Research Document - 2009/114

Abundance of Northwest Atlantic harp seals (1952-2010)

By M.O. Hammill and G.B. Stenson

Abstract

A population model was used to examine changes in the size of the Northwest Atlantic harp seal population between 1952 and 2009. The model incorporated information on reproductive rates, reported removals, as well as estimates of non-reported removals and losses through bycatch in other fisheries to determine the population trajectory. The model was fitted to eleven estimates of pup production beginning in 1952, including two survey estimates of 2008 pup production, by adjusting the initial pup production size and estimates of adult mortality. Juvenile mortality was fixed at three times adult mortality rates. Fitting the model to the low estimates of 2008 pup production resulted in an estimated pup production in 2009 of 1,113,900 (95% CI=968 400 to 1,268 100) while total population size was 6 851 600 (95% CI=5 978 500 to 7,697 200). When the data are fitted to the high 2008 survey estimate, the estimated pup production increased to 1,316,000 (95% CI=1,090,200- 1,524,100) and the total population increased to 8,238,500 (95% CI=6,774,300 to 9,540,300), but the fit to the data was poor. The model fit to the high estimate of pup production was improved if we assumed reproductive rates in 2008 were the same as those observed in 1970. 

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