Estimations de l'abondance et du prélèvement biologique potentiel (PBP) pour les stocks de gestion du morse de l'Atlantique dans le Haut-Arctique du Canada, été 2022

Abstract

Coastal photographic aerial surveys of the High Arctic Atlantic walrus (Odobenus rosmarus rosmarus) population were conducted during the latter half of August 2022. Counts of walruses hauled out at terrestrial sites and on ice were used to estimate abundances of the three High Arctic walrus management stocks: Penny Strait-Lancaster Sound (PS-LS), West Jones Sound (WJS), and Baffin Bay (BB). Two fixed-wing aircraft (Twin Otter) flew simultaneously along coastlines encompassing the summer ranges of the PS-LS and WJS stocks and summer core use areas of the BB stock. Two independent surveys of both the PS-LS and WJS stocks were completed, and three surveys of the BB stock were completed. Total haulout counts (including walruses on sea ice) for the PS-LS stock were 266 and 495 (August 13-16 and 24-27), 347 and 656 for the WJS stock (August 17-18 and August 22), and 254, 3, and 6 for the BB stock (August 7, 16, and 26). Adjusting counts for availability bias using a previously published mean proportion of hauled out animals (p = 0.3) produced abundance estimates of 887 (95% confidence interval [CI] = 475–1,653) and 1,650 (95% CI = 696–3,909) for the PS-LS stock; 1,157 (95% CI = 618–2,166) and 2,187 (95% CI = 1,132–4,224) for the WJS stock, and 847 (95% CI = 254*–3,286), 10 (95% CI = 3*–44), and 20 (95% CI = 6*–83) for the BB stock. Higher counts for the PS-LS and WJS stocks during their second respective surveys may reflect transitioning of walruses from melting sea ice onto terrestrial haulouts or possibly an influx of walruses from the BB stock, for which counts were negligible over the same period. Using a distance/time criterion of 45 km/day, BB walrus could not have crossed into adjacent stock boundaries ~ 600-1,000 km away between August 7 and the first PS-LS and WJS surveys (August 13-18), but could possibly have covered those distances in the period leading up to the second surveys from August 22-27. Fuel closures also prevented some coastal areas of Ellesmere Island from being surveyed, introducing potential negative bias in BB stock counts. Potential Biological Removal (PBR) estimates were based on abundance estimates from the first surveys of each stock due to uncertainty regarding walrus movements among stocks during subsequent surveys, equaling 7 walruses for the PS-LS stock, 9 walruses for the WJS stock, and 5 walruses for the BB stock.