Stock assessment of Atlantic Harbour Seals (Phoca vitulina vitulina) in Canada for 2019–2021

Abstract

Aerial surveys to obtain counts of harbour seals were conducted in the Gulf of St. Lawrence (GSL, 2019), on the Scotian Shelf (SS, 2020), and on the Newfoundland and Labrador Shelves (NLS, 2021). A total of 10,327 seals were counted on haul-out sites, with 55%, 23%, and 22% of the seals counted in the GSL, SS, and NLS, respectively. To estimate abundance, counts were adjusted for the estimated proportion of seals which were at sea during the time of the surveys and were, therefore, unavailable to be counted. Correction factors were derived by combining recent data on haul-out behaviour of harbour seals in the St. Lawrence Estuary and haul-out correction factors reported in the literature. Haul-out correction factors of 2.55 (CV: 16.02%) and 1.64 (CV: 8.67%) for surveys flown during the pupping and moulting periods, respectively, were applied to the survey counts. The total estimated harbour seal abundance for Atlantic Canadian waters in 2019–21 was 25,200 individuals (95% CI 22,500–28,100; rounded to the nearest 100). The GSL, SS, and NLS accounted for 58%, 24%, and 19% of this total, respectively. Based on the estimated total abundance for 2019–21, the annual Potential Biological Removal (PBR) is 720 seals. The haul-out correction factors have a large impact on the abundance estimate but are informed by a limited amount of data on haul out behaviour in Atlantic Canada.