10.1016/s0967-0653(98)81617-7

From the mid-1970's to the mid-80's, Stellwagen Bank was an important humpba<:k whale feeding area with sand lance (Ammodytesspp.) as the major prey. Between 1988 and 1994. however, the number of hump­ back whales we identified each year on Stellwagen declined from a high of258 (1990) to 7 (1994), and the mean num­ ber of whales identified per day fell from 17.7 (1988) to 0.9 (1994). Adult whales decreased steadily after 1988; juveniles decreased rapidly after 1991. Echo-sounder data from Stellwagen showed that prey trace levels declined from 19.1% ofthe vertical water column in 1990 to 2.8% in 1992 (no readings were taken in 1988-89,or 1993-94). Si­ multaneously, the number of whales identified on Jeffreys Ledge, north of Stellwagen Bank, increased dramati­ cally beginning in 1992. Sixty-four per­ centofthe whales identified on Jeffreys in 1992-94 were seen on Stellwagen Bankin 1988 and 1989. We hypothesize that humpback whales shift their dis­ tribution in order to prey upon recov­ ering herring populations, their pri­ mary source offood.