MEPS 605:207-223 (2018)  -  DOI: https://doi.org/10.3354/meps12745

ABSTRACT: The little auk Alle alle is the most abundant seabird in the North Atlantic, and >80% of the global population breeds along Greenland’s shores of the North Water (NOW) polynya region. We questioned why the NOW is such an important little auk breeding area, and hypothesized that the key factor may involve chick feeding opportunities. We studied the oceanography, and the distribution and abundance of little auks and their zooplankton prey between 73 and 78.5°N in August 2015, and concurrently sampled little auk chick diets. Zooplankton in the diet were dominated by Calanus hyperboreus and C. glacialis, but biomasses, community compositions and depth distributions differed across the latitudinal range. Little auk chicks were mainly fed Calanus spp. between 3 and 5 mm. Within the foraging range of the breeding colonies, areas where phytoplankton was concentrated in patches in the water column were important for the foraging distribution of little auks, and increasingly so at shorter distances from the colonies. In the NOW region, in contrast to other areas in Baffin Bay, high abundances of large Calanus spp. are present within little auk diving range both in spring/early summer and in late summer during the little auk chick-rearing period. We conclude that this unusually long and continuous presence of suitable prey items in the surface waters, covering the full little auk breeding cycle, is the main reason why the NOW region, under current climate conditions, is the most important little auk breeding area globally.

KEY WORDS: Little auk · Alle alle · Zooplankton · Phytoplankton · Arctic · Calanus · Baffin Bay · North Water polynya