Seasonal sea ice dynamics drive movement and migration of juvenile bearded seals Erignathus barbatus

Abstract

We analyzed how juvenile bearded seals Erignathus barbatus use and move through sea ice and consider how future ice conditions might affect bearded seal distribution and behavior. In October 2004, 2005, 2006, and 2009, we tagged 29 (16 female and 13 male) juvenile (0-2 yr old) bearded seals with Argos satellite transmitters in Kotzebue Sound, Alaska, USA, who then freely moved through the Chukchi and Bering Seas. Movement data were initially analyzed using behavior discriminating state-space models. These results were subsequently analyzed with mixed-effects models to relate inferred behavioral state to environmental variables (sea ice, water depth, season, distance to ice edge) and then with a modified resource selection function using the same environmental variables. Sea ice concentration was highly predictive of use, but had a non-linear effect, with seals preferring intermediate concentrations and areas closer to the ice edge (defined here as 15% sea ice concentration). Behavior was also affected by sea ice and other environmental conditions. When seals were in dense sea ice, they were likely to express an encamped movement pattern; when in open water or sparse ice, they tended to express transiting behavior. The seasonal migratory behavior of bearded seals, at least in juveniles, appears to result from tracking the sea ice edge as it seasonally expands and recedes over the Bering and Chukchi continental shelves. The association with the ice edge suggests that bearded seal habitat will shift as the climate warms.