Variation in predator diet and prey size affects perceived impacts to salmon species of high conservation concern

Management of protected species is difficult when objectives include the recovery both predator and its prey. Ideally, identifying trade-offs between competing involves evaluating management alternatives with a quantitative model that integrates information on species, but data are often limited. We used new diet simulation modeling to update our understanding seal predation juvenile Chinook (Oncorhynchus tshawytscha) coho salmon kisutch) in Puget Sound. Under prey size assumptions by previous studies, estimates suggest could be significant source mortality for (mean: 37% ocean age-0 juveniles), varied considerably among years (range median estimates: 22%–49%). However, we estimated from otoliths recovered scats, impact (numbers fish consumed) decreased 71%. Predation was relatively low under scenarios (6%–8% juveniles) 21% decrease consumption using otolith-derived size. Our analysis highlights importance updating inputs re-evaluating multi-species models ecosystem-based fisheries management.