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Utah State University

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food resources, temperature, distribution, energy balance, Bear Lake, sculpin, Cottus extensus

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Changes in the abundance, diet, and daily ration of adult and sub-adult Bear Lake sculpin (Cottus extensus) were investigated seasonally along a littoral to profundal transect in Bear Lake to determine if or when sculpin were food limited. During different seasons, sculpin migrated inshore or offshore. These were most pronounced for age 1 + sculpin, 35-55 mm in length. This age class was most abundant in the littoral zone, particularly in August. The migrations of age two and older sculpin were less pronounced, and most of these fish were located in the profundal zone (>30 m). The sculpin diets also changed seasonally in response to their movements and to seasonal changes in the abundance of chironomids in the littoral and metalimnetic areas, and to increases in the abundance of Daphnia in the profundal areas in the summer and fall. The composition of the benthic invertebrates in Bear Lake has changed considerably in recent years, primarily due to increases in Daphnia. An analysis of the net energetic balance of sculpin (consumption - respiratory costs) in different depth strata suggested that the migrations were food-related in June and August, but not in October and December. In all seasons, gut fullness of sculpin and daily consumption rates were less than observed in the laboratory under ad libitum feeding, indicating that the sculpin were strongly food limited.

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