Abundance of ice-associated seals in the eastern Bering Sea in spring of 2012 and 2013

Résumé fourni par la source

Ice-associated seals in the Arctic are of conservation concern because of declines in spring sea ice extent, but are difficult to study given their remoteness and expansive range. In 2012 and 2013, we used a combination of thermal imaging and digital photography to study the abundance and distribution of 4 species of seals (ringed seals Pusa hispida; bearded seals Erignathus barbatus; spotted seals Phoca largha; and ribbon seals Histriophoca fasciata) from aircraft in the eastern (U.S.) Bering Sea. Applying species distribution models that account for zero inflation, overdispersion, incomplete detection, and species misclassification, we estimated that the abundance of each species in 2012 was 489,720 ringed seals, 270,842 bearded seals, 289,962 spotted seals, and 69,602 ribbon seals. In 2013, abundance was estimated as 356,656 ringed seals, 251,451 bearded seals, 133,685 spotted seals, and 25,215 ribbon seals. Spotted and ribbon seal estimates for 2012 were sensitive to model assumptions, with spotted seal estimates potentially subject to extrapolation bias, so those estimates should be treated with caution. We used conservative decisions when modeling ringed seal haul-out and denning behavior, which may have biased our estimates downward; these decisions may need to be refined in the future if additional behavior data are gathered in the Bering Sea. We are unable to determine whether decreases in abundance estimates between 2012 and 2013 for all four species represent true decreases in abundance, substantial changes in availability (i.e., proportion of seals basking on ice), or poor estimation in 2012 for ribbon and spotted seals. However, apparent decreases are concerning because they coincide with an unusual mortality event from 2011-2016 and because similar decreases were observed in 2012-2013 surveys in Russian Federation waters of the western Bering Sea.

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