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D/~llS Qsmurdson ,.. ~er(~ 7:: )q?to / ;J; / - /(1 //J;;I,~/ / () 6 Wl~ 6M-1 'I-- eUv~ )q '? (,p LARGEMOUTH BASS PREDATION ON STOCKED COLORADO SQUAWFISH Douglas B. Osmundson and Charles R. Berry Jr. Utah Cooperative Fish & Wildlife Research Unit Department of Fisheries & Wildli fc Utah State University Logan, Utah 84322 ABSTRACT / '..,/ ... Hatchery-reared Colorado squawfish (45 to 145 mm long) were stocked at 1,250 fish/acre in five gravel-pit ponds adjacent to the Colorado River in the fall of 1983 and 19R4, and in the swmner of .1984. Resident largemouth bass and several species of forage fish varied in relative abundance among ponds. The field study was complemented by a laboratory study where largemouth bass of three sizes were offered a diet of four forage species (Colorado squawfish, fathead minnow. green sunfish. red shiner), and three sizes of Colorado squawfish (50-65 mm, 75-90 Mm, and 100--120 JIID). Wild largemout.h bass switched from customary forage to Colorado squawfish after stocking. Captive largemouth bass preferred Colorado squawfish over green sunfish and red shiners but selected fathead minnows and Colorado squawfish equally. Both wild and captive largemouth bass ate more small squawfish than large. Survival of stocked fish after four months was minimal because of predation; but parasitism by anchorworm and water quality in the winter may have also affected survial. In a predator-free pond where there was ample forage (carp) and favorable water quality, growth of stocked fish was higher than previously documented for any wild or captive Colorado squawfish population. Hence, riverside ponds may be useful as grow'.out ponds for Colorado squawfish if predators are absent and forage fish are present in adequate numbers. 146 -N"~-;I>}""-'~C~~... ,'-".....~""' ~...... ..... , ~ .dJ". ~-.<f-~:~~!fIlTr1r, .-