Gannon et al.: Food habits of Phocoena phocoena 
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Figure 1 
Capture locations of harbor porpoises taken during the autumn ( 1989-94) in 
the Gulf of Maine sink gillnet fishery and used in this analysis of food habits. 
The isobath shown is 91.4 m (50 fathoms). 
ery or because they feed on the same 
prey as the target species. 
In this paper, we examine the stom- 
ach contents of harbor porpoises in the 
Gulf of Maine during autumn and in- 
vestigate dietary differences amongst 
various sex and maturity categories. 
Our main objectives were to elucidate 
seasonal changes in the harbor por- 
poise diet and expand our knowledge 
of the dynamics between porpoises and 
their prey that may be responsible for 
entanglement of porpoises in gill nets. 
Methods 
Sample collection 
The sample consisted of 95 porpoises 
killed in gill nets during autumn (1 
September- 31 December) of 1989 and 
1991-94. All porpoises were captured 
in bottom tending gill nets set for 
groundfish, principally cod ( Gadus 
morhua), pollock (Pollachius virens), 
goosefish ( Lophius americanus ), and 
several species of flatfish. Most por- 
poises were taken in the vicinity of 
Jeffreys Ledge in the west central Gulf 
of Maine, at water depths between 35 
and 185 m (Fig. 1). All samples were 
obtained by fisheries observers work- 
ing onboard gillnet vessels. Observers 
were instructed to retain whole por- 
poise carcasses whenever possible, but 
when sea conditions or other factors prevented re- 
tention of carcasses, observers excised stomachs in 
the field. Carcasses and excised stomachs were fro- 
zen after the vessels returned to shore (usually 12- 
48 hours post mortem) for later examination. 
On the basis of age (determined from dentinal 
growth layers and body length; see Read and Hohn, 
1995) and reproductive condition (determined by 
examination of gonads and mammary glands; see 
Read and Hohn, 1995), porpoises were classified to 
the following sex, maturity, and reproductive catego- 
ries: porpoises were considered calves (less than one 
year of age, not fully weaned), juveniles (older than 
one year but sexually immature), or sexually mature. 
The sex and maturity composition of the sample was 
as follows: (males and females combined) calves = 
13; female juveniles = 12; male juveniles = 18; fe- 
male mature adults = 10; male mature adults = 34; 
and unknown sex or maturity = 8. Because sample 
sizes were small, pregnant (n= 4), simultaneously 
pregnant and lactating (n=5), and resting adult fe- 
males (rc=l) were pooled in the “mature female” group 
for statistical analyses. However, to facilitate com- 
parisons with the findings of Recchia and Read 
(1989), data for lactating and nonlactating mature 
females are also presented separately. 
Prey identification 
The contents of all three stomach chambers were 
examined in the laboratory. Intact prey were removed 
first, then loose flesh was decanted. The remaining 
stomach contents were poured through a 1-mm metal 
sieve to separate hard parts from liquefied digesta. 
Solid prey remains used for identification were sepa- 
rated from other skeletal remains by hand. Struc- 
tures used to identify partially digested food items 
included sagittal otoliths, dentary bones, and skulls 
