Proposed Rule2025-10785
Endangered and Threatened Wildlife and Plants; Removal of Gila Chub From the List of Endangered and Threatened Wildlife
Primary source
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Published
June 17, 2025
Issuing agencies
Interior DepartmentFish and Wildlife Service
Abstract
We, the U.S. Fish and Wildlife Service (Service), propose to remove the Gila chub (Gila intermedia) from the Federal List of Endangered and Threatened Wildlife. Our review indicates that, based on the best scientific and commercial data available, the Gila chub is not a valid taxonomic entity and does not meet the definition of a species under the Endangered Species Act of 1973, as amended (Act). Accordingly, we propose to delist the Gila chub. If we finalize this rule as proposed, the prohibitions and conservation measures provided by the Act, particularly through sections 7 and 9, would no longer apply to the Gila chub.
Full Text
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[Federal Register Volume 90, Number 115 (Tuesday, June 17, 2025)]
[Proposed Rules]
[Pages 25552-25559]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2025-10785]
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DEPARTMENT OF THE INTERIOR
Fish and Wildlife Service
50 CFR Part 17
[Docket No. FWS-R2-ES-2022-0001; FXES1113090FEDR-256-FF09E22000]
RIN 1018-BG36
Endangered and Threatened Wildlife and Plants; Removal of Gila
Chub From the List of Endangered and Threatened Wildlife
AGENCY: Fish and Wildlife Service, Interior.
ACTION: Proposed rule.
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SUMMARY: We, the U.S. Fish and Wildlife Service (Service), propose to
remove the Gila chub (Gila intermedia) from the Federal List of
Endangered and Threatened Wildlife. Our review indicates that, based on
the best scientific and commercial data available, the Gila chub is not
a valid taxonomic entity and does not meet the definition of a species
under the Endangered Species Act of 1973, as amended (Act).
Accordingly, we propose to delist the Gila chub. If we finalize this
rule as proposed, the prohibitions and conservation measures provided
by the Act, particularly through sections 7 and 9, would no longer
apply to the Gila chub.
DATES: We will accept comments received or postmarked on or before
August 18, 2025. Comments submitted electronically using the Federal
eRulemaking Portal (see ADDRESSES, below) must be received by 11:59
p.m. eastern time on the closing date. We must receive requests for
public hearings, in writing, at the address shown in FOR FURTHER
INFORMATION CONTACT by August 1, 2025.
ADDRESSES: Comment submission: You may submit comments by one of the
following methods:
(1) Electronically: Go to the Federal eRulemaking Portal: <a href="https://www.regulations.gov">https://www.regulations.gov</a>. In the Search box, enter FWS-R2-ES-2022-0001,
which is the docket number for this rulemaking. Then, click on the
Search button. On the resulting page, in the Search panel on the left
side of the screen, under the Document Type heading, check the Proposed
Rule box to locate this document. You may submit a comment by clicking
on ``Comment.''
(2) By hard copy: Submit by U.S. mail to: Public Comments
Processing, Attn: FWS-R2-ES-2022-0001, U.S. Fish and Wildlife Service,
MS: PRB/3W, 5275 Leesburg Pike, Falls Church, VA 22041-3803.
[[Page 25553]]
We request that you send comments only by the methods described
above. We will post all comments on <a href="https://www.regulations.gov">https://www.regulations.gov</a>. This
generally means that we will post any personal information you provide
us (see Information Requested, below, for more information).
Availability of supporting materials: This proposed rule and
supporting documents, such as the species status assessment (SSA)
report, the SSA addendum, and comments from peer review, are available
at <a href="https://www.regulations.gov">https://www.regulations.gov</a> under Docket No. FWS-R2-ES-2022-0001.
FOR FURTHER INFORMATION CONTACT: Heather Whitlaw, Field Supervisor,
U.S. Fish and Wildlife Service, Arizona Ecological Services Field
Office, 9828 North 31st Avenue Suite C3, Phoenix, AZ 85051-2517;
telephone 602-242-0210. Individuals in the United States who are deaf,
deafblind, hard of hearing, or have a speech disability may dial 711
(TTY, TDD, or TeleBraille) to access telecommunications relay services.
Individuals outside the United States should use the relay services
offered within their country to make international calls to the point-
of-contact in the United States. Please see Docket No. FWS-R2-ES-2022-
0001 on <a href="https://www.regulations.gov">https://www.regulations.gov</a> for a document that summarizes this
proposed rule.
SUPPLEMENTARY INFORMATION:
Information Requested
We intend that any final action resulting from this proposed rule
will be based on the best scientific and commercial data available and
be as accurate and as effective as possible. Therefore, we request
comments or information from other concerned governmental agencies,
Native American Tribes, the scientific community, industry, or any
other interested parties concerning this proposed rule.
We particularly seek comments concerning:
(1) Reasons we should or should not remove the Gila chub from the
List of Endangered and Threatened Wildlife; and
(2) Relevant data concerning the taxonomy of the Gila chub,
particularly genetic relationships to other members of the genus Gila
that occur in the Colorado River basin.
Please include sufficient information with your submission (such as
scientific journal articles or other publications) to allow us to
verify any scientific or commercial information you include.
Please note that submissions merely stating support for, or
opposition to, the action under consideration without providing
supporting information, although noted, do not provide substantial
information necessary to support a determination. Section 4(b)(1)(A) of
the Act (16 U.S.C. 1533(b)(1)(A)) directs that determinations as to
whether any species is an endangered species or a threatened species
must be made solely on the basis of the best scientific and commercial
data available.
You may submit your comments and materials concerning this proposed
rule by one of the methods listed in ADDRESSES. We request that you
send comments only by the methods described in ADDRESSES.
If you submit information via <a href="https://www.regulations.gov">https://www.regulations.gov</a>, your
entire submission--including any personal identifying information--will
be posted on the website. If your submission is made via a hardcopy
that includes personal identifying information, you may request at the
top of your document that we withhold this information from public
review. However, we cannot guarantee that we will be able to do so. We
will post all hardcopy submissions on <a href="https://www.regulations.gov">https://www.regulations.gov</a>.
Comments and materials we receive, as well as supporting
documentation we used in preparing this proposed rule, will be
available for public inspection on <a href="https://www.regulations.gov">https://www.regulations.gov</a>.
Our final determination may differ from this proposal because we
will consider all comments we receive during the comment period as well
as any information that may become available after this proposal. For
example, based on the new information we receive (and if relevant, any
comments on that new information), we may conclude that the species
should remain listed as endangered, or we may conclude that the species
should be reclassified from endangered to threatened. We will clearly
explain our rationale and the basis for our final decision, including
why we made changes, if any, that differ from this proposal.
Public Hearing
Section 4(b)(5) of the Act provides for a public hearing on this
proposal, if requested. Requests must be received by the date specified
in DATES. Such requests must be sent to the address shown in FOR
FURTHER INFORMATION CONTACT. We will schedule a public hearing on this
proposal, if requested, and announce the date, time, and place of the
hearing, as well as how to obtain reasonable accommodations, in the
Federal Register and local newspapers at least 15 days before the
hearing. We may hold the public hearing in person or virtually via
webinar. We will announce any public hearing on our website, in
addition to the Federal Register. The use of these virtual public
hearings is consistent with our regulation at 50 CFR 424.16(c)(3).
Peer Review
A species status assessment (SSA) team prepared an addendum to the
SSA report for the Lower Colorado River roundtail chub (Gila robusta)
Distinct Population Segment (DPS) (Service 2022, entire) that
summarizes information on the taxonomic status of the Gila chub
(Service 2024, entire). The SSA team was composed of Service
biologists, in consultation with other species experts. The SSA
addendum represents a compilation of the best scientific and commercial
data available concerning the taxonomic status of the Gila chub.
In accordance with our joint policy on peer review published in the
Federal Register on July 1, 1994 (59 FR 34270), and our August 22,
2016, memorandum updating and clarifying the role of peer review of
listing and recovery actions under the Act (<a href="https://www.fws.gov/sites/default/files/documents/peer-review-policy-directors-memo-2016-08-22.pdf">https://www.fws.gov/sites/default/files/documents/peer-review-policy-directors-memo-2016-08-22.pdf</a>), we solicited independent scientific review of the information
contained in the SSA addendum (Service 2024, entire). The Service sent
the SSA addendum to three independent peer reviewers and received three
responses. The peer reviews can be found at <a href="https://www.regulations.gov">https://www.regulations.gov</a>. In preparing this proposed rule, we incorporated
the results of these reviews, as appropriate, into the SSA addendum,
which is the foundation for this proposed rule.
Summary of Peer Reviewer Comments
As discussed above in Peer Review, we received comments from three
peer reviewers on the draft SSA addendum. We reviewed all comments we
received from the peer reviewers for substantive issues and new
information regarding the information contained in the SSA addendum.
All reviewers acknowledged the complexity and challenges associated
with elucidating the taxonomy of the three Gila species in the Lower
Colorado River basin, which includes the Gila chub, roundtail chub, and
headwater chub (Gila nigra). None of the reviewers disagreed with our
interpretation of the available information that the Gila and headwater
chubs are not distinct species. They also did not provide new
information conflicting with our interpretation.
[[Page 25554]]
Two of the reviewers noted that Gila display morphological and
genetic variation that is geographically structured across the Lower
Colorado River basin and this structure may be relevant for
conservation. In other words, their interpretation is that the
available information indicates that the geographical structuring by
watershed reflects the evolutionary history of the putative species and
may serve as an appropriate scale on which to base conservation, akin
to evolutionary significant units. However, these reviewers did not
challenge our conclusion that patterns of morphological and genetic
differences across the range do not correspond to the geographic ranges
of the three putative species.
One reviewer acknowledged that there may be other species concepts
(i.e., definitions of a species) that could be applied to this genus
that could result in continued recognition of the Gila chub as a
distinct species. However, the reviewer was clear that this argument
has not been made in the literature, and no evidence is available to
support alternative species concepts. The reviewer provided a
hypothetical argument to emphasize other potential scenarios, not to
argue for continued support for recognizing the Gila chub.
One reviewer provided further interpretation and assessment of the
recent genomics studies cited in the SSA addendum, specifically Chafin
et al. (2021, entire) and Suchocki et al. (2023, entire). The reviewer
commented that we placed too much emphasis on the influence of sampling
bias in the Chafin et al. study and should focus more on the lack of
statistical support for the phylogenetic groups they identified. They
also provided additional interpretation on the discriminant analysis
conducted by Suchocki et al. (2023, pp. 5-8). We made changes to the
SSA addendum to reflect this reviewer's perspective.
Previous Federal Actions
On August 9, 2002, we published in the Federal Register (67 FR
51948) a proposed rule to list the Gila chub as an endangered species
and to designate the species' critical habitat under the Act. On
November 2, 2005, we published in the Federal Register (70 FR 66664) a
final rule listing the Gila chub as an endangered species and
designating its critical habitat under the Act.
On October 7, 2015, following completion of an SSA, we published in
the Federal Register (80 FR 60754) a proposed rule to list the
headwater chub and the Lower Colorado River roundtail chub DPS as
threatened species under the Act. Subsequently, on April 7, 2017, we
published in the Federal Register (82 FR 16981) a document withdrawing
the 2015 proposed rule. The withdrawal was based on a thorough review
of the best scientific and commercial data available at that time,
which indicated that the headwater chub and the roundtail chub DPS were
not discrete taxonomic entities--these fish were recognized as a part
of a single taxonomic species, the roundtail chub (Gila robusta) (Page
et al. 2017, p. 459)--and did not meet the Act's definition of a
species. The 2015 proposed rule and the 2017 withdrawal of the proposed
rule did not address the status of the Gila chub; the Gila chub
remained listed as an endangered species on the List of Endangered and
Threatened Wildlife.
In 2018, the Center for Biological Diversity (CBD) challenged our
2017 withdrawal of the 2015 proposed rule to list the headwater chub
and Lower Colorado River roundtail chub DPS as threatened species under
the Act. On March 31, 2021, the U.S. District Court found the 2017
withdrawal of the 2015 proposed rule was arbitrary and capricious
because we withdrew the proposed rule based on taxonomic revisions, but
never fully reevaluated the petitioned entity, the Lower Colorado River
roundtail chub DPS. In other words, the taxonomic revisions created a
new biological entity in the Lower Colorado River basin that, under the
Act, we were still obligated to assess under the original 2003
petition. The court vacated the withdrawal of the proposed rule and
ordered that a new 12-month finding be completed by March 31, 2022.
On April 5, 2022, following completion of an SSA, we published in
the Federal Register our finding that listing the Lower Colorado River
roundtail chub DPS as an endangered or threatened species was not
warranted (87 FR 19657). Additionally, the SSA (USFWS 2022, pp. 4-5)
included a review of taxonomic information for the genus Gila in the
Lower Colorado River basin and concluded that the available information
did not support recognizing the Gila chub as a distinct taxonomic
entity. Accordingly, in the same April 5, 2022, Federal Register
publication (87 FR 19657), we issued an advance notice of proposed
rulemaking to gather information to support a decision on whether or
not we should propose to remove the Gila chub from the List of
Endangered and Threatened Wildlife.
Background
The Gila chub (G. intermedia) was first described as Tigoma
intermedia (Girard 1856, p. 42) and underwent numerous taxonomic
placements but was later treated as a subspecies of the roundtail chub
(G. robusta) (Miller 1945, p. 109). G. intermedia was then recognized
as a distinct species, and its range was described as a series of
populations distributed in central and southern Arizona within the Gila
River basin, located within the Lower Colorado River basin (Rinne 1969,
entire). It was one of three species of Gila recognized from the Lower
Colorado River basin at that time, including the roundtail chub and the
headwater chub (G. nigra) (Minckley and DeMarais 2000, entire).
The authoritative description of these three putative species is
based on mean counts of meristic characters (i.e., countable physical
features) such as number of lateral line scales, fin rays, and
vertebrae (Minckley and DeMarais 2000, p. 253). This description
included an identification key for differentiating among Gila in the
Lower Colorado River. Crucially, substantial overlap occurs in the
variation of these meristic characters among the three putative
species. Thus, accurate identification of these putative species
requires knowledge of the watershed from which the specimens
originated, as character differences vary across the Lower Colorado
River basin. In other words, when two or more of these putative species
occur in the same watershed, there are specific differences that can be
used to differentiate between them within that watershed. However,
these same differences cannot be applied universally across the Lower
Colorado River basin.
The extensive overlap in meristic characters between the three
putative species and watershed-specific differences has challenged
attempts to accurately identify individual Gila in the field (Carter et
al. 2018, entire). Subsequent studies have documented substantial
overlap in morphological characteristics among the three putative
species (Carter et al. 2018, entire; Copus et al. 2018, pp. 12-15;
Moran et al. 2017, pp 307-309). There are no diagnostic characters that
distinguish the three putative species. Based on these findings, a
joint report from the American Fisheries Society and the American
Society of Ichthyologists and Herpetologists concluded that the
available morphological data do not indicate that populations of Gila
within the Lower Colorado River basin constitute more than one species.
Genetic studies have arrived at similar conclusions. As with the
morphological data, the three putative species do not form distinct
genetic groups (DeMarais
[[Page 25555]]
1992, pp. 131-151; Schwemm 2006, entire; Sch[ouml]nhuth et al. 2014,
pp. 215-217; Dowling et al. 2015, pp. 12-14; Copus et al. 2018, entire;
Suchocki et al. 2023, entire). These studies have found that genetic
variation is partitioned by geography, namely watershed, rather than
putative species relationships (Schwemm 2006, p. 19; Dowling et al.
2015, p. 9; Copus et al. 2018, pp. 15-17; Suchocki et al. 2023, pp. 4-
5). In other words, there are greater genetic differences between Gila
occurring in different watersheds than between putative species that
occur in the same watershed.
Chafin et al. (2021, entire) used genome-wide markers to test
several hypotheses regarding the evolution of Gila in the Colorado
River basin, with an emphasis on populations in the lower basin. In
several of their analyses, they found three distinct genetic clades
(i.e., groupings) in the lower basin that generally corresponded to the
three putative species. Populations assigned to same species using the
Minckley and DeMarais (2000, p. 253) key fell within the same clade.
However, statistical support for these three clades was low relative to
the clades formed by other Gila species across the broader Colorado
River basin (Chafin et al. 2021, p. 5). This means that there was weak
statistical support for the Gila and headwater chubs forming lineages
distinct from the roundtail chub. Their conclusion was that populations
of Gila rapidly diversified in the Lower Colorado River basin following
their initial colonization, resulting in shallow genetic differences
(Chafin et al. 2021, pp. 8-12). While they interpreted this as support
for the three putative species, their results paralleled those of other
genetic studies in finding substantial genetic variation among
watersheds and weak differentiation among the species.
As noted by nearly all researchers investigating the systematics of
Gila, the taxonomic situation is complicated and problematic (Holden
and Stalnaker 1970, pp. 418-419; Minckley 1973, pp. 102-103; Minckley
and DeMarais 2000, p. 251; Gerber et al. 2001, p. 2028; Sch[ouml]nhuth
et al. 2014, p. 210; Copus et al. 2018, p. 2; Chafin et al. 2021, p. 7;
Suchocki et al. 2023, pp. 7-11), and ongoing genetic and morphologic
analyses of chubs in the Gila River basin continue to yield conflicting
results (Page et al. 2017, entire; Copus et al. 2018, entire; Chafin et
al. 2021, entire; Suckocki et al. 2023, entire). There are several
conclusions that can reasonably be drawn based on the available
information. First, there are no clear diagnostic phenotypic or genetic
characters that distinguish between the three putative species across
the entirety of their ranges. Second, the putative species can only be
differentiated from each other when specimens are grouped into putative
species assignments (Moran et al. 2017, pp. 310-311; Suchocki et al.
2023, p. 9). Accurate taxonomic assignment of specimens is, therefore,
dependent on knowledge regarding the location of collection, meaning
that taxonomy is contingent on geography. Third, much of the genetic
variation observed among Lower Colorado River basin Gila is partitioned
by watershed (Schwemm 2006, p. 19; Dowling et al. 2015, p. 9; Suckocki
et al. 2023, p. 3). Populations within the same watershed are more
similar to each other than populations that occur outside that
watershed, meaning genetic differences are more tied to geography than
nominal taxonomy. These findings indicate that, at best, the
differences between the three putative Gila species are subtle and not
readily apparent to even skilled observers (e.g., Carter et al. 2018,
entire). Multiple studies have shown that patterns of variation,
whether phenotypic or genetic, do not unambiguously fit into the three
species model proposed by Minckley and DeMarais (2000, entire).
The joint report from the American Fisheries Society and American
Society of Ichthyology and Herpetology Joint Committee on the Names of
Fishes, which evaluated evidence available at the time, concluded that
there was no support for species-level status for Gila chub and
headwater chub and recommended collapsing them into roundtail chub,
recognizing only a single species (Page et al. 2017, p. 459). Recently,
the American Fisheries Society published the latest edition of the
accepted scientific names of North American fishes. They list G.
intermedia and G. nigra as valid scientific names, while noting the
taxonomic uncertainty of the G. robusta complex (Page et al. 2023, pp.
70, 224). However, inclusion of G. intermedia and G. nigra on this list
reflects that the names themselves are considered valid according to
taxonomic convention, not that the species themselves are valid
entities.
Since the publication of this report (Page et al. 2017, entire),
more information has become available that supports the conclusion that
Gila chub and headwater chub are not distinct taxonomic entities (Moran
et al. 2017, entire; Carter et al. 2018, entire; Copus et al. 2018,
entire; Suchocki et al. 2023, entire; but see Chafin et al. 2023,
entire). Minckley and DeMarais (2000, entire) defined these two
putative species based on a particular analysis of phenotypic data.
Subsequent studies have failed to distinguish these as two species
using alternative analyses and could not even successfully assign
individuals collected in the field to the supposed correct species
using the Minckley and DeMarais taxonomic key (Moran et al. 2017,
entire; Carter et al. 2018, entire). Genetic studies have also failed
to demonstrate strong statistical support for the presence of distinct
genetic lineages that correspond to the Gila and headwater chubs
(Schwemm 2006, entire; Dowling et al. 2015, entire; Copus et al. 2018,
entire; Chafin et al. 2021, entire; Suchocki et al. 2023, entire). In
conclusion, based on the best scientific and commercial data available,
G. intermedia (Gila chub) and G. nigra (headwater chub) are not valid
taxonomic entities, and populations previously assigned to those two
species should be reclassified as G. robusta (roundtail chub).
Comments on the April 5, 2022, Advance Notice of Proposed Rulemaking
In the April 5, 2022, advance notice of proposed rulemaking
concerning the delisting of the Gila chub (87 FR 19657), we requested
that all interested parties submit written comments by June 6, 2022. We
also contacted appropriate Federal and State agencies, scientific
experts and organizations, and other interested parties and invited
them to comment on the action under consideration. We received 12
comments in total. Three State agencies provided comments, all of which
were supportive of the delisting of the Gila chub based on taxonomic
changes. Two of the public comments cited the findings of Chafin et al.
(2021, entire) as justification to not delist the Gila chub but did not
elaborate beyond that argument. We received the most substantive
comments from a group of experts who disagreed with our interpretation
of the taxonomy of Gila chub. Below are their specific comments and our
responses.
(1) Comment: Commenters argued that we did not give enough
consideration to findings of Chafin et al. (2021, entire) in the 2022
SSA report and that the other recent genomics studies cited in the 2022
SSA report (for example, Copus et al. 2018, entire) should not be
considered to be equivalent to Chafin et al. (2021) in terms of value.
They contend that Chafin et al. (2021, entire) should be considered the
best available information to inform taxonomy because that study
included more individual samples and more populations.
[[Page 25556]]
Our response: Both the Copus et al. (2018, entire) and Chafin et
al. (2021) studies differ in terms of number of individual fish and
number of populations included in the analysis. However, having a
larger sample size does not necessarily make the findings of a study
more robust. As noted in our discussion of the available information
(see Background), statistical support for the presence of the Gila chub
was low relative to the support for clades formed by other Gila species
across the broader Colorado River basin (Chafin et al. 2021, p. 5).
Furthermore, Suchocki et al. (2023, entire) included more individual
samples and populations than either study. After considering these
studies, we determined that using sample size as the sole benchmark to
determine best available data creates an inappropriate standard that
neglects the importance of critically evaluating the methodology and
conclusions of all available studies when interpreting taxonomy.
Additionally, the SSA addendum provides a more thorough review of
Chafin et al. (2021, entire) (see Service 2024, pp. 7-10) that is
incorporated into our determination in this proposed rule.
(2) Comment: Commenters stated that we inappropriately interpreted
the basis that Minckley and DeMarais (2000, entire) used to distinguish
between the three species of Gila in the Lower Colorado River basin.
They state that the diagnostic key of Minckley and DeMarais (2000,
entire), which uses morphological characteristics, is based on the data
and analyses reports in several other studies (Rinne 1976, entire;
DeMarais 1986, entire; Douglas et al. 1999, entire).
Our response: We have adjusted the language of the SSA addendum to
better reflect the origin of the data used to inform the conclusions of
Minckley and DeMarais (2000, entire). Regardless, subsequent
researchers have been unable to accurately assign specimens to putative
species using this key (Moran et al. 2017, pp. 307-309; Carter et al.
2018, p. 286). There are two logical conclusions from this line of
evidence. One is that the key itself is flawed, and due to some aspect
of its development (e.g., choice of characters, measurement errors,
etc.) is unable to sufficiently discriminate among three species that
are indeed distinct. The second conclusion is that the three putative
species themselves are not distinct from each other and thus any key
would be unable to reliably assign specimens to the correct species.
Based on our analysis of the best available scientific data, including
morphological and genetic studies, we find that the second conclusion
is most likely to be correct; the totality of information indicates
that the three putative species cannot be consistently discriminated
from one another using morphological data.
(3) Comment: Commenters stated that the results of Moran et al.
(2017, entire) support the conclusion that the three species of Gila in
the Lower Colorado River basin can be distinguished using morphological
characteristics.
Our response: The commenters are correct that Moran et al. (2017,
pp. 310-311) were able to differentiate among the three putative
species (roundtail chub, headwater chub, and Gila chub) using
morphological analysis. However, this was achieved only for a specific
type of analysis. When they grouped specimens a priori by presumed
species assignment and ran multivariate tests designed to maximize
differences between groups, they were able to distinguish the three
putative species (Moran et al. 2017, pp. 310-311). In contrast, when
they used analyses that did not consider prior species assignment of
specimens, they could not discriminate between the three putative
species (Moran et al. 2017, pp. 307-309). They also failed to reliably
identify specimens when using the Minckley and DeMarais (2000)
diagnostic key. In other words, Moran et al. (2017, pp. 310-311) were
only able to distinguish among the three species when they assumed the
three species were indeed present. This creates a circular argument
where statistical support for the presence of three species only occurs
when the three species are assumed to be present. The commenters did
not provide further explanation for emphasizing one aspect of Moran et
al. (2017) to support their claim while ignoring non-supporting
evidence from the same study. Furthermore, the commenters did not
acknowledge other morphological studies (e.g., Carter et al. 2018,
entire; Copus et al. 2018, pp. 12-15) that were unable to distinguish
among the three putative species using morphological data. Our SSA
addendum (Service 2024, pp. 5-7) provides a more thorough synthesis of
the available studies and supports our conclusion that the three
putative species cannot be readily differentiated using phenotypic
data.
(4) Comment: Commenters stated that we misinterpreted Dowling et
al. (2015, entire) and that study should not be used to inform
taxonomy. They argue that given the rapid rate of microsatellite
deoxyribonucleic acid (DNA) evolution, it is not unexpected that there
are no diagnostic markers for the three species.
Our response: Dowling et al. (2015, entire) used nuclear
microsatellite DNA markers to assess patterns of genetic variation
among Gila in the Lower Colorado River basin. They generated genotypes
for populations that had been previously identified as roundtail, Gila,
or headwater chub and performed several genetic analyses to ascertain
differences among these populations. Across the various analyses they
performed, they failed to identify genetic groupings that correspond to
the three putative species. In fact, one analysis (an analysis of
molecular variance) specifically compared whether patterns of genetic
variation were best explained by putative taxonomy (i.e., three
distinct species) or differences corresponding to river drainages. They
found stronger statistical support for genetic variation being
partitioned among drainages and populations than species groups
(Dowling et al. 2015, p. 9). Other analyses, such as their neighboring-
joining network and Bayesian clustering analysis, did not group
populations by putative species identity. Instead, these analyses
grouped populations by watershed (Dowling et al. 2015, pp. 12-14),
indicating that patterns of genetic structure correspond with river
drainages instead of putative taxonomy. A similar pattern has been
observed in other genetic studies (Copus et al. 2018, entire; Suchocki
et al. 2023, entire).
We agree with the commenters that basing taxonomic decisions solely
on genetic information generated with nuclear microsatellites can be
problematic given the characteristics of these markers. However,
microsatellites have long been used to characterize population
differentiation, even at species-level differences, and if the three
presumed species were genetically distinct, they likely would have been
observed in the dataset generated by Dowling et al. (2015, entire). The
commenters argue that we should ignore the findings of Dowling et al.
(2015, entire) when it comes to informing taxonomy, but the findings
fit a pattern observed in other genetic studies that there is a lack of
genetic differentiation among the three putative species. Aside from
Chafin et al. (2021, entire), there have been multiple studies using
mitochondrial sequences (DeMarais 1992, pp. 131-151; Schwemm 2006,
entire; Sch[ouml]nhuth et al. 2014, pp. 215-217, 219), microsatellite
markers (Dowling et al. 2015, entire), and/or single nucleotide
polymorphisms (Copus et al. 2018, entire; Suchocki et al. 2023, entire)
that were unable to identify diagnostic markers unique to any of the
three putative species or failed to observe patterns of genetic
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differentiation that correspond to the three putative species. Thus, we
conclude that the best available scientific and commercial data
indicate there are no observable genetic differences among the three
putative species, which questions recognition of their taxonomic
validity.
(5) Comment: Commenters cited the following statement from Dowling
et al. (2015, p. 15): ``these results highlight the role that local
evolution has played in shaping patterns of variation in these taxa and
the importance of accounting for this variation when managing the
complex [i.e., Gila in the Lower Colorado River basin].'' They argue
our 12-month finding (87 FR 19657) ignored the potential value this
variation has in conservation and adaptive capacity of these putative
species.
Our response: We agree that Gila in the Lower Colorado River basin
display a complex genetic structure that would promote the adaptive
capacity of the species and should inform conservation activities.
Current management plans for the roundtail chub emphasize the
importance of maintaining genetic diversity and preserving genetically
distinct populations (Colorado River Fish and Wildlife Council 2019,
pp. 41-42). Thus, consideration of local adaptation is built into on-
going conservation efforts for Gila populations in this basin. As per
our statutory requirements, for this proposed rule we are only
assessing whether the Gila chub is a valid taxonomic entity, not
evaluating alternative groupings that may be relevant for the
management and conservation of Gila.
(6) Comment: Commenters noted that Douglas et al. (1999, entire)
was not cited in the SSA report. They argue that the findings of
Douglas et al. (1999, entire) are consistent with those of Chafin et
al. (2021, entire) and provide support for the recognition of the three
species.
Our response: Douglas et al. (1999, entire) explicitly tested
several evolutionary hypotheses to explain observed patterns of
phenotypic variation among Gila in the Lower Colorado River basin. In
other words, they statistically tested whether specific evolutionary
scenarios were correlated with patterns in body shape variation. They
concluded that the vicariance hypothesis was most supported, meaning
that ancient hydrology (i.e., prehistorical waterways) facilitated
colonization of distinct phenotypes of Gila at various points in time
over the past 16 million years.
We do not contest the findings of Douglas et al. (1999, entire),
but instead contend that they have little relevance to the question of
Gila chub taxonomy. They tested whether body shapes, composed of 10
measured traits, among 1,106 Gila specimens were correlated with three
different evolutionary hypotheses. The study does not specifically
address taxonomic relationships or distinctness between the three
putative species; instead, it makes inferences about evolutionary
drivers of phenotypic diversity among Gila. It is not clear from
Douglas et al. (1999, entire) whether the phenotypic diversity they
observed even corresponded to the three putative species. Thus, they
only infer that the phenotypes they analyzed correlated with ancient
waterways, which may or may not match the putative distributions of the
roundtail, Gila, and headwater chubs. In fact, it provides further
support to the claim that patterns of diversity among Gila in the Lower
Colorado River basin are associated with watershed (Dowling et al.
2015, entire; Copus et al. 2018, entire; Suchocki et al. 2023, entire;
Service 2024, pp. 9-10). Although valuable for informing evolutionary
drivers of phenotypic diversity, Douglas et al. (1999, entire) does not
address the distinctness or taxonomic validity of the Gila chub.
Furthermore, contrary to the commenters' claim, the findings of
Douglas et al. (1999, entire) and Chafin et al. (2021, entire) are not
congruent. Douglas et al. (1999, p. 243-244) concluded that phenotypic
diversity was most strongly associated with the mid Miocene and
Pliocene epochs, indicating multiple colonization events during those
time periods. The mid-Miocene covers a period of geological history
spanning from 16 to 11.5 million years ago and the Pliocene from 5.3 to
2.5 million years ago. However, based on genomic data, Chafin et al.
(2021, p. 9) estimated that the roundtail, Gila, and headwater diverged
from each other less than 2 million years ago. These incongruent
findings do not invalidate either study but reveal that there is still
uncertainty in the evolutionary history of Gila in the Lower Colorado
River basin. Therefore, we conclude that Douglas et al. (1999, entire)
and Chafin et al. (2021, entire) do not provide congruent,
uncontestable evidence that the Gila chub is a distinct species and
valid taxonomic entity.
(7) Comment: Commenters stated that in the 2022 SSA report we
deferred to the American Fisheries Society and American Society of
Ichthyology and Herpetology Joint Committee on the Names of Fishes
(hereafter ``Committee'') decision to reject the taxonomic validity of
the Gila chub rather than providing our own review of the literature.
They also argue we have been inconsistent in our application of the
Committee's list of species to other situations, such as our continued
recognition of the scientific name Tiaroga cobitis for the loach minnow
rather than Rhinichthys cobitis as recommended by the Committee.
Our response: Under our implementing regulations at 50 CFR
424.11(a), we rely on standard taxonomic distinctions and the
biological expertise of the Department of the Interior and the
scientific community concerning the relevant taxonomic group. Thus, we
are charged with basing our decisions on interpretations provided by
taxonomic authorities and the biological expertise of the Department of
the available information. When taxonomic opinion is not unanimous, we
use that biological expertise and provide a rational basis to arrive at
our own conclusions. Our listing determination for the Gila chub is
based on our review of the best available scientific and commercial
data, which is provided in the SSA addendum (Service 2024, entire). We
did not defer to any taxonomic authority in basing our decision. In
fact, the most recent publication of the Committee lists G. intermedia
and G. nigra as valid scientific names, while noting the taxonomic
uncertainty of the G. robusta complex (Page et al. 2023, pp. 70, 224).
However, inclusion of G. intermedia and G. nigra on the Committee's
list reflects that the names themselves are considered valid according
to taxonomic convention, not that the species themselves are valid
entities. When asked to review the available information on the
taxonomy of Gila in the Lower Colorado River basin, the Committee
concluded that the Gila chub was not a distinct species (Page et al.
2017, p. 459). After reviewing the same information as the Committee,
as well as information that has published since then, we have
independently concluded that the Gila chub is not a distinct species
(i.e., does not meet the definition of a ``species'' in the Act), is
not a listable entity under the Act, and therefore should be delisted
(50 CFR 424.11(e)(4).
Regarding the commenters' assertion of our inconsistencies, we
acknowledge that the circumstances surrounding every taxonomic
situation are unique. Under our regulations at 50 CFR 17.11(c), we
rely, to the extent practicable, on the Integrated Taxonomic
Information System (ITIS) to determine a species' scientific name.
Further, recognition of a particular scientific name requires rigorous
[[Page 25558]]
taxonomic review that may be subject to changes with new information.
Translating these changes into official agency usage requires
rulemaking to amend text in the Code of Federal Regulations and
revisions to our databases. There is often a lag between official
changes in scientific naming convention and agency adoption of those
changes.
Regulatory and Analytical Framework
Regulatory Framework
Section 4 of the Act (16 U.S.C. 1533) and the implementing
regulations in title 50 of the Code of Federal Regulations set forth
the procedures for determining whether a species is an endangered
species or a threatened species, issuing protective regulations for
threatened species, and designating critical habitat for endangered and
threatened species.
``Species'' is defined by the Act as including any subspecies of
fish or wildlife or plants, and any distinct population segment of any
species of vertebrate fish or wildlife that interbreeds when mature (16
U.S.C. 1532(16)).
Our regulations at 50 CFR 424.11(e) identify four reasons why,
after conducting a status review based on the best scientific and
commercial data available, we will delist a species: (1) The species is
extinct; (2) the species has recovered to the point at which it no
longer meets the definition of an endangered species or a threatened
species; (3) new information that has become available since the
original listing decision shows the listed entity does not meet the
definition of an endangered species or a threatened species; or (4) new
information that has become available since the original listing
decision shows the listed entity does not meet the definition of a
species.
Determination of Gila Chub's Status
In accordance with our regulations at 50 CFR 424.11(e)(4), our
review of the best scientific and commercial data available indicates
that the Gila chub does not meet the Act's definition of a species (16
U.S.C. 1532(16)). Therefore, we propose to remove Gila chub from the
Federal List of Endangered and Threatened Wildlife. The Gila chub does
not require a post-delisting monitoring (PDM) plan because the
requirements for PDM only apply to species delisted due to recovery (16
U.S.C. 1533(g)(1)), not those delisted due to the listed entity no
longer meeting the statutory definition of a species.
Effects of This Rule
This proposed rule, if made final, would revise 50 CFR 17.11(h) by
removing the Gila chub from the Federal List of Endangered and
Threatened Wildlife. The prohibitions and conservation measures
provided by the Act, particularly through sections 7 and 9, would no
longer apply to the Gila chub. Federal agencies would no longer be
required to consult with the Service under section 7 of the Act in the
event that activities they authorize, fund, or carry out may affect the
Gila chub.
In addition, if this proposal is made final, 50 CFR 17.95(e) would
be revised by removing the designated critical habitat for the Gila
chub.
Required Determinations
Clarity of the Proposed Rule
We are required by Executive Orders (E.O.s) 12866 and 12988 and by
the Presidential memorandum of June 1, 1998, to write all rules in
plain language. This means that each rule we publish must:
(1) Be logically organized;
(2) Use the active voice to address readers directly;
(3) Use clear language rather than jargon;
(4) Be divided into short sections and sentences; and
(5) Use lists and tables wherever possible.
If you feel that we have not met these requirements, send us
comments by one of the methods listed in ADDRESSES. To better help us
revise the rule, your comments should be as specific as possible. For
example, you should tell us the numbers of the sections or paragraphs
that are unclearly written, which sections or sentences are too long,
the sections where you feel lists or tables would be useful, etc.
Government-to-Government Relationship With Tribes
In accordance with the President's memorandum of April 29, 1994
(Government-to-Government Relations with Native American Tribal
Governments; 59 FR 22951, May 4, 1994), Executive Order 13175
(Consultation and Coordination with Indian Tribal Governments), the
President's memorandum of November 30, 2022 (Uniform Standards for
Tribal Consultation; 87 FR 74479, December 5, 2022), and the Department
of the Interior's manual at 512 DM 2, we readily acknowledge our
responsibility to communicate meaningfully with federally recognized
Tribes and Alaska Native Corporations on a government-to-government
basis. In accordance with Secretary's Order 3206 of June 5, 1997
(American Indian Tribal Rights, Federal-Tribal Trust Responsibilities,
and the Endangered Species Act), we readily acknowledge our
responsibilities to work directly with Tribes in developing programs
for healthy ecosystems, to acknowledge that Tribal lands are not
subject to the same controls as Federal public lands, to remain
sensitive to Indian culture, and to make information available to
Tribes. We coordinated with several Tribes, most notably the White
Mountain Apache Tribe and the San Carlos Apache Tribe, in development
of the Lower Colorado River roundtail chub DPS SSA (Service 2022,
entire). We also contacted these Tribes, along with others in the
region, following publication of the advance notice of proposed
rulemaking to delist the Gila chub (87 FR 19657). No Tribes provided
comments during the public comment period. We will continue to work
with Tribal entities during the development of a final delisting
determination for the Gila chub.
References Cited
A complete list of references cited in this rulemaking is available
on the internet at <a href="https://www.regulations.gov">https://www.regulations.gov</a> and upon request from
the Arizona Ecological Services Field Office (see FOR FURTHER
INFORMATION CONTACT).
List of Subjects in 50 CFR Part 17
Endangered and threatened species, Exports, Imports, Plants,
Reporting and recordkeeping requirements, Transportation, Wildlife.
Signing Authority
Paul Souza, Regional Director, Region 8, Exercising the Delegated
Authority of the Director of the U.S. Fish and Wildlife Service,
approved this action on May 1, 2025, for publication. On June 9, 2025,
Paul Souza authorized the undersigned to sign the document
electronically and submit it to the Office of the Federal Register for
publication as an official document of the U.S. Fish and Wildlife
Service.
Proposed Regulation Promulgation
Accordingly, we propose to amend part 17, subchapter B of chapter
I, title 50 of the Code of Federal Regulations, as set forth below:
PART 17--ENDANGERED AND THREATENED WILDLIFE AND PLANTS
0
1. The authority citation for part 17 continues to read as follows:
Authority: 16 U.S.C. 1361-1407; 1531-1544; and 4201-4245,
unless otherwise noted.
[[Page 25559]]
Sec. 17.11 [Amended]
0
2. In 17.11, in paragraph (h), amend the List of Endangered and
Threatened Wildlife under FISHES by removing the entry for ``Chub,
Gila''.
Sec. 17.95 [Amended]
0
3. In Sec. 17.95, amend paragraph (e) by removing the entry for ``Gila
Chub (Gila intermedia)''.
Madonna Baucum,
Regulations and Policy Chief, Division of Policy, Economics, Risk
Management, and Analytics of the Joint Administrative Operations, U.S.
Fish and Wildlife Service.
[FR Doc. 2025-10785 Filed 6-16-25; 8:45 am]
BILLING CODE 4333-15-P
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