Weinrich et al.: A shift in distribution of humpback whales, Megaptera novaeangliae, in reponse to prey 
827 
sand lance (Fogarty et al., 1991). Sight- 
ings of humpback whales off the Maine 
coast, where herring were the primary 
whale prey, decreased dramatically dur- 
ing the late 1970’s (Payne et al., 1986; 
Mullane and Rivers 2 ). Sand lance fre- 
quently use shallow areas with sandy 
bottoms, such as Stellwagen Bank in 
the southern Gulf of Maine (Meyer et 
al., 1979). This shift in distribution, and 
corresponding change in primary prey 
type, may have also led to changes in 
feeding behavior (Weinrich et al., 1992). 
Humpback whales remained abundant 
in the southwestern Gulf of Maine 
throughout the 1980’s, with a brief de- 
crease in some areas during 1986-87 
(Payne et al., 1990; Cetacean Res. 
Unit 3 ). 
We documented a gradual but con- 
tinuous decrease in the use of Stell- 
wagen Bank by humpback whales dur- 
ing 1988-94. Our data suggest that 
whales have returned to a distribution 
similar to that documented until the 
late 1970’s. We hypothesize that this re- 
turn is due to the recovery of herring 
stocks in the Gulf of Maine and to a cor- 
responding decrease in available prey 
for humpback whales on Stellwagen 
Bank and in other areas favored by sand 
lance in the southwestern Gulf of 
Maine. 
Methods 
Survey methods 
From 1 May to 30 October, 1988 to 1994, daily ship- 
board surveys were carried out aboard commercial 
whale- watching boats. These departed from Gloucester 
and Boston, Massachusetts, and were typically 4-5 
hours in duration. There were usually two cruises per 
vessel per day. A typical cruise included 90-120 min- 
utes in areas where whales were often observed, as 
well as 2-3 hours of transit time. Whale watches 
usually emphasized the northern half of Stellwagen 
Bank. On occasion, whale watches surveyed the 
southern half of Jeffreys Ledge to the northeast of 
2 Mullane, S. J., and A. Rivers. 1982. Mt. Desert Rock, 
Maine. Annual Report, 27 p. [Available from Allied Whale, 
College of the Atlantic, Bar Harbor, ME.] 
3 Cetacean Research Unit. 1980-89. Cetacean Research Unit, 
PO Box 159, Gloucester MA 01930. Unpubl. data. 
Figure 1 
The study area in the Gulf of Maine. 
Cape Ann (Fig. 1). This effort is detailed in Table 1. 
Within each whale-watching trip, protocol and typi- 
cal amount of observation time were consistent on 
all vessels. 
Whale-watching cruises were supplemented by oc- 
casional day-long ( 7-13 h) excursions on research ves- 
sels. These took place 1 April to 15 November of each 
year, with emphasis on April and October-Novem- 
ber, as well as during periods of significant whale 
concentration from May to September. During each 
cruise, a specific attempt was made to conduct a com- 
prehensive photo-identification survey of a specific 
area (i.e. northern Stellwagen Bank, southern 
Jeffreys Ledge, etc.). As time allowed, coverage was 
devoted to a larger portion of the entire geographic 
feature (either Stellwagen Bank or Jeffreys Ledge). 
Specific areas were determined by recent sightings 
of whale aggregations, reliable reports of whale 
sightings from local boaters, or a determination that 
an area had not been recently surveyed. Jeffreys 
