Research Document 2023/062

How many walrus are there in the Hudson Bay Davis Strait stock?

By Hammill, M.O., Mosnier, A. and Matthews, C.J.D.

Abstract

A Bayesian surplus production model was fitted to aerial survey estimates of abundance (n = 10) and reported harvests of walruses from the Hudson Bay-Davis Strait (HBDS) stock from 1954–2017. Model fit was poor, owing to the high abundance estimate resulting from the most recent survey conducted in 2017. Modelling exercises to explore possible reasons for the high estimate in 2017 included higher than assumed proportion of animals hauled out during the survey, as well as an influx of animals moving into Hudson Bay and Hudson Strait from neighbouring regions. Model fit improved when the possibility of mixing of animals between the HBDS and Foxe Basin management stocks was considered, and when the assumed proportion of animals hauled out was increased from 0.3 to 0.8. The survey abundance estimate from 2017 likely reflected one or a combination of these factors. The model-derived abundance estimate for the northern Hudson Bay-Strait component of the stock was 8,200 (95% CI = 5,800–19,700). Adding this to the survey-estimated abundance for walruses along the east coast of Baffin Island (3,900; 95% CI = 2,200–7,200), for which a sufficient time series of abundance estimates for population modelling was unavailable, provided a total HBDS stock abundance estimate of 12,200 (95% CI = 7,000–20,800) in 2017. The estimated potential biological removal (PBR) using this estimate and a recovery factor of 1 was 360 animals. The total annual removal through hunting, after adjusting reported catches for struck-and-loss and non-reporting, is estimated at 137 animals for the HBDS stock.

Key words: walrus, Odobenus rosmarus, abundance, Nunavik, Nunavut, harvest.

Research Document 2023/062 (PDF, 1,107 KB)

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