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

C:
between years using the same analyses. Data collected from electrofishing effort was not analyzed
separately due to a limited amount of information to analyze.
Length-Frequency
Length-frequency distributions were determined for humpback chub and roundtail chub through the
period of the study.
Growth
Mean annual growth rates were determined from one year of growth on recaptured humpback chub
and roundtail chub from 1992-2000 and compared with respect to the length-frequency distributions
~ determined each year of the study. Mean annual growth rates were also estimated and compared
among annual recaptured individuals from 1999 and 2000, and all recaptured individuals from 1992-
2000.
Movement
~ Movement of individuals was also described within Westwater Canyon and between Westwater
Canyon and Black Rocks (Chuck McAda, USFWS, Grand Junction, Colorado personal
communication).
Comparison with ISMP
Interagency standardized monitoring program (ISMP) protocol was followed within one pass during
each year of this study to allow comparison with historic humpback chub and roundtail chub CPUE
information. CPUE was compared between years (1988-2000) using the Kruskal-Wallis
nonparametric ANOVA with Dunn's multiple comparisons test to examine the equality of samples
~ and the two-sample Kolmogorov-Smirnov to compare the distribution of catch rates.
RESULTS
Humpback Chub
Population Estimates
The model selection function of Program CAPTURE resulted in variability among years in
i determination of the most appropriate estimator for the humpback chub capture-recapture data
(Appendix I). The null estimator (Mo) ranked highest in 1998 and 2000 (1.00 and 0.74,
respectively). There was no appropriate estimator for the data from 1999. In that year, the highest
ranking of the estimator routinely used to calculate population estimates in this study was 0.36
(Chao M,h). Considering the results of the model selection function, the lack of any real justification
to consider another estimator (i.e., changes in the probability of capturing an individual due to
t behavior, flow, etc.), and the outcome of consultation with Dr. Ron Ryel (Utah State University,
~ 4