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<br />Squawfish Population Viability Analysis --July 1993 <br /> <br />Page 23 <br /> <br />squawfish handled during this roughly ten-year period. They are doubtless <br />biased by different effort levels. They are intended for relative <br />comparisons, not for estimates of actual population size. <br /> <br />Number of Colorado Squawfish <br />per 20 mile stretch <br />· 1-10 <br />: 11-20 <br />. 21-40 <br />41-80 <br />. 81-160 <br />. 161+ <br /> <br /> <br /> <br />ca..awx:> <br /> <br />/ <br /> <br />t <br /> <br />Figure 2.2. Distribution of Colorado squawfish in the Upper Colorado <br />river basin (see text for explanation of the data). <br /> <br />2.9 Gene Flow and Population Integration <br /> <br />While there is evidence that Colorado squawfish return to the same <br />spawning area year after year (Wick et al. 1983, Tyus 1990) it has not been <br />proven that this is their natal area~ if it is not then gene flow could be quite <br />high, as juveniles from one population would be genetically incorporated <br />into a different population. Tyus (1990) found some adult squawfish to <br />"stray" between rivers~ if these few are indeed changing spawning areas <br />then the gene flow should be sufficient to maintain a single panmictic <br />population throughout the entire upper Colorado river basin (see below). <br /> <br />Information on the movements of adult fish should become more <br />comprehensive in the near future with the use of PIT tags. Also a method <br />of marking the otoliths of larval squawfish by immersion in a tetracycline <br />solution offers prospects for study of the movements of age-O fish (Muth <br />and Bestgen 1991). <br />