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Spatial and temporal ranges of resource exploitation by stream-dwelling cutthroat trout
Department: Biology
Specimen Elements
Unknown to Unknown
Hope W. Owens
Idaho State University
City: Pocatello
Salmonid fishes in streams are commonly thought to forage on drifting aquatic invertebrates during daylight hours. However, past studies indicate variation in foraging behavior despite the predominant view of salmonids as diurnal drift-foraging predators. I used in-stream videography to assess foraging mode and energy intake for stream dwelling Yellowstone cutthroat trout (Oncorhynchus clarkii bouvieri). I recorded the foraging behavior of wild fish with a waterproof video camera and estimated energy intake based on fish size and known values for prey. Fish chiefly obtained food from drifting invertebrates during daytime hours; however, alternative behaviors also were found, with foraging towards the stream benthos and in nocturnal hours observed at moderate levels throughout the year. I found foraging behavior to have significantly more variation than has been previously estimated, with alternative strategies comprising up to 30% of energy intake. Several variables had a strong influence on foraging rate and intake location, including the time of day, season, and fish size. In terms of energy content, nocturnal and benthic behavior had less total energy contribution to the fish than diurnal drift foraging behavior. Energy intake was highest from diel drift foraging behavior, even exceeding fish’s modeled metabolic limit in October and November. These results indicate that despite cutthroat trout being primarily drift-foraging predators, cutthroat trout supplemental strategies are a part of foraging behavior and should be considered in salmonid ecology and bioenergetics. Keywords: Foraging behavior, animal behavior, energy intake, salmonid, cutthroat trout, camera system.

Spatial and temporal ranges of resource exploitation by stream-dwelling cutthroat trout

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