Bowhead Whale Feeding in the Western Beaufort Sea: Oceanographic Conditions, Whale Prey Distributions, and Whale Feeding and 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 (shoreshelfbreak)
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. A companion project funded by the NSF through the Arctic Observing
Network program will document interannual variability in biological and physical ocean
conditions across sentinel transects that extend from the nearshore across the Beaufort Shelf to
deep water and across Barrow Canyon. Results from biophysical sampling conducted during
August-September 2005-2010 demonstrated that the oceanography of the Beaufort Shelf is
complex, dynamic, and highly variable both interannually and on shorter time scales (daysweeks)
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 2011. 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 nearshore
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.