Effects of grey seals (Halichoerus grypus) on Atlantic cod (Gadus morhua) in the southern Gulf of St. Lawrence

Grey seals have been implicated in the continued decline of Atlantic cod in the southern Gulf of St. Lawrence. Experts were surveyed to identify plausible ecological hypotheses about the effect of seals on cod. Three interaction hypotheses ranked highly by experts (i.e. Aggregation, Belly-Biting, and Foraging Restriction) were translated into mathematical models and combined with a cod population base model. Ability of each model to explain changes in relative cod abundance was evaluated. The Belly-Biting Hypothesis was highly ranked by model selection, however, none of the three selected hypotheses or combinations of hypotheses accounted for most of the variation observed in cod-seal interactions. Managers and researchers should continue to quantitatively evaluate other ecological hypotheses of cod population dynamics in a statistically defensible manner.