Feeding interactions between Atlantic salmon (Salmo salar) postsmolts and other planktivorous fish in the Northeast Atlantic

In recent decades, there has been a decline in the marine growth of Atlantic salmon (Salmo salar) over large parts of the distribution range. One hypothesis for this reduced growth is increased interspecific competition with other planktivorous pelagic fish in the ocean. Here, interactions between salmon postsmolts and other pelagic fish (mackerel (Scomber scombrus) and herring (Clupea harengus)) in the Northeast Atlantic were investigated. There was a low diet overlap between postsmolts and the two other planktivorous pelagic species. Both mackerel and herring were feeding predominantly on copepods and other small zooplankton, while salmon were feeding mostly on fish larvae. All three species feed on euphausiids and amphipods. Furthermore, postsmolts geographically overlapped with mackerel but had a low geographic overlap with herring. There was no correlation between the abundance or survival of salmon from key index rivers and the abundance of pelagic fish. This study did not find evidence to support the hypothesis that observed temporal changes in marine growth and survival of salmon can be explained by feeding interactions with pelagic fish.