Seasonal Diet of Eastern Arctic Bowhead Whales (Balaena mysticetus) Determined Using Stable Isotope Signatures in Baleen

Bowhead whales (Balaena mysticetus) in the eastern Canadian Arctic migrate seasonally between Hudson and Davis Straits in winter to northwestern Hudson Bay/Foxe Basin and Gulf of Boothia in summer. Changes in Arctic sea-ice patterns due to climate change may affect the timing and range of eastern Arctic bowhead whale migrations through seasonal or regional shifts in prey (zooplankton) availability. However, limited information about eastern Arctic bowhead whale ecology and habitat use restricts our ability to identify and address threats posed by Arctic climate change. Chemical signatures in baleen provide a means to study eastern Arctic bowhead whale ecology and habitat use. Baleen grows continually and is biochemically inert once formed, so dietary changes over short time increments are recorded in its stable isotope composition (Lee et al 2005). Zooplankton δ¹³C and δ¹⁵N differ across the eastern Arctic due to underlying geological processes, so δ¹³C and δ¹⁵N deposited in baleen can be used to assess the relative importance of different foraging regions. In 2009, we measured δ¹³C and δ¹⁵N along plates of seven eastern Arctic bowhead whales, and found evidence for annual oscillations in both δ¹³C and 15N. Annual δ¹³C oscillations typically differed by less than 1°, but the magnitude varied from year to year. Annual δ¹⁵N oscillations were more consistent than δ¹³C oscillations, and typically differed by 0.5-1°. The magnitude and patterns of annual oscillations varied among individuals and could be due to seasonal fasting (e.g. enrichment in δ¹⁵N resulting from protein catabolism) or feeding in locations across their annual range with different isotopic signatures. Further interpretation of isotope ratio patterns in baleen will enable assessment of seasonal feeding patterns and habitat usage as it relates to seasonal sea ice conditions.