sonar. The documented strandings of marine
    mammals that have been linked to the use of MFA sonar
    overwhelmingly involve beaked whales.49 Indeed, according
    to the International Whaling Commission the evidence associ-
    ating the use of MFA sonar with beaked whale strandings is
    “very convincing” and “appears overwhelming.” Similarly, a
    Navy-sponsored study found “completely convincing” the
    evidence that MFA sonar had caused strandings of beaked
    whales.
    Moreover, to the extent that a paucity of scientific data pre-
    vents the Navy from establishing meaningful impact thresh-
    olds for beaked whales, that is a reason to conduct further
    research and prepare an EIS—not a reason to ignore the data
    that does exist and proceed with the SOCAL exercises with-
    49
    We reject the Navy’s argument that the district court erred by relying
    on evidence not included in the Navy’s administrative record in reaching
    its conclusion that NRDC had demonstrated probable success on the mer-
    its. While generally a district court’s review under the APA is limited to
    the administrative record before the agency, it may consider evidence
    beyond the administrative record in certain situations. See, e.g., Ranchers
    Cattlemen Action v. USDA, 
    499 F.3d 1108
    , 1117 (9th Cir. 2007). The dis-
    trict court properly considered extra-record evidence here because the
    Navy never submitted an administrative record to the district court despite
    having had almost a year to do so since NRDC filed its complaint on
    March 22, 2007. The Navy has not offered any valid explanation for why
    it failed to submit an administrative record. We note that the Navy filed
    a fourteen-volume record in the related litigation concerning the 2006
    RIMPAC exercise only two days after NRDC filed its complaint in that
    case.
    2140                      NRDC v. WINTER
    out adequate mitigation measures. As we explained in
    National Parks:
    An agency must generally prepare an EIS if the envi-
    ronmental effects of a proposed agency action are
    highly uncertain. Preparation of an EIS is mandated
    where uncertainty may be resolved by further collec-
    tion of data or where the collection of such data may
    prevent speculation on potential . . . effects. The pur-
    pose of an EIS is to obviate the need for speculation
    by insuring that available data are gathered and ana-
    lyzed prior to the implementation of the proposed
    action.
    Nat’l Parks & Conservation 
    Ass’n, 241 F.3d at 732
    (internal
    citations and quotations omitted).
    The Navy also contends that the district court misunder-
    stood the significance of the nearly 170,000 predicted Level
    B harassments. First, the Navy argues that this number is an
    overestimate resulting from conservative assumptions in its
    model and from the fact that it does not take into account the
    mitigation measures the Navy would employ. However, the
    Navy stated in the EA that its prediction of the harm to marine
    mammals was “consistent with the best available science.”
    And while the Navy “assumed” that its prediction was an
    overestimate, it acknowledged that the science was “incom-
    plete,” which apparently precluded the Navy from even
    approximating by how much it had overestimated the harm.
    Likewise, the Navy made no attempt to approximate how
    many Level B harassments its mitigation measures would pre-
    vent.50 Accordingly, we, like the Navy, must rely on the esti-
    mate of nearly 170,000 predicted Level B harassments.
    50
    The Navy has estimated that in the 2006 RIMPAC exercise, the
    employed mitigation measures prevented approximately 100 marine mam-
    mals from being exposed to MFA sonar. Even ignoring the fact that the
    mitigation measures employed in the 2006 RIMPAC exercise were more
    NRDC v. WINTER                           2141
    Second, the Navy argues that most of the predicted Level
    B harassments are below the threshold for causing temporary
    hearing loss and will induce only temporary behavioral
    responses which can be as minor as causing an animal to
    avoid the noise source. But according to the Navy’s own defi-
    nition of Level B harassment, those temporary behavioral
    responses are nevertheless profound, as they cause “disruption
    of natural behavioral patterns . . . to a point where such
    behaviors are abandoned or significantly altered.”51 As the
    NMFS’ Biological Opinion makes clear, such disruption of
    natural behavioral patterns can be lethal for marine mammals.
    While the EA also states that it is “highly unlikely” that
    Level B harassments would cause disturbance to a point
    where behavioral patterns are abandoned or significantly
    altered, the EA provides no support for that statement and
    fails to explain why those harassments are nevertheless classi-
    fied as Level B under the EA’s own definition. The district
    court did not abuse its discretion in determining that such a
    conclusory statement does not dispense with the requirement
    of preparing an EIS. See Ocean 
    Advocates, 402 F.3d at 864
    (“[An agency] cannot avoid preparing an EIS by making con-
    clusory assertions that an activity will have only an insignifi-
    cant impact on the environment.”).
    Next, the Navy argues that it was “entitled to rely” on the
    stringent than those the Navy has agreed to employ in the SOCAL exer-
    cises, that estimate would suggest that in the fourteen SOCAL exercises
    the mitigation measures would prevent only 1,400 exposures to marine
    mammals (14 exercises x 100 prevented exposures). Accordingly, the esti-
    mate of 170,000 Level B harassments would hardly be diminished by the
    Navy’s current mitigation measures.
    51
    The Navy derived this definition from the MMPA, 16 U.S.C.
    § 1362(18)(B)(ii), which was amended in 2003 to exclude from the defini-
    tion those acts that disrupted natural behavioral patterns but not to the
    point where the behaviors were abandoned or significantly altered. See
    H.R. Rep. No. 99(I), 108th Cong. 1 Sess. 2003 (5/14/03).
    2142                      NRDC v. WINTER
    conclusion of the NMFS in its Biological Opinion, which the
    district court held satisfied the NMFS’ statutory obligation,
    see 16 U.S.C. § 1536(a)(2), that the SOCAL exercises were
    not likely to jeopardize the continued existence of threatened
    or endangered marine mammal species. But the NMFS opined
    only on the effects of MFA sonar on six species of marine mam-
    mal,52 which do not include several rare or uncommon species
    of marine mammal that are expected to be exposed to a signif-
    icant number of sonar harassments.53 For example, the EA
    predicts 436 Level A harassments of Cuvier’s beaked whales.
    According to NOAA, as few as 1,121 Cuvier’s beaked whales
    may exist in California, Oregon and Washington combined.
    Likewise, the EA predicts 1,092 Level B harassments of bot-
    tlenose dolphins, of which only 5,271 may exist in the Cali-
    fornia Coastal and Offshore stocks.
    The Navy suggests that the test is whether the continued
    existence of marine mammal species is jeopardized. This is
    wrong. An agency action can have “significant effects” on the
    environment short of threatened extinction. NEPA regulations
    promulgated by CEQ provide that “significantly” has two
    components: context and intensity. 40 C.F.R. § 1508.27. Con-
    text refers to the setting in which the proposed action takes
    place, in this case the Southern California Operating Area.
    See 
    id. § 1508.27(a).
    Intensity means “the severity of impact.”
    
    Id. § 1508.27(b).
    In considering the severity of the potential
    52
    Those six species are the fin whale, humpback whale, sei whale,
    sperm whale, and Guadalupe fur seal.
    53
    While in a recent memorandum—written well after the Navy prepared
    its EA—the NMFS concluded that the Navy’s own mitigation measures
    “will minimize the likelihood of beaked whales being caught in circum-
    stances that characterize known strandings of beaked whales,” Jan. 9,
    2008 Memorandum from NMFS to the Under Secretary of Commerce for
    Oceans and Atmosphere at 3, the NMFS did not conclude that the Navy’s
    measures would prevent direct physical injury (such as tissue damage) to
    beaked whales. Indeed, the NMFS acknowledged that “the mechanism by
    which MFA sonar appears to be injurious to beaked whales is poorly
    understood.” 
    Id. at 4.
                           NRDC v. WINTER                      2143
    environmental impact, a reviewing agency may consider up to
    ten factors to help inform the “significance” of a project,
    including the degree to which the effects on the quality of the
    human environment are likely to be “highly controversial”
    and the degree to which the possible effects on the human
    environment are “highly uncertain or involve unique or
    unknown risks.” 
    Id. §§ 1508.27(b)(4),
    (b)(5). We have held
    that “one of these factors may be sufficient to require prepara-
    tion of an EIS in appropriate circumstances.” Ocean Advo-
    
    cates, 402 F.3d at 865
    ; see Ctr. for Biological Diversity v.
    Nat’l Highway Traffic Safety Admin., 
    508 F.3d 508
    , 553 (9th
    Cir. 2007); Nat’l Parks & Conservation 
    Ass’n, 241 F.3d at 731
    .
    Notably, whether an agency action will jeopardize the con-
    tinued existence of an endangered or threatened species is not
    among these factors. See 40 C.F.R. § 1508.27(b). However,
    the degree to which the action may “adversely affect” an
    endangered or threatened species is. See 
    id. § 1508.27(b)(9).
    While the NMFS’ Biological Opinion concluded that the
    SOCAL exercises were not likely to jeopardize the continued
    existence of the six endangered species it studied, it neverthe-
    less acknowledged that the exercises “may adversely affect”
    those species. Thus, while the Navy was not required to disre-
    gard the NMFS’ “no jeopardy” opinion, see Envtl Prot. Info.
    Ctr. v. U.S. Forest Serv., 
    451 F.3d 1005
    , 1012 (9th Cir. 2006),
    the Biological Opinion by its own terms makes clear that the
    SOCAL exercises may “significantly” affect the environment,
    see Greater Yellowstone Coalition v. Flowers, 
    359 F.3d 1257
    ,
    1275-76 (10th Cir. 2004) (regarding as not determinative for
    NEPA purposes the Fish and Wildlife Service’s “no jeopardy”
    opinion as to bald eagles).
    The Navy further argues that its finding of no significant
    impact was not arbitrary and capricious because no sonar-
    inflicted injuries have been observed in the Southern Califor-
    nia Operating Area in almost forty years of MFA sonar use
    by the Navy. But as explained above, that fact has limited
    2144                   NRDC v. WINTER
    probative value in establishing whether marine mammals will
    in fact be harmed by the Navy’s use of MFA sonar. Exposure
    to MFA sonar may physically and behaviorally harm marine
    mammals even if it does not cause them to strand. And absent
    stranding, such harm is difficult to observe. That is particu-
    larly true for the beaked whale—the marine mammal most
    vulnerable to MFA sonar—in which a population decline of
    50% over 15 years would go undetected as a decline at all in
    90% of the beaked whale stocks.
    Finally, the Navy claims that the correlation between the
    past marine mammal strandings and MFA sonar is irrelevant
    because the combination of environmental conditions “found
    at the locations of documented marine mammal stranding
    incidents” is not present in the Southern California Operating
    Area. But contrary to this claim, the EA indicates that the
    Navy has studied only the stranding in the Bahamas in 2000
    and not any of the other stranding events.
    Moreover, while the Navy’s study of the Bahamas strand-
    ing identified a combination of factors that contributed to the
    whales’ injury—the presence of a strong surface duct, unusual
    water bathymetry, intensive use of multiple sonar units over
    an extended period of time, a constricted channel with limited
    egress, and the presence of beaked whales that appear to be
    sensitive to the frequencies produced by these sonars—the EA
    provided no supporting data or analysis for its conclusion that
    this combination of factors does not exist in the Southern Cal-
    ifornia Operating Area. Thus, we find no abuse of discretion
    in the district court’s conclusion that the Navy has failed to
    provide the support for its conclusion that NEPA requires. See
    40 C.F.R. § 1502.24.
    In addition, the Navy’s Bahamas study acknowledged that
    combinations of factors different from the one present in the
    Bahamas “may be more or less likely to cause strandings”
    (emphasis added). Thus, even if the combination of factors
    present in the Bahamas in fact does not exist in the Southern
    NRDC v. WINTER                     2145
    California Operating Area, the combination of factors that
    does exist may be even more likely to cause injury to marine
    mammals. The EA does not explore that possibility.
    [11] In sum, the district court did not abuse its discretion
    in concluding that NRDC raised substantial questions as to
    whether the SOCAL exercises would have a significant
    impact on the environment. All of the reasons stated in the EA
    for why the Navy believed the SOCAL exercises would not
    have the deleterious effect that the Navy’s own model pre-
    dicted were cursory, unsupported by cited evidence, or uncon-
    vincing. Thus, we find ample support for the district court’s
    conclusion that the Navy has not “articulate[d] a rational con-
    nection between the facts found and the conclusion[ ]
    reached.” Earth Island 
    II, 442 F.3d at 1156-57
    (quoting Mid-
    water Trawlers Co-op v. Envtl. Def. Ctr., 
    282 F.3d 710
    , 716
    (9th Cir. 2002)).
    c.   The Navy’s Mitigation Measures
    The district court also concluded that NRDC had demon-
    strated probable success on the merits of its claim that the
    Navy’s mitigation measures were inadequate to obviate the
    need for preparing an EIS. Again, we find no reliance on an
    erroneous legal premise and no abuse of discretion in the dis-
    trict court’s conclusion.
    [12] The Navy correctly points out that “[a]n agency’s
    decision to forego issuing an EIS may be justified in some cir-
    cumstances by the adoption of [mitigation] measures” and
    that those measures, if significant, “need not completely com-
    pensate for adverse environmental impacts.” Nat’l Parks &
    Conservation 
    Ass’n, 241 F.3d at 733-34
    (citations and internal
    quotation marks omitted). However, we have also held that a
    “perfunctory description” or “mere listing of mitigation mea-
    sures, without supporting analytical data,” is insufficient to
    support a finding of no significant impact. Okanogan High-
    lands Alliance v. Williams, 
    236 F.3d 468
    , 473 (9th Cir. 2000)
    2146                      NRDC v. WINTER
    (citations and internal quotation marks omitted). We find no
    reversible error in the district court’s conclusion that the
    Navy’s list of proposed mitigation measures was precisely
    such a perfunctory description devoid of supporting data.
    [13] The explanation contained in the EA as to why the
    mitigation measures are effective is contained in four short
    bullet points, stating that whales and dolphins spend extended
    periods of time on the surface, have relatively short dive peri-
    ods, tend to move in large groups (pods), and frequently come
    to the surface and have a high level of activity there. Three of
    those bullet points in effect state the same thing, namely that
    whales and dolphins spend little time under water. This expla-
    nation is inadequate for several reasons.
    [14] First, the Navy’s explanation overlooks the fact that
    beaked whales spend much of their time under water, surface
    infrequently, and are generally difficult to detect. A study by
    NMFS scientists observed that “beaked whales are always dif-
    ficult to see when they are on the surface, spend most of their
    time below the surface, and are found at low densities over
    large areas.” Likewise, NRDC submitted a declaration by a
    biologist who opines that visual monitoring by ship-based
    lookouts would result in the detection of only 2% of beaked
    whales in the Southern California Operating Area, in part
    because of the speed at which Navy vessels travel. Declara-
    tion of Dr. Robin William Baird ¶ 6.
    [15] Second, the Navy’s explanation fails to address the
    effectiveness of the Navy’s safety zones—the only measure
    that directly reduces exposure of marine mammals to MFA
    sonar. Specifically, the EA fails to explain why a safety zone
    of only 1,000 yards is adequate, why reducing the sonar level
    by 6dB and 10dB at the 1,000-yard and 500-yard marks,
    respectively, is adequate, and why it is effective to halt MFA
    sonar transmission altogether only at the 200-yard mark.54 The
    54
    As stated earlier, the Navy has recently agreed to adopt safety zones
    with radii of 1,000, 500 and 200 meters instead of 1,000, 500 and 200
    NRDC v. WINTER                            2147
    Navy’s explanation also does not relate to the effectiveness of
    the measure requiring passive sonar to be used to detect
    sounds made by marine mammals.
    While the Navy claims in the EA that it is “very likely” that
    lookouts would detect a group of common dolphins because
    of “frequent surfacing” and group sizes of “over a thousand
    animals,” it notably makes no such claims about Cuvier’s
    beaked whales, Mesoplodont beaked whales or Ziphiid
    beaked whales. Indeed, the EA acknowledged that Cuvier’s
    beaked whales and Mesoplodont beaked whales exhibit a
    range of dives lasting up to 87 minutes.
    Moreover, while the EA claims that it is “very likely” that
    Baird’s beaked whales will be detected by lookouts, it states
    nothing about the frequency with which those whales surface.
    While it may be that, as the EA states, beaked whales are
    large in size and travel in groups of between nine and thirteen
    animals, those facts hardly prove the effectiveness of visual
    surveillance measures considering that beaked whales gener-
    ally come to the surface infrequently.
    We find further support for the district court’s conclusion
    that the Navy’s mitigation measures did not obviate the need
    to prepare an EIS in the fact that, as explained above, the
    Navy refused to adopt several of the more aggressive mitiga-
    tion measures recommended by the CCC, employed in the
    2006 RIMPAC exercise, or imposed by the Department of
    yards. However, the radius of the Navy’s outer safety zone is still half of
    the radius recommended by the CCC, resulting in a safety zone that is
    75% smaller than the one found necessary by the CCC.
    Notably, NRDC has submitted declarations by scientists who state that
    sonar levels even below the Navy’s lowest impact threshold of 173 dB
    may be fatal and that sonar sound can travel up to hundreds of miles under
    water, which suggests that the Navy’s significantly smaller safety zones
    are inadequate. See Parsons decl. ¶ 13, Weilgart decl. ¶ 10.
    2148                       NRDC v. WINTER
    Defense for non-RIMPAC exercises in 2006. Specifically, the
    Navy refused to:
    •   Expand the outer safety zone to 2 kilometers;55
    •   Reduce sonar power in conditions of low visibil-
    ity or strong surface ducting;
    •   Avoid training in areas known to have high con-
    centrations of marine mammals or during the
    gray whale’s migratory season;
    •   Monitor for 30 minutes prior to commencement
    of MFA sonar use;
    •   Restrict operation of MFA sonar within 25 kilo-
    meters from the 200-meter isobath;
    •   Restrict operation of MFA sonar within 12 nauti-
    cal miles from the coast;56 and
    •   Restrict operation of MFA sonar in choke points,
    constricted channels, or canyon-like areas.57
    55
    The Navy did not discuss this measure in its EA, let alone explain why
    it would not be effective. In its “after action report” following the 2006
    RIMPAC exercise, the Navy disposed of this mitigation measure simply
    by declaring it “not prudent” and “without scientific merit.”
    56
    The Navy asserts on appeal that the SOCAL exercises will occur more
    than twelve nautical miles from the mainland coastline, but concedes that
    the exercises will occur within twelve nautical miles of Clemente Island,
    which falls within the Southern California Operating Area. In its January
    3, 2008 preliminary injunction order the district court required the Navy
    to refrain from using MFA sonar within 12 nautical miles from the Cali-
    fornia coastline. Jan. 3, 2008 Dist. Ct. Order at 14.
    57
    The parties disagree as to whether there are any choke points in the
    Southern California Operating Area. In its January 3, 2008 preliminary
    injunction order the district court found that the Catalina Basin poses the
    same concerns as a choke point: ingress and egress to the basin are
    restricted and the area has a high density of marine mammals. Jan. 3, 2008
    Dist. Ct. Order at 17. Accordingly, the district court ordered the Navy to
    refrain from using MFA sonar in the Catalina Basin. 
    Id. at 17-18.
                               NRDC v. WINTER                            2149
    Notably, as to most of these measures the Navy does not
    contest that they would be effective. While the Navy claims
    that some of the measures would adversely affect its ability to
    achieve the objectives of the exercises, that does not render
    the measures the Navy has adopted adequate to avoid the
    need for preparing an EIS. Indeed, the Navy states in its “after
    action report” following the first three SOCAL exercises that
    in future exercises it intends to incorporate data collection
    necessary to address the question of how many marine mam-
    mals not observed by lookouts may have been exposed to
    dangerous sonar levels, and will integrate additional monitor-
    ing tools and techniques. While the Navy’s intent is com-
    mendable, it implicitly acknowledges that its current
    mitigation and data collection efforts are less than adequate.
    [16] We conclude that the district court did not abuse its
    discretion in determining that the Navy’s cursory explanation
    in the EA for why its mitigation measures are effective does
    not demonstrate that those measures “constitute an adequate
    buffer against the negative impacts” that may result from the
    SOCAL exercises. See Nat’l Parks & Conservation 
    Ass’n, 241 F.3d at 734
    . Accordingly, we uphold the district court’s
    conclusion that the Navy’s reliance on its incomplete mitiga-
    tion plan in deciding not to prepare an EIS was likely arbi-
    trary and capricious and affirm its determination that NRDC
    has demonstrated probable success on the merits of its NEPA
    claims. Cf. Wetlands Action Network v. U.S. Army Corps of
    Eng’rs, 
    222 F.3d 1105
    , 1112 (9th Cir. 2000).58
    58
    The district court also concluded that NRDC had demonstrated proba-
    ble success on the merits of its claims that the Navy violated NEPA by
    preparing an EA that failed to adequately consider reasonable alternatives
    to its proposed action, see, e.g., Bob Marshall Alliance v. Hodel, 
    852 F.2d 1223
    , 1228 (9th Cir. 1998) (explaining that under NEPA federal agencies
    must sufficiently study, develop, and describe alternatives as part of the
    “environmental decisionmaking process”), as well as the cumulative
    impacts of its actions, see, e.g., Klamath-Siskiyou Wildlands Ctr. v.
    Bureau of Land Mgmt., 
    387 F.3d 989
    , 994 (9th Cir. 2004) (explaining that
    an EA must provide a “useful analysis of the cumulative impacts of past,
    2150                        NRDC v. WINTER
    B.    Possibility of Irreparable Injury
    In our November 13, 2007 order we affirmed the district
    court’s conclusion that NRDC had met its burden of demon-
    strating the possibility of irreparable injury. 
    NRDC, 508 F.3d at 886
    . We now explain that decision.
    [17] As the district court noted, “[w]here, as here, plaintiffs
    demonstrate a likelihood of prevailing on the merits of their
    claims, injunctive relief is appropriate where there is a ‘possi-
    bility of irreparable harm.’ ” Jan. 3, 2008 Dist. Ct. Order at 12
    (quoting Faith Ctr. Church Evangelistic Ministries v. Glover,
    
    480 F.3d 891
    , 906 (9th Cir. 2007)). NRDC must show the
    possibility of irreparable harm to its membership. See Friends
    of the Earth, Inc. v. Laidlaw Environmental Services (TOC),
    Inc., 
    528 U.S. 167
    , 180-81 (2000). After analyzing the “nu-
    merous scientific studies, declarations, reports, and other evi-
    dence submitted,” the district court concluded that NRDC had
    established “to a near certainty” that use of MFA sonar in the
    SOCAL exercises will cause irreparable harm to the environ-
    ment and to NRDC’s membership. Jan. 3, 2008 Dist. Ct.
    Order at 12.
    [18] The Navy argues that the harm resulting to the envi-
    ronment from the use of MFA sonar in the SOCAL exercises
    is merely “speculative.” But the Navy’s own EA proves other-
    wise. The EA estimates that the use of MFA sonar in the
    SOCAL exercises will result in 564 instances of physical
    injury including permanent hearing loss (Level A harassment)
    and nearly 170,000 behavioral disturbances (Level B harass-
    ment), more than 8,000 of which would also involve tempo-
    present, and future projects”). Jan. 3, 2008 Dist. Ct. Order at 8-10. We
    decline to address this aspect of the district court’s order as we have
    already concluded that the court did not abuse its discretion in finding that
    NRDC has demonstrated probable success on the merits of its other NEPA
    claims.
    NRDC v. WINTER                       2151
    rary hearing loss. As explained above, while the Navy
    protests that these figures are overestimates resulting from its
    conservative approach, the EA makes clear that the figures are
    “consistent with the best available science.” Indeed, the
    Navy’s failure to suggest by how much its figures overesti-
    mate the actual harm to marine mammals confirms that the
    EA’s figures are the best available estimates. Those estimates,
    in turn, contradict the Navy’s suggestion that the harm caused
    by MFA sonar in the SOCAL exercises is merely speculative.
    Moreover, while the record contains no evidence that
    marine mammals have been harmed by the use of MFA sonar
    in the Southern California Operating Area, the scientific con-
    sensus that MFA sonar may cause injury and death to marine
    mammals combined with the evidence that such injury, absent
    a stranding, is difficult to detect—especially in the case of the
    vulnerable beaked whale—further disproves the suggestion
    that the harm caused by MFA sonar in the SOCAL exercises
    is merely speculative.
    The Navy also argues that its use of MFA sonar will cause
    only temporary harm to marine mammals and therefore will
    not result in irreparable injury. But the EA again undermines
    the Navy’s argument. The EA’s estimate that 564 instances of
    Level A harassment will occur demonstrates that the use of
    MFA sonar will also cause permanent harm to marine mam-
    mals. Likewise, the EA’s own definition of Level B harass-
    ment indicates that the nearly 170,000 estimated instances of
    such harassment may result in the outright abandonment of
    important behaviors by marine mammals.
    Finally, the Navy argues that NRDC failed to meet its bur-
    den of demonstrating that marine mammals “will suffer irrep-
    arable injury at the species or stock-level.” For two reasons,
    the Navy has not shown that the district court relied on an
    erroneous legal premise or abused its discretion in rejecting
    this argument.
    2152                   NRDC v. WINTER
    First, NRDC had only the burden of demonstrating the
    “possibility of irreparable injury,” Freecycle 
    Network, 505 F.3d at 902
    , not that irreparable injury “will” necessarily
    occur. See Earth Island 
    II, 442 F.3d at 1159
    (holding that the
    district court erred in requiring that the plaintiff show a “sig-
    nificant threat of irreparable injury” because that standard
    imposes a higher burden of proof than the “mere possibility
    of irreparable harm” standard).
    Second, the Navy has cited no support for the proposition
    that NRDC was required to demonstrate the possibility of
    irreparable injury at the species or stock-level. While the
    Navy relies on Water Keeper Alliance v. Dep’t of Defense,
    
    271 F.3d 21
    (1st Cir. 2001), the court in that case only con-
    cluded that the district court did not abuse its discretion in
    concluding that the “death of even a single member of an
    endangered species” would be an insufficient basis for the
    plaintiffs to demonstrate the possibility of irreparable injury.
    See 
    id. at 34.
    Here, the district court found that, according to
    the Navy’s EA, the SOCAL exercises “will cause widespread
    harm to nearly thirty species of marine mammals, including
    five species of endangered species, and may cause permanent
    injury and death.” January 3, 2008 Dist. Ct. Order at 12.
    In any event, even if NRDC were required to demonstrate
    the possibility of irreparable injury at the species or stock-
    level, it would have satisfied that requirement here. As dis-
    cussed earlier, the EA predicts 436 Level A harassments of
    Cuvier’s beaked whales, of which, according to NOAA, as
    few as 1,121 may exist in California, Oregon and Washington
    combined. Similarly, the EA predicts 1,092 Level B harass-
    ments of bottlenose dolphins, of which only 5,271 may exist
    in the California Coastal and Offshore stocks.
    [19] Accordingly, we hold that the district court did not
    rely on an erroneous legal premise or abuse its discretion in
    concluding that NRDC has demonstrated the possibility of
    irreparable injury.
    NRDC v. WINTER                                2153
    C.    Balance of Hardships
    [20] Having determined that the district court neither relied
    on erroneous legal premises nor abused its discretion in deter-
    mining that NRDC has demonstrated a strong likelihood of
    success on the merits of its NEPA claim and the possibility
    of irreparable injury, we turn to the “balance of hardships.”
    See Freecycle 
    Network, 505 F.3d at 902
    . The Supreme Court
    has held that environmental injury, in addition to often being
    permanent or of long duration, can seldom, by its nature, “be
    adequately remedied by money damages”; therefore, “[i]f
    such injury is sufficiently likely, . . . the balance of harms will
    usually favor the issuance of an injunction to protect the envi-
    ronment.” Amoco Prod. Co. v. Vill. of Gambell, AK, 
    480 U.S. 531
    , 545 (1987).
    The Navy maintains, and the district court did not contest,
    that its ability to train and certify its west-coast strike groups
    for combat deployment is critical.59 The Navy argues that its
    59
    For example, Captain Martin M. May states that “[m]odern, quiet sub-
    marines . . . pose the primary threat to the littorals, control of strategic
    maritime choke points, transit through international straits, and protection
    of sea lines of communication vital to international commerce.” May decl.
    ¶ 19. These submarines are “nearly undetectable to U.S. and allied naval
    forces without the use of [MFA] sonar.” 
    Id. at ¶
    20. Captain May also
    asserts that “[s]onar operators and crews must train regularly and fre-
    quently to develop the skills necessary to master the art and processes of
    identifying submarines in the complex subsurface environment[,]” and
    that computer simulations are not adequate for teaching these skills. 
    Id. at ¶
    22. Captain May maintains that if sonar use is enjoined, the Navy would
    be unable to gauge a fleet’s ability to use active sonar. 
    Id. at ¶
    26.
    Captain May also contends that “[t]he ranges that comprise the South-
    ern California Operating Area make up a unique area in which strike
    groups can meet all required training objectives at the same time. 
    Id. at ¶
    25. Another significant factor is that many of the operating areas have
    been surveyed and closely mirror the prospective operating environments
    in many of the world’s ‘hot’ spots where U.S. Naval forces may be
    required to fight.” 
    Id. Training “in
    our own littorals . . . also build[s] profi-
    ciency and experience in our own waters should the enemy attempt to
    interdict U.S. forces deploying to the area of conflict.” 
    Id. 2154 NRDC
    v. WINTER
    ability to engage in these critical activities is severely
    degraded by: (1) the requirement that it shut down its use of
    MFA sonar when a marine mammal is detected within 2,200
    yards of a sonar-emitting source; and (2) the requirement that
    it power down its sonar use by 6 dB (75%) when significant
    surface ducting conditions are detected. Without proper train-
    ing and certification, the Navy asserts that it will not be able
    to deploy a sufficient number of combat-ready forces to pro-
    vide for the national defense.
    The district court rejected the Navy’s argument that the bal-
    ance of hardships tipped in its favor. It concluded that
    although “the imposition of these mitigation measures will
    require the Navy to alter and adapt the way it conducts anti-
    submarine warfare training—a substantial challenge,” the
    measures would not preclude the Navy from effectively train-
    ing and certifying forces for deployment to combat zones in
    the western Pacific and the Middle East.60 Feb. 4, 2008 Dist.
    Ct. Order.
    The gravity of the Navy’s asserted hardship requires that
    we review the district court’s determination, as well as the
    affidavits submitted by the Navy, with the utmost care. We
    have done so here and, for the reasons set forth below, we
    conclude that the district court did not abuse its discretion in
    reaching its determination.
    We note that any negative impact on the Navy’s ability to
    successfully conduct its exercises under the challenged miti-
    60
    The district court crafted its mitigation order after carefully weighing
    evidence submitted by the parties over a period of “longstanding involve-
    ment” with the matters at issue. It took into account the Navy’s need for
    training in certain bathymetry and under certain conditions, and declined
    to impose several of plaintiffs’ proposed “sweeping geographic exclu-
    sions” which would have precluded the Navy from training with MFA
    sonar within 25 nautical miles of the coast, in waters shallower than 1,500
    meters to the maximum extent possible, and in the Westfall seamount and
    the Cortez and Tanner Banks. Jan. 3, 2008 Dist. Ct. Order at 13 n.6.
    NRDC v. WINTER                               2155
    gation measures is necessarily speculative because the Navy
    has never before employed these measures in the context of
    MFA sonar training.61 The speculative nature of the Navy’s
    asserted harm is reflected in its own characterization of the
    hardship; the Navy does not claim that the challenged mea-
    sures will categorically preclude effective training and certifi-
    cation, but rather that they will give rise to an “unacceptable
    risk” of such a result. Our task, then, is to determine, as best
    we are able from the record before us, whether the district
    court erred by giving insufficient weight to the Navy’s
    asserted hardship or by resting its conclusions on clearly erro-
    neous factual findings.
    In support of its assessment that the challenged measures
    will significantly impair its training exercises, the Navy offers
    the declarations of various high-ranking officers. For exam-
    ple, Admiral John Locklear explains that the 2,200 yard safety
    zone will in “[his] opinion . . . have crippling implications on
    Navy’s ability to conduct realistic pre-deployment [ASW]
    training employing MFA sonar” and “will significantly
    impact ASW training.” Locklear decl. ¶¶ 9, 13. The Chief of
    Naval Operations refers to an unacceptable risk to strike
    group certification posed by both the safety zone and surface
    ducting measures. The judgment of these naval officers and,
    in particular, that of the Chief of Naval Operations, who is
    charged with the statutory responsibility under 10 U.S.C.
    61
    The Navy has not represented that, if the challenged measures are
    upheld, it will cease its training exercises. Further, the Navy acknowl-
    edged at oral argument on February 27, 2008, that it can certify strike
    groups despite the inability to train in surface ducting conditions. We
    therefore proceed under the assumption that the exercises will continue to
    take place, thereby preserving the possibility of successful training and
    certification of strike groups. Thus, the district court did not err in failing
    to weigh the hardship to the Navy, and the public, that would result if the
    Navy stopped training altogether. Rather, the district court did not abuse
    its discretion and properly considered the hardship that would result if the
    Navy were required to abide by the challenged mitigation measures during
    its remaining exercises in 2008 and 2009.
    2156                       NRDC v. WINTER
    § 5062 for organizing, training, and equipping the Navy, is
    entitled to substantial deference. See Khalsa v. Weinberger,
    
    779 F.2d 1393
    , 1400 n.4 (9th Cir. 1985) (“The degree of def-
    erence due to factual assertions by the military is proportion-
    ate to the need for the application of military experience,
    judgment, and expertise in evaluating the assertion.”).
    Nevertheless, a court’s deference is not absolute, even
    when a government agency claims a national security interest.
    See, e.g., Campbell v. U.S. Dep’t of Justice, 
    164 F.3d 20
    , 30
    (D.C. Cir. 1998) (“[D]eference is not equivalent to acquies-
    cence . . . .”). The district court therefore did not abuse its dis-
    cretion when it considered the Navy’s declarations along with
    the evidence contained in the record as a whole. This evi-
    dence, much of it submitted by the Navy itself, supports the
    district court’s conclusion that the challenged mitigation mea-
    sures will not likely compromise the Navy’s ability to effec-
    tively train and certify its west-coast strike groups. We
    address the evidence with respect to each of the challenged
    mitigation measures in turn.
    1.    The 2,200 Yard Shutdown Zone
    We first consider the requirement that the Navy shut down
    its use of MFA sonar when a marine mammal is detected
    within 2,200 yards of a sonar-emitting source.62 Upon a care-
    ful review of the record, we find no clear error in the district
    court’s factual finding that this measure would not compro-
    mise the Navy’s ability to train and certify its strike groups.
    62
    Although our 
    discussion supra
    addresses the evidence contained in the
    record with respect to the likely impact that the increase in the safety
    zone’s size will have on training and certification, the Navy also contests
    this measure’s application to all sonar sources, including helicopter dip-
    ping sonar and sonobuoys which emit less powerful sonar waves. See, e.g.,
    Locklear decl. ¶ 11. Despite the fact that the dipping sonar and sonobuoys
    have lower energy source levels, they still operate at levels above those
    shown to pose a danger to marine mammals. See, e.g., Parsons decl. ¶ 13.
    Accordingly, the district court’s decision to include these sonar sources in
    its mitigation measure was not an abuse of discretion.
    NRDC v. WINTER                             2157
    [21] The “after action reports” compiled by the Navy fol-
    lowing eight prior COMPTUEX and JTFEX exercises in the
    Southern California Operating Area undermine the Navy’s
    assessment of the significance of the hardship that this mitiga-
    tion measure would impose.63 The reports contain several rel-
    evant data points. First, the data reveal a relatively low
    likelihood that a marine mammal will be sighted during a time
    when the Navy’s MFA sonar is in use, thereby triggering
    implementation of this mitigation measure. During two of the
    eight exercises, no marine mammals were sighted while MFA
    sonar was in use. In the remaining exercises, sightings rarely
    occurred while MFA sonar was in use.64 In fact, over the
    course of eight exercises lasting one or more weeks each, the
    Navy observed marine mammals only 51 times while using
    MFA sonar, which represents less than 15% of all marine
    mammal observations (345) during those exercises. Second,
    the data show that the Navy shut down its MFA sonar twenty-
    seven times over the course of its eight prior exercises. If the
    district court’s mitigation measure had been in place, the
    Navy would have had to shut down at most an additional
    twenty-one times: an increase of only two to three shutdowns
    per exercise.65 Moreover, of the twenty-one additional times
    63
    During these exercises, the Navy’s preferred 1,000 yard safety zone
    was implemented requiring a 6 dB power-down when a marine mammal
    was detected within 500-1,000 yards, an additional 4 dB power-down
    within 200 and 500 yards, and a mandatory shutdown within 200 yards.
    We note that the first four of the eight exercises for which the record
    contains “after action reports” were not part of the current SOCAL exer-
    cises.
    64
    The low likelihood of a sighting occurring while MFA sonar is being
    used does not mean it is rare for marine mammals to be exposed to dan-
    gerous noise levels. Rather, two facts demonstrate that the number of
    sightings does not equate to the number of mammals affected by an MFA
    sonar event: (1) the presence of marine mammals is difficult to detect by
    “sight” because many spend significant amounts of time submerged
    underwater; and (2) sound travels long distances in water (in some cases
    up to many hundreds of miles) creating the potential for adverse effects
    beyond the range of sight.
    65
    The Navy argues that this mitigation measure will result in a five-fold
    increase in the number of times it is required to shut down during training
    2158                        NRDC v. WINTER
    that the Navy would have been required to shut down, in
    eleven of these instances, the Navy powered down its sonar.
    During these power-downs, the Navy’s detection capability
    was significantly reduced. See, e.g., Bird decl. ¶ 49. Accord-
    ingly, if the district court’s injunction had been in place, the
    Navy would have had to compromise detection capability
    only approximately one more time per exercise. Third, the
    “after action reports” do not establish any serious, negative
    effects on operational impact from the smaller safety zone
    imposed in the eight exercises.66 Because the broader safety
    zone likely will not require significantly more shutdowns, the
    exercises. The Navy arrives at this higher number by excluding from its
    calculation shutdowns that occurred beyond the 200 yard mandatory shut-
    down zone. But this calculation fails to account for the Navy’s actual prac-
    tice of shutting down sonar in a significant number of cases where marine
    mammals were detected beyond 200 yards, including at distances as far as
    3,100, 4,000, and 6,000 yards. In fact, the “after action reports” reveal that
    of the twenty-seven times the Navy shut down MFA sonar, it did so fifteen
    times when the observed marine mammals were outside the 200 yard man-
    datory shutdown zone and four times when the marine mammals were at
    an “unknown” distance.
    There is no dispute that the Navy continued to certify its strike groups
    throughout these exercises. The Navy defends its exclusion of any non-
    mandatory shutdowns in its count by claiming that any shutdowns that
    occurred beyond the 200 yard range “likely occurred during tactically
    insignificant times.” Locklear decl. ¶ 11. The record fails to support this
    claim. The “after action reports” do not distinguish between shutdown
    events in evaluating training impacts. Indeed, the very same language is
    used to describe the loss of detection opportunities during all of the exer-
    cises, without regard to whether the shutdowns occurred within or beyond
    200 yards.
    66
    Indeed, the “after action reports” contain only one instance in which
    the Navy comments that its operation was actually affected by a safety
    zone mitigation measure. See After Action Report for COMPTUEX 07-01
    (19 November-19 December 2006) at 6. All the other reports state that the
    impact of the safety zone measure was “not determinable in the reactions
    of the particular units” and only speculate that “the proximity of a subma-
    rine in the vicinity meant there was a potential submarine detection oppor-
    tunity missed by the exercise participants.”
    NRDC v. WINTER                              2159
    district court’s conclusion that this mitigation measure does
    not pose a significant risk of rendering the Navy’s training
    exercises ineffective is well-supported. We cannot, on this
    record, find that the district court abused its discretion.
    In addition to data drawn from “after action reports,” the
    record contains other evidence of the feasibility of mandatory
    shutdown zones of this size, and even greater, during naval
    training exercises. Indeed, the size of the district court’s
    imposed shutdown zone was based on the CCC’s proposed
    mitigation measure, which in turn was drawn from the Navy’s
    own imposition of a 2,000 meter shutdown requirement when
    it uses low-frequency active sonar.67 While the record does
    not indicate whether low-frequency active sonar has the same
    effect on marine mammals as MFA sonar, the Navy offers no
    explanation as to why a 2,000 meter safety zone is feasible
    during its operation of low-frequency active sonar but not
    during its use of MFA sonar.68
    67
    While we recognize that each Navy has unique operating require-
    ments, the record shows that NATO imposes a 2,000 meter shutdown zone
    when a marine mammal is detected—the same zone that the district
    court’s preliminary injunction requires. The Australian Navy goes farther,
    mandating a shutdown of activities if a marine mammal is detected within
    4,000 yards of a sonar-emitting vessel.
    68
    To the contrary, in its initial submissions to the court, the Navy repre-
    sented that “[p]rior to [the district court’s] requirement, the maximum
    mandatory shutdown zone the Navy ever employed was 200 meters.” Jan.
    15 Emergency Motion at 16 (emphasis added). This representation is
    plainly contradicted by the record. In its most recent brief to the court, the
    Navy clarified that, “Prior to this requirement, the maximum mandatory
    shutdown zone ever employed for MFA sonar was 200 meters.” However,
    the Navy still does not discuss nor defend its ability to implement a 2,000
    meter safety zone in its low-frequency, but not in its mid-frequency, sonar
    activities.
    2160                   NRDC v. WINTER
    2.   The Requirement to Power-Down in Significant
    Surface Ducting Conditions
    [22] We next consider the requirement that the Navy
    power-down its sonar use by 6 dB when significant surface
    ducting conditions are detected. Although the Navy stresses
    the importance of training in surface ducting conditions, it
    admits—and the record confirms—that such conditions occur
    relatively rarely in the southern California waters in which the
    Navy has chosen to conduct its exercises. Indeed, the “after
    action reports” from JTFEX and COMPTUEX exercises con-
    ducted in the Southern California Operating Area in 2006
    show that significant surface ducting conditions were not
    detected during any of those exercises. Yet despite the strike
    groups’ inability to train under such conditions, the Navy cer-
    tified them. The record, then, undermines the Navy’s conten-
    tion that the district court’s mitigation measure regarding
    surface ducting conditions will significantly impact its ability
    to certify strike groups.
    [23] Thus, although the actual effect of the challenged miti-
    gation measures on the exercises at issue is necessarily specu-
    lative, data from past Navy exercises and practices supports
    the district court’s conclusion that the imposition of these
    measures is not likely to prevent effective training and certifi-
    cation of strike groups. After a thorough review of this record,
    we are not “left with the definite and firm conviction that a
    mistake has been committed.” Sports Form, 
    Inc., 686 F.2d at 752
    . To the contrary, there is significant evidence of the
    Navy’s ability to successfully train and certify its strike
    groups under the conditions imposed by the district court. We
    therefore conclude that the district court did not abuse its dis-
    cretion in ordering the Navy to comply with the challenged
    mitigation measures.
    3.   Balancing
    As explained earlier, the scientific studies, declarations and
    reports in the record confirm the district court’s determination
    NRDC v. WINTER                              2161
    that irreparable harm to marine mammals will almost cer-
    tainly result should the Navy be permitted to conduct its
    remaining exercises without appropriate mitigation measures.
    See, e.g., Bain decl. ¶ 14 (explaining that “the monitoring and
    mitigation adopted by the Navy is insufficient to detect, much
    less prevent, marine mammal injury and mortality”); Declara-
    tion of Dr. Thomas A. Jefferson decl. ¶ 4 (describing the link
    between military sonar and the stranding and deaths of beaked
    whales and other cetaceans). As the district court observed,
    the 2,200 yard shutdown zone might protect marine mammals
    from only “the harshest of sonar-related consequences.” Jan.
    3, 2008 Dist. Ct. Order at 15.
    Further, as the district court noted, the exercises in southern
    California are only a subset of the Navy’s training activities
    involving active sonar.69 
    Id. at 12-13.
    NRDC submitted evi-
    dence that the Navy uses active sonar in hundreds of exercises
    each year throughout the world. The evidence linking several
    whale strandings to the Navy’s use of active sonar in training
    exercises around the world further confirms that the Navy
    trains in its use of active sonar in many different areas.
    [24] While we are mindful of the importance of protecting
    national security, courts have often held, in the face of asser-
    tions of potential harm to military readiness, that the armed
    forces must take precautionary measures to comply with the
    law during its training. See, e.g., NRDC v. Evans, 
    364 F. Supp. 2d 1083
    , 1143 (N.D. Cal. 2003) (“A tailored injunc-
    tion reconciles the very compelling interests on both sides of
    69
    Indeed, the EA shows that the Navy considered as alternatives con-
    ducting the exercises in other locations, including Alaska and Hawaii,
    reducing the number of exercises, and using exercise simulation. While
    the Navy’s EA provides reasonably detailed justifications for why the
    Southern California Operating Area is uniquely suited to these exercises,
    and demonstrates that the Navy would suffer a certain hardship if the con-
    sidered alternatives were employed instead, the EA nonetheless shows the
    Navy is still able to conduct its exercises in alternate locations, in reduced
    number, or through simulation.
    2162                   NRDC v. WINTER
    this case, by enabling the Navy to continue to train with and
    test [low-frequency active] sonar as it needs to do, while tak-
    ing some additional measures to better protect against harm to
    marine life.”); Makua v. Rumsfeld, 
    163 F. Supp. 2d 1202
    , 1221
    (D. Haw. 2001) (“Although the court recognizes the impor-
    tance of national security and live-fire training, the potential
    harm to the Army resulting from a brief preliminary injunc-
    tion will not be significant.”). As in those cases, the district
    court here carefully balanced the significant interests and
    hardships at stake to ensure that the Navy could continue to
    train without causing undue harm to the environment. We
    review that balance to determine whether it rests on clearly
    erroneous findings of fact. Having concluded that it does not,
    we determine that the district court did not abuse its discretion
    and therefore do not disturb its carefully considered injunc-
    tion.
    We recognize that although the record indicates that the
    Navy will be able to continue to train and certify strike groups
    effectively despite the two challenged mitigation measures,
    there remains the possibility that, when they are actually
    implemented, it will be unable to do so. In light of the hard-
    ship that the Navy and the public would suffer should the
    imposed measures actually result in an inability to train and
    certify sufficient naval forces to provide for the national
    defense, we conclude that, in the unlikely event that such a
    situation arises, the Navy may return to the district court to
    request relief on an emergency basis.
    D.   Advancement of the Public Interest
    There are two dimensions to the public interest in this case.
    The public has an interest both in national security and in pro-
    tection of the marine environment. The public interest with
    respect to national security is the same as that discussed in our
    consideration of the hardship the Navy would suffer if it were
    unable to effectively train and certify its strike groups. The
    public interest with respect to protection of the marine envi-
    NRDC v. WINTER                       2163
    ronment is the same as that discussed in our consideration of
    the irreparable injury NRDC would suffer if the SOCAL exer-
    cises were carried out in the absence of appropriate mitigation
    measures. As our discussion makes clear, we conclude that
    the district court did not rely on an erroneous legal premise
    or abuse its discretion in analyzing either of these interests.
    Accordingly, there is no need for any additional discussion of
    the public interest.
    V.   Conclusion
    The district court concluded that plaintiffs have met the
    necessary burden of proof to demonstrate that preliminary
    injunctive relief is appropriate. It held that plaintiffs have
    shown a strong likelihood of success on the merits, as well as
    the possibility of irreparable injury if relief is not granted. It
    also held that plaintiffs have shown that the balance of hard-
    ships tips in their favor in light of the preliminary injunction’s
    narrowly-tailored mitigation measures which provide that the
    Navy’s SOCAL exercises may proceed as planned if con-
    ducted under circumstances that provide satisfactory safe-
    guards for the protection of the environment. Finally, it held
    that the public interest is advanced by a preliminary injunc-
    tion that imposes adequate mitigation measures. In reaching
    these conclusions, the district court neither relied on errone-
    ous legal premises nor abused its discretion. We therefore
    affirm the district court’s preliminary injunction.
    AFFIRMED.
    

Document Info

Docket Number: 08-55054

Filed Date: 2/29/2008

Precedential Status: Precedential

Modified Date: 10/14/2015

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