Apparent bottom feeding by humpback whales on Stellwagen Bank

Humpback whales, Megaptera novaeangliae, on Stellwagen Bank off eastern Massachusetts, U.S.A., apparently bottom feed on northern sand lance, Ammodytes dubius. The feeding behavior is characterized by the whales brushing the bottom in depths of less than 40 m, causing sand lance burrowed in the bottom to be flushed up into the water column. The greatest densities of sand lance were in beds of shells and shell debris, termed “shell hash.” The brushing against or along the bottom, particularly in these shell hash areas, caused the humpbacks to acquire abrasions and wounding, sometimes rather extensive, of the lateral lower jaw, and lateral and dorso-lateral upper jaw, here termed “jaw scuffing.” Scuffing of the dorsal fin and fluke edges was also common and may be at least partially related to this feeding behavior. Both mature and immature, and male and female, humpbacks exhibited jaw scuffing. The bottom-feeding behavior was not exclusive, as jaw-scuffed individuals were also observed to use other feeding behaviors. In recent years (1991-1993), however, bottom feeding appears to have become relatively more common, particularly among young animals. Overall, in the Stellwagen Bank area between 1979 and 1993, a majority of the population engaged in, or had engaged in, bottom feeding and the associated prey flushing.

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