9378

• UCREFRP Catalog Number: 9378
• Author: Nesler, T. P.
• Title: Recovery of the Colorado River Endangered Fishes
• USFW Year: 2000.
• USFW - Doc Type: Biological recovery goals and criteria for Colorado pikeminnow, Humpback chub, Razorback sucker & Bonytail.
• Copyright Material: NO

26

I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

Annual recruitment into the adult populations of humpback chub in both
Black Rocks and Westwater Canyon appear relatively similar and stable, ranging
between 11-16%.

Recovery Goals and Criteria At the time of this species' consideration and
inclusion under ESA as an endangered species, the reasons for decline were
"unknown." Threats were obvious to the two known existing humpback
populations due to the construction of Glen Canyon and Flaming Gorge Dams in
the early 1960s. Other potential threats were perceived in the Recovery Plan, but
not documented, including predation/competition from introduced, nonnative fish
species and hybridization. Presently, a list of potential threats for each population
segment can be identified (Valdez et al. 2000), but the contributions of any of
these threats to an ongoing population or species decline toward extirpation or
extinction have not been documented.

Five populations or population complexes are proposed as necessary to
recovery. Among the seven population segments that currently exist, data on chub
movements indicate the Black Rocks-Westwater Canyon and Little Colorado-
Grand Canyon populations are genetically linked (Valdez and Ryel 1995, Chart
and Lentsch 1999, Valdez and Clemmer 1982, Kaeding et al. 1990). Considering
the objective of achieving an effective population size to maintain genetic diversity,
these four population segments can be linked as two population complexes.
Linkages with or between the other existing populations have not been
documented via movement data, but identification of ecologically credible
population complexes can be proposed.

Given movement data for humpback chub between Yampa Canyon and the
Little Snake River (Wick et al. 1991), it is proposed here to identify a population
complex inhabiting of Yampa-Whirlpool-Split Mountain canyons within Dinosaur
National Monument. Even though the only population segment known to exist is
found in Yampa Canyon (Karp and Tyus 1990), it is feasible to postulate the
movement of these fish into suitable habitats in the downstream canyon reaches.
Historical presence data in Tyus (1998), Smith (1960), Bosley (1960, Gaufin et al.
(1960), McDonald and Dotson (1960), and Vanicek et al. (1970) suggest that
humpback chub were more widely distributed in the Green River segment of
Dinosaur National Monument prior to the construction and operation of Flaming
Gorge Dam. This presents the best opportunity for expansion of an existing
population if operation of Flaming Gorge Dam and amelioration of other limiting
factors can be achieved. Desolation-Gray Canyons may form their own complex
despite lack of corroborating data. Only the Cataract Canyon population lacks a
basis for multiple population segments or a credible link with another known
humpback chub population.

The existence of 7 population segments aggregated into 5 populations or
population complexes is proposed to be adequate in number and necessary as a
foundation upon which to base further recovery goals. The only documented loss