Fish carcasses alter subyearling Chinook salmon dispersal behavior and density but not growth in experimental mesocosms

Similar to many fish, juvenile Pacific salmon rearing in temperate streams face a growth and survival bottleneck early in their first summer due to limitations in space and food. Fish carcasses have been shown to affect juvenile salmon growth in many systems, but carcasses likely also alter behavioral and dispersal response of hatchery-origin young-of-the-year salmon. We tested the social and emigration response of subyearling chinook salmon to carcasses of Pacific lamprey or rainbow trout using semi-open flow-through mesocosm experiments. We expected the presence of carcasses to increase salmon growth and density while decreasing intraspecific aggression and downstream emigration compared to controls without carcasses. Consistent with expectations, salmon emigrated at lower rates when carcasses were present, resulting in significantly higher holding densities. Contrary to our expectations and results from previous studies, we did not detect differences in growth rate of juvenile salmon among treatments. Our findings suggest that indirect responses of consumers to concentrated resources may have measurable effects on density mediated by movement behaviors. Differences in lamprey and trout decomposition also suggest that carcass traits mediate the behavioral responses of consumers and incorporation of carcass subsidies into food webs.

Automated summary

The presence of carcasses can increase the density of juvenile salmon and decrease emigration rates, but contrary to expectations, there were no differences in growth rates among treatments. The decomposition traits of lamprey and trout carcasses mediate consumer behavioral responses and the incorporation of carcass subsidies into food webs.