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Last modified
7/14/2009 5:02:33 PM
Creation date
5/20/2009 5:14:00 PM
Metadata
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UCREFRP
UCREFRP Catalog Number
8105
Author
Haines, G. B., D. W. Beyers and T. Modde.
Title
Estimation of Winter Survival, Movement and Dispersal of Young Colorado Squawfish in the Green River, Utah.
USFW Year
1998.
USFW - Doc Type
Recovery Program Project 36,
Copyright Material
NO
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<br /> <br />Executive Summary <br />Population estimates for age-O and age-l Colorado squawfish in two 32-km reaches of <br />the Green River were made using capture-recapture procedures. Comparisons of autumn and <br />spring population estimates were used to assess overwinter survival and evaluate factors that <br />affect it. Previous research using traditional methodology has demonstrated that estimates <br />obtained using catch per unit effort (CPUE) are unreliable for assessing overwinter survival. <br />Capture-recapture provides a more rigorous basis for estimating abundance of young Colorado <br />squawfish because it can account for variable capture probabilities. <br />Objectives of this study were to employ capture-recapture methods to (1) compare <br />estimates of abundance from capture-recapture and CPUE methods; (2) estimate overwinter <br />survival of age-O Colorado squawfish; (3) estimate seining catchability coefficients for autumn <br />and spring sampling; (4) determine extent of downstream movement of marked Colorado <br />squawfish between 1 November and 1 April; and (5) determine the effect of timing and <br />magnitude of spring flows on dispersal of age-l Colorado squawfish. <br />We found little evidence that abundance estimates from CPUE accurately reflect the <br />number of young Colorado squawfish in study reaches in the Green River. There was only a <br />weak correlation (r = 0.50, P = 0.14) between estimates of abundance from CPUE and <br />capture-recapture. On several occasions, CPUE estimates had precision that was comparable to <br />that achieved with capture-recapture, but the estimates differed by as much as 217%. Inaccuracy <br />and greater variability of CPUE was attributed to effects of water temperature on capture <br />probability. Evidence suggests that young Colorado squawfish are less likely to be caught when <br />water temperatures are cool, regardless of their abundance. <br />Overwinter survival probabilities of age-O fish ranged from 0.06 to 0.62. Three of four <br />estimates were similar and ranged from 0.56 to 0.62. Low overwinter survival (0.06) during <br />1995-1996 may have been due to small size of age-O fish in autumn or relatively high winter <br />discharge. <br />Recaptures of marked age-O and age-l Colorado squawfish showed that they moved less <br />than 16 km downstream during sampling periods that ranged from 2 to 21 days. Similarly, age-O <br />fish that were marked in autumn and recaptured the following spring moved less than 16 km <br /> <br />viii <br />
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