Experimental Populations Under the Endangered Species Act
Updated July 27, 2023
Experimental Populations Under the Endangered Species Act
Section 10(j) of the Endangered Species Act (ESA; 16
Wholly Separate Geographically
U.S.C. §§ 1531 et seq.) allows for the establishment of
The Services’ regulations provide that the geographic
experimental populations of endangered or threatened
separation between the released population and existing
species listed under the act and delineates how they are to
populations must be “reasonably predictable.” For example,
be regulated. Congress added Section 10(j) to the ESA as
fixed migration patterns or natural or manmade barriers
part of the Endangered Species Act Amendments of
between the populations may create sufficiently predictable
1982.The amendments gave the U.S. Fish and Wildlife
separation. When making this determination, the Services
Service (FWS) and National Marine Fisheries Service
focus on the population as a whole rather than individuals
(NMFS) (together, the Services) more flexibility to
within the population. Individuals from an experimental
determine how to protect and manage experimental
population that venture into an area of overlap with the non-
populations, and they altered certain agency consultation
experimental population are not recognized as part of the
requirements for nonessential experimental populations.
experimental population while they are intermixed with a
non-experimental population.
With certain exceptions, experimental populations are
treated as threatened species under the ESA regardless of
Contribution to the Conservation of the Species
the designation of the listed species generally. This
The ESA requires that the establishment of an experimental
treatment allows the Services to tailor the protections and
population must contribute to the conservation of the listed
exceptions that apply to the population, providing for
species. The Services must consider whether removing
flexible management while contributing to the conservation
individuals from existing populations to establish the
of the species.
experimental one will adversely affect those populations.
They must also consider whether the experimental
The Services have established more than 60 experimental
population is likely to survive for the foreseeable future and
populations for many kinds of species. Examples include
meet population goals. The agencies must further examine
the gray wolf, grizzly bear, black-footed ferret, California
the anticipated effects that establishing an experimental
condor, Chinook salmon, Anthony’s riversnail, and
population will have on the species’ recovery. Finally, the
American burying beetle. Two experimental populations of
Services must determine whether and to what extent
gray wolf that were released in Idaho, Montana, and
existing or anticipated federal or state actions or private
Wyoming in the mid-1990s eventually allowed the resultant
activities may be affected by establishing an experimental
distinct population segment to be delisted through
population. Each factor must be determined based on the
administrative and legislative action.
best commercial and scientific data available.
This In Focus describes the criteria and process for
Designation as Essential or Nonessential
establishing and regulating 10(j) experimental populations.
When the Services designate an experimental population,
Section 10(j) of the ESA also requires that they determine
Experimental Population Criteria
whether the experimental population is “essential to the
Section 10(j) authorizes the Secretary of the Interior or of
continued existence” of the species. The Services designate
Commerce, as delegated to FWS or NMFS, respectively, to
such experimental populations as essential experimental
release endangered or threatened species into the wild
populations and all others as nonessential experimental
outside the current range of the species, provided the
populations. These determinations are made based on the
Services determine that the release will contribute to the
“best available information.” Pursuant to their regulations,
conservation of the species. Experimental populations must
the Services consider an experimental population to be
be wholly separate geographically from any non-
essential if losing the population would likely “appreciably
experimental populations of the species. The Services have
reduce the likelihood” of the species surviving in the wild.
each enacted regulations to implement Section 10(j).
To date, no experimental population has been designated as
essential.
Outside the Species’ Current Range
Section 10(j) requires that the Services release experimental
Implications of Designation
populations outside the species’ current range. FWS
In general, even if a species is listed as endangered,
regulations further require the experimental population to
experimental populations of that species are treated as
be released into “suitable natural habitat.” In addition, FWS
threatened species under the statute. The prohibitions in
generally requires that when an experimental population is
Section 9 of the ESA, such as on importing or exporting
to be released outside the species’ historical range, FWS
species, automatically apply to endangered species, but they
consider any possible adverse effects on the ecosystem
only apply to threatened species (and, by extension,
from the release.
experimental populations) if provided by regulation. When
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Experimental Populations Under the Endangered Species Act
the Services extend Section 9 prohibitions to experimental
identify the experimental population, such as specifying the
populations, those regulations are referred to as 10(j) rules.
proposed location or anticipated migration. It must identify
any special management concerns, such as management
For threatened species, the Services must designate critical
restrictions or protective measures to isolate or contain the
habitat to the maximum extent prudent and determinable.
population from the rest of the species. It must also create a
Critical habitat generally consists of habitat that is essential
process for periodic evaluation of how effective the
to the conservation of the species. Section 10(j) allows the
experimental population is at conserving the species.
Services to designate critical habitat for essential
experimental populations but precludes such designations
For an essential experimental population, the agency may
for nonessential experimental populations.
also designate critical habitat. The Service may also choose
to implement a 10(j) rule or designate critical habitat as part
ESA Section 7 (16 U.S.C. § 1536) generally requires
of the rule establishing the experimental population or
federal agencies to consult with the Services when their
through a separate rulemaking process.
actions may affect endangered or threatened species. Under
Section 10(j), however, nonessential experimental
Judicial Review of Designation and 10(j) Rules
populations are generally subject instead to the Section 7
Both the ESA and the APA provide a basis for judicial
requirements that apply to species that are proposed to be
review of the Services’ final designation and 10(j) rules for
listed. For proposed species, Section 7 requires federal
experimental populations, depending on the plaintiffs’
agencies to confer with the Services about actions that may
particular allegations. The ESA allows citizens to sue in
affect the species, which is a more informal process than
federal district court to enforce provisions of the ESA or its
consultation that allows the agency to proceed with its
regulations. That includes suits claiming that the Services
action in the meantime and results in only advisory
have violated Section 10(j) or challenging regulations
recommendations about minimizing adverse effects to the
issued under Section 10(j).
species. For proposed actions within the National Park
System or the National Wildlife Refuge System, Section 7
In reviewing those claims, courts apply the “arbitrary and
applies to nonessential experimental populations as it would
capricious” standard contained in the APA. The ESA,
to threatened species.
however, does not provide for suit against the Services in
certain instances. Some challenges to the Services’
Process for Designating Experimental
administration of the ESA through the rulemaking process
Populations and Crafting 10(j) Rules
must proceed under the APA, not the ESA.
The Services establish experimental populations and
protections for those populations through the federal
Considerations for Congress
rulemaking process. Federal agency rulemaking procedures
Although Section 10(j) affords the Services more flexibility
are largely governed by the Administrative Procedure Act
to manage experimental populations than other listed
(APA). The Services’ designations and 10(j) rules are thus
populations, some stakeholders still raise concerns that
governed primarily by requirements established in the ESA,
designating an experimental population may affect
implementing regulations, and the APA.
development in particular areas. In addition, experimental
populations of large predators such as gray wolves and
Issuing Designation and 10(j) Rules
grizzly bears can raise conflicting views about possible
To designate an experimental population, the Service first
interactions with livestock and big game herds.
publishes a proposed rule providing notice of its intent to
designate an experimental population, its proposed
For example, FWS’s proposal to release an experimental
designation of essential or nonessential, and any proposed
population of gray wolves in Colorado in 2023 has raised
10(j) rule for the population.
this issue. At the same time, other stakeholders criticize
10(j) rules that permit killing or harassing experimental
The Services’ regulations require the agencies to consult
populations of large predators, claiming those rules fail to
with relevant state fish and wildlife agencies and local
fulfill the goals of the ESA, limit the species’ ability to fully
governmental entities, as well as affected federal agencies
recover, and prevent the species from reestablishing natural
and private landowners, when developing and
relationships with large ungulate populations.
implementing experimental population regulations. This
consultation process may involve holding public meetings.
Congress may consider whether to leave such decisions to
Likewise, the APA requires the Services to provide an
the discretion of the agency or to provide more direction as
opportunity for the public to comment on the proposal.
to how experimental populations should be managed, either
After considering any public comments, the Service may
in general or for specific species. Congress may also
choose to complete the rulemaking process by publishing a
consider legislation directly targeting stakeholder concerns
final rule. The final rule must provide a reasoned
outside the 10(j) context, such as through depredation grant
justification supporting the agency’s action, including
programs for livestock owners.
responses to significant comments.
Erin H. Ward, Legislative Attorney
The Services’ regulations require rules establishing
Benjamin M. Barczewski, Legislative Attorney
experimental populations to include certain information in
addition to demonstrating that the released population meet
IF12407
the statutory criteria. The rule must provide a means to
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Experimental Populations Under the Endangered Species Act
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https://crsreports.congress.gov | IF12407 · VERSION 2 · UPDATED