Spatial patterns in activity of leopard seals Hydrurga leptonyx in relation to sea ice

Abstract

Rapid changes to climate in the western Antarctic Peninsula region over the last 50 yr, which have led to decreases in the extent and duration of sea ice, are likely to have significant impacts upon the Antarctic ecosystem as a whole. Understanding the behaviour of higher trophic level animals occupying these regions is important, as they may be indicators of changes in prey availability and food-web structure. Leopard seals Hydrurga leptonyx are important components of the Antarctic ecosystem, because they are widespread and adapted to consuming prey at a range of trophic levels. They rely on sea ice for breeding, moulting and as a resting platform. Using tracks of 12 leopard seals, we calculated first-passage times (indicative of the intensity of area-restricted behaviour) and quantified relative habitat use, including both foraging and resting areas, using Cox proportional hazard models, in relation to coastline, bathymetry and sea ice. We also correlated monthly home range size with monthly sea-ice extent. We found that when sea-ice extent was low, leopard seals were restricted to coastal habitat, but that this effect was lost when sea-ice extent was greater. This was supported by the finding that leopard seal home range size decreased as the sea-ice extent decreased. Since leopard seals and other animals that consume krill are likely to be increasingly limited by sea-ice cover if the warming trend continues, we suggest that the krill fishery be restricted to offshore areas to avoid conflict with krill predators.