Survival of Trout Strains as Affected by Limnological Parameters

Juvenile rainbow trout Oncorhynchus mykiss. (ca. 80 mm S.L.) stocked into mid-elevation reservoirs in Utah are vulnerable to predation from piscivorous fish and birds. I determined how effectively juvenile trout used cover to avoid these predators by using direct observations (snorkel transects) on habitat selection in two reservoirs. Observations of juvenile trout were conducted within five weeks of stocking in 1988 and 1989. During the day juvenile trout were abundant in complex inshore habitats. Juvenile trout actively fed during the day but the time of peak feeding was variable. Large Daphnia made of \u3e 95% of the diet of juvenile trout. Because large Daphnia was often higher offshore than inshore in both reservoirs. selection of inshore cover is believed to be primarily a response to lessen predation risk. At night. trout in both reservoirs selected more exposed areas and rested on the bottom