 United States Court of Appeals
         FOR THE DISTRICT OF COLUMBIA CIRCUIT



Argued September 11, 2017         Decided November 7, 2017

                        No. 16-5282

                      TIMOTHY MAYO,
                         APPELLEE

                       KENT NELSON,
                        APPELLANT

                             v.

MICHAEL T. REYNOLDS, IN HIS OFFICIAL CAPACITY AS ACTING
 DIRECTOR OF THE U.S. NATIONAL PARK SERVICE, ET AL.,
                      APPELLEES


        Appeal from the United States District Court
                for the District of Columbia
                    (No. 1:14-cv-01751)


   Eric R. Glitzenstein argued the cause for appellant. With
him on the briefs was Katherine A. Meyer.

   Rachel Heron, Attorney, U.S. Department of Justice,
argued the cause for federal appellees. With her on the brief
were Jeffrey H. Wood, Acting Assistant Attorney General,
and Andrew Mergen, J. David Gunter II, and Judith Coleman,
Attorneys.
                             2
    Erik E. Petersen, Assistant Attorney General, Office of
the Attorney General for the State of Wyoming, argued the
cause for intervenor-appellee State of Wyoming. With him on
the brief was James Kaste, Senior Assistant Attorney General.

    Douglas S. Burdin, Anna M. Seidman, and Jeremy E.
Clare were on the brief for intervenor-appellee Safari Club
International.

   Before: MILLETT, Circuit Judge, and EDWARDS and
WILLIAMS, Senior Circuit Judges.

  Opinion for the Court filed by Senior Circuit Judge
EDWARDS.

    EDWARDS, Senior Circuit Judge: This case involves a
challenge to decisions made by the National Park Service
(“Park Service”) authorizing recreational hunting of elk in
Wyoming’s Grand Teton National Park (“Grand Teton”).
Appellant claims that the Park Service violated the National
Environmental Policy Act (“NEPA”) by authorizing
recreational hunts each year without first conducting a NEPA
review to assess whether and to what extent hunting was in
fact necessary for the proper management and protection of
the elk. Appellant’s Br. 26.

     Grand Teton and the National Elk Refuge (“Refuge”) are
home to the “Jackson herd,” one of the largest concentrations
of elk in North America. Two federal agencies share primary
responsibility for managing the Jackson herd: the Park
Service, which has jurisdiction over Grand Teton, and the
U.S. Fish and Wildlife Service (“FWS”), which manages the
Refuge. In 2007, the two agencies, acting together, adopted a
fifteen-year plan (“2007 Plan”) to manage the Jackson herd.
The 2007 Plan set objectives to reduce the population size of
                                3
the herd, limit their risk of disease, and conserve their habitat.
In conjunction with the 2007 Plan, the agencies also issued a
final environmental impact statement (“EIS”), as required by
NEPA.

    The 2007 Plan analyzed six alternative long-term
strategies for managing the Jackson herd. The EIS, in turn,
carefully assessed the environmental risks posed by the
alternative strategies. In the end, the agencies adopted an elk-
reduction program pursuant to which the Park Service would
authorize elk hunting as needed to attain the Plan’s population
objectives. The program also contemplated that the FWS
would reduce supplemental feed given to the elk during
winter months on the Refuge. Between 2007 and 2015, the
Park Service adhered to the elk-reduction program in
determining the number of elk authorized to be harvested and
the number of hunters deputized to participate in a hunt. As a
result, from 2007 to 2015, the size of the herd decreased, as
did the number of deputized hunters and the number of elk
authorized to be harvested. During this same period, however,
the FWS failed to meet the 2007 Plan’s objective to wean the
herd from supplemental feed.

    Kent Nelson and Timothy Mayo, wildlife photographers,
filed suit in the District Court challenging the Park Service’s
2015 program for elk hunting. See Mayo v. Jarvis, 177 F.
Supp. 3d 91, 107–24 (D.D.C. 2016). They argued that the
Park Service was required to prepare a new NEPA analysis
every year that it implemented the fifteen-year elk-reduction
program, disclosing and analyzing the unique environmental
effects of each year’s hunt. Because no such analysis was
done for the 2015 hunt authorization, they claimed that the
Park Service’s action violated NEPA. Appellants also
contended that the FWS’s failure to reduce supplemental
feeding in line with the Plan’s goals necessitated the
                              4
preparation of a supplemental EIS. However, supplemental
feeding is managed by the FWS and Nelson and Mayo did not
seek to pursue any action against the FWS with respect to that
program. With respect to the NEPA claims, the District Court
denied the plaintiffs’ summary judgment motion and granted
the Park Service’s cross-motion for summary judgment. Id. at
146. Nelson, but not Mayo, now appeals the District Court’s
judgments.

    In its brief to this court, the Park Service cogently
explains why the judgment of the District Court should be
affirmed:

        Under NEPA, an agency must take a hard look at
   the environmental impacts of its proposed actions. The
   statute does not, however, require the agency to take a
   new look every time it takes a step that implements a
   previously-studied action, so long as the impacts of that
   step were contemplated and analyzed by the earlier
   analysis. Here, the Park Service’s 2007 Management
   Plan contemplated that the Park Service would
   authorize annual elk-reduction programs, and the 2007
   EIS accompanying that plan specifically analyzed the
   effects of such programs. . . . [Appellant] has not
   identified any impact from the 2015 reduction program
   that was not studied in the 2007 EIS . . . . The Park
   Service has therefore satisfied NEPA.

Appellees’ Br. 24. We agree. We therefore affirm the District
Court’s judgment on the NEPA issues.

   In the District Court, the plaintiffs also claimed that the
agencies’ consultation over the effects of the elk-reduction
program on the grizzly bear population did not satisfy the
requirements of the Endangered Species Act (“ESA”). All
                               5
parties agree that this claim is now moot because the grizzly
bear is no longer listed as a threatened species under the ESA.
See Endangered Species and Threatened Wildlife and Plants,
82 Fed. Reg. 30,502 (June 30, 2017) (to be codified at 50
C.F.R. pt. 17). We therefore vacate the District Court’s
judgment on the ESA claim. See United States v.
Munsingwear, Inc., 340 U.S. 36, 39–40 (1950).

                      I.   BACKGROUND

A. Statutory and Regulatory Background

   1.   National Environmental Policy Act
    Congress enacted the National Environmental Policy Act
(“NEPA”) in part “to promote efforts which will prevent or
eliminate damage to the environment and biosphere and . . .
enrich the understanding of the ecological systems and natural
resources important to the Nation.” 42 U.S.C. § 4321 (2012).
To those ends, NEPA requires all federal agencies to include
a detailed environmental impact statement (“EIS”) “in every
recommendation or report on . . . major Federal actions
significantly affecting the quality of the human environment.”
Id. § 4332(2)(C). This process ensures that an agency will
“consider every significant aspect of the environmental
impact of a proposed action” and “inform the public” of its
analysis. Balt. Gas & Elec. Co. v. Nat. Res. Def. Council, Inc.,
462 U.S. 87, 97 (1983); see also Dep’t of Transp. v. Pub.
Citizen, 541 U.S. 752, 768 (2004). “In other words, agencies
must ‘take a hard look at [the] environmental consequences’
of their actions, and ‘provide for broad dissemination of
relevant environmental information.’” Pub. Emps. for Envtl.
Responsibility v. Hopper, 827 F.3d 1077, 1082 (D.C. Cir.
2016) (quoting Robertson v. Methow Valley Citizens Council,
490 U.S. 332, 350 (1989)) (internal quotation marks omitted).
                               6

    Not every agency action requires the preparation of a full
EIS, however. See, e.g., Duncan’s Point Lot Owners Ass’n
Inc. v. FERC, 522 F.3d 371, 376 (D.C. Cir. 2008) (“[F]ederal
control and responsibility for an action is not enough to
trigger the EIS requirement.”). Thus, in determining whether
a major federal action “significantly affect[s]” the
environment, 42 U.S.C. § 4332(2)(C), an agency may prepare
a more concise environmental assessment (“EA”), see
Council on Environmental Quality (“CEQ”) regulations, 40
C.F.R. § 1508.9, which may result in the agency issuing a
“finding of no significant impact” in lieu of a full EIS, see id.
§ 1508.13.

    Where NEPA analysis is required, its role is “primarily
information-forcing.” Sierra Club v. FERC, 867 F.3d 1357,
1367 (D.C. Cir. 2017). As the Supreme Court has explained,
“[t]here is a fundamental distinction . . . between a
requirement that mitigation be discussed in sufficient detail to
ensure that environmental consequences have been fairly
evaluated, on the one hand, and a substantive requirement that
a complete mitigation plan be actually formulated and
adopted, on the other.” Robertson, 490 U.S. at 352. “NEPA is
‘not a suitable vehicle’ for airing grievances about the
substantive policies adopted by an agency, as ‘NEPA was not
intended to resolve fundamental policy disputes.’” Grunewald
v. Jarvis, 776 F.3d 893, 903 (D.C. Cir. 2015) (quoting Found.
on Econ. Trends v. Lyng, 817 F.2d 882, 886 (D.C. Cir. 1987)).

    It is now well-established that “NEPA imposes only
procedural requirements on federal agencies with a particular
focus on requiring agencies to undertake analyses of the
environmental impact of their proposals and actions.” Pub.
Citizen, 541 U.S. at 756–57; see also Vt. Yankee Nuclear
Power Corp. v. Nat. Res. Def. Council, Inc., 435 U.S. 519,
                               7
558 (1978) (NEPA’s mandate “is essentially procedural”). It
is equally clear that NEPA does not impose a duty on
agencies “to include in every EIS a detailed explanation of
specific measures which will be employed to mitigate the
adverse impacts of a proposed action.” Robertson, 490 U.S. at
353 (emphasis omitted) (internal quotation omitted).

     An agency is required to supplement an existing EIS only
if the agency “makes substantial changes in the proposed
action that are relevant to environmental concerns,” or if there
are “significant new circumstances or information relevant to
environmental concerns and bearing on the proposed action or
its impacts.” CEQ regulations, 40 C.F.R. § 1502.9(c). Under
this standard, an agency is not required to make a new
assessment under NEPA every time it takes a step that
implements a previously studied action, so long as the impacts
of that step were contemplated and analyzed by the earlier
analysis. See, e.g., Wyoming v. U.S. Dep’t of Agric., 661 F.3d
1209, 1257–58 (10th Cir. 2011).

    In Marsh v. Oregon Natural Resources Council, 490 U.S.
360 (1989), the Supreme Court explained that under the “rule
of reason,” “an agency need not supplement an EIS every
time new information comes to light after the EIS is
finalized.” Id. at 373. Rather, “a supplemental EIS must be
prepared” only when a new action will affect the quality of
the environment “in a significant manner or to a significant
extent not already considered.” Id. at 374; see also Nat’l
Comm. for the New River, Inc. v. FERC, 373 F.3d 1323, 1330
(D.C. Cir. 2004) (explaining that a supplemental impact
statement is “only required where new information provides a
seriously different picture of the environmental landscape”
(quoting City of Olmsted Falls v. Fed. Aviation Admin., 292
F.3d 261, 274 (D.C. Cir. 2002))); Davis v. Latschar, 202 F.3d
359, 369 (D.C. Cir. 2000) (requiring a supplemental impact
                               8
statement only for “changes that cause effects which are
significantly different from those already studied”). And
because an agency’s decision whether to prepare a
supplemental EIS requires “substantial agency expertise,”
courts must defer to the agency’s “informed discretion.”
Marsh, 490 U.S. at 366–77.

   2.   The 2007 Elk-Management Plan and Environmental
        Impact Statement
    As noted above, the Park Service and Fish and Wildlife
Service jointly manage the Jackson elk herd. In the spring and
summer, the Jackson herd tends to reside primarily in
Wyoming’s Grand Teton National Park, under the jurisdiction
of the Park Service. In the winter, however, much of the herd
migrates to the neighboring National Elk Refuge, which is
managed by the FWS.

    Since 1955, the Park Service has annually authorized the
hunting of elk in the Park. Although hunting is frequently
prohibited in national parks, Congress authorized the practice
in Grand Teton in 1950 when it established the Park in its
current form. See Pub. L. 81-787 § 6(a), 64 Stat. 849, 851–52
(1950), codified at 16 U.S.C. § 673c. Specifically, Congress
required the Park Service and Wyoming Game and Fish
Commission to “devise . . . a program to insure the permanent
conservation of the elk within the Grand Teton National Park”
and directed that such conservation program “shall include the
controlled reduction of elk in such park, . . . when it is found
necessary for the purpose of proper management and
protection of the elk.” 16 U.S.C. § 673c(a).

   Part of the Park Service’s justification for the elk-hunting
program has to do with the practices of the FWS on the
Refuge. The FWS provides supplemental feed to elk on the
                                9
Refuge during winter months on the assumption that there is
an insufficient amount of winter range to support the numbers
of elk that occupy the Jackson Hole area. This practice
reduces incidents of elk starvation, but it also creates
“significant problems” of its own. Defs. of Wildlife v. Salazar,
651 F.3d 112, 113 (D.C. Cir. 2011). Supplemental feeding
artificially increases the size and density of the elk herd, and it
has also contributed to the spread of disease among the elk
and erosion of their habitat. Id. at 113–14. Authorized hunting
offsets some of the adverse effects of supplemental feeding by
containing the herd’s population size, while also managing
the gender and age distributions of the Jackson elk herd.

    In 2007, the Park Service and the FWS adopted a fifteen-
year plan for managing the Jackson elk herd and prepared an
EIS to assess the environmental effects of the plan. See Final
Bison and Elk Management Plan and Environmental Impact
Statement for the National Elk Refuge/Grand Teton National
Park/John D. Rockefeller, Jr., Memorial Parkway (Feb. 1,
2007)      (“2007     Plan    and     EIS”),     available    at
http://bisonandelkplan.fws.gov. The Plan listed four goals for
managing the elk: (1) conserving their habitat, (2) making the
population sustainable, (3) contributing to Wyoming’s
population objectives for the elk, and (4) managing the risk of
disease. Id. at ix. To achieve those ends, the agencies
analyzed six alternative management programs, each of which
varied in terms of its goals for the elk reduction level sought,
the number of elk wintering on the Refuge, the use of hunting
to control the population, and the extent to which
supplemental feeding would continue on the Refuge. See id.
at ix–x.

    The agencies chose a program denominated Alternative
Four. That option called for reducing the total number of elk
in the Jackson herd from approximately 13,000 to 11,000, and
                               10
the number of elk wintering on the Refuge, where
supplemental feed is served, from 6,800 down to 5,000. Id. at
48. The Plan aimed to meet these targets through an “adaptive
management approach” involving public education, habitat
conservation, and a decreasing use of supplemental feeding
“based on established criteria and changing social, political,
or biological conditions.” Id. at 48, 65. In addition, the
agencies assumed that hunting would be authorized “on the
refuge, and when necessary . . . in the park, to assist the state
in managing herd sizes, sex and age ratios, and summer
distributions” of elk. Id. at 48. Specifically, the 2007 Plan
predicted that in Grand Teton over the “long term an
estimated average of 232–287 elk per year would be
harvested by 773–957 deputized hunters, compared to
baseline figures of 1,600 hunters and 480 elk per year.” Id. at
472.

    As noted above, the Park Service and the FWS also
prepared an environmental impact statement in conjunction
with the 2007 Plan, as required by NEPA. The final EIS
carefully addressed the impact of the Plan’s six alternatives –
including the preferred elk-reduction program – on, inter alia,
the Park and Refuge’s physical environment, id. at 194–210,
the habitat of the elk, id. at 211–54, other wildlife, including
threatened and endangered species, id. at 351–66, human
health and safety, id. at 443–56, and recreational and tourism
related activities, id. at 457–93. Importantly, the EIS noted
that “[t]he level of analysis [in the report was] sufficient to
allow several management actions to be carried out without
having to complete additional environmental analyses (e.g.,
environmental assessments) prior to implementation.” Id. at
191.

   The 2007 Plan also was required to comply with the
Endangered Species Act (“ESA”) due to the Plan’s potential
                              11
to affect the Greater Yellowstone Ecosystem (“GYE”)
population of grizzly bears, see id. at 351, a species that had
been listed as “threatened” since 1975, see Amendment
Listing the Grizzly Bear of the 48 Coterminous States as a
Threatened Species, 40 Fed. Reg. 31,734 (July 28, 1975).
Accordingly, the Park Service consulted with the FWS over
the matter. The FWS then issued a biological opinion
determining that the implementation of the 2007 Plan’s
preferred alternative was not likely to jeopardize the existence
of the grizzly bear, but might result in some take of grizzlies
by elk hunters. See Bison and Elk Management Plan: National
Elk Refuge and Grand Teton National Park (Apr. 2007),
Appendix E, at 171–98, reproduced at J.A. 645–72, 830–61,
available at https://www.fws.gov/bisonandelkplan/. In 2012,
an elk hunter killed a grizzly bear, prompting the Park Service
to consult again with the FWS. In 2013, the FWS issued an
addendum to its 2007 biological opinion, estimating that a
total of five grizzly bears would be taken in the Park during
the fifteen-year period covered by the 2007 Plan.
Memorandum from Field Supervisor, U.S. FWS to
Superintendent, Nat’l Park Service (Sept. 13, 2013),
reproduced at J.A. 867–904, 870.

B. Procedural Background

    The Park Service has authorized elk hunting in Grand
Teton in reliance on its 2007 Plan and EIS in every year since
the Plan was adopted. On October 20, 2014, local wildlife
photographers Timothy Mayo and Kent Nelson brought suit
in the District Court, challenging the annual hunting
authorizations as contrary to the Grand Teton National Park
Act (“Enabling Act”), 16 U.S.C. § 673c(a), National Park
Service Organic Act (“Organic Act”), 16 U.S.C. § 1,
Administrative Procedure Act (“APA”), 5 U.S.C. § 706(2),
ESA, 16 U.S.C. § 1531, and NEPA, 42 U.S.C. § 4321 et seq.
                               12
Complaint for Declaratory and Injunctive Relief, ¶¶ 68–80,
reproduced at J.A. 33–37. On July 1, 2015, the plaintiffs filed
a supplemental complaint, incorporating by reference each of
the statutory claims to also apply to the Park Service’s 2015
authorization of elk hunting in the Park. Supp. Complaint,
¶¶ 1–8, J.A. 39–41. The State of Wyoming and Safari Club
International intervened as defendants before the District
Court. Mayo, 177 F. Supp. 3d at 105.

    With respect to their NEPA claims, the plaintiffs argued
that the Park Service was required to issue a new EA or EIS
every year during the fifteen-year term of the elk-reduction
program. Complaint, ¶¶ 73–74, J.A. 35; Mayo, 177 F. Supp.
3d at 107. They contended that changes had occurred after the
agency promulgated the 2007 Plan and EIS – most notably,
the FWS’s continued use of supplemental feeding on the
Refuge – necessitating a supplemental EIS. Mayo, 177 F.
Supp. 3d at 117, 122.

    The plaintiffs also challenged the biological opinion and
its 2013 addendum as arbitrary and capricious for failing to
address the possibility that elk viscera left by hunters “harass”
grizzly bears within the meaning of the ESA’s take
prohibition. Id. at 142–45. As explained above, this claim is
now moot, so it will not be addressed in this opinion.

    Mayo and Nelson moved for summary judgment on July
21, 2015. The Park Service, FWS, and intervenors opposed
that motion and cross-moved for summary judgment in their
favor.

   On March 29, 2016, the District Court entered summary
judgment for the government on the Enabling Act, Organic
Act, and NEPA claims. Id. at 91, 146. With respect to the
NEPA claims, the District Court held that the Park Service
                             13
could rely on the 2007 EIS in making its annual elk-reduction
decisions because that document “took the requisite ‘hard
look’ at the potential environmental effects that might result
from continuing the elk reduction program in the Park as a
method of managing the herd.” Id. at 109. The District Court
rejected the plaintiffs’ contention that the agencies had
abandoned the 2007 Plan, and held that a supplemental EIS
was not required since the record lacked evidence that the
FWS’s supplemental feeding practices “on the Refuge [have]
had a spillover effect on the environmental impacts of elk
hunting in the Park.” Id. at 122.

    Accordingly, on August 1, 2016, the District Court
entered final judgment on all counts in the government’s
favor. Mayo v. Jarvis, 203 F. Supp. 3d 31, 42 (D.D.C. 2016).
Kent Nelson, but not Timothy Mayo, has now appealed the
denial of his motion for summary judgment and the entry of
judgment for Appellees.

                        I. ANALYSIS

A. Standard of Review

    We review the District Court’s grant and denial of
summary judgment de novo. Theodore Roosevelt Conserv.
P’ship v. Salazar, 661 F.3d 66, 72 (D.C. Cir. 2011).
Because NEPA does not provide a private right of action, the
agencies’ compliance with NEPA is reviewed under the
Administrative Procedure Act (“APA”) “and its deferential
standard of review.” Sierra Club, 867 F.3d at 1367.

    The APA requires that we “hold unlawful and set aside
agency action” that is “arbitrary, capricious, an abuse of
discretion, or otherwise not in accordance with law.” 5 U.S.C.
§ 706(2)(A). Agency action is arbitrary and capricious “if the
                              14
agency has relied on factors which Congress has not intended
it to consider, entirely failed to consider an important aspect
of the problem, [or] offered an explanation for its decision
that runs counter to the evidence before the agency.” Motor
Vehicle Mfrs. Ass’n v. State Farm Mut. Auto. Ins. Co., 463
U.S. 29, 43 (1983); see also Duncan’s Point Lot Owners, 522
F.3d at 376 (“We will overturn an agency’s decision not to
prepare an EIS only if that decision was arbitrary, capricious,
or an abuse of discretion.”). In evaluating whether the agency
has met this standard, the court must “not . . . substitute its
[own] judgment for that of the agency.” State Farm, 463 U.S.
at 43.

    As noted above, the Supreme Court has emphasized that
“inherent in NEPA and its implementing regulations is a ‘rule
of reason.’” Pub. Citizen, 541 U.S. at 767 (quoting Marsh,
490 U.S. at 373). The rule of reason governs our review of an
agency’s environmental analysis, N. Slope Borough v.
Andrus, 642 F.2d 589, 600 (D.C. Cir. 1980), decision not to
prepare a NEPA analysis, Pub. Citizen, 541 U.S. at 767, and
decision not to supplement an existing EIS, Marsh, 490 U.S.
at 373–74. The standard “ensures that agencies determine
whether and to what extent to prepare an EIS based on the
usefulness of any new potential information to the
decisionmaking process.” Pub. Citizen, 541 U.S. at 767; see
also Marsh, 490 U.S. at 373–74. “The overarching question is
whether an EIS’s deficiencies are significant enough to
undermine informed public comment and informed
decisionmaking.” Sierra Club, 867 F.3d at 1368 (citing
Nevada v. Dep’t of Energy, 457 F.3d 78, 93 (D.C. Cir. 2006)).

   A court’s “role in reviewing an agency’s decision not to
prepare an EIS is a ‘limited’ one, ‘designed primarily to
ensure that no arguably significant consequences have been
ignored.’” Myersville Citizens for a Rural Cmty., Inc. v.
                              15
FERC,      783      F.3d      1301,    1322     (D.C.     Cir.
2015) (quoting TOMAC v. Norton, 433 F.3d 852, 860 (D.C.
Cir. 2006)). Necessarily, then, “[w]here the preparation of an
EIS would serve ‘no purpose’ in light of NEPA’s regulatory
scheme as a whole, no rule of reason worthy of that title
would require an agency to prepare an EIS.” Pub. Citizen, 541
U.S. at 767 (internal quotation marks omitted).

B. Appellant’s Claim Regarding the Need for an Annual
   NEPA Assessment

    Appellant’s primary argument on appeal is that each
annual hunting authorization constitutes a “major Federal
action” that triggers NEPA’s mandate that the agency prepare
an EA or EIS. 42 U.S.C. § 4332(2)(C); see CEQ regulations,
40 C.F.R. § 1508.18 (defining “Federal action” to include
“continuing activities” and approvals by federal agencies of
“specific projects, such as . . . management activities located
in a defined geographic area” and “actions approved by
permit”); id. § 1508.27 (defining “significantly”). Appellant
offers three arguments in support of his claim that the 2007
EIS cannot satisfy this statutory requirement: (1) the 2007
Plan did not disclose the particulars of each future annual
hunt; (2) the agencies have stopped implementing the Plan;
and (3) significant new information bearing on the
environmental effects of hunting have never been analyzed.

    Intervenor-Appellee Wyoming argues that the Park
Service’s authorization of the 2015 elk-reduction program is
not a “major Federal action” since it is “simply one step in the
agency’s ongoing management of the elk and bison herds
under the fifteen-year term of the 2007 Plan.” Wyoming’s Br.
34. The Park Service, in turn, contends that even if each
hunting authorization is a “major Federal action” which may
“significantly affect” the environment, the 2007 EIS relieved
                             16
the Park Service of the obligation to prepare fresh NEPA
documentation each year it implements the elk-reduction
program in conformity with the 2007 Plan. Appellees’ Br. 28–
44. We agree with the Park Service.

    Once an agency has taken a “hard look” at “every
significant aspect of the environmental impact” of a proposed
major federal action, Balt. Gas, 462 U.S. at 97 (quoting Vt.
Yankee, 435 U.S. at 553), it is not required to repeat its
analysis simply because the agency makes subsequent
discretionary choices in implementing the program. As
discussed above in part I.A, an agency may rely on an
already-performed, “thorough and comprehensive” NEPA
analysis. New York v. U.S. Nuclear Regulatory Comm’n (New
York II), 824 F.3d 1012, 1019 (D.C. Cir. 2016).

    In this case, the Park Service published a thorough and
detailed EIS in 2007. Appellant has identified no significant
way in which the subsequent hunting authorizations deviated
from the assessment made in 2007. NEPA does not impose a
duty on agencies “to include in every EIS a detailed
explanation of specific measures which will be employed to
mitigate the adverse impacts of a proposed action.”
Robertson, 490 U.S. at 353 (internal quotation marks and
emphasis omitted). And an agency is not required to make a
new assessment under NEPA every time it takes a step that
implements a previously studied action. See Marsh, 490 U.S.
at 373. So long as the impacts of the steps that the agency
takes were contemplated and analyzed by the earlier NEPA
analysis, the agency need not supplement the original EIS or
make a new assessment. See Nat’l Comm. for the New River,
373 F.3d at 1330. The 2007 EIS was clearly sufficient to
cover elk hunting during the ensuing fifteen years under the
2007 Plan absent a material change causing unforeseen
environmental consequences.
                               17

   1.   Adequacy of the 2007 EIS
    In preparing the 2007 EIS, the agencies took a hard look
at the potential environmental effects of the program to
reduce the Jackson elk herd through annual hunting
determinations. Spanning more than 600 pages, the EIS
analyzed the effects of elk hunting on a variety of relevant
environmental factors. For example, the EIS described how
the elk-reduction program would likely affect the elks’
mortality potential, see 2007 Plan and EIS at 258, 296, the
overall size of the Jackson herd, and the concomitant ability
of the Park Service to accomplish the Plan’s population goals
for the elk, see id. at 466–67, 471–72. The EIS considered the
effect of hunting on the density of the herd and distribution of
the elk throughout the Park and Refuge, id. at 288–90, as well
as on calving, age, and sex ratios of the elk, id. at 294–95. The
EIS additionally explained how hunting might affect the elks’
social practices, potentially increasing the elks’ “nervousness,
energetic expenditures, and possibly decreasing nutrition
because of reductions in foraging.” Id. at 291.

    The EIS also took into account the elk-reduction
program’s likely consequences on other wildlife, including
various amphibians, id. at 434, as well as mule deer, moose,
and pronghorn and bighorn sheep, e.g., id. at 399, 377–78. It
specifically addressed the effects of hunting on species listed
under the ESA, such as the grizzly bear, describing how the
presence of hunters in particular hunting areas within the Park
and the changing scope of the hunt over time might impact
such species. Id. at 353. For example, the EIS considered the
possibility that elk hunters might kill grizzly bears, id. at 357,
and, more optimistically, produce an additional source of
nutrition for grizzlies, wolves, and bald eagles by creating elk
“gut piles” for the animals to scavenge, id. at 359.
                               18

    In addition, the EIS considered the elk-reduction
program’s relation to the region’s human environment. It
evaluated the likelihood that hunting would cause injury, id.
at 449, increase the risk of traffic accidents, id. at 448–49, and
reduce visitors’ opportunities to observe the elk, id. at 462–
64, including for purposes of wildlife photography, id. at 457–
58. The EIS further explained that by bringing people into
proximity with the elk, hunting might increase the risk that
humans catch diseases from the animals. Id. at 449, 451.

   The EIS analyzed more than just the environmental effects
of the elk-reduction program. It also evaluated alternative
uses of hunting as an elk-management tool. For instance, it
considered changing hunting practices by closing traditional
hunting areas and opening non-traditional areas. Id. at 279–
80. It thoroughly discussed the possibility of eliminating
hunting completely from the Park and Refuge. E.g., id. at
265–68, 272–73, 321. And it contained a detailed discussion
of possible mitigation measures where relevant to the
environmental risks it identified.

    All in all, given the level of detail in the assessment, there
is no question that the 2007 EIS “adequately considered and
disclosed the environmental impact of” the 2007 Plan’s
preferred elk-reduction program, its necessity, and its
alternatives. Nevada, 457 F.3d at 93 (quoting Balt. Gas, 462
U.S. at 97–98).

    This appeal does not involve an arbitrary and capricious
challenge to the Park Service’s annual decisions to authorize
elk hunting in Grand Teton. Instead, Appellant faults the Park
Service for not preparing a NEPA analysis each year during
the fifteen-year term of the 2007 Plan to document each
“hunt’s timing, location, restrictions, and . . . potential
                              19
alternatives for avoiding or minimizing impacts.” Appellant’s
Br. 41. As we have already explained, what Appellant seeks is
much more than is required by NEPA. The Park Service’s
mere implementation of the 2007 Plan, without more, did not
result in any “seriously different picture of the environmental
landscape.” Nat’l Comm. for the New River, 373 F.3d at 1330.
All the environmental effects seen during the years after the
promulgation of the 2007 Plan and EIS had been anticipated
and analyzed in the original environmental assessment.
Therefore, the Park Service had no duty to prepare a
supplemental or new EIS.

   2. Agency Discretion to Determine When and How to
      Engage in NEPA Analysis
    NEPA does not prevent an agency from satisfying future
NEPA obligations by performing a NEPA analysis at the
outset of a long-term project. The decision in New York II,
824 F.3d at 1016, confirms this point. In that case, the
Nuclear Regulatory Commission had prepared a “Generic
Environmental Impact Statement” concerning the effects of
on-site storage of spent nuclear fuel. The agency issued a rule
that “incorporate[d] the findings of the [EIS] into all future
reactor licensing proceedings,” id., and this court upheld that
rule and EIS as lawful under NEPA, id. at 1016–23.
Therefore, it is clear here that the agencies’ decision to adopt
a fifteen-year plan supported by one EIS was permissible
under NEPA.

    To be sure, agencies are not always free to comply with
NEPA by issuing a single EIS at the outset of a long-term
project. An environmental analysis that occurs too early in the
planning process may lack “meaningful information”
necessary for informed consideration. Scientists’ Inst. for Pub.
Info., Inc. v. Atomic Energy Comm’n, 481 F.2d 1079, 1093–
                              20
94 (D.C. Cir. 1973). Thus, if a program “involves . . . separate
sub-projects and will take many years,” NEPA’s
implementing regulations allow the agency to “evaluate[]
each sub-project as it becomes ready” and tailor its
subsequent analyses to particularized considerations not
already addressed in a prior “programmatic EIS.” Nevada,
457 F.3d at 91; see CEQ regulations, 40 C.F.R. § 1508.28.
“Tiering” – as this process is known – is “appropriate when it
helps the lead agency to focus on the issues which are ripe for
decision and exclude from consideration issues already
decided or not yet ripe.” CEQ regulations, 40 C.F.R.
§ 1508.28(b) (emphasis added).

    In Theodore Roosevelt Conservation Partnership v.
Salazar, for example, the Bureau of Land Management
approved drilling permits based on EAs that tiered to a
programmatic EIS. 616 F.3d 497, 506 (D.C. Cir. 2010).
Plaintiffs argued that the specific approvals were arbitrary and
capricious because the underlying EIS used an outdated
scientific method for measuring the project’s effects on ozone
concentrations. Id. at 510–11. This court rejected that
argument, stating, “[w]hile courts have required [EAs] to
analyze certain impacts for the first time when the broader
analysis did not address the impact in question at all, this is
not such a case.” Id. at 512 (citation omitted). The earlier EIS
already “address[ed] the impact drilling would have on ozone
concentrations” and “[n]othing in the law requires agencies to
reevaluate their existing environmental analyses each time the
original methodologies are surpassed by new developments.”
Id.

   Appellant claims that Theodore Roosevelt supports his
argument. In that case, Appellant argues, the court rejected
the plaintiffs’ challenges in part because the agency
committed to performing an EA before approving any specific
                              21
application to drill. Appellant’s Br. 42–45. That is true
enough, as far as it goes. When an earlier impact statement
fails to take a hard look at a component of a plan that is major
and may itself significantly affect the environment, the
agency must do so through an EA or EIS prior to taking the
action. But Theodore Roosevelt expressly excused the agency
from conducting subsequent environmental analyses of issues
already thoroughly evaluated in the earlier impact statement.
See 616 F.3d at 512. Under the rule of reason, subsequent
“site-specific” NEPA analyses are required only for “those
localized environmental impacts that were not fully evaluated
in the program statement.” Scientists’ Inst. for Pub. Info., 481
F.2d at 1093. When all relevant environmental issues have
already been analyzed and decided, additional EAs or
supplementation are not required.

    Furthermore, it was for the Park Service to decide whether
to perform the environmental analysis in a comprehensive EIS
or in narrower annual documentation. In Natural Resources
Defense Council, Inc. v. U.S. Nuclear Regulatory
Commission, we explained that the agency, “in its discretion,
could have chosen to explore alternatives to the particular
tanks in either a ‘programmatic’ or ‘site-specific’ format.”
606 F.2d 1261, 1271 (D.C. Cir. 1979); see also Izaak Walton
League of Am. v. Marsh, 655 F.2d 346, 374 n. 73 (D.C. Cir.
1981) (“[T]he decision whether to prepare a programmatic
impact statement is committed to the agency’s discretion.”).
Appellant has not shown that it was arbitrary and capricious
for the Park Service to perform the required NEPA analysis in
a single EIS.

   3. Consistency of the Annual Hunts with the 2007 Plan
      and 2007 EIS’s Projections
                              22
    The record indicates that the Park Service has
implemented the elk-reduction program in the manner
envisioned by the 2007 Plan and analyzed in the 2007 EIS.
The Plan and EIS predicted that the number of deputized
hunters in the Park would decline from an average of 1,600
hunters per year to 773–957 and, over “the long term,” the
number of elk harvested would decline from an average of
480 elk per year to 232 to 287 elk per year. 2007 Plan and EIS
at 472. Over the last ten years, the number of elk authorized to
be hunted in the Park has declined from 600 to 300, with
fewer hunters deputized to hunt elk in both the Park and
Refuge combined than the Plan allowed for the Park alone. In
sum, the record confirms that the Park Service’s elk hunting
authorizations have been within the range of the Plan’s
expectations, on which the 2007 EIS based its analysis.

    Appellant’s argument that the agencies have abandoned
the 2007 Plan has no merit. The record indicates only one
implementation failure under the 2007 Plan – the FWS’s
failure to decrease supplemental feeding on the Refuge –
which is addressed below. However, the record also shows
that the 2007 Plan as a whole – including its monitoring,
education, adaptive management, and hunting programs – has
been followed. Furthermore, as noted above, “NEPA is ‘not a
suitable vehicle’ for airing grievances about the substantive
policies adopted by an agency, as ‘NEPA was not intended to
resolve fundamental policy disputes.’” Grunewald, 776 F.3d
at 903 (quoting Found. on Econ. Trends, 817 F.2d at 886).
Therefore, Appellant’s policy preference for reduced
supplemental feeding is beyond the scope of our review of his
NEPA challenge. The agencies’ 2007 NEPA assessment
satisfied the requirements of the law for the annual elk hunts.
The subsequent failure of the FWS to cut back on
supplemental feeding does not undermine this conclusion,
especially when the record indicates that all of the potential
                              23
environmental effects of the Plan were fully addressed in the
2007 EIS and the principal policy objectives of the 2007 Plan
are being met.

C. Appellant’s Challenge to the FWS’s Supplemental
   Feeding

   The question remains whether the FWS’s failure to cut
back on supplemental feeding is otherwise unlawful.
Appellant makes much of the fact that the weaning of the herd
from supplemental feeding was one of the methods adopted
by the 2007 Plan to manage the population of the elk herd.
And Appellant complains that, despite committing to working
toward a “complete transition” away from supplemental feed
to “free-standing forage” on the Refuge, the FWS’s
supplemental feeding has continued on the Refuge and the
number of elk wintering there has increased over the last ten
years. Although the FWS never committed to ending
supplemental feeding by any specific date, its failure to
decrease supplemental feeding obviously is not in keeping
with one of the goals of the Plan. See Defs. of Wildlife, 651
F.3d at 117 (noting that “the agencies are committed to
ending supplemental feeding”).

   There are two glaring problems with Appellant’s
complaint. First, as noted above, the failure of the FWS to cut
back on supplemental feeding does not indicate that the 2007
Plan has failed with respect to elk hunting.

    Second, as Appellant’s counsel conceded during oral
argument before this court, this case does not directly
challenge supplemental feeding. Oral Arg. Recording 37:00–
48. The Fish and Wildlife Service, not the Park Service, is
responsible for the supplemental feeding program, which
takes place on the Refuge, not in the Park. And Appellant has
                              24
brought no viable legal action against the FWS to contest the
supplemental feeding program. In an effort to overcome this
problem, Appellant argues that the FWS’s failure to decrease
supplemental feeding represents a substantial change in the
environmental consequences of the elk-reduction program
requiring supplemental NEPA analysis. This is a clever claim,
but it fails.

    The heart of Appellant’s claim appears to be that if
supplemental feeding is not reduced then hunting necessarily
must continue in order to ensure that the size of the elk herd
does not exceed the projections of the 2007 Plan. On this
theory, Appellant argues that the Park Service must publish
new NEPA analyses evaluating whether hunting continues to
be necessary in light of the fact that supplemental feeding has
not declined. We reject this argument. The EIS clearly and
exhaustively contemplated the continuation of the elk-
reduction program over the life of the fifteen-year Plan. And
while it is not implausible to assume that the Park Service
might have authorized more hunting than the 2007 Plan
contemplated because of the FWS’s failure to decrease
supplemental feeding, the record refutes this assumption.

    As explained above, the Park Service’s implementation of
the annual elk-reduction program has met the population
goals of the 2007 Plan and EIS. From 2007 to 2015, the size
of the herd decreased, as did the number of deputized hunters
and the number of elk authorized to be harvested. In other
words, the number of elk authorized to be harvested and the
number of hunters deputized to participate in hunts did not
increase as a result of the FWS’s continued use of
supplemental feeding. Therefore, Appellant has failed to
demonstrate any “substantial change[] in the proposed action”
– elk hunting in Grand Teton – “relevant to environmental
concerns” or any “significant new circumstances or
                             25
information relevant to environmental concerns and bearing
on the proposed action or its impacts.” CEQ regulations, 40
C.F.R. § 1502.9(c) (emphases added).

    We reiterate that, in reaching this conclusion, a crucial
consideration here is the fact that the “proposed action”
challenged in this case is the Park Service’s authorization of
elk hunting in Grand Teton, not the FWS’s supplemental
feeding practices on the Refuge. The admitted variance
between the Plan’s proposed supplemental feeding program
and that program’s implementation simply does not
“provide[] a seriously different picture of the environmental
landscape” of hunting. Nat’l Comm. for the New River, 373
F.3d at 1330 (quoting Olmsted Falls, 292 F.3d at 274). No
supplementation is therefore required. See Marsh, 490 U.S. at
373 (“[A]n agency need not supplement an EIS every time
new information comes to light after the EIS is finalized.”);
Blue Ridge Envtl. Def. League v. Nuclear Regulatory
Comm’n, 716 F.3d 183, 196 (D.C. Cir. 2013) (rejecting
supplementation claim because the “[p]etitioners failed to
indicate any environmental data that were not considered in
the EIS”).

   If Appellant wishes to challenge the merits of the FWS’s
supplemental feeding program, he will have to pursue an
appropriate action against the FWS directly.

                     III. CONCLUSION

    For the reasons set forth above, we affirm the judgment of
the District Court on the NEPA claims. We vacate the District
Court’s judgment as to the ESA claim, which is now moot.

                                                  So ordered.
