Abundance and distribution of ringed and bearded seals in the Chukchi Sea: a reference for future trends

Abstract

Ringed (Pusa hispida) and bearded (Erignathus barbatus) seals are vulnerable to decreasing sea ice habitat in the rapidly warming Arctic. In April and May 2016, we conducted an aerial survey over the ice-covered areas of the Chukchi Sea using thermal and color cameras to detect and count these seals on sea ice. We related seal counts to environmental variables, and used the relationships to estimate the species’ distributions and abundance. We accounted for incomplete detection due to: seals missed by sensors or image processing errors; behavioral responses to aircraft; or incomplete availability (seals in the water or in snow dens on the ice, called lairs). To our knowledge, this is the first abundance estimate that accounts for use of lairs by ringed seals. We estimated there were 592 577 (95%, 478 448–733 929) ringed seals and 147 421 (95%, 114 155–190 380) bearded seals in the Chukchi Sea. The influence of remotely sensed environmental variables, such as snow depth and ice type, was consistent with the species’ natural history, particularly ringed seals’ need for snow of adequate depth for lairs. Our study provides the first comprehensive abundance estimates for these seals in a large portion of their ranges and establishes a reference for monitoring how their populations respond to Arctic warming.

Keywords

• Beringia
• wildlife remote sensing
• infrared imaging
• Phoca hispida
• shorefast ice
• snow on sea ice