Alaskan Seabird Die-Offs

Abstract

Prior to 2015, seabird die-offs in Alaskan waters (Northern Gulf of Alaska, eastern Bering Sea, eastern Chukchi Sea) were rare, typically occurred in mid-winter, and were linked to epizootic disease events (Bodenstein et al., 2015) or above-average ocean temperatures associated with strong El Nino-Southern Oscillation events. An exception was late summer of 1997, a year with unusually warm waters in the southeastern Bering Sea, when possibly as many as 10% of the several million short-tailed shearwaters (Ardenna tenuitortris) present in the area died of starvation because their principal prey, euphausiids, were scarce or hard to find in a widespread coccolithophore bloom (Baduini et al., 2001). Since 2015, such mass mortality events have been annual occurrences. In 2015, between 470,000 and 1.03 million common murres (Uria aalge) were estimated to have died in the Gulf of Alaska due to anomalous ocean conditions and the impacts on forage fish associated with the 2014–2016 Pacific marine heatwave (Piatt et al., 2020; Arimitsu et al., 2021). Another large die-off event occurred during late summer of 2019 (Figure 1), when over 10,000 carcasses of short-tailed shearwaters washed onto beaches of Bristol Bay and the Alaska Peninsula in the southeastern Bering Sea. Total mortality during that summer was likely much greater than reported given the region’s expansive coastline and sparse human population.