9466

• UCREFRP Catalog Number: 9466
• Author: McAda, C. W.
• Title: Population Size and Structure of Humpback Chub in Black Rocks, 1998-2000.
• USFW Year: 2002.
• USFW - Doc Type: Grand Junction.
• Copyright Material: NO

INTRODUCTION
The humpback chub (Gila cypha) is a mid-sized cyprinid endemic to the Colorado River
Basin (Minckley 1973) that is currently listed as endangered under the Endangered Species
Act of 1973 (USFWS 2000). The species was not described until 1946 (Miller 1946) and
little was known about its distribution until relatively recently. Humpback chub are currently
found in discrete populations within canyon-bound reaches of large rivers in the Colorado
River basin (Valdez and Clemmer 1982). The largest population occurs in the Little Colorado
and Colorado rivers in Grand Canyon (Valdez and Ryel 1995; Douglas and Marsh 1996). All
other populations occur in the upper Colorado River basin, including the Yampa and Green
rivers within Dinosaur National Monument (Karp and Tyus 1990), the Green River in
Desolation and Gray canyons (Chart and Lentsch 1999a), and the Colorado River in Black
Rocks (Kaeding et al. 1990), Westwater Canyon (Chart and Lentsch 1999b), and Cataract
Canyon (Valdez 1990).
Conflicts between water development in the upper basin and endangered fish began soon
after the Endangered Species Act (as amended) was passed in 1973 (Wydoski and Hamill
1991). In an attempt to resolve those conflicts, the Upper Colorado River Endangered Fish
Recovery Program (Recovery Program) was developed to provide money for management
actions to recover humpback chub (and other listed fishes) and allow the states of the upper
basin to continue to develop water to satisfy the needs of a growing population (Wydoski and
Hamill 1991). During formation of the Recovery Program, an Interagency Standardized
Monitoring Program (ISMP) was developed to monitor trends in the humpback chub
populations in Black Rocks and Westwater Canyon (USFWS 1987; McAda et al. 1994).
ISMP sampling was limited to short periods of trammel netting at 2 or 3 year intervals. This
sampling was sufficient to develop catch-per-effort indices indicating that humpback chub
still occupied Black Rocks and Westwater Canyon and that young chubs continued to recruit
to the adult population, but it. was not sufficient to develop reliable estimates of population
size.
During development of quantifiable Recovery Goals for humpback chub (USFWS 2002)
it was determined that regular estimates of size and structure of the major populations were