Sea ice influence on male polar bear survival in Hudson Bay

Abstract

Environmental variability and seasonality of resources influence species distribution and demographic parameters such as survival. We quantified the spatiotemporal dynamics of sea ice that remains in Hudson Bay during breakup (remnant ice) and assessed relationships with apparent survival for three age classes of male polar bears (Ursus maritimus Phipps, 1774): subadult (1-4 years), prime age (5-19 years), and senescent (≥20 years) captured in western Hudson Bay in 1980-2019. The distribution of remnant ice varied between years, and we identified ice-related covariates that were correlated with the occurrence of transients (prime age males only captured once) and male apparent survival. Apparent survival declined by 11% for prime age males and declined by 17% for senescent bears for earlier retreat dates within Hudson Bay. Subadult apparent survival was reduced by 9% when remnant ice occurred in the east compared to the western half of Hudson Bay. Transients in our capture sample increased from 10% to 28% when remnant ice occurred within 50km of our study area. Our results suggest that spatiotemporal distribution of male polar bears was related to the spatial distribution of remnant ice across Hudson Bay and had important impacts on estimating apparent survival and may have implications for assessing population status.