Date of Award

5-17-2024

Document Type

Thesis

Abstract

Izembek Lagoon, located in the Alaskan southern Bering Sea, is designated as critical molting and wintering habitat for the Alaska-breeding population of Steller's eiders (Polysticta stelleri), listed as Threatened under the United States Endangered Species Act. During the nonbreeding season, the lagoon also hosts a large proportion of the Pacific population of Steller's eiders that nest along the coast of northeastern Russia, and the lagoon is an important stopover site for many other species of migratory water birds. Since the early 1980s, there has been a decline of Steller's eiders in their known nonbreeding range in the southern Bering Sea, but especially in Izembek Lagoon during their remigial molt in the fall. The cause of this decline is unknown; however, in recent years, higher sea temperatures have been observed in Izembek Lagoon and warming ocean temperatures have been associated with shifts in benthic community structure elsewhere. If forage conditions are less favorable in Izembek Lagoon, Steller's eiders may need to redistribute to other locations, or the population at Izembek Lagoon may decline due to reduced survival. To determine if forage conditions have changed, we replicated a 1998 benthic sampling effort in fall of 2018 and 2019 to understand if prey availability has become less favorable to Steller's eiders during their molt in Izembek Lagoon. We compared forage conditions based on the relative biomass (%), overall biomass (g/m2), and size (mm) of organisms belonging to the marine benthic groups: Bivalvia, Gastropoda, Crustacea, and Polychaeta between the two time points. The results suggest a shift in these taxa with an associated change in their biomass and size. The community shifted from being dominated by bivalves in 1998 to more predominantly polychaetes in 2018 and 2019. In addition to a significant reduction of bivalve and crustacean biomass in 2019 as compared to 1998 (p = 0.04, p = 0.02, respectively), bivalves and gastropods were significantly smaller (p < 0.01, p < 0.01, respectively). The decline of Steller's eiders' use of this critical habitat may reflect shifting benthic prey availability. As it has been suggested that Steller's eiders may prefer hard-shelled prey (e.g., bivalves, gastropods) and larger sized bivalves during the molt period specifically, contemporary foraging conditions at Izembek Lagoon may be less favorable or insufficient for supporting historical numbers of Steller's eiders during an energetically taxing time in their annual cycle. Therefore, the molting Steller's eider population at Izembek Lagoon may have difficulty recovering to historical numbers if available forage conditions are of inadequate quality and abundance.

Handle

http://hdl.handle.net/11122/15158

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