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 relati vely little evidence to judge competitive effects at any scale. More than h alf were unreplicated and so inadequate to test either the existence or rel ative strength of interspecific competition. Most replicated experiments us ed one of two designs appropriate to address questions of interest, such as whether nonnative species affect Atlantic salmon via competition or whethe r interspecific competition from coevolved salmonids is greater than intras pecific competition. Replicated experiments spanned a broad range of spatia l and temporal scales, and one well-designed field experiment yielded the s trongest inference at useful scales. Nonnative salmonids being introduced w orldwide into Atlantic salmon waters have the potential to invade, so exper iments testing their effects are most urgently needed. Overall, juvenile co ho salmon (Oncorhynchus kisutch) are suspected to have the greatest effect, partly due to their inherent size advantage. The potential for complex int eractions or indirect effects to modify effects of nonnative species is com pletely unknown but may be important and needs investigation.