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<br />(3.2-mm by 4.8-mm mesh) in fall. Fish were killed and fixed in 10% formalin <br />immediately after collection. <br />Up to five specimens =s;; 20 mm TL and five > 20 mm TL of each fish species per <br />sample were selected for analysis of gut contents; each length group contained <br />fish representing a graded size series from shortest to longest. The entire <br />digestive tract (from esophagus to vent) was removed from each fish, opened, and <br />visually assessed for percent fullness. Food items were identified to the lowest <br />practical taxon, and a visual estimate was made of the percentage contributed by <br />each taxon to the total volume of food in each digestive tract (Larimore 1957, <br />Mathur 1977). For diet analyses, food-item taxa (total of 124) were grouped into <br />20 food categories. <br />Data on gut contents for each fish species were stratified into subsets <br />according to 10-mm TL or larger intervals by season (summer or fall) within each <br />river reach (upper or lower). Only subsets with at least six fish containing food <br />were included in analyses. Diet measures calculated for each subset to determine <br />relative importance of each food category were (1) mean percentage contributed by <br />each food category to the total volume of food in each digestive tract (mean of <br />volume percentages) and (2) percentage of all digestive tracts in which each food <br />category occurred (percentage of occurrence). Wallace (1981) evaluated several <br />diet measures and concluded that mean of volume percentages is the best measure <br />when calculating overlap. However, percentage of occurrence is useful for <br />describing general variations in diet (Wallace 1981, Bowen 1983). <br />Overall similarities in diet by subset between Colorado squawfish and other <br />fishes were evaluated by Schoener's (1970) resource-overlap index: <br /> <br />5 <br />