Population status assessment and potential biological removal (PBR) for the Atlantic Harbour Seal (Phoca vitulina vitulina) in Canadian waters

Abstract

Aerial surveys were conducted between June and August of 2019–21 to assess harbour seal (Phoca vitulina vitulina) abundance and distribution in Atlantic Canada. The surveys covered three regions: the Gulf of St. Lawrence (GSL), the Scotian Shelf (SS), and the Newfoundland and Labrador Shelves (NLS). These surveys counted seals at haul-out sites in each region. A total of 10,327 individuals were counted, with 55%, 23%, and 22% of the individuals counted in the GSL, SS, and NLS, respectively. To estimate abundance, these counts were adjusted for the proportion of seals which were at sea during the time of the survey and were, therefore, unavailable to be counted. We applied correction factors (CF) of 2.55 (coefficient of variation [CV]: 16.02%) and 1.64 (CV: 8.67%) for surveys taking place during the pupping and moulting periods, respectively, as developed in a companion study based on recent telemetry data and CFs reported in the literature. Applying these CFs to survey counts yielded a total estimated harbour seal abundance for Atlantic Canadian waters for 2019–21 of 25,183 individuals (95% CI 22,548–28,126). The GSL, SS, and NLS regions accounted for 58%, 24%, and 19% of the total estimated abundance, respectively. These are likely minimum estimates as a result of seals entering the water prior to the count due to disturbance, imperfect detection of hauled out seals, and a lack of coverage in some areas. The uncertainty around the abundance estimate may also be underestimated since there was no reported uncertainty in survey counts and data to develop CFs for the study area were limited. The Potential Biological Removal (PBR) for Atlantic Canada’s harbour seal population, based on this abundance estimate, was 720 individuals.