Research Document - 2011/066

Pup Production at Scotian Shelf Grey Seal (Halichoerus grypus) Colonies in 2010

By W.D. Bowen, C. den Heyer, J.I. McMillan, and M.O. Hammill

Abstract

We conducted a digital-photographic aerial survey on Sable Island and Hay Island, Nova Scotia and along the coast of Nova Scotia and the outer Bay of Fundy in January 2010 to estimate grey seal (Halichoerus grypus) pup production. A total of 57,504 pups was counted on the digital imagery from Sable Island. Given the high quality of the imagery, no correction for missed pups was necessary after analysis of ground-truthing plots. Correction for proportion of pups that died prior to the survey (0.0279) and the proportion of pups born before the survey (0.961 East colony, 0.931 West colony), estimated total pup production was 62,100 with 95% confidence limits of 60,900 to 63,200. The 2010 estimate indicates that pup production on Sable Island has continued to increase, but that the rate of increase has declined over the past two successive surveys. We estimated that 89.5% of pups had been born by the time of the Hay Island survey. Correcting for the proportion born, the estimated number of pups born on Hay Island was 2,492 with 95% confidence limits of 2,240 to 2,770. This is similar to the uncorrected pup count in 2007 (2,616), suggesting that this colony may have reached carrying capacity. A total of 417 pups was counted on four small islands in the vicinity of Seal Island, southwest Nova Scotia. The breeding colony in southwest Nova Scotia has increased since 2007 (pup count 207) and expanded to two adjacent Islands. In 2010, about 50 pups were born at other coastal Nova Scotian colonies; most of these were born on several islands off the eastern shore of Nova Scotia (White Islands 49, Bowen’s Ledge 1). The 2007 total in Bowen’s Ledge and White Islands was 113. 

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