Competition among juvenile brown trout, grayling, and landlocked Atlantic salmon in flumes - predicting effects of interspecific interactions on salmon reintroduction success

Worldwide declines in salmonid populations have generated major interest in conservation and restoration of wild populations and riverine habitats. Species reintroductions to previous habitats raise questions about their potential impact on these systems. In River Klaralven, landlocked Atlantic salmon (Salmo solar) have been extinct from upper reaches for over 50 years due to hydropower dams. Here we study competitive interactions among juvenile salmon, grayling (Thymallus thymalius), and brown trout (Salmo trutta) that occur in the upper reaches of the river. We examine foraging rates, aggression, and activity of juvenile fish in allopauy at three different densities and in sympatry with one or both potential competitors in laboratory flumes. Salmon captured prey less frequently in the presence of brown trout and grayling, whereas grayling and brown trout were unaffected by salmon, but affected each other. Grayling was the most aggressive and active species, whereas salmon the least. Consequently, reintroduction of salmon probably will have little impact on grayling and brown trout, whereas grayling and brown trout could affect the success of reintroducing salmon.

Automated summary

This study explored competitive interactions among juvenile salmon, grayling, and brown trout in the upper reaches of a river, finding that grayling was the most aggressive and active species, while salmon was the least. The research suggests that reintroduction of salmon may have little impact on grayling and brown trout, but these species could affect the success of reintroducing salmon.