Spatial behaviour of a keystone Arctic marine predator and implications of climate warming in Hudson Bay

Abstract

Climate change has led to briefer winter ice-cover and reduced snow depth in Hudson Bay. These conditions have been linked to increased mortality of both polar bear cubs and their ringed seal prey. In ringed seals, increased mortality may be due to changes in foraging and movement patterns around sea ice, and how these animals interact with and move through sea ice may explain why deteriorating ice conditions are affecting survival. To investigate, we analysed the movement and space use of Hudson Bay ringed seals using a switching state-space model to discriminate at-sea behavioural state from satellite-observed movements followed by a series of mixed-effects models to understand how sea ice concentration, age, and sex affect at-sea behaviour. Our analysis revealed a strong annual cycle, whereby the probability of resident movement behaviour increased through the open-water period (summer and fall), reaching its maximum in the fall when sea-ice begins to reform. This tendency then declines through the ice-covered period (winter and spring), reaching a minimum as ice breaks up. Cyclical behaviour was more pronounced in adults, which restricted movements to a greater extent than juveniles during the winter ice-covered period, consistent with predictions of mammalian life history. Consequently, reduced stable fast ice area and less predictable ice conditions associated with climate change should be expected to have a disproportionately larger effect on adults, potentially reducing their ability to accrue resources for reproduction or produce milk for dependant pups. Furthermore, we found large sex-related differences in behaviour in this monomorphic species, suggesting that changing ice conditions may impact one sex more strongly. This finding also implies that similar behavioural differences in sexually size-dimorphic species may be explained by sex-related life history trade-offs associated with the reproductive strategies of each sex and not necessarily body size differences.