384 
Fishery Bulletin 111(4) 
72°W 71 "W 70°W 69"W 68" W 67" W 66”W 
Figure 1 
Map of locations where 10 specimens of the Sowerby’s beaked whale ( Mesoplodon bidens ) were taken 
in the pelagic drift gillnet fishery for Swordfish ( Xiphias gladius ) in the western North Atlantic 
between August 1989 and July 1996. The stomach contents of 8 of these whales were examined to 
determine the food habits of this species. 
Discussion 
The Sowerby’s beaked whales that we examined had 
been feeding primarily on large numbers of relative- 
ly small meso- and benthopelagic fishes before their 
death; cephalopod prey constituted a very minor part 
of the diet of these animals. Our findings are simi- 
lar to those of Pereira et al. (2011), who examined the 
stomach contents of 10 stranded Sowerby’s beaked 
whales from the Azores and found a predominance of 
small fish prey. It is important to note that all but 
one of the whales that we examined were killed at 
sea, and, with the exception of the single stranded 
animal, they were apparently healthy at the time of 
their death. The presence of intact prey in the esopha- 
gus of one specimen and the large numbers of prey 
items in the stomachs that we examined indicate that 
these animals had been foraging before death. The av- 
erage minimum number of prey in the stomachs that 
we examined was more than 600 (4789 fishes, plus 73 
squids, in all 8 stomachs combined), compared with 85 
prey in the stranded specimens examined by Pereira 
et al. (2011). 
We believe the stomach contents of the whales that 
we examined are representative of the summer diet of 
Sowerby’s beaked whales along the continental shelf 
break off the northeastern coast of the United States. 
Nevertheless, biases from several sources could affect 
our conclusions. For example, our analysis of the stom- 
ach contents of these bycaught cetaceans could have 
been biased if these whales had been feeding in or 
around a fishing gear. Such behavior has not been re- 
ported for beaked whales, however, and the Sowerby’s 
beaked whales that we examined were taken in pelagic 
drift gillnets that targeted large Swordfish and tunas 
in the top 10 m of the water column. These large-mesh 
gillnets could not have captured the prey we identi- 
fied in stomachs of Sowerby’s beaked whales; the only 
whole fish we recovered were 13 small (<10.0 cm) Coc- 
co’s Lanternfish found in one esophagus. Therefore, the 
Sowerby’s beaked whales that we examined were not 
actively feeding in nets when captured. 
