Cooperative Institute for Research in Environmental Sciences

Is retreating Arctic sea ice affecting the body condition of bowhead whales?

Matthew L. Druckenmiller (1) and J. Craighead George (2)

(1) CIRES Visiting Postdoctoral Fellow, CIRES, University of Colorado Boulder (2) North Slope Borough Department of Wildlife Management, Barrow, AK

Recent studies suggest that Arctic summer sea ice retreat may drive increased phytoplankton blooms in the Arctic Ocean, which may in turn promote greater zooplankton production. Zooplankton provides an important food source to bowhead whales (Balaena mysticetus), which are migratory ice-associated baleen whales that spend summer in Arctic waters, including the eastern Beaufort Sea. Thus, do summer sea ice conditions affect the health of bowhead whales by influencing food availability? Alaska’s North Slope Borough Department of Wildlife Management has collected body-condition measurements (girth, length, and thicknesses of blubber and hypodermis) from bowhead whales of the Western Arctic Stock harvested by Inupiat subsistence hunters since the early 1970’s. In this study we investigate relationships between summertime ice severity and bowhead whale body condition from 1979 to 2011. We examine monthly averaged sea ice concentration from SMMR and SSM/I passive microwave data for the summer months of June through September within different feeding areas in the Beaufort Sea. Whale age, sex, and pregnancy status are considered. Preliminary analysis suggests that the body condition of juvenile whales may be more responsive to variability in ice conditions than that of adults. Additional investigations may include analysis of (1) satellite derived ocean color using Chl-a as an indicator for phytoplankton biomass, and (2) a time- and regionally-weighted sea ice severity index that not only considers ice conditions of the previous summer but rather ice concentration over a preceding three-year period across the whale’s entire migratory habitat of the Bering, Chukchi and Beaufort Seas.