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

urogenital opening, T. Chart, personal communication; Chart and Lentsch 1999b). After
handling, Gila were placed into a 1.5% salt bath for 0.5-1 min and then released at the central
processing point. About 9% of the humpback chubs handled were held overnight in a soft-
mesh live cage to assess short-term mortality.
Data Analysis
Mean catch per effort for trammel netting (CPE, fish per net hour) was calculated for
humpback chub and roundtail chub for each sampling rotation within this study and for earlier
ISMP sampling (1988, 1991, 1994, 1997; McAda et al. 1994). Mean CPE was compared
among individual sampling efforts with the Kolmogorv-Smirnov two sample test after initial
differences were established with analysis of variance. Linear regression was used to estimate
trends in mean CPE over time. All statistical testing was done with SYSTAT (Wilkinson
1997); significance was accepted at Ps0.05. Mean CPE was not calculated for electrofishing
or angling because of limited effort.
Capture-recapture data for all humpback chubs handled were placed into a matrix
organized by sampling rotation. Population estimates were made for adult humpback chubs
(z 200 mm TL, USFWS 2002) and for all humpback chubs collected (all sizes combined). The
matrix identified whether a specific humpback chub was captured or not during each sampling
rotation. The population estimation program CAPTURE (White et al. 1982) was then used to
calculate annual abundance estimates for humpback chub in Black Rocks. CAPTURE allows
a variety of different models to be run and provides a model selection algorithm to suggest the
best model for the data set used. After estimates were generated for each year sampled, an
average was calculated for the 3 years to provide a population estimate for the study period.
Length-frequency distributions were calculated for each year of sampling. Humpback
chubs recaptured within a year were only used once in the analysis. Length-frequency
distributions were also calculated for earlier ISMP sampling. Sex ratio was calculated for fish
handled during the last rotation of 1999; chi-square analysis was used to determine if the ratio
was significantly different than 1:1. Annual growth was estimated by comparing total length
of recaptured fish that had been handled in previous years.
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