826 
Abstract.™ From the mid-1970’s to 
the mid-80’s, Stellwagen Bank was an 
important humpback whale feeding 
area with sand lance (Ammodytes spp.) 
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 of 258 
(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% of the 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- 
cent of the whales identified on Jeffreys 
in 1992-94 were seen on Stellwagen 
Bank in 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 of food. 
Manuscript accepted 21 April 1997. 
Fishery Bulletin 95:826-836 (1997). 
A shift in distribution of humpback 
whales, Megaptera novaeangliae, 
in response to prey in the southern 
Gulf of Maine 
Mason Weinrich 
IVSaScoIm Martin* 
Rachel Griffiths 
Jennifer Bove 
Mark Schilling 
Cetacean Research Unit, PO Box 1 59 
Gloucester, Massachusetts 0 1 930 
'Present address: Department of Biology 
Rutgers University, Brunswick, New Jersey 
E-mail address (for M. Weinrich): mason@cetacean.org 
Humpback whales, Megaptera novae- 
angliae, migrate seasonally between 
low-latitude breeding grounds and 
high-latitude feeding areas (Kellogg, 
1929; Mackintosh, 1965; Katona, 
1986). In the western North Atlan- 
tic, whales that winter in Caribbean 
waters migrate to feeding grounds 
in New England (the Gulf of Maine), 
in the Gulf of St. Lawrence, and in 
waters off Newfoundland, Green- 
land, Iceland, and Norway (Katona 
and Beard, 1990). The whales us- 
ing each feeding area appear to con- 
sist of extended matrilines (Baker 
et al., 1990; Clapham et al., 1992). 
Within feeding areas, prey distribu- 
tion has been a primary influence 
on the local distribution and micro- 
movements of all baleen whales ex- 
amined to date (Whitehead and 
Carscadden, 1985; Payne et al., 
1986, 1990; Piatt et al., 1989). 
Studies of humpback whale move- 
ment, ecology, demography, behavior, 
and social organization on their 
feeding grounds in the Gulf of 
Maine have been ongoing since the 
mid-1970’s, (Payne et al., 1986; 
Clapham and Mayo, 1987, 1990; 
Weinrich, 1991; Weinrich and Kuhl- 
berg, 1991; Clapham et al., 1992; 
Weinrich et al., 1992; Katona et 
al. 1 ). During this period, several 
shifts in the distribution of hump- 
back whales have been reported. 
Payne et al. (1986) showed that 
humpback whales in the late 1970’s 
had moved from primary abun- 
dance on Georges Bank and in the 
waters of the northern Gulf of 
Maine to the inshore southwestern 
Gulf of Maine, especially Stell- 
wagen Bank and the Great South 
Channel. They attributed this shift 
to a fishery-induced collapse of her- 
ring (Clupea harengus) populations 
(Anthony and Waring, 1980; Gross- 
lein et al., 1980) and a correspond- 
ing increase in sand lance ( Ammo- 
dytes spp.) (Meyer et al., 1979; 
Sherman et al., 1981, 1988; Sher- 
man 1986; Sissenwine 1986). Both 
species are known prey for hump- 
back whales (Mitchell, 1973; Over- 
holtz and Nicholas, 1979; Kawa- 
mura, 1980). These fish species are 
potential ecological competitors 
(Reay, 1970; Meyer et al., 1979; 
Sherman et al., 1981); moreover, 
herring are known predators of 
1 Katona, S. K., P. Harcourt, J. S. Perkins, 
and S. D. Kraus. 1980. Humpback 
whales: a catalog of individuals identified 
by fluke photographs. College of the At- 
lantic, Bar Harbor, ME, var. pagination. 
