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Last modified
7/14/2009 5:02:35 PM
Creation date
5/18/2009 12:40:46 AM
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UCREFRP
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
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bracketed the average of 741 individuals observed for 1998-2000. Because of the variation in <br />these estimates and the inability to select the correct estimate for 1994-1997, it is not possible <br />to detect any change in the Black Rocks population through the 1994s. <br />The marked decline in mean CPE does suggest that the population has declined since <br />1986. However, the apparent decline in relative abundance of humpback chub is probably not <br />as dramatic as depicted in Figure 4 because of differences in sampling area between this and <br />previous efforts. ISMP sampling was concentrated in the deep water habitats where <br />humpback chub were most abundant, while this study sampled all available habitats within the <br />general Black Rocks area. Sampling points above and below the center of Black Rocks <br />generally resulted in much lower catch rates than in the deep-water habitats where humpback <br />chubs concentrated. These reduced catch rates undoubtedly lowered the mean CPE observed <br />in this study. However, sampling effort was consistent throughout the current study and the <br />low values in 2000 could reflect a true decrease in humpback chub abundance (or at least <br />catchability) as was reflected in the abundance estimate. <br />Movement of tagged fish between Westwater Canyon and Black Rocks suggests that fish <br />in the two locations may comprise a single population and draft recovery goals reflect that <br />opinion (USFWS 2002). Chart and I.entsch (1999b) estimated population size for Westwater <br />Canyon as 5,621 in 1994, 10,148 in 1995 and 5,186 in 1996 (mean, 6,985). More recently, a <br />study specifically designed to estimate population size using three pass mark-recapture was <br />completed for Westwater Canyon (1998-2000). However, data analysis is ongoing and a final <br />report has not been completed. A similar study for Desolation and Gray Canyon is in its <br />second year of data collection and an estimate is scheduled to begin in Cataract Canyon in fall <br />2003 (T. Czapla, personal communication). <br />The only other upper basin population where amark-recapture population estimate for <br />humpback chub has been completed is in Yampa Canyon (1998-2000; Haines and Modde <br />2002). However, humpback chub are law in numbers in Yampa Canyon and fish were only <br />recaptured in one of the three years of study. The recapture rate was very low and Haines and <br />Modde (2002) concluded that they were unable to make a robust estimate using the available <br />13 <br />
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