Laserfiche WebLink
<br />Valdez and Cowdell (1992) compared several methods of calculating catch per effort <br />(CPE) and recommended the two methods used in this report (with slight modifications). <br />Geometric-mean CPE was calculated using each backwater as the basic element rather than <br />each seine haul. The ('corrected') total number of Colorado squawfish collected in both <br />seine hauls in a backwater was divided by the total area seined (with both seine hauls) to <br />determine CPE for that backwater. Geometric-mean CPE was then calculated for each <br />monitoring reach and for ten-mile intervals within monitoring reaches. To save space, <br />Geometric-mean CPE will be referred to as Gmean CPE throughout the remainder of this <br />report. A second index of relative abundance was calculated by totaling the number of <br />Colorado squawfish collected within each ten-mile interval and dividing that number by the <br />total area seined within that interval. This index will be referred to as Total CPE in the rest <br />of this report (see Figure 2 and Table 2 for further explanation of the two CPR-indices). <br />An index to the total number of YOY Colorado squawfish in backwaters each year was <br />calculated by multiplying Total CPE (fish/m2) by total area of backwaters (> 30 m2; <br />determined by aerial video) for each ten-mile interval. The index for each monitoring reach <br />was determined by totaling the number of fish in all 10-mile intervals within the reach. <br />These numbers will be referred to as 'estimated number of Colorado squawfish' in this <br />report. Nonetheless, it represents only another index to relative abundance rather than an <br />actual estimate of fish numbers. Further, it does not include the small number of YOY <br />Colorado squawfish that may have occupied habitat other than backwaters when sampling <br />occurred. However, if we assume that abundance of Colorado squawfish outside of <br />backwaters is positively related to abundance of Colorado squawfish in backwaters (a <br />reasonable assumption), it is still a reasonable index to abundance of all YOY Colorado <br />squawfish. Confidence intervals were not calculated, although they could be calculated in <br />the future if it would be meaningful to do so. <br />Gmean CPE, Total CPE, total area of backwaters, total number of backwaters, and <br />estimated number of Colorado squawfish (Total CPE x total area of backwaters) were plotted <br />as histograms to compare among years and reaches. Gmean CPE, Total CPE, and estimated <br />number of Colorado squawfish were plotted and regressed against each other to evaluate <br />relations between the different abundance indices. <br />6 <br /> <br />1 <br /> <br /> <br /> <br />1 <br /> <br /> <br />1 <br /> <br />1 <br /> <br /> <br /> <br /> <br /> <br /> <br />