9531

• UCREFRP Catalog Number: 9531
• Author: Hudson, J. M. and J. A. Jackson.
• Title: Populaiton Estimates for Humpback Chub ‎(Gila cypha)‎ and Roundtail Chub ‎(gila robusta)‎ in Westwater Canyon, Colorado River, Utah, 1998-2000.
• USFW Year: 2003.
• USFW - Doc Type: Salt Lake City.
• Copyright Material: NO

INTRODUCTION
~ The humpback chub (Gila cypha) was first described in 1945 (Miller 1946). Due to declines in
distribution and abundance throughout its range, the humpback chub is currently protected under
the Endangered Species Act of 1973, as amended (ESA, 16 U.S.C. 1531 et. seq.). Previously, it
was protected under the Endangered Species Conservation Act of 1969 (16 U.S.C. 668aa). The
most recent recovery plan was finalized in 1990 (USFWS 1990), with an amendment and
/, supplement to that plan approved in 2002 (USFWS 2002). The amendment and supplement to the
1990 recovery plan identifies objective, measurable recovery criteria to downlist and delist
humpback chub in both the upper basin recovery unit and the lower basin recovery unit. Within the
upper basin recovery unit, one of the criteria to downlist humpback chub is the maintenance of one
of the five upper basin populations (Black Rocks, Westwater Canyon, Cataract Canyon, Yampa
~ Canyon, Desolation/Gray Canyon) as a core population with a minimum viable population of
2,100 adults (>_ 200 mm) for five consecutive years. To delist humpback chub, the upper basin
recovery unit will have to maintain this minimum viable population for an additional three years in
two of the five upper basin humpback chub populations. The adult humpback chub population will
be determined via point estimates in 2-3 of every five years to measure progress toward achieving
~ and maintaining the minimum viable population. Within each core population, there must not be a
significant decline of the trend in adult point estimates to downlist and delist humpback chub.
The Westwater Canyon adult humpback chub population estimate, along with the Black Rocks
humpback chub population estimate, is one of the first upper basin population estimates to be
conducted in accordance with these recovery goals. This study was conducted from 1998 to 2000
~ with the objective of obtaining a population estimate of adult humpback chub in Westwater
Canyon. A secondary objective was to obtain a population estimate for roundtail chub (Gila
robusta) in Westwater Canyon. Previous efforts (e.g., Chart and Lentsch 1999) to estimate the
adult humpback chub population in this canyon had been relatively unsuccessful due to a sampling
approach that was not designed to obtain a population estimate. Recommendations from that report
~ included the need to initiate a specific study to generate population estimates in Westwater Canyon
with a more aggressive sampling program and a more rigid study design.
The result was the current study design. This study was initiated with the understanding that
modifications would be made to the approach as more information was gained toward obtaining
~ the most accurate and precise population estimate for adult humpback chub in Westwater Canyon.
The results of this study will provide valuable information for conducting future population
estimates of chub in the upper Colorado River basin in addition to providing three point estimates
that will aid in reclassification of humpback chub under ESA (i.e., downlist, delist).
~ The objectives of this study are:
• To obtain a population estimate of adult humpback chub (>_ 200 mm) in Westwater Canyon.
To obtain a population estimate of adult roundtail chub (>_ 200 mm) in Westwater Canyon.
r These objectives are specific to Task 4 of the Upper Colorado River Endangered Fish Recovery
Program Project 22c -Interagency Standardized Monitoring Program -Utah. This task was added