Interspecific competition and juvenile Atlantic salmon (Salmo salar):: on testing effects and evaluating the evidence across scales

A review of 17 controlled experiments of interspecific competition between juveniles of Atlantic salmon (Salmo salar) and other fishes revealed relatively little evidence to judge competitive effects at any scale. More than half were unreplicated and so inadequate to test either the existence or relative strength of interspecific competition. Most replicated experiments used one of two designs appropriate to address questions of interest, such as whether nonnative species affect Atlantic salmon via competition or whether interspecific competition from coevolved salmonids is greater than intraspecific competition. Replicated experiments spanned a broad range of spatial and temporal scales, and one well-designed field experiment yielded the strongest inference at useful scales. Nonnative salmonids being introduced worldwide into Atlantic salmon waters have the potential to invade, so experiments testing their effects are most urgently needed. Overall, juvenile coho salmon (Oncorhynchus kisutch) are suspected to have the greatest effect, partly due to their inherent size advantage. The potential for complex interactions or indirect effects to modify effects of nonnative species is completely unknown but may be important and needs investigation.