Ecological shift from piscivorous to planktivorous seabirds in the Chukchi Sea, 1975-2012

Sea ice now forms later and melts earlier than it did 4 decades years ago, and it now melts completely in all parts of the Chukchi Sea. This decline in sea ice is expected to have repercussions on the trophic structure in this environment, and there are indications that changes already have taken place in the seabird community. We compared boat-based densities of seabirds in the eastern Chukchi Sea between July and October during 1975-1981 (historical data) with densities during 2007-2012 (recent data). We related the composition of the seabird community to sea-ice cover to explore how the community may be responding to changes in oceanography. The seabird community historically was composed predominantly of piscivorous Black-legged Kittiwakes (Rissa tridactyla) and murres (Uria spp.). In contrast, the seabird community now is composed predominantly of planktivorous seabirds such as Crested Auklets (Aethia cristatella) and Short-tailed Shearwaters (Puffinus tenuirostris). Total abundance of seabirds declined in three of four strata in the eastern Chukchi Sea, largely due to declines in densities of piscivorous and omnivorous species. These changes in the abundance and community composition of seabirds were associated with changes in ice cover. Earlier ice retreat appears to contribute to an environment that is more favorable to the sustained production of large oceanic copepods and euphausiids. We propose that long-term changes (4 decades) in the abundance and composition of the seabird community reflect an increase in the availability of large zooplankton prey in the region.