428 
Abstract .—This study describes the 
stomach contents of 95 harbor por- 
poises (Phocoena phocoena) killed in 
groundfish gill nets in the Gulf of Maine 
between September and December, 
1989-94. The importance of prey was 
assessed by frequency of occurrence, 
numerical proportion, and proportion 
of ingested mass. Atlantic herring 
( Clupea harengus) was the most impor- 
tant prey, occurring in 78% of noncalf 
porpoise stomachs and contributing 
44% of ingested mass. Pearlsides 
( Maurolicus weitzmani ), silver hake 
(Merluccius bilinearis ), and red and 
white hake (Urophycis spp. ) were com- 
mon prey items. There were no signifi- 
cant differences among diets of sex and 
maturity groups, but the calf diet dif- 
fered significantly from adults in num- 
ber of Atlantic herring eaten and the 
total mass of food consumed. At four to 
seven months of age, calves were eat- 
ing pearlsides, small silver hake, and eu- 
phausiids ( Meganyctiphanes norvegica) 
while still nursing. 
Manuscript accepted 10 December 1997 
Fishery Bulletin 96:428-437 (1998). 
Autumn food habits of harbor 
porpoises, Phocoena phocoena, 
in the Gulf of Maine 
Damon R Gannon 
Duke University Marine Laboratory, Nicholas School of the Environment 
1 35 Duke Marine Lab Road, Beaufort, North Carolina 285 1 6 
E-mail address: dpg3@acpub.duke.edu 
James E. Craddock 
Woods Hole Oceanographic Institution 
Woods Hole, Massachusetts 02543 
Andrew J. Read 
Duke University Marine Laboratory, Nicholas School of the Environment 
1 35 Duke Marine Lab Road, Beaufort, North Carolina 285 1 6 
Harbor porpoises ( Phocoena pho- 
coena) from the Bay of Fundy and 
Gulf of Maine are believed to com- 
prise a single population, hereafter 
referred to as the Gulf of Maine 
population (Palka et al., 1996; Wang 
et al., 1996). To date, studies of the 
food habits of this population have 
been restricted to samples collected 
in the Bay of Fundy during summer, 
where porpoises feed primarily on 
Atlantic herring ( Clupea harengus ; 
Smith and Gaskin, 1974; Recchia 
and Read, 1989; Smith and Read, 
1992). Many porpoises leave the 
Bay of Fundy in fall, moving south- 
ward into the Gulf of Maine (Gas- 
kin, 1977; Gaskin, 1984; Read and 
Westgate, 1997). During winter, a 
portion of the population disperses 
over the continental shelf from New 
England to North Carolina (Pola- 
check et al., 1995; Read et al., 1996). 
Because of their small size and 
limited energy stores, harbor por- 
poises must remain close to food 
resources to avoid starvation (Koop- 
man, 1994). Moreover, their un- 
usual life history incurs high ener- 
getic costs; most females attain 
sexual maturity at three years of 
age and give birth to a calf each year 
(Read and Hohn, 1995). Lactation 
lasts for at least eight months; thus 
mature females spend most of their 
lives simultaneously pregnant and 
lactating. This intensive reproduc- 
tive schedule requires calves to be- 
come nutritionally independent at 
a relatively early age, usually before 
the end of their first year (Smith and 
Read, 1992). 
Large numbers of harbor por- 
poises are killed each year in gill 
nets in the Bay of Fundy, Gulf of 
Maine, and Mid-Atlantic Bight 
(Read and Gaskin, 1988; Read et al., 
1993; Bravington and Bisack, 1996). 
For the Gulf of Maine, the estimated 
average annual harbor porpoise 
bycatch for 1990 to 1995 was 1800 
(Bisack 1 ). Little is known about the 
process by which porpoises become 
entangled in gill nets, and thus ef- 
forts are hampered in mitigating this 
conservation problem. Porpoises may 
become entangled because they feed 
on fish species targeted by the fish- 
1 Bisack, K. 1996. Harbor porpoise bycatch 
estimates in the U.S. Gulf of Maine sink 
gillnet fishery: 1994 and 1995. Paper pre- 
sented to the International Whaling Com- 
mission Scientific Committee Meeting in 
Aberdeen, Scotland, June 1996 (in review). 
