Depth, velocity, and foraging success in two sympatric stream salmonids: implications for habitat selection and segregation

Friday seminar by John Piccolo.

Coho salmon (Oncorhynchus kisutch) and steelhead (O. mykiss irideus) are distributed around the Pacific Rim from central Californiato south-central Alaska, and into parts of Asia. Juveniles of both species rear in freshwater for one or more summers before smolting, and are often found in sympatry. Although they occur within the same streams, coho and steelhead have been documented to segregate microhabitat, with coho using slower, deeper pools and steelhead using faster, shallower riffles. Similar patterns of pool/riffle segregation have been reported for other sympatric salmonids, such as brown trout and Atlantic salmon. Ecological theory suggests that the niches of two sympatric species cannot entirely overlap, and habitat segregation in sympatric stream salmonids is thought to be based in part on species-specific differences in foraging abilities. This hypothesis, however, has received little rigorous testing.


I will present the results of experiments designed to assess the effects of water depth and velocity on the foraging abilities of coho and steelhead. I use the results to develop models that predict optimal foraging velocities for coho and steelhead based on net energy intake rates. I conclude that ecologists have a long way to go in explaining the distribution of stream salmonids, which limits our ability to predict the effects of natural or human-induced habitat disturbance. During my time in Sweden I hope to continue related studies using brown trout and Atlantic salmon.

John Piccolo, Karlstad University, Sweden

Published Feb. 2, 2012 4:03 PM