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Research Document 2021/006

Trends in abundance of harp seals, Pagophilus groenlandicus, in the Northwest Atlantic, 1952-2019

By Hammill, M.O., Stenson, G.B., Mosnier, A. and Doniol-Valcroze, T.

Abstract

Harp seals require pack ice as a platform for resting, to give birth and nurse their young. They are also subject to commercial and subsistence harvesting. We examined the status of the Northwest Atlantic harp seal population using a three parameter population model that fits to estimates of pup production and reproductive rates, and incorporates information on annual catches in Canada and Greenland (including by-catch and struck and lost), and unusual pup mortality due to poor ice conditions. After applying the model formulation used during previous assessments, the fit to the reproductive data and aerial survey data was poor. Using an alternative formulation where adult mortality was fixed and juvenile mortality estimated, and a Comprehensive Environmental Index used to vary the population carrying capacity, improved the model fit to the data. Based upon a population model that included pup production estimates up to 2017, annual estimates of age-specific reproductive rates, removals and ice related mortality up to 2019, the harp seal population appears to have been relatively stable since the mid-1990s, but has been increasing in recent years likely due to higher reproductive rates and lower removals. The model estimated a pup production of 1,039,000 (95% CI 927,000 - 1,100,000) animals and a total population size of 6.8 (95% CI 5.8 - 8.0) million animals in 2017. Projecting forward to 2019, the model estimated that the population increased to 7.6 (95% CI 6.6 - 8.8) million harp seals. Climate change is having an impact on ice-cover, particularly in the Gulf of St Lawrence, but even the northeast Newfoundland area is expected to be ice-free by the end of the century. This will have a negative impact on harp seals unless new areas for pupping are found to the north of current whelping areas.

Key words: harp seal, Pagophilus groenlandicus, abundance, juvenile survival, environmental index, Northwest Atlantic

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