Evaluating the potential for grey seal predation to explain elevated natural mortality in three fish species in the southern Gulf of St. Lawrence

Despite 2 decades of very low fishing levels, numerous NW Atlantic demersal fish stocks have failed to recover from collapsed states or are presently collapsing. In the southern Gulf of St. Lawrence, adult natural mortality (M) appears to be the demographic rate that most limits population productivity in at least 3 species: Atlantic codGadus morhua, white hakeUrophycis tenuisand winter skateLeucoraja ocellata. The causes of elevatedMare not well understood, though there is indirect evidence consistent with an effect of predation by grey sealsHalichoerus grypus. However, direct evidence is lacking due to uncertainty in the seal diet. Consequently, Monte Carlo simulations were undertaken using data on the spatial overlap between the seals and the fishes and a seal food-consumption model, to estimate the plausibility that different seal-diet compositions could explain observedMlevels. Under the simulation assumptions, we find that predation could explain up to 20 to 50% ofMin adult white hake and cod even if these species comprise a small percentage of grey seal diets (