Research Document - 2007/087
Continued reduction in population growth rate of grey seals at Sable Island
By Bowen, W.D., J.I. McMillan, D. Lidgard and W. Blanchard
Abstract
We conducted a digital-photographic aerial survey on Sable Island, Nova Scotia in January 2007 to estimate grey seal (Halichoerus grypus) pup production. A total of 48,036 pups was counted on the digital imagery. 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 (0.0276) and the proportion of pups born before the survey (east colony 0.91, west colony 0.89), estimated total pup production was 54,500 with 95% confidence limits of 52,000 to 57,100 and standard error of 1,288. The 2007 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. Proportion of females giving birth at ages 4-7 yr, from the 1998-2002 cohorts, were significantly lower than those in the mid-late 1980s. The new estimate of pup production and new data on age of primiparity provide further indication of changes in vital rates of this population.
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