                       PUBLISHED


UNITED STATES COURT OF APPEALS
             FOR THE FOURTH CIRCUIT


DOW AGROSCIENCES LLC;                  
MAKHTESHIM AGAN OF NORTH
AMERICA, INC.; CHEMINOVA, INC.
USA,
              Plaintiffs-Appellants,
                 v.
NATIONAL MARINE FISHERIES
SERVICE; JAMES W. BALSIGER,
Acting Assistant Administrator of
                                       
the National Marine Fisheries
Service; NORTHWEST CENTER FOR               No. 11-2337
ALTERNATIVES TO PESTICIDES;
PACIFIC COAST FEDERATION OF
FISHERMEN’S ASSOCIATIONS;
INSTITUTE FOR FISHERIES RESOURCES;
DEFENDERS OF WILDLIFE,
             Defendants-Appellees.


CROPLIFE AMERICA,
    Amicus Supporting Appellants.
                                       
        Appeal from the United States District Court
         for the District of Maryland, at Greenbelt.
          Alexander Williams, Jr., District Judge.
                    (8:09-cv-00824-AW)

                 Argued: October 24, 2012

                Decided: February 21, 2013
2        DOW AGROSCIENCES v. NATIONAL MARINE FISHERIES
    Before NIEMEYER, SHEDD, and AGEE, Circuit Judges.



Reversed, the agency’s biological opinion vacated, and the
case remanded by published opinion. Judge Niemeyer wrote
the opinion, in which Judge Shedd and Judge Agee joined.


                         COUNSEL

ARGUED: Christopher Landau, KIRKLAND & ELLIS,
LLP, Washington, D.C.; David Burton Weinberg, WILEY
REIN, LLP, Washington, D.C., for Appellants. Mark R.
Haag, UNITED STATES DEPARTMENT OF JUSTICE,
Washington, D.C.; Stephen Daniel Mashuda, EARTHJUS-
TICE, Seattle, Washington, for Appellees. ON BRIEF:
Aaron Nielson, KIRKLAND & ELLIS, LLP, Washington,
D.C.; Elbert Lin, Eric Andreas, WILEY REIN, LLP, Wash-
ington, D.C.; David Menotti, Warren U. Lehrenbaum, CRO-
WELL & MORING LLP, Washington, D.C., for Appellants.
Robert G. Dreher, Acting Assistant Attorney General, Mere-
dith Flax, UNITED STATES DEPARTMENT OF JUSTICE,
Environment & Natural Resources Division, Washington,
D.C.; Pamela B. Lawrence, NATIONAL OCEANIC AND
ATMOSPHERIC ADMINISTRATION, Silver Spring, Mary-
land, for Appellees National Marine Fisheries Service and
James W. Balsiger. Amanda W. Goodin, EARTHJUSTICE,
Seattle, Washington, for Appellees Northwest Center for
Alternatives to Pesticides, Pacific Coast Federation of Fisher-
men’s Associations, Institute for Fisheries Resources, and
Defenders of Wildlife. William K. Rawson, Claudia M.
O’Brien, Stacey L. VanBelleghem, LATHAM & WATKINS
LLP, Washington, D.C., for Amicus Supporting Appellants.
       DOW AGROSCIENCES v. NATIONAL MARINE FISHERIES           3
                          OPINION

NIEMEYER, Circuit Judge:

   In this appeal, we decide whether a "biological opinion"
("BiOp") issued by the National Marine Fisheries Service
("Fisheries Service" or "the Service") to the Environmental
Protection Agency ("EPA") is arbitrary and capricious under
the Administrative Procedure Act, 5 U.S.C. § 706. The BiOp,
which the Fisheries Service provided as part of the EPA’s
process of reregistering the pesticides chlorpyrifos, diazinon,
and malathion, concluded that these pesticides would jeopar-
dize the viability of certain Pacific salmonids and their habitat
and that the pesticides could not be reregistered and therefore
used without substantial restriction.

   Three manufacturers of these pesticides commenced this
action, challenging the BiOp by contending that it rested on
numerous unsupported assumptions and conclusions and
faulty analyses and that therefore it was arbitrary and capri-
cious. The district court, unpersuaded, granted the Fisheries
Service’s motion for summary judgment, finding that the
BiOp was rationally supported by the "voluminous facts and
studies considered by the [Fisheries Service]."

   On appeal, we reverse, concluding that the BiOp was not
the product of reasoned decisionmaking in that the Fisheries
Service failed to explain or support several assumptions criti-
cal to its opinion. To enable a renewed agency process, we
vacate the BiOp and remand this case to the district court with
instructions to remand it to the Fisheries Service for further
proceedings consistent with this opinion.

                                I

   Dow AgroSciences LLC, Makhteshim Agan of North
America, Inc., and Cheminova, Inc. USA (collectively, "Pesti-
cide Manufacturers" or "Manufacturers") hold EPA registra-
4      DOW AGROSCIENCES v. NATIONAL MARINE FISHERIES
tions for the pesticides chlorpyrifos, diazinon, and malathion.
Under the Federal Insecticide, Fungicide, and Rodenticide
Act ("FIFRA"), pesticide products must be registered with the
EPA before they can be distributed or sold. 7 U.S.C. § 136 et
seq. Once a product is registered, "[a] registrant may distrib-
ute or sell [the] registered product with the composition, pack-
aging and labeling currently approved by the [EPA]." 40
C.F.R. § 152.130(a). To ensure that registrations are up to
date, 1988 amendments to FIFRA required the EPA to rereg-
ister any pesticide that was first registered before November
1, 1984. 7 U.S.C. § 136a-1(a). In reregistering products, the
EPA must examine data to determine whether the pesticides
still meet FIFRA’s requirements, including the requirement
that the pesticide perform without "unreasonable adverse
effects" on the environment.

   Chlorpyrifos was first registered in 1965; diazinon, in
1956; and malathion, in 1956. Therefore, these pesticides had
to be reregistered for use because of the 1988 amendments to
FIFRA.

   As an agency "action," the reregistration of pesticides by
the EPA is subject to the requirements of the Endangered Spe-
cies Act, which provides that every federal agency must "in-
sure" that its actions are "not likely to jeopardize the
continued existence of any endangered species or threatened
species or result in the destruction or adverse modification of
habitat" deemed critical to such species. 16 U.S.C.
§ 1536(a)(2). If an agency’s proposed action is likely to affect
an endangered species, the agency must consult with the Sec-
retary of the Interior, acting through either the Fisheries Ser-
vice or the U.S. Fish and Wildlife Service, to obtain an
opinion evaluating the agency’s action under the Endangered
Species Act. Id. § 1536; 50 C.F.R. §§ 402.01, 402.14. As part
of the consulting process, the consulted agency issues a BiOp
that explains whether the agency’s proposed action "is likely
to jeopardize the continued existence of listed species or
result in the destruction or adverse modification of critical
       DOW AGROSCIENCES v. NATIONAL MARINE FISHERIES           5
habitat." 50 C.F.R. § 402.14(g)(4), (h). And in issuing the
BiOp, the consulted agency, whether it be the Fisheries Ser-
vice or the U.S. Fish and Wildlife Service, must use "the best
scientific and commercial data available." 16 U.S.C.
§ 1536(a)(2).

   In reregistering chlorpyrifos, diazinon, and malathion, the
Pesticide Manufacturers and the EPA agreed on steps to
reduce the volume of those pesticides being used. Among
other measures, the Manufacturers agreed to voluntarily phase
out chlorpyrifos for residential use and phase in buffer zones,
reduced application rates, and other restrictions for that pesti-
cide. Additionally, they agreed to curtail the use of diazinon
and malathion so as to eliminate homeowner use of diazinon
and reduce application rates of malathion. In this reregistering
process, however, the EPA did not consult or confer with the
Secretary of the Interior to obtain a BiOp under the Endan-
gered Species Act.

   In January 2001, several environmental groups filed suit
against the EPA in the Western District of Washington, alleg-
ing that the EPA failed, as required, to consult with the Secre-
tary of the Interior with respect to the reregistration of 55
active ingredients in pesticides. The district court agreed with
the groups and ordered the EPA to determine whether it was
necessary to consult with the Secretary of the Interior. Wash.
Toxics Coalition v. EPA, Civ. No. 01–132, 2002 WL
34213031 (W.D. Wash. July 2, 2002), aff’d, 413 F.3d 1024
(9th Cir. 2005). Thereafter, the EPA evaluated the effects of
the pesticide ingredients; concluded that 37 active pesticide
ingredients, including chlorpyrifos, diazinon, and malathion,
might "affect" specific salmonid species and their habitats;
and consequently initiated a formal consultation with the
Fisheries Service.

   When, after a long delay, the Fisheries Service had failed
to issue a BiOp, an environmental group filed a second suit,
again in the Western District of Washington, to require the
6      DOW AGROSCIENCES v. NATIONAL MARINE FISHERIES
Fisheries Service to issue its BiOp. See Northwest Coalition
for Alternatives to Pesticides v. Nat’l Marine Fisheries Serv.,
Civ. No. 07–1791 (W.D. Wash. Nov. 5, 2007). The Fisheries
Service settled this suit on July 30, 2008, agreeing to issue a
BiOp within 90 days. A day after the settlement agreement,
the Fisheries Service delivered a 389-page draft BiOp to the
EPA, in which the Service proposed to conclude that chlorpy-
rifos, diazinon, and malathion would "jeopardize the contin-
ued existence" of 28 Pacific salmonid species and impact 26
critical habitats. The EPA also opened an online docket on
August 14, 2008, to permit comments in response to the draft
BiOp.

   The EPA itself, as well as the Pesticide Manufacturers, sev-
eral States, and others, responded to the draft BiOp, criticizing
many of its assumptions and much of its analysis. The EPA
noted that "[t]he Draft lacks a level of transparency necessary
for EPA to understand [the Fisheries Service’s] rationale for
its opinion that the use of any of these pesticides will jeopar-
dize the continued existence of any of the species at issue."
The EPA identified a number of specific problems, including
the Fisheries Service’s failure to consider already in-place
mitigation measures; the Fisheries Service’s assumption that
pesticides would be applied unlawfully; the Fisheries Ser-
vice’s use of historical data; and the Fisheries Service’s criti-
cal assumption in its model that the subject species would be
exposed to a lethal level of pesticides on a continual basis for
a four-day period.

   In response to comments, the Fisheries Service revised its
draft, adding information on in-place pesticide-use reductions
and supplementing its original data with additional studies. It
issued a final BiOp on November 18, 2008, now some 482
pages, in which it still concluded that chlorpyrifos, diazinon,
and malathion would jeopardize numerous salmonid species
and adversely affect critical habitat for them. It found that
exposure to these pesticides would kill salmonids and, even
at low levels, would reduce salmonid growth, reduce the
       DOW AGROSCIENCES v. NATIONAL MARINE FISHERIES         7
availability of prey, and impair salmonids’ swimming and
olfactory senses. And it found ultimately that the reregistra-
tion of the pesticides would jeopardize the survival of 27 of
28 listed salmonid species and adversely affect the critical
habitat of 25 of 26 listed species.

   As required by applicable regulations, the Fisheries Service
recommended "reasonable and prudent alternatives" that
"would avoid the likelihood of jeopardizing the continued
existence of listed species or resulting in the destruction or
adverse modification of critical habitat." 50 C.F.R. § 402.02.
To that end, the Fisheries Service recommended imposing: (1)
a requirement to create specific "buffers" in which pesticides
could not be used; (2) limitations on applying pesticides in
high winds; (3) a requirement to create a 20-foot strip of veg-
etation near surface waters connected to salmonid habitats; (4)
monitoring and regular reporting concerning salmonid mortal-
ity; and (5) limitations on applying pesticides when soil mois-
ture is, or is likely to become, high.

   Following the Fisheries Service’s issuance of its final
BiOp, the Pesticide Manufacturers commenced this action
under the Administrative Procedure Act, 5 U.S.C. § 704,
alleging that the Fisheries Service’s BiOp was arbitrary and
capricious and that the Service did not comply with the
Endangered Species Act’s mandate to use the "best scientific
and commercial data available." On the Fisheries Service’s
motion, the district court entered an order dismissing the
Manufacturers’ complaint on the ground that, pursuant to
FIFRA, the BiOp was judicially reviewable only after the
EPA issued a final reregistration order. Dow AgroSciences
LLC v. Nat’l Marine Fisheries Serv., 638 F. Supp. 2d 508,
513 (D. Md. 2009). On appeal, we reversed and remanded the
case, concluding that the BiOp was indeed a final agency
action subject to judicial review. Dow AgroSciences LLC v.
Nat’l Marine Fisheries Serv., 637 F.3d 259, 260-61 (4th Cir.
2011).
8       DOW AGROSCIENCES v. NATIONAL MARINE FISHERIES
   On remand, the parties filed cross-motions for summary
judgment. In connection with its motion, the Fisheries Service
submitted an explanatory affidavit from Anthony Hawkes, a
toxicologist at the Fisheries Service, in which he discussed the
sources of data and information that the Service considered
and rebutted a number of arguments that the Pesticide Manu-
facturers had made in their motion for summary judgment.
The Manufacturers objected to the Hawkes affidavit, contend-
ing that it contained improper post-hoc rationalizations for the
Fisheries Service’s BiOp.

   In an opinion dated October 31, 2011, the district court
rejected the Pesticide Manufacturers’ challenge to the Hawkes
affidavit and, on the merits, granted summary judgment to the
Fisheries Service. While the court conceded that the Hawkes
affidavit provided "an explanation not already given in the
administrative record," it nonetheless found that the explana-
tions did not "constitute post-hoc rationalizations because
they stem[med] from information provided in the administra-
tive record." In granting summary judgment to the Fisheries
Service, the court concluded that there was a "rational con-
nection between the voluminous facts and studies considered
by the [Fisheries Service] and the decisions reached in the
[Fisheries Service’s] final BiOp." Acknowledging that the
BiOp was of "less than ideal clarity," the district court none-
theless concluded that the Pesticide Manufacturers had not
"shown that the [Fisheries Service] ignored the best scientific
and commercial data available or that the [Fisheries Service’s]
conclusions [were] irrational."

    This appeal followed.

                               II

   As a threshold matter, the Pesticide Manufacturers contend
that the district court erred "by permitting [the Fisheries Ser-
vice] to supplement the record and fill gaps in the BiOp with
post hoc justifications, including arguments by counsel and a
       DOW AGROSCIENCES v. NATIONAL MARINE FISHERIES          9
declaration from agency staff." They fault the district court
for relying on "new justifications provided solely by counsel"
in the judicial review process, pointing out that the district
court relied on counsel’s purportedly new explanations for (1)
the Fisheries Service’s assumption that salmonids will be
exposed to pesticides continuously for 96 hours; (2) the Fish-
eries Service’s modeling assumption that one-size-fits-all
when imposing buffers; and (3) the Fisheries Service’s reli-
ance on water monitoring data developed during a period
when pesticides were more heavily used. The Manufacturers
also fault the district court for relying on the Hawkes affida-
vit, which they argue provided new justifications and facts not
contained in the agency record.

   In response, the Fisheries Service contends that the argu-
ments of counsel and the Hawkes affidavit were simply "post-
decision explanation[s] supported by citations to the adminis-
trative record."

   The principles applicable to this issue are well established.
In reviewing agency action, a court may not "intrude upon the
domain which Congress has exclusively entrusted to an
administrative agency." SEC v. Chenery Corp., 318 U.S. 80,
88 (1943). Thus, a court must only consider the record made
before the agency at the time the agency acted. Citizens to
Preserve Overton Park v. Volpe, 401 U.S. 402, 420 (1971).
The agency record does not refer simply to the facts presented
to the agency but also includes the reasons given by the
agency for taking the action. And a reviewing court may look
only to these contemporaneous justifications in reviewing the
agency action. Chenery, 318 U.S. at 87-88. As such, facts and
justifications for agency action provided to a reviewing court
for the first time are generally not to be considered by the
court. See, e.g., Motor Vehicle Mfr. Ass’n v. State Farm Auto.
Ins. Co., 463 U.S. 29, 50 (1983) ("[C]ourts may not accept
appellate counsel’s post hoc rationalizations for agency
action").
10      DOW AGROSCIENCES v. NATIONAL MARINE FISHERIES
   In this case, the district court explicitly found that the Fish-
eries Service’s BiOp did not include adequate explanations in
at least two critical areas. First, the court concluded that "the
[Fisheries Service] provide[d] scant explanation for [its]
assumption in the BiOp" that salmonids would be exposed to
lethal levels of the pesticides continuously for a 96-hour
period. Nonetheless, the court upheld the Fisheries Service’s
assumption, crediting an argument made by the Fisheries Ser-
vice’s summary judgment brief that the 96-hour exposure
assumption was not the final step in the Fisheries Service’s
analysis.

   Second, the district court concluded that "the BiOp does
not explain why the buffers it requires do not vary according
to channel depth and width." Nonetheless, the court again
upheld the uniform buffers requirement, relying on an argu-
ment made by counsel during the summary judgment process
that "uniform buffers are the industry standard."

   In short, even though the district court recognized that the
BiOp was infirm in two critical respects, it inappropriately
overlooked the infirmity based not on the record, but on justi-
fications provided by counsel during the judicial proceedings.
Thus, the court erred in failing to confine itself to a review of
the agency record.

  As to the Hawkes affidavit, the Pesticide Manufacturers
argue that it impermissively expanded the agency’s record by
providing justifications, explanations, and facts not relied on
by the Fisheries Service in its BiOp. Again we agree with the
Manufacturers’ argument.

   In Overton Park, the Supreme Court noted that litigation
affidavits generally amount to post-hoc rationalizations that
have "traditionally been found to be an inadequate basis for
review." Overton Park, 401 U.S. at 419. But a court may, in
rare circumstances, consider such materials. For example, in
Overton Park, the Court recognized that a reviewing court
       DOW AGROSCIENCES v. NATIONAL MARINE FISHERIES          11
could require the administrative officials who participated in
the decision to give testimony explaining their action. Id. at
420. But it did so in the circumstances where the Court had
no administrative record from which to evaluate the agency’s
decision in the case. See id. at 408. This contextual limitation
was further refined by the Court in later decisions when it
noted that affidavits not contained in the agency record are
permissible only where "there was such failure to explain
administrative action as to frustrate effective judicial review."
Camp v. Pitts, 411 U.S. 138, 142-43 (1973). And the Court
recognized that the more generally applicable rule is "to
remand to the agency for additional investigation or explana-
tion." Fla. Power & Light Co. v. Lorion, 470 U.S. 729, 744
(1985).

    Here, where the Fisheries Service provided a 482-page
BiOp, it can hardly be argued that the administrative record
was so lacking in explanations as to necessitate reliance on a
litigation affidavit in conducting judicial review. See Camp,
411 U.S. at 142-43. We therefore conclude that the district
court erred in receiving and considering the Hawkes affidavit.

   Additionally, the district court would probably have erred
in receiving the Hawkes affidavit even in the limited circum-
stances approved in Overton Park because Hawkes did not
explain how he had authority to speak on behalf of the Fish-
eries Service to explain or justify its decisions. He stated only
that he was "a toxicologist for the National Marine Fisheries
Service," who had helped write the BiOp.

  For these reasons, we will review the Fisheries Service’s
action in this case—its BiOp of November 18, 2008—on the
basis of the agency record before the district court, disregard-
ing the justifications and rationalizations given to the district
court by counsel and by the Hawkes affidavit.

                               III

   The Pesticide Manufacturers contend, on the merits, that
the Fisheries Service’s BiOp failed to justify numerous criti-
12     DOW AGROSCIENCES v. NATIONAL MARINE FISHERIES
cal components of its analysis, rendering the BiOp substan-
tially arbitrary and capricious. Rather than address each
claimed deficiency, we address what we consider to be their
three most significant claims: (1) that the Fisheries Service
failed to justify its model’s assumption that juvenile sal-
monids would be exposed to a lethal level of pesticides con-
tinuously for 96 hours; (2) that the BiOp fails to justify its
reliance on water monitoring data that the Manufacturers
allege were outdated and not representative of current condi-
tions; and (3) that it failed to explain why it imposed uni-
formly sized buffers to all bodies of water, whether they be
rivers or drainage ditches, and regardless of the economic fea-
sibility of such uniform buffers.

   In reaching the conclusions made in the BiOp, the Fisheries
Service considered numerous studies and data to analyze (1)
the levels of pesticide exposure that the salmonids were likely
to experience; (2) the individual salmonid’s likely response to
those exposures; and (3) the likely consequences of that expo-
sure to the population of the relevant salmonid species. Upon
completing these analyses, the Fisheries Service concluded
that the pesticides chlorpyrifos, diazinon, and malathion were
likely to jeopardize the continued existence of 27 salmonid
species and destroy or adversely modify the critical habitat of
25 of the species.

   Important to the Fisheries Service’s analysis and conclu-
sions was a population model that sought to extrapolate the
effects on individual salmonids to an entire population of
those salmonids. The model assumed that salmonids would be
exposed to lethal levels of the pesticides continuously for a
96-hour period. The BiOp explained that the 96-hour expo-
sure assumption was a laboratory standard: "A large body of
laboratory toxicity data indicates that anadromous salmonids
die following short term (< 96 h) exposure to the three insecti-
cides," defining the standard as an "acute test." The BiOp then
explained its use of this acute test:
       DOW AGROSCIENCES v. NATIONAL MARINE FISHERIES         13
    An acute toxicity model was constructed that esti-
    mated the population-level impacts of juvenile mor-
    tality resulting from exposure to lethal
    concentrations of chlorpyrifos, diazinon, and mala-
    thion. These models excluded sublethal and indirect
    effects of the pesticide exposures and focused on the
    population-level outcomes resulting from an annual
    4-day exposure to juveniles to chlorpyrifos, diazinon,
    or malathion.

(Emphasis added). Using the model that applied the acute test,
the BiOp thus found:

    These results indicate that salmonid populations
    exposed to chlorpyrifos, diazinon, or malathion for
    4 days at the reported LC50s [a lethal concentration
    sufficient to kill 50% of the test population] would
    have severe consequences to the population’s growth
    rate.

But then, without explaining why the 96-hour exposure
assumption accurately reflected real-world conditions, the
BiOp concluded that "all but Ozette Sockeye populations . . .
will experience reductions in viability, which ultimately
reduces the likelihood of survival and recovery of these spe-
cies."

   Also important to the Fisheries Service’s conclusions
(especially with respect to the level of pesticide exposure)
was the water monitoring study conducted by the U.S. Geo-
logical Survey during the period from 1992 to 2006. That
study tested water samples from streams across the United
States and found that chlorpyrifos was present in 26% of the
samples, diazinon in 40%, and malathion in 6%. Based pri-
marily on that study, even though it also considered other
more limited data, the BiOp concluded:

    Pacific salmon and steelhead use a wide range of
    freshwater, estuarine, and marine habitats and many
14      DOW AGROSCIENCES v. NATIONAL MARINE FISHERIES
     migrate hundreds of miles to complete their lifecy-
     cle. Chlorpyrifos, diazinon, and malathion are
     widely used pesticides and their detection is com-
     mon in freshwater habitats within the four western
     states where listed specific salmonids are distributed.
     Therefore, we expect some individuals within all the
     listed Pacific salmon and steelhead [evolutionary
     significant units] will be exposed to these chemicals
     and other stressors of the action. Concentrations of
     chlorpyrifos, diazinon, and malathion can occur at
     levels well over 100 ug/l and upwards of 1000 ug/l
     based on measured environmental concentrations
     and exposure models.

(Emphasis added).

   After the BiOp reached its ultimate conclusion that chlor-
pyrifos, diazinon, and malathion were likely to jeopardize the
viability of 27 species of salmonids, it turned, as it was
required to do, to recommending "reasonable and prudent
alternatives" in using the pesticides. In this case, the alterna-
tives limited the scope of the pesticides’ use and required
monitoring and reporting. In the recommended limitations of
use, the BiOp required that the pesticides not be used in
ground applications within 500 feet and in aerial applications
within a 1000 feet of "salmonid habitats," "intermittent
streams" that connect to salmon-bearing waters, and "all
known types of off-channel habitats as well as drainages,
ditches, and other manmade conveyances to salmonid habitats
that lack salmonid exclusion devices."

   The Pesticide Manufacturers contend that the Fisheries Ser-
vice’s BiOp was deficient, among other ways, in (1) failing to
provide support for its 96-hour modeling assumption; (2) rely-
ing on the U.S. Geological Survey’s water monitoring study;
and (3) failing to justify the uniform buffers. We address
these points seriatim.
       DOW AGROSCIENCES v. NATIONAL MARINE FISHERIES          15
A.   The 96-Hour Exposure Assumption

   In its BiOp, the Fisheries Service used an analytical model
that incorporated an assumption that all "subyearling" juve-
nile salmonids in the wild are exposed for 96 straight hours
to a lethal concentration of the pesticides. It candidly recog-
nized that the 96-hour exposure assumption was derived from
a laboratory protocol, but it never explained why the labora-
tory protocol was appropriately reflective of conditions in the
real-world environment. The Pesticide Manufacturers assert
that the application of the laboratory standard was the "only
‘quantitative’ evidence [in the BiOp] that salmonid popula-
tions are likely to be affected by the EPA’s reregistration of
the products at issue."

   When the Fisheries Service released its draft BiOp and
posted it for comment, the 96-hour exposure assumption was
severely criticized. Indeed, the EPA itself argued that the
assumption was "unreasonable," particularly given the "infre-
quency of those concentrations in the [actual] monitoring data
sets." The EPA added that the Fisheries Service had "pro-
vide[d] no explanation of how [the 4-day exposure assump-
tion] can be characterized as realistic or reasonable." Other
commentary made the same point.

   Despite this critical commentary, the Fisheries Service
added nothing to the final BiOp to respond to it, and the dis-
trict court acknowledged, as it had to, that the BiOp "pro-
vide[d] scant explanation for this assumption." The court,
crediting the Service’s interpretation, found that the "4-day
period is one of the standard periods for acute toxicity testing"
in "laboratories under controlled conditions." The district
court also observed that if the Fisheries Service

     were to rely solely on this four-day test in drawing
     conclusions about the degree to which actual popula-
     tions of salmonids are affected, it would have an
     obligation to explain why such a test, which relies on
16      DOW AGROSCIENCES v. NATIONAL MARINE FISHERIES
     laboratory-based assumptions of consistent expo-
     sure, serves as a basis for predicting population
     exposure or survival in the field.

Nonetheless, the court forgave the absence of an explanation
because the BiOp stated that the 96-hour exposure standard
was only among a host of factors that had to be considered in
determining the viability of the salmonid species. The court
concluded:

     While four days may seem arbitrary to a lay person,
     it is not the duty of the Court to sit in judgment of
     scientific standards. The Court also declines to
     second-guess the [Fisheries Service’s] decision to
     utilize this standard, ordinarily confined to labora-
     tory tests, as part of its larger analysis in determina-
     tion of population-level effects.

On that basis, the court concluded that the assumption was not
arbitrary and capricious. See 5 U.S.C. § 706(2)(A).

   Yet the district court failed to recognize that the Fisheries
Service had to "articulate a ‘satisfactory explanation for its
action [that demonstrates] a rational connection between the
facts found and the choice made.’" Satellite Broadcasting &
Commc’ns Ass’n v. FCC, 275 F.3d 337, 370 (4th Cir. 2001)
(alterations in original) (quoting Motor Vehicle Mfrs. Ass’n v.
State Farm Mut. Auto. Ins. Co., 463 U.S. 29, 43 (1983)).
Rather than doing so, the court instead deferred to the agency
and failed even to address whether there was any rational con-
nection between the agency’s use of the 96-hour laboratory
exposure assumption and field conditions.

  The Fisheries Service argues that "while the BiOp does not
explicitly discuss the basis for the assumption, [the Fisheries
Service’s] path ‘may be reasonably discerned’ from the BiOp
and the administrative record." In an attempt to show us that
path, the Service directs us to four observations scattered
       DOW AGROSCIENCES v. NATIONAL MARINE FISHERIES          17
throughout the BiOp, which state (1) that 96 hours is the typi-
cal period in "acute toxicity" tests; (2) that because young sal-
monids use "shallow, low flow habitats at some point in their
life cycles," they are exposed to waters that have only a "lim-
ited ability to dilute pesticide contamination"; (3) that pesti-
cides can persist in water for longer than 96 hours; and (4)
that pesticides are applied multiple times in a single area.
Even if we accept that these observations delineate a "path,"
that path still does not lead to an explanation of why the Ser-
vice decided that the 96-hour exposure assumption taken from
laboratory testing was the appropriate proxy for real-world
conditions. The fact remains that the Fisheries Service postu-
lates an environment where salmonids are exposed to lethal
levels of pesticides continuously for 96 hours based on a labo-
ratory protocol without explaining how the assumption
matches up with real-world conditions.

   In an attempt to save the assumption, the Fisheries Service
argues that because its BiOp "candidly recognizes the limita-
tions of this modeling," its disclosure of limitations justifies
using the 96-hour exposure assumption. But acknowledging a
model’s limitations does not go to explaining why it was cho-
sen and the rationality of its relationship to real-world condi-
tions. If anything, an acknowledgement that the assumption is
flawed would seem to necessitate more explanation of why
the assumption was used.

   At bottom, we conclude that the Fisheries Service’s failure
to explain why it used the 96-hour exposure assumption ren-
ders the BiOp arbitrary and capricious.

B.   The Water Monitoring Data

   The Pesticide Manufacturers next challenge the BiOp’s
reliance on purportedly outdated water monitoring data,
which were the only type of data used in the BiOp to describe
field conditions. The principal source of the data used by the
Fisheries Service was a National Water-Quality Assessment
18     DOW AGROSCIENCES v. NATIONAL MARINE FISHERIES
conducted by the U.S. Geological Survey from 1992 to 2006,
in which the U.S. Geological Survey tested water samples
from hundreds of streams across the United States. Using
those data, the Fisheries Service reported high concentration
levels of chlorpyrifos, diazinon, and malathion in relevant
waterways.

   When the draft BiOp was released for comment, the Pesti-
cide Manufacturers, as well as many other commentators,
promptly noted the flaws in the U.S. Geological Survey data
and directed the Fisheries Service to more recent available
data. The EPA explained to the Fisheries Service that the "his-
torical data [in the draft BiOp] more appropriately reflect[ed]
pesticide use prior to substantive mitigation that ha[d] been
put in place by EPA." The States of Idaho, California, and
Washington also provided references to more recent data,
demonstrating that the U.S. Geological Survey data were out-
dated.

   In the final BiOp, the Fisheries Service continued to rely on
the older U.S. Geological Survey data. Indeed, the BiOp
acknowledged the data’s deficiency but did not address it. It
stated that "reduced rates are likely to result in corresponding
reductions in exposure"; that the older data may not be repre-
sentative of "current and future pesticide uses and condi-
tions"; and that "recent data show a decrease in use of
chlorpyrifos and diazinon in California that may be associated
with restrictions on residential uses of those active ingredi-
ents." But ultimately, the Fisheries Service continued to rely
primarily on the U.S. Geological Survey sampling data.

   The Pesticide Manufacturers argue that because the older
data do not reflect the "use cancellations, usage rate reduc-
tions, and protective application techniques required by the
EPA’s re-registration process," the data were nonrepresenta-
tive and any reliance on them was arbitrary and capricious.

  Although we do not address how representative the U.S.
Geological Survey data continue to be, we do note that the
       DOW AGROSCIENCES v. NATIONAL MARINE FISHERIES          19
BiOp never adequately explained why it relied on older data
despite the existence of new data and the potential drawbacks
of using the older data. The Fisheries Service argues that it
was nonetheless justified in using the older water monitoring
data because the BiOp (1) acknowledged the cancelled uses
and decreases in pesticides in California; (2) observed that the
mitigation measures did not mean that pesticide use necessar-
ily changed, as old stockpiles of pesticides were still being
used that were labeled with the less restrictive registrations;
(3) noted that any effect of the use of cancellations and appli-
cation reductions on exposure levels was uncertain because of
the lack of relevant data; and (4) took into account the various
criticisms when it acknowledged that the water monitoring
data might not be representative of the current and future use
of these pesticides.

   But these observations in the BiOp do not alleviate the con-
cerns that the Manufacturers raise and that we share. Each of
the Fisheries Service’s arguments goes to its effort to bolster
the reliability of the data that it actually used, but not one of
the explanations addresses the issue of why the Fisheries Ser-
vice relied on these old data when new data were available.
To be sure, the Fisheries Service need not have analyzed or
explicitly rejected every data source presented, but it surely
was required to "cogently explain why it ha[d] exercised its
discretion" in relying on a data set that was so highly criti-
cized. State Farm, 463 U.S. at 48.

   We should point out that an agency need not revise its
action every time new data or a new model is announced
because doing so "would lead to significant costs and poten-
tially endless delays in the approval processes." Sierra Club
v. EPA, 356 F.3d 296, 308 (D.C. Cir. 2004) (concluding that
the EPA’s approval of State plans that used an old model was
appropriate where a new modeling tool was available for only
one year before the EPA approved the plans). But when an
agency acknowledges that its data are either outdated or inac-
curate, it should, at the very least, analyze the new data or
20     DOW AGROSCIENCES v. NATIONAL MARINE FISHERIES
explain why it nevertheless chose to rely on the older data.
See, e.g., Sierra Club v. EPA, 671 F.3d 955, 966-68 (9th Cir.
2012) (finding the EPA’s action arbitrary and capricious for
not utilizing a more recent model). As the Ninth Circuit
explained, "we should not silently rubber stamp agency action
that is arbitrary and capricious in its reliance on old data with-
out meaningful comment on the significance of more current
compiled data." Id. at 968.

   Here, we face just that situation. The Fisheries Service rec-
ognized that it was relying on outdated data and that it had
been presented with more recent data, but it chose to continue
relying on the outdated data without explaining why.

C.   The Prescribed Use of Uniform Buffers

   Because the Fisheries Service found that the reregistration
of chlorpyrifos, diazinon, and malathion would jeopardize sal-
monid populations, it was obligated to recommend "reason-
able and prudent alternatives, if any." 50 C.F.R.
§ 402.14(h)(3); see also 16 U.S.C. § 1536(b)(3)(A). In this
case, the Fisheries Service recommended, among other things,
that ground applications of the pesticides be prohibited within
500 feet and aerial applications be prohibited within 1,000
feet of "salmonid habitats," "intermittent streams" that con-
nect to salmon-bearing waters, and "all known types of off-
channel habitats."

   The Pesticide Manufacturers contend that the prescription
of such fixed buffer zones is unreasonable in view of the vari-
able water environments throughout the Pacific Northwest.
And they assert that because buffers were aimed at protecting
only the most sensitive, off-channel salmonid habitats, the
Service was obligated to explain why that same buffer zone
should apply to larger bodies of water. In addition, the Manu-
facturers contend that the BiOp failed to explain, as required
by law, the economic feasibility of the one-size-fits-all buff-
ers.
       DOW AGROSCIENCES v. NATIONAL MARINE FISHERIES         21
   It is not disputed that the BiOp fails to address why the
buffers do not vary according to channel depth and width.
Indeed, the district court so found, noting that "the BiOp does
not explain why the buffers it requires do not vary according
to channel depth and width, and the [Pesticide Manufactur-
ers’] suggestion appeals to common sense." The district court,
however, accepted the single-size buffers because counsel for
the Fisheries Service asserted, without providing further justi-
fication, that uniform buffers were the industry standard.

   To be sure, the BiOp did address the fact that some form
of buffer was appropriate as a "recognized tool[ ] to reduce
pesticide loading into aquatic habitats from drift." And large
buffers are appropriate where the pesticides could drift to
"off-channel habitats" because these off-channel habitats,
serving as a nursery for young salmonids, are particularly vul-
nerable. But while this explanation supports the use of buff-
ers, it does not explain why buffers designed to protect "off
channel habitats" should also apply to protect large, flowing
rivers.

   In response, the Fisheries Service argues that the Endan-
gered Species Act does not require the Fisheries Service "to
explain why [it] chose one recommended and prudential alter-
native over another," relying on and quoting from Southwest
Center for Biological Diversity v. U.S. Bureau of Reclama-
tion, 143 F.3d 515, 523 (9th Cir. 1998). But Southwest Center
does not address the problem here. In that case, the court
found that the agency did not have to explain why it chose
one reasonable and prudent alternative over another when
both were sufficiently justified in the report itself. See id.
Here, uniform buffers were the only alternative included in
the BiOp, and the Fisheries Service did not explain why it was
appropriate.

  The absence of a justification becomes especially relevant
in view of the potential economic consequences of such a
requirement and the mandate that reasonable and prudent
22     DOW AGROSCIENCES v. NATIONAL MARINE FISHERIES
alternatives be "economically and technologically feasible."
50 C.F.R. § 402.02. Every recommended alternative must be
a measure that "can be taken by the Federal agency or appli-
cant in implementing the agency’s action." 16 U.S.C.
§ 1536(b)(3)(A). And in determining this, the Service must
consider several factors, including "economic feasibility." See
50 C.F.R. § 402.02 ("Reasonable and prudent alternatives
refer to alternative actions identified during formal consulta-
tion . . . that [are] economically and technologically feasi-
ble").

   The Fisheries Service does not claim that it considered eco-
nomic feasibility or that the BiOp addressed it. Thus, the dis-
trict court correctly found that "[the Fisheries Service] does
not discuss the economic feasibility of the buffers in the BiOp
or elsewhere in the administrative record." Rather, the Fish-
eries Service reads the economic feasibility requirement to be
trumped by the statement of the Endangered Species Act’s
purpose "to halt and reverse the trend toward species extinc-
tion, whatever the cost." TVA v. Hill, 437 U.S. 153, 184
(1978) (emphasis added). Under the Fisheries Service’s read-
ing, the economic feasibility requirement becomes simply a
limitation that the reasonable and prudent alternative be eco-
nomically possible, without any need for discussion.

  We cannot agree with this position, as it effectively reads
out the explicit requirement of Regulation 402.02 that the
agency evaluate its reasonable and prudent alternative recom-
mendation for, among other things, economic and technologi-
cal feasibility. Moreover, economic feasibility becomes
especially relevant when recommending uniform buffers
because, as the Pesticide Manufacturers point out, pesticide
applications would be prohibited within 500 feet (for ground
applications) and 1,000 feet (for aerial applications) of any
waterway that is connected, directly or indirectly, at any time
of the year, to any water body in which salmonids might be
found at some point. Such a broad prohibition readily calls for
some analysis of its economic and technical feasibility.
       DOW AGROSCIENCES v. NATIONAL MARINE FISHERIES          23
   We hasten to add that the Fisheries Service "is not required
to pick the best option for the industry any more than for the
species, [but] it must provide some analysis of the options it
selects." Greenpeace v. Nat’l Marine Fisheries Serv., 55 F.
Supp. 2d 1248, 1268-69 (W.D. Wash. 1999). By not address-
ing the economic feasibility of its proposed "reasonable and
prudent" alternative providing for one-size-fits-all buffers, the
Fisheries Service has made it impossible for us to review
whether the recommendation satisfied the regulation and
therefore was the product of reasoned decisionmaking. This
failure provides another basis for our conclusion that the
BiOp was arbitrary and capricious.

                               IV

   In sum, the Fisheries Service’s November 2008 BiOp relied
on a selection of data, tests, and standards that did not always
appear to be logical, obvious, or even rational. While the Ser-
vice may have had good and satisfactory explanations for its
choices, the BiOp did not explain them with sufficient clarity
to enable us to review their reasonableness. For that reason,
we conclude the BiOp is arbitrary and capricious.
   In reaching this conclusion, we have addressed what we
consider to be the more obvious flaws, but others are claimed
to exist. We have not addressed all of the Pesticide Manufac-
turers’ complaints because, on remand, they can be aired and
addressed in the renewed agency process. We find it sufficient
at this point to vacate the BiOp in its present form and require
the Fisheries Service to address not only the flaws we identi-
fied but also any additional matters that may be raised on
remand.
   Accordingly, the judgment of the district court is reversed;
the BiOp is vacated; and the case is remanded to the district
court with instructions to remand the case to the Fisheries Ser-
vice for further proceedings consistent with this opinion.
                                           IT IS SO ORDERED.
