Contrasting trends in gray seal ( Halichoerus grypus ) pup production throughout the increasing northwest Atlantic metapopulation

Abstract

The northwest Atlantic subspecies of gray seal ( Halicheorus grypus grypus ) has been increasing for more than a half century and has reestablished breeding colonies in Canadian and US waters. In 2016, visual, oblique, and vertical large‐format digital photographic surveys were conducted at all known breeding colonies in the northwest Atlantic. Total pup production in the northwest Atlantic was estimated to be 109,000 ( SE = 17,500) pups. At 87,500 ( SE = 15,100) pups, Sable Island accounts for 80% of total pup production. Regional differences in pup production trends are evident. Pup production in the Gulf of St. Lawrence and along the eastern shore of Nova Scotia has been relatively stable. Since 2004, the rate of increase in pup production at Sable Island has slowed to about 5%–7% per year, while the newer colonies in southwest Nova Scotia and the northeastern United States are increasing rapidly. In 2016, the Muskeget Island (MA) breeding colony produced 3,900 ( SE = 200) pups, making it the third largest breeding colony in the northwest Atlantic. This southward shift in production may reflect climate‐mediated changes in population growth as well as reestablishment of colonies throughout the former range associated with increased protection.

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