Research Document 2023/063
Abundance estimate of the Hudson BayDavis Strait walrus (Odobenus rosmarus rosmarus) stock from aerial surveys flown in September 2017
By Mosnier, A., Matthews, C.J.D. and Hammill, M.O.
Abstract
From September 1st to 17th, 2017, three planes conducted an aerial photographic survey to estimate the abundance of walrus from the Hudson Bay–Davis Strait stock (HBDS). Most of the distribution range of this stock was covered, including the eastern, southern and southwestern coasts of Baffin Island, Hudson Strait, Southampton Island and the northwestern coast of Hudson Bay. A total of 13,375 walrus were counted within the HBDS distribution area, including 1,179 individuals along the east coast of Baffin Island and 12,196 in Hudson Strait and northern Hudson Bay. Correcting raw counts using the mean proportion of hauled out animals obtained from the literature (P = 0.3) resulted in an abundance estimate of 44,582 animals (95% CI = 19,485–102,004). This abundance estimate is considerably larger than the estimate of the last survey conducted in 2014 (i.e., 7,100 animals [95% CI = 2,500–20,400]). However, the 2014 survey coverage did not include the HBDS range along the east coast of Baffin Island and part of northwestern Hudson Bay overflown in 2017. Considering only the area in common between the two surveys still results in a large difference, with 11,554 walruses detected in 2017 and a population estimate of 38,514 (95% CI = 15,091–98,290) individuals. Walrus haulout behaviour and possible exchange from other stocks/regions (e.g., Foxe Basin) are among the hypotheses proposed to explain this difference.
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