Document: MAR-3-72-1

Foraging ecology of kokanee salmon (Oncorhynchus nerka): Effects of prey density and light.

KOSKI, M.L.* and B.M.JOHNSON

Colorado State University, Fort Collins, CO 80523, USA ¹

Abstract:
Bioenergetics models can provide insights about the effects of environmental conditions on foraging behavior and trophic dynamics. Forecasting with these models requires a functional response to link predator consumption and prey abundance. We are refining a functional response for kokanee salmon (Oncorhynchus nerka) for a bioenergetics model that predicts how growth rates and foraging behavior of kokanee change in response to shifts in prey abundance. In our laboratory experiments, fingerling kokanee were presented with varying densities of zooplankton prey (Daphnia spp.) ranging from 5 to 40 per liter. Light intensity was also manipulated to determine its relative importance to kokanee feeding rates; we used four light levels: 65, 38, 1, and < 0.01 Lux (darkness). Kokanee exhibited a Type-I functional response with consumption rates varying between 14 and 110 Daphnia per minute. Consumption rates were highest at the low light level (1 Lux) indicating that kokanee forage most efficiently at lower light levels, which could be adaptive as a means of predator avoidance while still being able to find prey visually. In addition, video analysis of feeding behavior indicated that kokanee achieved maximum consumption rates during the first minute or two of feeding; feeding rate decreased by almost half afterwards. Hence, functional response may depend on how long the fish has been feeding in addition to prey density. Results will be used to modify a bioenergetics-based foraging model for kokanee.

Keywords: kokanee salmon foraging ecology

This abstract is being presented at: 4:45 PM in session:
Oral Session #62: Freshwater Fish Ecology.