Bowhead Whale Feeding in the Western Beaufort Sea; Oceanographic Conditions, Whale Prey Distribution and Whale Foraging Behavior

Carin Ashjian and Mark Baumgartner, Woods Hole Oceanographic Institution

The Beaufort Sea Shelf is a critical feeding area for migrating bowhead whales, particularly during the fall migration from their summer grounds in the Canadian Arctic to their overwintering grounds in the northern Bering Sea (e.g., Lowry et al., 2004). The present proposal is a component of the larger “Bowhead Whale Feeding in the Western Beaufort Sea” project coordinated by the National Marine Mammal Laboratory. The proposed work will describe relationships between the formation and distribution of bowhead whale prey (zooplankton) aggregations, oceanographic conditions, and bowhead whale distributions and feeding behavior (e.g., diving patterns relative to prey distribution) in the Western Beaufort Sea by deploying oceanographic moorings, by conducting oceanographic sampling on both the coarse (shore-shelfbreak) and fine (on the shelf, near feeding bowhead whales) scales and by tagging feeding bowhead whales for periods of hours to describe foraging and feeding behavior relative to prey distributions. Results from biophysical sampling conducted during August- September 2005-2009 demonstrated that the oceanography of the Beaufort Shelf is complex, dynamic, and highly variable both interannually and on shorter time scales (days-weeks) and that advection is closely coupled to the direction and magnitude of the winds. These results also demonstrated that oceanographic and atmospheric conditions impact the composition, distribution, and availability of plankton prey for the bowhead whale. Sampling will be conducted on the Beaufort Sea shelf from Barrow, AK east to ~154 °E during mid-August to mid-September 2010. High vertical-resolution oceanographic sampling using a 43’ boat will be conducted along several shore-shelfbreak transects; whale prey distributions also will be determined along the transects. Finer scale oceanographic and prey sampling adjacent to feeding bowhead whales, and to tagged feeding whales, will be conducted using two boats (43’ and 32’). Whale tagging and tracking will be conducted simultaneously using a third, smaller (20’) boat. Oceanographic moorings will be deployed seasonally to monitor shelf-slope exchange events that are believed to influence the availability of zooplankton on the shelf and lagoon-shelf exchange events that appear to influence the near-shore distribution of zooplankton. Ultimately, these observations will lead to a greater understanding of the shelf environment as well as providing important ground-truth for modeling and predictive efforts. Such information is critical to development of mitigation strategies associated with potential future oil and gas development and with anticipated increases in vessel traffic in this region.