High-arctic seabird trophic variation revealed through long-term isotopic monitoring

Arctic ecosystems are especially vulnerable to anthropogenic influences including increasing contaminant levels and climatic change. To predict effects of these changes, it is important to understand trophic relationships of arctic organisms and how they change in response to environmental perturbations, especially those involving changes in sea-ice extent. We investigated feeding ecology of four seabird species, Thick-billed Murres (Uria lomvia), Northern Fulmars (Fulmarus glacialis), Black-legged Kittiwakes (Rissa tridactyla) and Glaucous Gulls (Larus hyperboreus), at Prince Leopold Island, Nunavut, 2000-2003, and 2008, using stable isotope measurements to indicate relative use of benthic or pelagic foodwebs (delta C-13) and relative trophic level (delta N-15). Trophic level and carbon source differed among years for all species and were related to differences in foraging strategies caused by variation in sea-ice conditions. Northern Fulmars, long-distance foragers, showed the least variation in either trophic level or foraging location among years. Kittiwakes, restricted to foraging near the surface, decreased in trophic level when ice cover was light. Murres, with the most flexible foraging techniques, were most varied in foraging location and trophic level across years. Stable isotope values of Glaucous Gull nestlings closely tracked those of their (seabird) prey species. In 2002, a year of extensive ice cover and poor breeding success for all species, only Murres showed a concurrent decrease in the estimated proportion of fish in their diet. Further analysis of 2002 data showed Murre and Kittiwake body mass and trophic level were correlated. We suggest that, in this system, ice plays an important role in prey availability with a lag of 1-2 years but effects vary with species.