Recent Changes in Benthic Prey Populations in Relation to Gray Whale Feeding in the Pacific Arctic

The shallow continental shelves of the Pacific Arctic are currently experiencing a rapid decline in seasonal sea ice cover as seawater temperatures warm. The tight coupling between water column production and the underlying benthos in spring and summer in this region earmarks benthic macrofauna, such as amphipods and bivalves, as important components of ecosystem biomass that are efficiently used by upper trophic level benthic foragers, such as gray whales, walrus, and sea ducks. Recent documented changes in crustacean macrofaunal species (e.g., amphipod, cumacean, and isopod) abundance and biomass over the shallow continental shelf of the northern Bering and Chukchi Seas, an area of known foraging for the benthic-feeding Pacific gray whale, may be related to the recent observations of increased dead gray whales throughout their range. Whether these whales were impacted by changing (and declining) benthic prey and/or newly emerging environmental stressors such as harmful algal blooms is uncertain, but our 30-year time-series of benthic data in the Pacific Arctic indicate a decline in the spatial extent and biomass of the amphipod communities that gray whales historically fed on in the northern Bering Sea. For example, data from a subset of 4 time-series (1999-2015) sites in the northern Bering Sea, between St. Lawrence Island and Bering Strait, show that 3 of the 4 sites are clearly declining in crustacean biomass (Sen’s Medium Slope statistic from -0.18 to -13.39 gC/m2/decade). However, gray whales commonly forage in the Chukchi Sea and sometimes the Beaufort Sea, where other species of amphipods and crustacean species occur, albeit at lower biomass. This presentation will describe attributes of benthic prey communities for gray whales that have been sampled from the 1980s up to 2019 in known gray whale feeding areas in the Pacific Arctic.