Seabirds Signal a Changing Pacific Arctic

Alterations of the Northern Bering-Chukchi Sea ecosystem affect upper trophic levels such as seabirds, which can serve as indicators of ecosystem function. Using at-sea seabird surveys totaling >150,000 km of transects from 2007–2018, we examined trends in their abundance and distribution with respect to other seabird studies and environmental conditions. Planktivorous auklets that nest in the Northern Bering Sea (NBS), and shearwaters (which nest in the southern hemisphere) numerically dominate the avifauna, but only piscivorous seabird species nest in the Chukchi Sea (CS). In the CS, cross-community Mantel correlations found associations between planktivorous seabirds and zooplankton, but not between piscivorous seabirds and fishes, perhaps due to the influence of colony location on breeding seabirds. Persistent habitat (or site) features, in general, influenced distribution more than annual environmental conditions, with exception of late summer migrants. However, in 2017-2018, with warm seas and changes in the prey base, abundance of some locally breeding seabird species were below long term means. Planktivorous auklets increased in the NBS and decreased in the CS, suggesting that unlike in previous years, there was little post-breeding movement into the CS to forage; breeding attempts were also low at NBS colonies. These observations corresponded to a large biomass of small copepods in the NBS and lack of large copepods in the CS. In 2017-2018, piscivorous murre and kittiwake densities at sea were well below the long term mean in the NBS, and nesting attempts were few or failed, but abundance and productivity of these species varied in the CS. Seabird mortality events, with birds emaciated, occurred in the NBS and CS in 2017-2018. Together, the seabird’s low abundance, low reproductive success, and mortality events, signal environmental stress. Detrimental effects were more prevalent in the NBS, but effects on both planktivorous and piscivorous seabirds throughout the NBS-CS region suggest impacts at multiple trophic levels.