Ctr. for Biological Diversity v. Ryan Zinke ( 2018 )


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  •                  FOR PUBLICATION
    UNITED STATES COURT OF APPEALS
    FOR THE NINTH CIRCUIT
    CENTER FOR BIOLOGICAL DIVERSITY;          No. 16-35866
    WESTERN WATERSHEDS PROJECT;
    GEORGE WUERTHNER; PAT                        D.C. No.
    MUNDAY,                                   2:15-cv-00004-
    Plaintiffs-Appellants,           SHE
    v.
    OPINION
    RYAN K. ZINKE, Secretary, U.S.
    Department of the Interior, in his
    official capacity; DAN ASHE,
    Director, U.S. Fish and Wildlife
    Service, in his official capacity; U.S.
    FISH & WILDLIFE SERVICE,
    Defendants-Appellees,
    and
    STATE OF MONTANA; MONTANA
    DEPARTMENT OF FISH, WILDLIFE
    AND PARKS,
    Intervenor-Defendants-Appellees.
    Appeal from the United States District Court
    for the District of Montana
    Sam E. Haddon, Senior District Judge, Presiding
    Argued and Submitted February 8, 2018
    Seattle, Washington
    2       CENTER FOR BIOLOGICAL DIVERSITY V. ZINKE
    Filed August 17, 2018
    Before: Raymond C. Fisher, Ronald M. Gould,
    and Richard A. Paez, Circuit Judges.
    Opinion by Judge Paez
    SUMMARY *
    Environmental Law
    The panel affirmed in part and reversed in part the
    district court’s summary judgment in favor of the U.S. Fish
    and Wildlife Service, in an action challenging the Service’s
    decision, based on a 2014 Finding, not to list the arctic
    grayling as an endangered or threatened species under the
    Endangered Species Act.
    In 2014, the Service promulgated its “Final Policy on
    Interpretation of the Phrase ‘Significant Portion of Its
    Range’ in the Endangered Species Act’s Definitions of
    ‘Endangered Species’ and ‘Threatened Species,’” 79 Fed.
    Reg. 37,578 (July 1, 2014) (“SPR policy”).
    The panel affirmed the district court’s holding that the
    Service did not err in considering only the current range of
    the arctic grayling when determining whether it was in
    danger of extinction “in all or a significant portion of its
    range.” 16 U.S.C. §§ 1532(6), (20). The panel rejected
    *
    This summary constitutes no part of the opinion of the court. It
    has been prepared by court staff for the convenience of the reader.
    CENTER FOR BIOLOGICAL DIVERSITY V. ZINKE             3
    plaintiffs’ contention that it was bound by two prior
    decisions, Defenders of Wildlife v. Norton, 
    258 F.3d 1136
    (9th Cir. 2001), and Tucson Herpetological Society v.
    Salazar, 
    566 F.3d 870
    (9th Cir. 2009), in deciding whether
    “range” meant historical rather than current range. Applying
    Chevron analysis, the panel held that the meaning of “range”
    in 16 U.S.C. § 1532(6) and (20) was ambiguous; and
    concluded that the SPR policy’s interpretation of “range” as
    “current range” for the purposes of 16 U.S.C. § 1532 was a
    reasonable interpretation of the statute, and warranted
    deference.
    The panel held that the Service acted in an arbitrary and
    capricious manner in finding that the fluvial arctic grayling
    population was increasing because it ignored available
    biological data showing that the arctic grayling population
    in the Big Hole River in Montana was declining.
    The panel held that the Service acted arbitrarily and
    capriciously by dismissing threats of low stream flows and
    high stream temperatures to the arctic grayling. Specifically,
    the panel held that the 2014 Finding’s reliance on cold water
    refugia in the Big Hole River was arbitrary and capricious
    and the district court’s summary judgment in favor of the
    Service of this issue was error, but the panel affirmed the
    district court’s ruling on the cold water refugia issue in all
    other aspects.
    The panel held that the Service acted in an arbitrary and
    capricious manner by failing to explain why the uncertainty
    of climate change favors not listing the arctic grayling when
    the 2014 Finding acknowledged the warming of water
    temperatures and decreasing water flow because of global
    warning.
    4      CENTER FOR BIOLOGICAL DIVERSITY V. ZINKE
    The panel considered the Service’s dismissal of threats
    of small population sizes. Affirming the district court, the
    panel held that the Service’s determination that the arctic
    grayling’s small population size did not pose a risk to genetic
    viability of the arctic grayling was not arbitrary or
    capricious. Reversing the district court, the panel held the
    2014 Finding did arbitrarily rely on the Ruby River
    population to provide redundancy of fluvial arctic grayling
    beyond the Big Hole River and to minimize the risk from
    random environmental events.
    The panel concluded that the 2014 Finding’s decision
    that listing arctic grayling was not “warranted” was arbitrary
    and capricious. The panel remanded with directions to
    remand to the Service to reassess the 2014 Finding in light
    of this opinion.
    COUNSEL
    Jenny K. Harbine (argued), Aurora R. Janke, and Timothy J.
    Preso, Earthjustice, Bozeman, Montana, for Plaintiffs-
    Appellants.
    Thekla Hansen-Young (argued), Nicole M. Smith, Allen M.
    Brabender, and Andrew C. Mergen, Attorneys; Jeffrey H.
    Wood, Acting Assistant Attorney General; Environment and
    Natural Resources Division, United States Department of
    Justice, Washington, D.C.; Kate Williams-Shuck, Office of
    the Solicitor, United States Department of the Interior,
    Denver, Colorado; for Defendants-Appellees.
    William A. Schenk (argued) and Zachary C. Zipfel, Special
    Assistant Attorneys General, Montana Department of Fish,
    Wildlife and Parks, Helena, Montana; Jeremiah Weiner,
    CENTER FOR BIOLOGICAL DIVERSITY V. ZINKE              5
    Assistant Attorney General, Office of the Attorney General,
    Helena, Montana; for Intervenor-Defendants-Appellees.
    Deborah A. Sivas, Alicia Thesing, and Isaac Cheng,
    Environmental Law Clinic, Mills Legal Clinic, Stanford,
    California, for Amici Curiae Law Professors and Scientists.
    OPINION
    PAEZ, Circuit Judge:
    This Endangered Species Act (“ESA”) case concerns the
    Upper Missouri River Valley Distinct Population Segment
    of Arctic Grayling (“arctic grayling”), a cold-water fish in
    the Salmonidae family. Before us is a challenge to the Fish
    and Wildlife Service (“FWS”)’s decision not to list the arctic
    grayling as an endangered or threatened species under the
    ESA. Plaintiffs-Appellants Center for Biological Diversity,
    Western Watersheds Project, George Wuerthner, and Pat
    Mundy (collectively “CBD”) argue that FWS erred in using
    an incorrect definition of “range” in determining whether the
    arctic grayling is extinct or in threat of becoming extinct “in
    a significant portion of its range.” Additionally, CBD
    challenges several aspects of the listing decision as arbitrary
    and capricious.
    The district court granted summary judgment in favor of
    FWS. We have jurisdiction under 28 U.S.C. § 1291.
    Because we conclude that in certain respects FWS acted in
    an arbitrary and capricious manner, we reverse the district
    court’s order granting summary judgment with instructions
    to remand the arctic grayling listing decision to FWS for
    further consideration.
    6      CENTER FOR BIOLOGICAL DIVERSITY V. ZINKE
    I.
    We begin by describing characteristics of the arctic
    grayling population, as relevant to the challenged listing
    decision. The arctic grayling is a cold-water fish belonging
    to the Salmonidae family. It has a trout-like body with a
    deeply forked tail and a sail-like dorsal fin. There are two
    types of arctic grayling: fluvial, which dwell in rivers and
    streams, and adfluvial, which dwell in lakes and migrate to
    streams to spawn.         Historically, fluvial populations
    predominated in the Upper Missouri River. The two types
    of arctic grayling are genetically distinct, although
    experiments have shown some plasticity in the
    characteristics between adfluvial and fluvial populations.
    Although fluvial arctic grayling have been shown to adapt to
    lake environments, all attempts to introduce adfluvial arctic
    grayling to streams have failed. Given its adaptability, the
    fluvial population of arctic grayling is considered to be
    especially important to the survival of the species.
    Within the contiguous United States, arctic grayling
    historically existed in Montana, Wyoming, and Michigan.
    Today, it exists only in the Upper Missouri River Basin in
    Montana. Due to a host of threats to the arctic grayling’s
    habitat, it presently occupies only a small fraction of its
    historical range. Fluvial arctic grayling, for example,
    currently occupy less than ten percent of their historical
    range in the Missouri River system. There are presently
    twenty-six populations of arctic grayling in the Upper
    Missouri River Basin. Six of these—the Big Hole River,
    Ennis Reservoir/Madison River, Centennial Valley’s lakes
    and tributaries, Mussigbrod Lake, Miner Lake, and Ruby
    CENTER FOR BIOLOGICAL DIVERSITY V. ZINKE                        7
    River populations—are native populations. 1 The other
    twenty populations have been introduced into habitat that
    was not part of the arctic grayling’s historical range. Six of
    these introduced populations have no significant
    conservation value, as they have not yet become fully
    established. The other twenty populations—both native and
    introduced—have conservation value. 2            Two of the
    populations—the       Big     Hole     River      and   Ennis
    Reservoir/Madison River populations—are located
    primarily on private land, whereas the remaining eighteen
    are found either entirely or primarily on federal land.
    Arctic grayling prefer cooler water temperatures;
    temperatures over 20 degrees Celsius (approximately
    70 degrees Fahrenheit) can cause physiological stress and
    impair biological functions such as breeding. The upper
    incipient lethal temperature (“UILT”) is 25 degrees Celsius
    (77 degrees Fahrenheit). 3 The twenty-six arctic grayling
    populations in the Upper Missouri River Basin are
    “biogeographically important to the species” because they
    have adapted to warmer water temperatures in contrast to
    populations of arctic grayling outside of the Upper Missouri
    River Basin. Despite this adaptation, climate change
    threatens the arctic grayling. Less water in streams poses a
    1
    Of these six native populations, only the Big Hole River population
    and Ruby River population—which contains just forty-two breeding
    adults—are entirely fluvial.
    2
    Of these twenty populations, sixteen are adfluvial, two are fluvial,
    and two more are mixed fluvial/adfluvial.
    3
    The UILT is the temperature at which there is a 50% survival for
    over a week in a “test population.” Thus, if the water temperature were
    to remain this high for a week, scientists would predict 50% of the fish
    in the test population would perish.
    8       CENTER FOR BIOLOGICAL DIVERSITY V. ZINKE
    threat to the arctic grayling. Droughts and warmer-than-
    normal air temperatures can reduce water levels and,
    consequently, raise water temperatures higher than the range
    of temperatures that the arctic grayling can tolerate.
    II.
    FWS must follow certain ESA requirements when
    deciding whether to list a species as endangered or
    threatened. We briefly review those requirements. We next
    discuss the decades-long history of FWS listing decisions
    involving the arctic grayling. We then briefly review the
    procedural history of this case.
    A.
    The ESA is “the most comprehensive legislation for the
    preservation of endangered species ever enacted by any
    nation.” Tenn. Valley Auth. v. Hill, 
    437 U.S. 153
    , 180
    (1978). It represents a commitment “to halt and reverse the
    trend toward species extinction, whatever the cost.” 
    Id. at 184;
    see also 16 U.S.C. § 1531(a)(1) (2012).
    Under the ESA, the Secretary of the Interior
    (“Secretary”) is charged with determining whether particular
    species should be listed as “threatened” or “endangered.”
    16 U.S.C. § 1533. 4 An endangered species is “any species
    which is in danger of extinction throughout all or a
    significant portion of its range.” 
    Id. § 1532(6).
    A threatened
    species is “any species which is likely to become an
    endangered species within the foreseeable future throughout
    all or a significant portion of its range.” 
    Id. § 1532(20).
    The
    4
    The Secretary has delegated his authority to implement the ESA—
    including his authority to make listing decisions—to FWS. See
    50 C.F.R. § 402.01(b) (2017).
    CENTER FOR BIOLOGICAL DIVERSITY V. ZINKE              9
    term “species” includes subspecies and “any distinct
    population segment of any species of vertebrate fish or
    wildlife which interbreeds when mature.” 
    Id. § 1532(16).
    Under this definition, a distinct population segment of a
    species can be listed as an endangered or threatened species.
    FWS must base its listing decision on “the best scientific
    and commercial data available.” 
    Id. § 1533(b)(1)(A).
    To
    comply with this requirement, FWS “cannot ignore available
    biological information.” Conner v. Burford, 
    848 F.2d 1441
    ,
    1454 (9th Cir. 1988); see also San Luis & Delta-Mendota
    Water Auth. v. Locke, 
    776 F.3d 971
    , 995 (9th Cir. 2014)
    (“An agency complies with the best available science
    standard so long as it does not ignore available studies, even
    if it disagrees with or discredits them.”). In making a listing
    decision, FWS must evaluate five factors: “(a) the present or
    threatened destruction, modification, or curtailment of [a
    species’] habitat or range; (b) overutilization for
    commercial, recreational, scientific, or educational
    purposes; (c) disease or predation; (d) the inadequacy of
    existing regulatory mechanisms; or (e) other natural or
    manmade factors affecting [the species’] continued
    existence.” 16 U.S.C. § 1533(a)(1).
    Anyone may petition FWS to list a species. 
    Id. § 1533(b)(3)(A).
    “To the maximum extent practicable,”
    within ninety days of the petition FWS must determine
    whether the petition presents “substantial scientific or
    commercial information indicating that the petitioned action
    may be warranted.” 
    Id. If it
    does, FWS reviews the status
    of the species and makes a “12-month finding” that listing
    the species is either (a) not warranted; (b) warranted; or
    (c) warranted but precluded by higher priority pending
    proposals. 
    Id. § 1533(b)(3)(B);
    50 C.F.R. § 424.14. Species
    in the third category become “candidates” for listing, and
    10     CENTER FOR BIOLOGICAL DIVERSITY V. ZINKE
    FWS continues to review their status until it makes a
    “warranted” or “not warranted” finding.         16 U.S.C.
    § 1533(b)(3)(C)(i). Additionally, FWS assigns these species
    a listing-priority number. See Endangered Species Listing
    and Recovery Priority Guidelines, 48 Fed. Reg. 43,098,
    43,098 (Sept. 21, 1983). A 12-month finding that listing is
    “not warranted” is subject to judicial review. 16 U.S.C.
    § 1533(b)(3)(C)(ii).
    B.
    FWS initially considered whether to list the arctic
    grayling as endangered or threatened in 1982. Endangered
    and Threatened Wildlife and Plants; Review of Vertebrate
    Wildlife for Listing as Endangered or Threatened Species,
    47 Fed. Reg. 58,454 (Dec. 30, 1982). FWS determined that
    listing the arctic grayling was “possibly appropriate” but
    chose not to list it due to a lack of sufficient data. 
    Id. at 58,454–55.
    Two of the plaintiffs in the current case—
    George Wuerthner and the Center for Biological
    Diversity 5—then petitioned FWS to list the fluvial arctic
    grayling as an endangered species. In response to that
    petition, FWS determined in 1994 that listing the arctic
    grayling was “warranted but precluded” by other listing
    obligations, as threats were of moderate-to-low magnitude
    due to “ongoing cooperative conservation actions.”
    Endangered and Threatened Wildlife and Plants; Finding on
    a Petition to List the Fluvial Population of the Arctic
    Grayling as Endangered, 59 Fed. Reg. 37,738, 37,740–41
    (July 25, 1994). FWS therefore gave the arctic grayling a
    listing priority of nine. 
    Id. The arctic
    grayling maintained
    this status until 2003, when the Center for Biological
    5
    The Center for Biological Diversity was at the time called the
    Biodiversity Legal Foundation.
    CENTER FOR BIOLOGICAL DIVERSITY V. ZINKE                    11
    Diversity and the Western Watersheds Project challenged
    the 1994 “warranted but precluded” decision in a complaint
    filed in the United States District Court for the District of
    Columbia. 6 In response, FWS raised the listing priority of
    the arctic grayling to three, the highest priority that could be
    afforded to a distinct population segment. The plaintiffs
    responded with an amended complaint, requesting that FWS
    emergency list the arctic grayling as either endangered or
    threatened. The parties settled, with FWS agreeing to issue
    a revised listing determination by April 2007.
    In April 2007, FWS concluded that the arctic grayling
    did not warrant protection because it was not a distinct
    population segment, and therefore could not be listed as an
    endangered or threatened species under the ESA.
    Endangered and Threatened Wildlife and Plants; Revised
    12-Month Finding for Upper Missouri River Distinct
    Population Segment of Fluvial Arctic Grayling, 72 Fed. Reg.
    20,305, 20,305 (Apr. 24, 2007). The Center for Biological
    Diversity, Federation of Fly Fishers, Western Watersheds
    Project, George Werthner, and Pat Munday filed an action in
    the District Court for District of Montana challenging the
    2007 listing decision. 7 The parties ultimately settled, with
    FWS stipulating that by August 30, 2010 it would determine
    whether listing the arctic grayling was warranted. In 2010,
    FWS published a revised listing decision, concluding that
    the arctic grayling was a distinct population segment and that
    listing was “warranted but precluded” by higher priority
    actions (“2010 Finding”). Endangered and Threatened
    6
    Ctr. for Biological Diversity v. U.S. Fish & Wildlife Serv., No.
    CIV.A. 03-1110(JDB) (D.D.C.).
    7
    Ctr. for Biological Diversity v. U.S. Fish & Wildlife Serv., 1:07-
    cv-00152-RFC (D. Mont.).
    12       CENTER FOR BIOLOGICAL DIVERSITY V. ZINKE
    Wildlife and Plants; Revised 12-Month Finding to List the
    Upper Missouri River Distinct Population Segment of Arctic
    Grayling as Endangered or Threatened, 75 Fed. Reg. 54,708,
    54,708 (Sept. 8, 2010).
    The 2010 Finding was based on a variety of threats
    facing the arctic grayling. For example, the 2010 Finding
    noted low abundance of arctic grayling and downward
    population trends, especially in the Big Hole River. 
    Id. at 54,723.
    These trends played a role in FWS’s evaluation of
    the arctic grayling’s range and habitat. 
    Id. The 2010
    Finding
    also determined that low stream flows and high stream
    temperatures imperiled the arctic grayling, and showed
    resulting present and threatened destruction of grayling
    habitat or range. 
    Id. at 54,726–30.
    Additionally, climate
    change was evaluated as an “other natural or manmade
    factor” that would “potentially intensify some of the
    significant current threats to all Arctic grayling populations.”
    
    Id. at 54,739–40.
    In evaluating other factors relevant to the
    “warranted but precluded” decision, the 2010 Finding also
    found that small population sizes threatened the survival of
    the species. 
    Id. at 54,740–41.
    The effective population was
    below the number needed for long-term genetic viability and
    stochastic events could threaten the survival of the arctic
    grayling due to its small population size. 
    Id. Shortly after
    the 2010 Finding, FWS settled numerous
    lawsuits in a multi-district litigation concerning the backlog
    of ESA listing decisions. 8 As part of that settlement, FWS
    stipulated that it would issue either a proposed listing rule or
    8
    These cases were known as In re Endangered Species Act Section
    4 Deadline Litigation, Misc. Action No. 10-377 (EGS), MDL Docket
    No. 2185 (D.D.C.).
    CENTER FOR BIOLOGICAL DIVERSITY V. ZINKE                    13
    a not-warranted finding for the arctic grayling by the end of
    fiscal year 2014.
    As required, in 2014 FWS released its decision finding
    that listing the arctic grayling as endangered or threatened
    was not warranted (“2014 Finding”). Endangered and
    Threatened Wildlife and Plants; Revised 12-Month Finding
    on a Petition to List the Upper Missouri River Distinct
    Population Segment of Arctic Grayling as an Endangered or
    Threatened Species, 79 Fed. Reg. 49,384 (Aug. 20, 2014).
    The 2014 Finding was based on a number of conclusions,
    including some that were directly at odds with conclusions
    in the 2010 Finding. In contrast to the 2010 Finding, FWS
    found that the population of arctic grayling was actually
    increasing, including an increase in abundance of the two
    fluvial populations. The 2014 Finding relied on the Big Hole
    River Candidate Conservation Agreement with Assurances
    (“CCAA”) and related Strategic Habitat Conservation Plan,
    in evaluating the threatened destruction, modification, or
    curtailment of arctic grayling habitat. 9 
    Id. at 49,400–02.
    FWS found that the CCAA would mitigate threats from low
    stream flows and high water temperatures. 
    Id. Additionally, FWS
    found that climate change was not a threat because the
    arctic grayling’s increased abundance and distribution in
    conjunction with riparian restoration efforts mitigated
    climate-change effects. 
    Id. at 49,407.
    The 2014 Finding also
    dismissed the risks from inbreeding and environmental
    9
    A CCAA is an agreement between FWS and non-Federal property
    owners. The property owners agree to manage their land in a manner
    that will reduce threats to a species in exchange for assurances against
    additional regulatory requirements if that species is later listed as
    threatened or endangered under the ESA. These CCAAs work to
    implement the broader Strategic Habitat Conservation Plan for the arctic
    grayling, which provides a framework for achieving positive biological
    outcomes for the arctic grayling.
    14     CENTER FOR BIOLOGICAL DIVERSITY V. ZINKE
    disturbances because of increasing population numbers and
    geographic separation between populations.
    In analyzing the curtailment of the arctic grayling’s
    range, habitat fragmentation, and the effect of man-made
    disturbances on the arctic grayling, FWS considered the
    arctic grayling’s historic range. In deciding whether the
    arctic grayling was threatened or endangered in a
    “significant portion of its range” as provided in 16 U.S.C.
    § 1532(6) and (20), however, FWS interpreted “range” as
    the arctic grayling’s “current range” rather than the range it
    had historically inhabited.
    C.
    In February 2015, CBD challenged FWS’s negative
    listing decision by filing this action in the District Court for
    the District of Montana. CBD alleged that the 2014 Finding
    (1) arbitrarily relied on unsupported population increases to
    conclude that the arctic grayling is not threatened by small
    population size; (2) did not properly evaluate whether the
    arctic grayling is threatened by lack of water in streams and
    high water temperatures, which will only be exacerbated by
    global warming; and (3) did not properly analyze whether
    lost historical range constitutes a “significant portion of [the
    arctic grayling’s] range.” The State of Montana and the
    Montana Department of Fish, Wildlife and Parks
    (collectively, “Montana”) intervened as defendants in the
    action. The parties filed cross-motions for summary
    judgment and the district court granted summary judgment
    in favor of FWS and Montana, rejecting each of CBD’s
    claims.
    CENTER FOR BIOLOGICAL DIVERSITY V. ZINKE           15
    III.
    We turn to the merits and address first CBD’s claim that
    FWS erred in considering only the current range of the arctic
    grayling when determining whether it was in danger of
    extinction “in all or a significant portion of its range.”
    16 U.S.C. § 1532(6), (20). The district court concluded that
    FWS did not err by doing so. Reviewing the district court’s
    summary judgment ruling de novo, we agree and affirm its
    ruling on this issue. Greater Yellowstone Coal., Inc. v.
    Servheen, 
    665 F.3d 1015
    , 1023 (9th Cir. 2011).
    In 2014, FWS promulgated its “Final Policy on
    Interpretation of the Phrase ‘Significant Portion of Its
    Range’ in the Endangered Species Act’s Definitions of
    ‘Endangered Species’ and ‘Threatened Species,’” 79 Fed.
    Reg. 37,578 (July 1, 2014) (“SPR policy”). This policy
    defined “range” as follows:
    The range of a species is considered to be the
    general geographical area       within which
    that species can be found at the time [FWS]
    makes any particular status determination.
    This range includes those areas used
    throughout all or part of the species’ life
    cycle, even if they are not used regularly
    (e.g., seasonal habitats). Lost historical range
    is relevant to the analysis of the status of the
    species, but it cannot constitute a significant
    portion of a species’ range.
    
    Id. at 37,609.
    As the SPR policy was enacted through notice-and-
    comment rulemaking procedures as required by 16 U.S.C.
    § 1533(h), we apply the deference framework established by
    16     CENTER FOR BIOLOGICAL DIVERSITY V. ZINKE
    Chevron. See Nw. Ecosystem All. v. U.S. Fish & Wildlife
    Serv., 
    475 F.3d 1136
    , 1141–42 (9th Cir. 2007). We ask if
    the meaning of “range” in 16 U.S.C. § 1532(6) and (20) is
    ambiguous. If the term “range” is ambiguous, then we must
    defer to the SPR policy unless it is an unreasonable
    interpretation of the statute. See Chevron U.S.A., Inc. v. Nat.
    Res. Def. Council, Inc., 
    467 U.S. 837
    , 842–43 (1984).
    A.
    Before addressing the first step of Chevron, we consider
    the significance of two of our prior decisions—Defenders of
    Wildlife v. Norton, 
    258 F.3d 1136
    (9th Cir. 2001), and
    Tucson Herpetological Society v. Salazar, 
    566 F.3d 870
    (9th
    Cir. 2009). CBD argues that these two cases hold that
    “range” means historical range rather than current range for
    the purposes of 16 U.S.C. § 1532(6) and (20), and therefore
    we are bound by our precedent to invalidate the SPR policy.
    A prior appellate court decision construing a statute controls
    over a later agency decision “only if the prior court decision
    holds that its construction follows from the unambiguous
    terms of the statute and thus leaves no room for agency
    discretion.” Nat’l Cable & Telecomms. Ass’n v. Brand X
    Internet Servs., 
    545 U.S. 967
    , 982–83 (2005). We conclude
    that neither of our previous decisions held that “range”
    unambiguously means “historical range.”
    In Defenders of Wildlife, we held that it was error for the
    Secretary to fail to list the flat-tailed horned lizard as
    “endangered” or “threatened” based on a finding that
    adequate habitat existed on public land for the lizard, despite
    recognizing that the lizard faced threats on private 
    land. 258 F.3d at 1140
    . We analyzed the phrase “in danger of
    extinction throughout . . . a significant portion of its range”
    to determine if it required considering the threats that the
    lizard faced on private land. 
    Id. at 1140–41.
    We concluded
    CENTER FOR BIOLOGICAL DIVERSITY V. ZINKE              17
    that “significant portion of its range” is inherently
    ambiguous, and therefore the Secretary has a “wide degree
    of discretion in delineating [what] ‘a significant portion of
    its range’” means. 
    Id. at 1145.
    We noted, however, that
    where “it is on the record apparent that the area in which the
    [species] is expected to survive is much smaller than its
    historical range, the Secretary must at least explain her
    conclusion that the area in which the species can no longer
    live is not a ‘significant portion of its range.’” 
    Id. Because the
    Secretary did not address whether the private land it
    discounted was sufficient to render the lizard “extinct . . . in
    a significant portion of its range,” we reversed and
    remanded. 
    Id. at 1146–47.
    Tucson Herpetological Society, which also involved the
    flat-tailed horned lizard, interpreted Defenders of Wildlife to
    mean that the criteria for “significance” is undefined, but that
    FWS must “develop some rational explanation for why the
    lost and threatened portions of a species’ range are
    insignificant before deciding not to designate the species for
    
    protection.” 566 F.3d at 876
    –77. Additionally, we
    concluded that Defenders of Wildlife required FWS to
    analyze lost historical range. 
    Id. We ultimately
    held that
    FWS had properly analyzed the flat-tailed horned lizard’s
    lost historical range. 
    Id. at 878.
    Although Defenders of Wildlife and Tucson
    Herpetological Society held that FWS must at least explain
    why the lost and threatened portions of a species’ range are
    insignificant before disregarding historical range, it does not
    follow from their holdings that the ESA’s use of “range” in
    16 U.S.C. § 1532 unambiguously refers to the species’
    current range. Rather, we have noted that the phrase “extinct
    throughout . . . a significant portion of [a species’] range” is
    ambiguous. See Defs. of 
    Wildlife, 258 F.3d at 1141
    . Because
    18     CENTER FOR BIOLOGICAL DIVERSITY V. ZINKE
    neither of these cases provide a clear statement that “range”
    unambiguously means “historical range,” we proceed to
    consider CBD’s other arguments in favor of such a reading.
    See Brand 
    X, 545 U.S. at 982
    –83.
    B.
    Under Chevron, first we must ask if the meaning of
    “range” in 16 U.S.C. § 1532(6) and (20) is ambiguous. CBD
    argues that the term “range” unambiguously means a
    species’ historical range. Although the term “range” is not
    defined in the ESA, CBD argues that using traditional tools
    of statutory construction, we can ascertain that Congress
    unambiguously intended “range” to mean “historical range”
    and therefore that “intention is the law and must be given
    effect.” 
    Chevron, 467 U.S. at 843
    n.9.
    Whether FWS’s interpretation of range in the SPR policy
    deserves deference under Chevron is a question of first
    impression in this circuit. The D.C. Circuit recently
    considered this question in Humane Society of the United
    States v. Zinke, 
    865 F.3d 585
    (D.C. Cir. 2017), and
    concluded that deference was warranted. In doing so it
    analyzed the dictionary definition of the word “range,” its
    use in 16 U.S.C. § 1532(6) and (20) and the use of “range”
    in three other parts of the ESA to determine that “range” was
    ambiguous. 
    Id. at 604.
    For the following reasons, we agree
    that “traditional rules of statutory construction do not answer
    the question of whether ‘range’ means current or historical
    range.” 
    Id. Starting with
    the text of 16 U.S.C. § 1532(6) and (20),
    the word “range” is ambiguous as to whether it means
    current or historical range. “Range” is commonly defined as
    “a geographical reference to the physical area in which a
    species lives or occurs.” 
    Id. (citing 8
    The Oxford English
    CENTER FOR BIOLOGICAL DIVERSITY V. ZINKE              19
    Dictionary 139 (def. 7) (1933)). This definition, however,
    does not provide clarity to the meaning of “range.” One
    could argue that the use of the present tense in the
    definition—“lives or occurs”—may suggest that range
    means “current range.” As the D.C. Circuit observed,
    however, the use of the present tense is likely a function of
    dictionary drafting. 
    Id. We agree
    with the D.C. Circuit that
    the dictionary definition of the word “range” itself does not
    shed much light on Congress’s intent.
    The text of 16 U.S.C. § 1532 as a whole tells us equally
    little. An endangered species is one that “is in danger of
    extinction throughout all or a significant portion of its
    range.” 16 U.S.C. § 1532(6). Similarly, a “threatened
    species” is “any species which is likely to become an
    endangered species within the foreseeable future throughout
    all or a significant portion of its range.” 16 U.S.C.
    § 1532(20). The SPR policy explains that because these
    definitions are phrased in the present tense, “range” means
    current range. “[T]o say a species ‘is in danger’ in an area
    where it no longer exists—i.e., in its historical range where
    it has been extirpated—is inconsistent with common usage.”
    79 Fed. Reg. at 37,583.
    Like the D.C. Circuit, we conclude that the use of the
    present tense in §1532(6) and (20) does not mean that
    “range” must mean “current range.” The placement of the
    present-tense “is” seems to require that the species
    “currently be endangered or threatened within its range, not
    to dictate the temporal scope of geographical evidence
    [FWS] is to consider.” Humane 
    Soc’y, 865 F.3d at 604
    . As
    we explained in Defenders of Wildlife, “a species can be
    extinct ‘throughout . . . a significant portion of its range’ if
    there are major geographical areas in which it is no longer
    viable but once 
    was.” 258 F.3d at 1145
    . CBD similarly
    20        CENTER FOR BIOLOGICAL DIVERSITY V. ZINKE
    notes that a species can be “in danger” even in an area where
    it does not currently exist but could in the future, if habitat
    degradation endangers the possibility of reintroduction to
    that habitat. 10 The statutory text does not demonstrate that
    Congress unambiguously intended “range” to mean either
    “current” or “historical range.”
    Because the text of 16 U.S.C. § 1532(6) and (20) does
    not conclusively shed light on the scope of the word “range,”
    we next consider the statutory framework of the ESA and the
    other uses of the word “range” throughout the statute. See
    Sullivan v. Everhart, 
    494 U.S. 83
    , 89 (1990) (“In
    ascertaining the plain meaning of the statute, the court must
    look to the particular statutory language at issue, as well as
    the language and design of the statute as a whole.” (citation
    omitted)). Outside of the definitions of “endangered” and
    “threatened” species, the term “range” appears three times in
    the ESA.
    The first use of “range” is in section 4(a)(1) of the ESA,
    which lists “the present or threatened destruction,
    modification, or curtailment of [a species’] habitat or range”
    as one factor that FWS considers in its listing decision.
    16 U.S.C. § 1533(a)(1)(A). This reference to “range” is “as
    textually indeterminate as the initial use of the term in
    [16 U.S.C. §] 1532.” Humane 
    Soc’y, 865 F.3d at 604
    .
    Indeed, while “present” may modify “habitat or range,” it
    more likely modifies “destruction, modification, or
    10
    This interpretation has some force in light of the ESA provisions
    that seek to recover lost range once a species is listed. See, e.g.,
    16 U.S.C. §§ 1533(a)(3), 1539(j)(2)(A). Indeed, in this case many of the
    current arctic grayling populations were reintroduced into their current
    habitats.
    CENTER FOR BIOLOGICAL DIVERSITY V. ZINKE             21
    curtailment.” The use of the word “range” in this section
    does not shed any light on Congress’s intent.
    The next use of “range” is in section 4(c)(1), which
    requires FWS to specify “over what portion of its range [the
    species] is endangered or threatened, and specify any critical
    habitat within such range.” 16 U.S.C. § 1533(c)(1). We
    acknowledge that legislative history indicates that in this
    section of the ESA, Congress used “[t]he term ‘range’ . . . in
    the general sense [to] refer[] to the historical range of the
    species.” H.R. Rep. No. 95-1625, at 18 (1978), reprinted in
    1978 U.S.C.C.A.N. 9453, 9468. Combined with the
    “presumption that a given term is used to mean the same
    thing throughout a statute,” see Brown v. Gardner, 
    513 U.S. 115
    , 118 (1994), this legislative history provides support for
    interpreting “range” as meaning historical range in 16 U.S.C.
    § 1532(6) and (20) as well.
    We are not convinced that this lone indicator of
    legislative intent disposes of all ambiguity as to the scope of
    “range” throughout the ESA. The SPR Policy reads section
    4(c)(1) as “an informational rather than a substantive
    provision,” that is, an instruction that the agency should
    specify where a species is endangered or threatened and
    identify the critical habitat in those areas. 79 Fed. Reg. at
    37,583. Indeed, as FWS recognizes, reading section 4(c)(1)
    as a substantive provision may actually limit the scope of
    protection for species under the ESA, as in that case critical
    habitat could only be designated in the species’ “range.” 
    Id. In sum,
    we agree with the D.C. Circuit that this section also
    does not unambiguously shed light on Congress’s intended
    meaning of “range.”
    The third use of “range” in the ESA is found in section
    10(j), which “authorize[s] the release . . . of any population
    . . . of an endangered species or a threatened species outside
    22     CENTER FOR BIOLOGICAL DIVERSITY V. ZINKE
    the current range of such species.”                 16 U.S.C.
    § 1539(j)(2)(A). As the D.C. Circuit noted, this provision
    cuts both ways. Humane 
    Soc’y, 865 F.3d at 604
    . On the one
    hand, the use of the word “current” as a qualifier to “range”
    in section 10(j) could indicate that elsewhere in the ESA
    “range” means “historical range.” See, e.g., Duncan v.
    Walker, 
    533 U.S. 167
    , 174 (2001) (describing the rule
    against surplusage). By using “current range” in section
    10(j), Congress knew how to limit “range” to mean “current
    range,” and therefore it could have intended the broader
    historical meaning in 16 U.S.C. § 1532(6) and (20). See
    Hamdan v. Rumsfeld, 
    548 U.S. 557
    , 578 (2006). On the
    other hand, the use of “current range” in section 10(j) “could
    also be read to corroborate [FWS’s] view, since ‘current
    range’ . . . may refer to the listed range of the endangered or
    threatened species.” Humane 
    Soc’y, 865 F.3d at 604
    . The
    use of “range” in section 10(j) does not compel the
    conclusion that “range” should be read to unambiguously
    mean “historical range.”
    Considering the statutory framework as a whole, then,
    the term “range” in 16 U.S.C. § 1532(6) and (20) is
    ambiguous.      Although traditional tools of statutory
    construction provide some support for interpreting “range”
    to mean “historical range,” we are not persuaded that the
    “unambiguously expressed intent of Congress” was to define
    “range” as “historical range.” 
    Chevron, 467 U.S. at 843
    . We
    therefore conclude that the term “range” is ambiguous and
    proceed to evaluate whether the SPR policy is “based on a
    permissible construction of the statute.” 
    Id. C. Since
    “range” is ambiguous, we must next determine
    whether the SPR policy’s interpretation of “range” as
    “current range” for the purposes of 16 U.S.C. § 1532 is a
    CENTER FOR BIOLOGICAL DIVERSITY V. ZINKE              23
    reasonable interpretation of the statute. 
    Id. We join
    the D.C.
    Circuit in holding that it is. Humane 
    Soc’y, 865 F.3d at 605
    .
    As we discussed above, the statutory framework of the ESA
    provides at least some support for interpreting “range” as the
    current range of a species, although it may not compel this
    interpretation. Additionally, despite CBD’s arguments to
    the contrary, the SPR policy does not run afoul of the
    purposes of the ESA. The largest threat to potentially
    endangered or threatened species is the loss of habitat that
    the species currently occupies. See 
    id. (noting that
    where a
    species “currently lives often affect its continued survival the
    most and thus bear influentially on whether it should be
    listed”). It would therefore be reasonable for FWS to focus
    on the area the species currently occupies when evaluating
    whether the species is endangered through “a significant
    portion of its range.” 
    Id. at 604.
    The SPR policy still requires that FWS consider the
    historical range of a species in evaluating other aspects of
    the agency’s listing decision, including habitat degradation.
    
    Id. at 605–06.
    The SPR policy recognizes that loss of
    historical range can lead to reduced abundance, inhibited
    gene flow, and increased susceptibility to extinction. 79 Fed.
    Reg. at 37,584. The SPR policy’s interpretation of “range”
    is “consonant with the purposes of the [ESA],” as it provides
    protections for species that have lost a substantial part of
    their historical range. See Human 
    Soc’y, 865 F.3d at 605
    .
    In sum, we hold that FWS’s interpretation of “range” in
    16 U.S.C. § 1532(6) and (20) as “current range” warrants
    deference. Consistent with that interpretation, FWS did
    consider the arctic grayling’s historical range in evaluating
    the factors that contributed to its negative listing decision.
    24     CENTER FOR BIOLOGICAL DIVERSITY V. ZINKE
    IV.
    We next turn to CBD’s other arguments that the 2014
    Finding was arbitrary and capricious. FWS’s decision not to
    list a species under the ESA is reviewed under the
    Administrative Procedure Act (“APA”), 5 U.S.C. §§ 701–
    706. Native Ecosystems Council v. Dombeck, 
    304 F.3d 886
    ,
    901 (9th Cir. 2002). We “shall” set aside agency actions,
    findings, or conclusions under the APA that are “arbitrary,
    capricious, an abuse of discretion, or otherwise not in
    accordance with law.” Japanese Vill., LLC v. Fed. Transit
    Admin., 
    843 F.3d 445
    , 453 (9th Cir. 2016) (quoting 5 U.S.C.
    § 706(2)(A)).
    In reviewing whether an agency decision is arbitrary or
    capricious, we “ensure that the agency considered the
    relevant factors and articulated a rational connection
    between the facts found and the choices made.” Greater
    Yellowstone 
    Coal., 665 F.3d at 1023
    (citation omitted).
    “[A]n agency rule would be arbitrary and capricious if the
    agency has relied on factors which Congress has not
    intended it to consider, entirely failed to consider an
    important aspect of the problem, offered an explanation for
    its decision that runs counter to the evidence before the
    agency, or is so implausible that it could not be ascribed to a
    difference in view or the product of agency expertise.” 
    Id. (quoting Motor
    Vehicle Mfrs. Ass’n v. State Farm Mut. Auto.
    Ins. Co., 
    463 U.S. 29
    , 43 (1983)).
    Agency decisions deserve the highest deference when
    “the agency is making predictions, within its area of special
    expertise.” Lands Council v. McNair, 
    537 F.3d 981
    , 993
    (9th Cir. 2008) (en banc) (alteration omitted). Even when an
    agency is acting within its area of expertise, however, we
    “need not defer to the agency when the agency’s decision is
    without substantial basis in fact.” Ariz. Cattle Growers’
    CENTER FOR BIOLOGICAL DIVERSITY V. ZINKE           25
    Ass’n v. Salazar, 
    606 F.3d 1160
    , 1163 (9th Cir. 2010). When
    an agency changes a policy based on factual findings that
    contradict those on which the prior policy was based, an
    agency must provide a “reasoned explanation . . . for
    disregarding facts and circumstances that underlay or were
    engendered by the prior policy.” FCC v. Fox Television
    Stations, Inc., 
    556 U.S. 502
    , 515–16 (2009); see also
    Organized Vill. of Kake v. U.S. Dep’t of Agric., 
    795 F.3d 956
    , 966 (9th Cir. 2015) (en banc).
    We review for substantial evidence an agency’s factual
    conclusions based on the administrative record. See
    Dickinson v. Zurko, 
    527 U.S. 150
    , 164 (1999). Where
    “evidence is susceptible of more than one rational
    interpretation,” we uphold the agency’s finding if a
    “reasonable mind might accept [it] as adequate to support a
    conclusion.” San Luis & Delta-Mendota Water Auth. v.
    Jewell, 
    747 F.3d 581
    , 601 (9th Cir. 2014).
    A.
    We first consider CBD’s argument that the 2014 Finding
    arbitrarily found that fluvial arctic grayling population is
    increasing. CBD argues that this determination was not
    based on the “best scientific and commercial data available,”
    as required by 16 U.S.C. § 1533(b)(1)(A). Although FWS
    has broad discretion to choose which expert opinions to rely
    on when making a listing decision, it cannot ignore available
    biological data. See 
    Conner, 848 F.2d at 1454
    . Here, FWS
    acted in an arbitrary and capricious manner by ignoring
    available biological data showing that the arctic grayling
    population in the Big Hole River was declining.
    FWS failed to account for a 2014 report (“DeHaan
    study”) by four scientists at the FWS Abernathy Fish
    Technology Center, which found that the number of
    26        CENTER FOR BIOLOGICAL DIVERSITY V. ZINKE
    effective breeders in the Big Hole River was declining. 11
    The DeHaan study arrived at this conclusion by measuring
    the effective number of breeders in the Big Hole River
    during four different time periods: 1987–88; 1995–96;
    2005–06; and 2011–12. The DeHaan study examined
    whether there was any change in the number of effective
    breeders between each time period and found that the
    number of effective breeders decreased in each time period,
    although the largest decrease occurred between 1996 and
    2005. 12
    FWS cited to a portion of the DeHaan study in its 2014
    Finding as indicating that a decrease in the number of
    effective breeders continued through the mid-2000s but did
    not mention that other aspects of the DeHaan study
    contradicted the data on which FWS relied (the “Leary
    study”). Although FWS is free to choose among experts, it
    must acknowledge that it is doing so. See 
    Conner, 848 F.2d at 1454
    . FWS clearly stated in the 2014 Finding that the
    number of breeding arctic grayling increased in the Big Hole
    River, and omitted the DeHaan study’s evidence to the
    11
    The number of effective breeders in the population is determined
    through genetic analysis, which is one way of measuring a species
    population. FWS relied on the number of effective breeders to document
    population increases.
    12
    The DeHaan study did find that several other population
    indicators, including effective population size, genetic diversity, and the
    number of individuals in the population, have remained relatively stable
    or increased over time. The DeHaan study also noted that despite a
    declining number of breeders “the number of offspring produced may
    not have similarly declined.” FWS used the number of effective breeders
    as an indication of population abundance, which leads us to focus on this
    aspect of the DeHaan study as well.
    CENTER FOR BIOLOGICAL DIVERSITY V. ZINKE                 27
    contrary. We conclude that in ignoring available data FWS
    acted in an arbitrary and capricious manner. 
    Id. FWS’s arguments
    to the contrary are unavailing. FWS
    points out that the 2014 Finding relied on yearly data that
    was “more current” than the longitudinal DeHaan study.
    Although that could be a reason ultimately to rely on the
    Leary study rather than the DeHaan study, the listing
    decision should have included “adequate explanation and
    support for its determinations.” San 
    Luis, 747 F.3d at 625
    .
    FWS must “provide[] a reasonable explanation for adopting
    its approach and disclose[] the limitations of that approach,”
    which it fails to do by not discussing the DeHaan study’s
    data that contradicts the Leary study. Alaska Oil & Gas
    Ass’n v. Pritzker, 
    840 F.3d 671
    , 679 (9th Cir. 2016).
    Because FWS did not provide a reason to credit the Leary
    study over the DeHaan study, “we are precluded from
    undertaking meaningful judicial review.” Humane Soc’y of
    U.S. v. Locke, 
    626 F.3d 1040
    , 1049 (9th Cir. 2010).
    Additionally, FWS cannot rely on its briefing in this case
    to explain why the 2014 Finding relied on the Leary study
    rather than the DeHaan study. The explanation must be
    evidenced from the listing decision itself. See Greater
    Yellowstone 
    Coal., 665 F.3d at 1027
    n.4 (“[A]n agency’s
    action must be upheld, if at all, on the basis articulated by
    the agency itself, not post-hoc rationalizations.” (internal
    quotation marks omitted)). By failing to consider the
    DeHaan study’s evidence of decreasing population, FWS
    acted in an arbitrary and capricious manner. 13 Because the
    13
    CBD also argues that FWS acted in an arbitrary and capricious
    manner by ignoring state population monitoring data. For the Big Hole
    River, FWS provided a valid reason for discounting the fluctuating
    population data. In the 2014 Finding, FWS explained that the state
    28        CENTER FOR BIOLOGICAL DIVERSITY V. ZINKE
    2014 Finding based its analysis of two of the five listing
    factors—the       “present    or    threatened     destruction,
    modification, or curtailment of [the arctic grayling’s] habitat
    and range” and “other natural or manmade factors affecting
    [the arctic grayling’s] continued existence”—on the fact that
    the arctic grayling’s population was increasing, we reverse
    the district court’s grant of summary judgment, with
    directions to remand the 2014 Finding to FWS for further
    consideration in light of this opinion. 14
    B.
    Next we consider CBD’s argument that the 2014 Finding
    arbitrarily dismissed threats of low stream flows and high
    stream temperatures to the arctic grayling. As discussed
    below, in rejecting these threats to the arctic grayling in the
    Big Hole River FWS acted arbitrarily and capriciously. The
    similar findings regarding the Centennial Valley’s lakes and
    population monitoring data showed a decline of arctic grayling in the Big
    Hole River in 2013 as resulting from unusually high flows that likely
    decreased capture efficiency, which is a sufficient explanation that is
    neither arbitrary nor capricious. See San 
    Luis, 747 F.3d at 625
    .
    Additionally, while the 2014 Finding did not explicitly address state
    population data for the Ruby River, the data does not show the decrease
    that CBD claims it does. Although the Ruby River data did show a
    decrease in fish in 2013, the size of the area surveyed also decreased.
    The number of fish per unit, however, stayed roughly the same. Under
    the circumstances, we are not persuaded that FWS acted arbitrarily and
    capriciously by failing to address state monitoring data in its 2014
    Finding.
    14
    Given our disposition of this issue, we need not decide CBD’s
    additional argument that the Leary study does not provide sufficient
    support for FWS’s determination that the arctic grayling population is
    increasing, and therefore even if FWS did not improperly disregard the
    DeHaan study, its determination that the arctic grayling population is
    increasing would be arbitrary and capricious.
    CENTER FOR BIOLOGICAL DIVERSITY V. ZINKE                    29
    tributaries, however, were adequately supported. Any error
    in the 2014 Finding regarding the Madison River and its
    tributaries was harmless, as FWS expressly did not rely upon
    the survival of arctic grayling in the Madison River Valley
    in deciding that listing the arctic grayling was not warranted.
    1.
    In the 2014 Finding, FWS determined that the arctic
    grayling’s ability to migrate to coldwater refugia minimizes
    the threat it faces from low stream levels and high water
    temperatures in the Big Hole River. FWS based this
    determination largely on a study that found that the
    tributaries of the Big Hole River provide important
    coldwater refugia to arctic grayling (“Vatland study”).
    Relying on the Vatland study, FWS determined that despite
    the existence of water temperatures that exceeded ideal
    temperatures for arctic grayling in many areas of the Big
    Hole River, arctic grayling could migrate to cold water
    refugia over the summer to survive. 15 Additionally, the 2014
    Finding reasons that because fish ladders are included in the
    CCAA’s conservation projects and the increased
    connectivity of the Big Hole River, the arctic grayling can
    15
    CBD highlights that despite decreases in water temperatures since
    implementing the CCAA, the water temperature still frequently exceeds
    70 degrees Fahrenheit. As mentioned above, 70 degrees Fahrenheit is
    the temperature above which arctic grayling experience “physiological
    stress.” Montana contends that harm does not result from temperatures
    of 70 degrees Fahrenheit and that stream temperatures in the Big Hole
    River tributaries did not exceed 70 degrees in 2013. These arguments,
    however, are directly contradicted by data in FWS’s 2014 Finding.
    30        CENTER FOR BIOLOGICAL DIVERSITY V. ZINKE
    access cold water tributaries that they could not access in
    2010. 16
    CBD disputes the 2014 Finding’s conclusion that the
    arctic grayling seek refuge in coldwater tributaries of the Big
    Hole River when water temperatures rise. CBD also
    disputes that the Vatland study shows that arctic grayling
    migrate, as the study found “[l]imited movement” among
    arctic grayling during the summer. Additionally, CBD
    argues that evidence does not suggest that tributaries actually
    provide cold water refugia, as the temperatures in these
    tributaries frequently exceed 70 degrees. CBD’s arguments
    are persuasive.
    FWS’s reliance on the ability of the arctic grayling to
    migrate to cold water refugia was arbitrary and capricious.
    The sole evidence of arctic grayling migrating to cold water
    refugia in the Big Hole River tributaries is the Vatland study.
    Notably, in 2010, FWS determined that despite the Vatland
    study’s findings that arctic grayling have the ability to
    migrate to cold water refugia in tributaries, water
    temperatures were sufficiently high to warrant listing the
    arctic grayling. Water temperatures remained high enough
    to cause physiological stress in 2014, but the 2014 Finding
    stated that this could be overcome by the arctic grayling’s
    ability to migrate to cold water refugia via CCAA fish
    ladders, without providing any additional evidence or
    scientific studies demonstrating that this would likely occur.
    16
    In the 2010 Finding, FWS also determined that CCAA
    conservation measures would reduce but not eliminate threats of
    dewatering. Since CCAA conservation measures took effect, the record
    reflects that minimum flow targets have been achieved 78 percent of the
    time, up from 50 percent of the time pre-CCAA. Although this is an
    improvement, CBD notes that FWS previously stated that the flow target
    represented minimum values to promote recovery of the arctic grayling.
    CENTER FOR BIOLOGICAL DIVERSITY V. ZINKE               31
    Because the 2010 Finding indicated that listing the arctic
    grayling was warranted irrespective of the Vatland study and
    recognized the ability of arctic grayling to migrate to
    tributaries, the 2014 Finding was required to provide a
    reasoned explanation for FWS’s change in position. See
    Organized Vill. of 
    Kake, 795 F.3d at 966
    (stating that an
    “[u]nexplained inconsistency” between two agency actions
    can be grounds for holding that agency action is arbitrary and
    capricious (quoting Brand 
    X, 545 U.S. at 981
    )).
    Nor do lower water temperatures or the CCAA
    conservation measures save the agency’s flawed 2014
    Finding. As discussed above, temperatures are still higher
    than the scientific benchmarks cited by FWS as tolerable
    water temperatures for arctic grayling.            Cf. Greater
    Yellowstone 
    Coal., 665 F.3d at 1028
    (“Having determined
    what is necessary, the [FWS] cannot reasonably rely on
    something less to be enough.” (internal quotation marks
    omitted)). Even the tributaries of the Big Hole River that
    supposedly serve as cold water refugia are above the desired
    temperature according to the scientific studies on which
    FWS relies. FWS disregarded this scientific evidence, and
    instead based its conclusion on a study finding “limited
    movements” of arctic grayling in the Big Hole River during
    summer months. Given that water temperatures—even in
    tributaries—still exceed temperatures where arctic grayling
    can live and breed, FWS did not sufficiently “articulate[] a
    rational connection between the facts found and the choices
    made.” 
    Id. at 1023
    (internal quotation marks omitted).
    Similarly, FWS’s reliance on the CCAA’s fish ladders as
    evidencing a change in the status quo without any studies
    finding that these measures will aid migration is arbitrary
    and capricious—even if the ladders aid the arctic grayling in
    migrating to tributaries, as this would be of little value if the
    water in the tributaries is still too warm. 
    Id. (stating that
    32     CENTER FOR BIOLOGICAL DIVERSITY V. ZINKE
    agency rulings are arbitrary and capricious if the agency
    offers “an explanation for its decision that runs counter to
    the evidence before the agency” (quoting State 
    Farm, 463 U.S. at 43
    )).
    Although there have been improvements in stream flow
    and water temperature since 2010, the water temperatures
    are still above those that are ideal for the arctic grayling both
    in the main stem of the Big Hole River and its tributaries. In
    sum, the 2014 Finding that thermal refugia in the Big Hole
    River would aid survival of the arctic grayling was arbitrary
    and capricious.
    2.
    The 2014 Finding relied solely on the existence of
    thermal refugia to dismiss the threat of increased water
    temperatures in the Centennial Valley lakes and tributaries.
    CBD argues that because the evidence does not adequately
    support the existence of thermal refugia, FWS’s decision as
    to the Centennial Valley lakes and tributaries was arbitrary
    and capricious.
    FWS supported its determination that cold water refugia
    exist in the Centennial Valley primarily by relying on a study
    that observed two arctic graylings in a tributary in 1994
    (“Mogen study”), and which stated that the tributary
    “possibly provid[ed] thermal refugia.” The Mogen study
    was discussed in the 2010 Finding, but FWS still concluded
    that high water temperatures were a threat. Indeed, the 2010
    Finding cited to the Mogen study’s observation of two fish
    seeking refuge to support a finding of high water
    temperatures in the Centennial Valley lakes and tributaries.
    FWS did not act in an arbitrary and capricious manner
    by reversing its 2010 Finding that cold water thermal refugia
    CENTER FOR BIOLOGICAL DIVERSITY V. ZINKE                      33
    were insufficient to mitigate high water temperatures in the
    Centennial Valley. Although FWS relies primarily on the
    same information in 2014 as it did in 2010, the 2014 Finding
    also relied on an email by a scientist named Matt Jaeger
    (“Jaeger email”). The Jaeger email stated that there was
    evidence that cold water refugia existed in the Centennial
    Valley, but noted uncertainty in terms of whether this would
    fully mitigate warm water temperatures. Given increasing
    population of arctic grayling in the Centennial Valley,
    however, the Jaeger email concluded that increasing
    temperatures likely are not a threat. The Jaeger email, and
    the corresponding increase in population in the Centennial
    Valley, provides a sufficient “reasoned explanation” for
    FWS’s change in position. See Organized. Vill. of 
    Kake, 795 F.3d at 968
    .
    3.
    CBD also challenges the findings of cold water refugia
    in the Madison River. The 2014 Finding cites no evidence
    to support a finding that cold water refugia exist in the
    tributaries of this river. Rather, FWS notes in the 2014
    Finding that there are high water temperatures in the
    Madison River and that the arctic grayling population has
    been decreasing. Without any evidentiary support in the
    2014 Finding record, FWS’s finding that cold water refugia
    exist is improper. 17 See State 
    Farm, 463 U.S. at 43
    .
    This error, however, was harmless. In the 2014 Finding,
    which recognizes that the arctic grayling in the Madison
    17
    FWS provides some support in its brief for the existence of cold
    water refugia, but this is an ex post rationalization, which is informative
    but of no force in evaluating FWS’s listing decision. Greater
    Yellowstone 
    Coal., 665 F.3d at 1027
    n.4.
    34     CENTER FOR BIOLOGICAL DIVERSITY V. ZINKE
    River are endangered by high water temperatures and low
    population, FWS concluded that even if the arctic grayling
    were no longer able to survive in the Madison River and its
    tributaries, the population in the upper Missouri River
    Valley as a whole would not be compromised. Under these
    circumstances, any error in finding that refugia exist is
    harmless, as FWS did not rest its ultimate 2014 Finding on
    the continued existence of arctic grayling in the Madison
    River. Cf. Organized. Vill. of 
    Kake, 795 F.3d at 969
    (stating
    that the burden is on “the opponent of the action to
    demonstrate [that] an error is prejudicial”).
    ***
    In sum, the 2014 Finding’s reliance on cold water refugia
    in the Big Hole River was arbitrary and capricious. The
    district court erred in granting summary judgment in favor
    of FWS on this issue. We affirm, however, the district
    court’s ruling on the cold water refugia issue in all other
    respects.
    C.
    We turn to CBD’s contention that FWS disregarded the
    additive effects of climate change in considering the effects
    of low stream flows and high water temperatures.
    Specifically, CBD argues that FWS’s 2014 assessment of the
    cumulative impacts of climate change arbitrarily relied on
    uncertainty to avoid making determinations about the threat
    of climate change. We have held that it is “not enough for
    [FWS] to simply invoke ‘scientific uncertainty’ to justify its
    action.” Greater Yellowstone 
    Coal., 665 F.3d at 1028
    (discussing uncertainty caused by the effects of climate
    change). Rather, FWS must explain why uncertainty
    justifies its conclusion, “[o]therwise, we might as well be
    deferring to a coin flip.” 
    Id. In its
    2014 Finding, FWS states
    CENTER FOR BIOLOGICAL DIVERSITY V. ZINKE              35
    that “[u]ncertainty about how different temperature and
    precipitation scenarios could affect water availability make
    projecting possible synergistic effects of climate change on
    the Arctic grayling too speculative at this time.” With this
    statement, FWS expressly disclaimed making any projection
    as to the synergistic effects of climate change, simply
    because of the uncertainty.
    Greater Yellowstone Coalition counsels that this
    approach is unacceptable. 
    See 665 F.3d at 1028
    . There, we
    held that because FWS had data showing that the population
    of whitebark pine was declining due to climate change, it
    could not simply state that it was uncertain what impact this
    would have on grizzly bears. 
    Id. Rather, FWS
    had to explain
    why this uncertainty favored delisting the grizzly bear rather
    than, for example, undertaking further studies to minimize
    the uncertainty. 
    Id. Similarly, in
    the 2014 Finding, FWS did not explain how
    uncertainty about water availability justifies not listing the
    arctic grayling as opposed to taking another course of action.
    Pursuing another course of action may have been
    particularly prudent given the ESA’s policy of
    “institutionalized caution,” Ariz. Cattle 
    Growers, 606 F.3d at 1167
    , especially since the 2014 Finding expressly cites to
    evidence that climate change will increase water
    temperatures and threats of low water flow. According to
    the 2014 Finding, “water temperatures will likely increase
    with climate change in the future,” 79 Fed. Reg. at 49,405,
    and dewatering threats will be exacerbated by “[i]ncreases
    in temperature and changes in precipitation [that] are likely
    to affect the availability of water in the West,” 
    id. at 49,419.
    By failing to explain why the uncertainty of climate change
    favors not listing the arctic grayling when the 2014 Finding
    acknowledges the warming of water temperatures and
    36     CENTER FOR BIOLOGICAL DIVERSITY V. ZINKE
    decreasing water flow because of global warming, FWS
    acted in an arbitrary and capricious manner. See Greater
    Yellowstone 
    Coal., 665 F.3d at 1028
    ; see also State 
    Farm, 463 U.S. at 43
    .
    D.
    CBD also argues that FWS acted arbitrarily in dismissing
    threats of small population sizes, especially since the 2010
    Finding was based in part on the finding that four of the five
    native arctic grayling populations are at risk because of their
    low population numbers. Specifically, CBD argues that
    FWS (1) did not provide a basis for determining the impact
    of low population numbers on long-term genetic viability
    and (2) concluded irrationally that stochastic events would
    not threaten the arctic grayling despite small populations.
    We address each argument in turn.
    1.
    When considering whether to list a species, FWS must
    determine whether the species “is likely to become an
    endangered species within the foreseeable future.”
    16 U.S.C. § 1532(20). Notably, FWS previously applied
    § 1532(20) to encompass long-term genetic effects. In the
    2010 Finding, FWS defined “foreseeable future” as thirty
    years on the basis of a population viability analysis. 75 Fed.
    Reg. at 54,725. Additionally, in 2010, FWS found that while
    population levels were large enough for inbreeding not to be
    an immediate concern, they were still “below the level
    presumed to provide the genetic variation necessary to
    conserve long-term adaptive potential.” 
    Id. at 54,741.
    In the
    2014 Finding, FWS found that genetic diversity does not
    pose a short-term threat to the arctic grayling. 79 Fed. Reg.
    at 49,418. It then discussed scientific literature debating the
    effective population size adequate to conserve genetic
    CENTER FOR BIOLOGICAL DIVERSITY V. ZINKE              37
    diversity over the long term, and concluded that generally
    genetic diversity does not drive species to extinction and that
    other processes are more important. 
    Id. at 49,418–19.
    The
    2014 Finding acknowledged that loss of genetic diversity is
    a threat, but concluded that there are a sufficient number of
    breeding adults to minimize this threat. 
    Id. FWS’s determination
    that the arctic grayling’s small
    population size does not pose a risk to genetic viability of the
    arctic grayling is not arbitrary or capricious. CBD insists
    that FWS did not consider long-term genetic viability, but
    the record does not support this argument. FWS did consider
    long-term genetic viability and simply concluded that, given
    increased population and “[u]pdated genetic information
    that was not available in 2010,” any concern about long-term
    genetic viability did not merit listing the arctic grayling.
    79 Fed. Reg. at 49,420. FWS provided a reasoned
    explanation for why it did not view lack of genetic diversity
    as a threat. And that determination was not arbitrary or
    capricious; difference of opinion does not warrant a contrary
    conclusion. See, e.g., Lands 
    Council, 537 F.3d at 988
    . We
    affirm the district court’s ruling on this issue.
    2.
    The 2014 Finding did, however, arbitrarily rely on the
    Ruby River population to provide redundancy of fluvial
    arctic grayling beyond the Big Hole River and to minimize
    the risk from random environmental events. In its 2010
    Finding, FWS recognized the importance of having multiple
    populations as genetic reservoirs in case of unexpected
    “stochastic” events or environmental catastrophes that may
    wipe out one or more populations of a species. FWS
    concluded that “the lack of additional fluvial populations
    [beyond the Big Hole River] represents a current threat to
    the upper Missouri River [arctic grayling].” 75 Fed. Reg. at
    38     CENTER FOR BIOLOGICAL DIVERSITY V. ZINKE
    54,741. In its 2014 Finding, FWS found that this was no
    longer a concern in part because the increase in the number
    of breeding individuals in the Ruby River over the last three
    years provided “a viable replicate of the fluvial ecotype.”
    79 Fed. Reg. at 49,419.
    The 2014 Finding’s reliance on the Ruby River’s
    viability as a genetic reservoir contradicts FWS’s criteria for
    judging viability, which requires “at least 10 years” of
    monitoring data to confirm that a population is viable.
    Additionally, the 2010 Finding noted that at least five to ten
    more years of monitoring would be needed at Ruby River to
    determine if it is a viable population. The 2014 Finding
    relies on the Leary study, which shows population increases
    in Ruby River, but does not provide a reasoned explanation
    for disregarding FWS’s prior criteria for judging viability or
    the statement in the 2010 Finding about needing five to ten
    more years of monitoring. See, e.g., Organized Vill. of 
    Kake, 795 F.3d at 968
    –69; see also Greater Yellowstone 
    Coal., 665 F.3d at 1028
    .
    Instead, the 2014 Finding describes the Ruby River
    population as viable despite only five years of monitoring
    data. This is less than the viability criteria recommends. It
    is also only four more years of data than that used to support
    the 2010 Finding, which indicated at least five to ten more
    years of data would be needed. This lack of data is a crucial
    omission as the Ruby River population is one of only two
    fluvial populations. The 2014 Finding’s determination that
    the Ruby River population was viable and could provide
    CENTER FOR BIOLOGICAL DIVERSITY V. ZINKE                      39
    redundancy was arbitrary and capricious, and we therefore
    reverse the district court’s ruling on this issue. 18
    V.
    For the foregoing reasons, we hold that the 2014
    Finding’s decision that listing the arctic grayling was “not
    warranted” was arbitrary and capricious because it
    (1) ignored the DeHaan study’s evidence that shows
    decreasing numbers of breeders and instead heavily relied on
    a contrary finding showing increasing population; (2) did not
    provide a reasoned explanation for relying on the existence
    of cold water refugia in the Big Hole River; (3) failed to
    consider the synergistic effects of climate change solely
    because of “uncertainty”; and (4) concluded that the Ruby
    River population is viable based on data collected over a
    shorter period than that underlying the 2010 Finding and
    FWS’s own established criteria for viability. We therefore
    reverse the district court’s grant of summary judgment with
    18
    CBD raises an additional argument that FWS acted arbitrarily in
    basing its 2014 Finding in part on the geographic separation between
    populations without explaining why it changed its position from 2010.
    See, e.g., Organized Vill. Of 
    Kake, 795 F.3d at 968
    –69. But, as FWS
    points out, the 2010 and 2014 Findings each discussed how separation
    of populations reduces the risk of multiple populations being negatively
    impacted by a single environmental catastrophe. In 2010, however, FWS
    concluded that these populations were at risk from other environmental
    factors, which in turn increased the risk of harm of a stochastic event. In
    2014, FWS determined that these other factors no longer counseled in
    favor of listing the arctic grayling. Therefore, its conclusion that
    separation between populations would help prevent a stochastic event
    was not arbitrary or capricious.
    40      CENTER FOR BIOLOGICAL DIVERSITY V. ZINKE
    directions to remand to FWS to reassess the 2014 Finding in
    light of this opinion.
    AFFIRMED in part; REVERSED in part; and
    REMANDED.
    The parties shall bear their own costs on appeal.