Challenges for ice-associated top trophic Arctic animals in a changing climate

Abstract

The Arctic is currently in a rapid state of change, with temperature increases in this region being three times the rate of the global average and sea-ice extent declining rapidly. In 2006, a sudden shift in the sea-ice regime in Svalbard, Norway, occurred with the altered sea-ice conditions persisting to the present day. In order to study the impacts of the environmental changes occurring in the Svalbard region, the movement patterns, behaviour and degree of spatial overlap for ringed seals (Pusa hisapida, n=60), polar bears (Ursus maritimus, n=160) and ivory gulls (Pagophila eburnea, n=40) were investigated using data from biotelemetry devices equipped on these species before (2002-2004; ringed seals and polar bears) and after (2010-2013; all three species) the shift in the sea-ice regime occurred. These three species are trophically linked; ringed seals are the primary prey of polar bears and ivory gulls scavenge on polar bear kills. Coastal ringed seals and ringed seals that took offshore foraging-migration trips had an increase in foraging effort and thus energetic costs and also a change in foraging behaviour following the sea-ice collapse, indicating that alterations in their prey base have occurred throughout the Svalbard region. Coastal polar bears spent less time in front of tidal glacier fronts in the summer (Jun-Aug) after the sea-ice collapse, leading to a significant decrease in spatial overlap between coastal polar bears and ringed seals. Following the sea-ice collapse, coastal polar bears moved greater distances per day in the summer and spent more time close to ground-nesting bird colonies, indicating increased predation on terrestrially-based prey sources. Offshore polar bears, ringed seals and ivory gulls travel to the Marginal Ice Zone (MIZ) of the Barents Sea in the summer and autumn to forage. All three species preferred areas with sea-ice concentrations between 40-80%. The main spatial overlap areas for this species assemblage occurred slightly north of the 50% sea-ice contour. The predicted seasonal disappearance of the MIZ and the continued retreat of tidal glacier fronts will have consequences for the growth, distribution and abundance of ringed seals, polar bears and ivory gulls in Svalbard. The effects on each of these ice-obligate, top trophic Arctic animals and the resultant changes in biological interactions will have ramifications for the wider Arctic marine and terrestrial ecosystems.