Spatial overlap among an Arctic predator, prey and scavenger in the marginal ice zone

Conducting multi-species studies is important when assessing current ecosystem state and predicting climate change impacts, as altered biological interactions can affect the wider ecosystem. The marginal ice zone (MIZ, transition zone between the sea ice edge and areas with complete sea ice coverage) is an important foraging area for Arctic marine mammals and seabirds. The location of the MIZ has shifted northwards over the last decades due to sea ice declines. Many ringed seals Pusa hispida, polar bears Ursus maritimus and ivory gulls Pagophila eburnea travel from Svalbard, Norway, to the MIZ to forage during summer and autumn. These species are trophically linked: ringed seals are the primary prey of polar bears and ivory gulls scavenge on polar bear kills. Biotelemetry data (ringed seals [n = 10]: 2010-2012; polar bears [n = 24]: 20072014; ivory gulls [n = 29]: 2010-2013) were used to characterize the MIZ habitats of these species and to identify areas of overlap. Individuals from all 3 species travelled long distances to forage in the MIZ, with maximum distances for each species exceeding 1400 km. All 3 species selected areas with sea ice concentrations between 40 and 80%. The highest spatial overlap between August and October for this species assemblage occurred slightly north of the 50% sea ice contour, with the precise location and density of overlap varying monthly and inter-annually in relation to the location and breadth of the MIZ. Further northward retreat and the potential total disappearance of the MIZ (in summer) is likely to have serious consequences for the distribution, abundance and trophic relations among these ice-obligate species.