Date of Award:


Document Type:


Degree Name:

Master of Science (MS)


Natural Resources

Department name when degree awarded

Fisheries and Wildlife

Committee Chair(s)

Wayne A. Wurtsbaugh


Wayne A. Wurtsbaugh


Robert Taylor


James Haefner


Juvenile rainbow trout Oncorhynchus mykiss 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 (1) direct observations (snorkel transects) of habitat selection in two reservoirs and (2) measurements of survival and growth rates in a pond experiment where adult brown trout Salmo trutta were predators. 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 and avoided simple habitats such as sand and gravel. Measurements of gut fullness indicated that juvenile trout fed during the day but not during the night. Large Daphnia comprised more than 95% of the diet of juvenile trout. Because large Daphnia were often higher offshore than inshore in both reservoirs, selection of inshore cover is believed to be primarily a response to reduce predation risk. At night, trout in both reservoirs selected more exposed areas and rested on the bottom. In the pond experiment, the presence of brown trout significantly increased mortality of juvenile trout, decreased their growth rates, and caused them to avoid offshore areas. The presence of cover significantly decreased predation rates but did not affect growth of the juvenile trout.