Research Document - 2011/014

Modelling Grey seal Abundance in Canadian waters

By M.O. Hammill and G.B. Stenson

Abstract

The model used in this study to describe the population dynamics of the Northwest Atlantic grey seal is a two parameter model that uses information on age specific reproductive rates, ice-related mortality of young seals, removals and estimates of pup production. The model was fitted to the three grey seal herds: Sable Island, Eastern Shore and Gulf of St. Lawrence separately to obtain estimates of pup production and population size. Model outputs were also compared to two other models that have been used to describe the dynamics of the Northwest Atlantic grey seal population (Thomas et al. 2007,2008; Trzcinski et al. 2006) and population trajectories were similar when run under similar conditions. Pup production in the Gulf herd is quite variable and is likely associated with variable mortality due to fluctuating ice conditions. A significant relationship was observed between pup production on the ice and ice cover in the southern Gulf. The Northwest Atlantic grey seal population has increased substantially over the last 5 decades increasing from approximately 13,000 (SE=1,100) to 402,700 (SE=7,700) in 2010.

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