| 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. |