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

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Humpback chub

Species status and trend Mark-recapture and length frequency data were
available in the Upper Basin centralized database from 1991-1997 for the Black
Rocks and Westwater populations (Tables A-5, A-6). Data for Yampa Canyon and
the Green River at Desolation-Gray canyons were inadequate for estimation of
population size or other parameters due to small sample size or few rec~ptures.
Abundance estimates for the humpback chub populations were also available for
Black Rocks (Pfeifer et al. 1998), Westwater Canyon (Chart and Lentsch 1999),
Little Colorado River (Douglas and Marsh 1996), Colorado River in Grand Canyon
(Valdez and Ryel 1997), Yampa Canyon (Karp and Tyus 1990), and Cataract
Canyon (Valdez 1990), and the Green River in Desolation-Gray canyons (Chart
and Lentsch 1998). The information from these reports has been synthesized in
Valdez et al. (2000, in draft).

The presence of humpback chub has been reported in canyon reaches of
the Colorado River Basin since as early as the 1940s when the species was
formally recognized. At the time of federal listing between 1967 and 1973, only
two populations in Grand Canyon (Miller 1946) and Flaming Gorge Canyon (Smith
1960) and individual occurrences in Yampa Canyon and Desolation-Gray Canyons
were known (Holden and Stalnaker 1975). Since then, seven populations have
been identified: Black Rocks, Colorado; Westwater Canyon, Utah; Little Colorado
River, Arizona; Colorado River in Grand Canyon, Arizona; Yampa Canyon,
Colorado; Desolation/Gray Canyons, Utah; and Cataract Canyon, Utah. Presently,
the Little Colorado River and Grand Canyon humpback chub are considered to be
one population, making a total of six geographically distinct populations. Each of
these populations has demonstrated persistence since its first date of discovery.
Valdez et al. (2000) suggests this species occupies about 68% of its historic
habitat and most of what was lost was the result of inundation by the major dams
on the Colorado and Green rivers and the release of cold, hypolimnetic waters
downstream.

Reproducing populations of humpback chub were first reported in Black
Rocks in 1977 (Kidd 1977) and Westwater"Canyon in 1979 (Valdez et al. 1982).
Population estimates for the Black Rocks population range from a low of 455 in
1997 using a 59% survival rate to a high of almost 2,500 fish in 1997 using a 90%
survival rate (Table A-5). Significant sampling effort is directed at the Black Rocks
population every 3 years (1991, 1994, and 1997)) via the standardized monitoring
program protocol. As such only two population estimates are possible (1994 and
1997) for this population using the 1991-1997 database. For the Westwater
population, mark-recapture data were sufficient to make population estimates each
year from 1993-1997 (Table A-6).

For the Black Rocks population, Nesler et al (1992) estimated an average
population size of about 1,000 fish (CV=33%) for 1979-1985 using a 59% survival
rate estimated from age series data provided in Kaeding and Zimmerman (1983)