434 
Fishery Bulletin 96(3), 1998 
Table 5 
Prey consumption by harbor porpoises of different maturity and reproductive conditions caught incidentally in Gulf of Maine sink 
gill nets during autumn 1989-94 (mean ± standard deviation). Clup. = Clupea harengus, Maur. = Maurolicus weitzmani, Mer. = 
Merluccius bilinearis, and Uroph. = Urophycis spp. 
Porpoise 
groups 
Average mass 
of individual prey 
Average no. 
of individual prey 
Average mass 
of stomach 
contents 
Average 
no. of 
Clup. 
Maur. 
Mer. 
Uroph. 
Clup. 
Maur. 
Mer. 
Uroph. 
Existing 
Reconstituted 
prey 
taxa 
Calves 
57 +40 
0.92 ±0.16 
19 ±30 
42 ±59 
0.3 ±0.9 
106.5 ±269.6 
38.2 ±74.2 
1.5 ±5.0 
33 ±23 
209 ±327 
2.4 ±1.4 
Juvenile 
males 
131 +35 
0.95 ±0.20 
51 ±56 
108 ±105 
4.2 ±5.0 
21.3 ±46.8 
19.1 ±38.7 
3.6 ±10.8 
284 ±288 
1304 ±1036 
3.2 ±1.3 
Juvenile 
females 
140 +37 
0.95 ±0.01 
82 ±78 
23 ±41 
6.9 ±7.5 
0.6 ±1.7 
9.0 ±19.5 
1.0 ±1.8 
363 ±356 
1389 ±1166 
2.8 ±2.4 
Mature 
males 
125 ±30 
0.95 ±0.05 
73 ±103 
50 ±46 
8.1 ±10.6 
117.0 ±372.3 
5.6 ±9.5 
0.6 ±1.6 
274 ±285 
1506 ±1526 
2.9 ±1.5 
Mature 
females 
107 ±28 
0.87 ±0.13 
77 ±65 
339 ±360 
4.4 ±7.6 
1.6 ±3.2 
14.3 ±35.0 
0.5 ±1.3 
343 ±371 
1378 ±1996 
2.8 ±1.4 
of porpoise stomachs in the autumn, representing 
67% of numerical abundance and 3% of food mass 
but were absent from the summer diet. Recchia and 
Read (1989) found 11 prey taxa in the stomachs of 
127 noncalf porpoises; we found 15 taxa in 82 noncalf 
stomachs. These results suggest that the diet of this 
population becomes more diverse as porpoises move 
out of the Bay of Fundy and into the Gulf of Maine. 
At the present time, we do not know whether these 
changes reflect seasonal differences in prey availabil- 
ity, interannual variability in prey populations, or 
choice on the part of foraging porpoises. Neverthe- 
less, Atlantic herring remains the single most im- 
portant prey of harbor porpoises in the Gulf of Maine 
during the autumn. 
The size range of prey in the noncalf porpoise diet 
is larger in fall than in summer (Recchia and Read, 
1989). Porpoises continue to eat large prey during 
autumn, such as adult herring and silver hake, but 
also eat a substantial number of smaller herring, sil- 
ver hake, pearlsides, and red and white hake. The 
large standard deviations in Tables 2 and 5 reflect 
the wide range of prey sizes eaten. 
With the exception of calves, the diet of porpoises 
did not vary significantly with age or sex. None of 
the comparisons of forestomach content mass, indi- 
vidual prey mass, or numbers of prey among the four 
noncalf categories yielded significant differences. 
Although previous studies of other marine mammal 
species have found measurable dietary differences 
between lactating and nonlactating adult females 
(Bernard and Hohn, 1989; Cockcroft and Ross, 1990; 
Cheal and Gales, 1991; Kastelein et al., 1993; Young 
and Cockcroft, 1994; Hobson et al., 1997; Robertson 
Table 6 
Relative food importance, measured by frequency of occur- 
rence (%FO), numerical proportion (%Num), and propor- 
tion of total mass (%Mass), in the autumn diets of lactating 
and nonlactating mature female harbor porpoises. 
Lactating Nonlactating 
(n= 5) (n= 5) 
% % % % % % 
Prey FO Num Mass FO Num Mass 
Clupea harengus 
80 
7 
14 
60 
52 
71 
Gadus morhua 
20 
1 
1 
0 
0 
0 
lllex illecebrosus 
40 
1 
<1 
0 
0 
0 
Maurolicus 
weitzmani 
0 
0 
0 
60 
25 
<1 
Merluccius 
bilinearis 
80 
87 
52 
60 
13 
10 
Myxine glutinosa 
60 
— 
— 
20 
— 
— 
Pollachius virens 
20 
1 
5 
20 
11 
19 
Urophycis spp. 
40 
3 
28 
0 
0 
0 
and Chivers, 1997), small sample sizes in this study 
prevented detailed investigation of potential dietary 
changes associated with changes in female reproduc- 
tive condition. Therefore, the findings on diets of lac- 
tating and nonlactating mature females should be 
viewed with caution. 
At four to seven months of age (Read and Hohn, 
1995), calves eat a variety of solid foods and continue 
to supplement their diet by nursing. The large stan- 
dard deviations for calves in Table 5 may be an indi- 
