Wenzel et al.: Food habits of Mesoplodon bidens in the western North Atlantic 
387 
Table 4 
Cephalopod prey from the stomachs of Sowerby’s beaked whales ( Mesoplodon bidens) taken in the pelagic drift gillnet fish- 
ery for Swordfish ( Xiphias gladius) in the western North Atlantic between August 1989 and July 1996. %N=percentage of 
number of total beaks. %FO=percentage of frequency of occurrence, on the basis of the number of stomachs studied. 
Prey item 
D00253 
D00341 
D01369 
D01380 
D03070 
D03202 
D03458 
D03486 
Total 
%N 
%FO 
Unidentified upper beaks 
0 
2 
2 
4 
10 
19 
12 
49 
39.8 
87.5 
Unidentified lower beaks 
0 
5 
8 
16 
29 
23.6 
50.0 
Histioteuthis spp. 
4 
13 
7 
9 
33 
26.8 
50.0 
Taonius pavo 
9 
2 
11 
8.9 
25.0 
Chiroteuthis veranyi 
1 
1 
0.8 
12.5 
Total beaks 
14 
0 
15 
9 
9 
18 
35 
23 
123 
100.0 
Total cephalopods 
73 
this species, but the results presented here indicate 
that their hunting strategies may be similar to those 
of their better-studied congener. 
Therefore, on the basis of knowledge of the habi- 
tat preferences of prey recovered from the stomachs 
of Sowerby’s beaked whales, we conclude that these 
animals feed in the meso- and benthopelagic environ- 
ments along the shelf break, foraging in the water col- 
umn and near the seafloor. Mesopelagic fishes in this 
region are important prey for several other cetacean 
species. Horned Lanternfish, in particular, is consumed 
by the Atlantic white-sided dolphin ( Lagenorhynchus 
acutus ) (Craddock et al., 2009) and by the common 
dolphin ( Delpliinus delphis), both of which are also 
caught incidentally in the pelagic drift gillnet fishery 
for Swordfish in the Atlantic (Craddock and Polloni 4 ). 
The stomach of a harbor porpoise ( Phocoena phocoena), 
captured in a pelagic drift net fishery off North Caro- 
lina was found to contain more than 1900 otoliths of 
Horned Lanternfish (Read et ah, 1996). 
Many marine organisms are concentrated in oceano- 
graphic frontal zones, as a result of increased produc- 
tion and advection (Jahn and Backus, 1976; Backus et 
al., 1977; Olson and Backus, 1985). As a consequence of 
these aggregations, predators (including swordfish) and 
fishermen exploit fronts. The mosaic of oceanic fronts 
associated with the Gulf Stream and its warm- and 
cold-core rings have long been targeted by fishermen 
of Swordfish, particularly along the shelf break (Smith 
et al., 1996). Swordfish have been reported to feed on 
some of the same prey items that we recovered from 
4 Craddock J. E., and P. T. Polloni. 2005. Food habits of 
small marine mammals from the Gulf of Maine and from 
slope water off the northeast US coast. Year 3, Final Re- 
port, revised, 31 p. Request no. EA 133F-02-RQ-0081. Req- 
uisition no. NFFM7320-2-15375. [Available from Northeast 
Fisheries Science Center, National Marine Fisheries Service, 
NOAA, 166 Water St., Woods Hole, MA 02543 http://www. 
nefsc.noaa.gov/publications/reports/EA 133F02RQ0081.pdf] 
Sowerby’s beaked whales (Scott and Tibbo, 1968; Still- 
well and Kohler, 1985). 
For example, barracudinas (Paralepididae) are im- 
portant food items for Swordfish in the northwestern 
Atlantic (Scott and Tibbo, 1968) and were common 
prey of the Sowerby’s beaked whales that we exam- 
ined; White Barracudina ( Arctozenus risso ) is the most 
common barracudina in this region (Moore et al., 2003). 
Lanternfishes (Myctophidae) also are consumed by 
Swordfish in large numbers, but, because of their rela- 
tively small size, they do not contribute significantly to 
the mass ingested by these predators (Scott and Tibbo, 
1968). The pelagic drift gillnet fishery in the Atlantic 
targeted Swordfish and tunas, and the fishing effort 
focused on thermal fronts along the shelf break, as de- 
scribed by Podesta et al. (1993). Therefore, the com- 
mon prey fields and habitats of Swordfish and Sow- 
erby’s beaked whales may help to explain the relatively 
high bycatch rates of Sowerby’s beaked whales in this 
fishery. 
Conclusions 
The diet of Sowerby’s beaked whales in the western 
North Atlantic is dominated by meso- and benthope- 
lagic fishes (98.5%), and cephalopods accounted for 
only 1.5% of their prey. Future research with digital 
acoustic tags would be helpful to examine the diving 
and echolocation behavior of Sowerby’s beaked whales 
in relation to the vertical and horizontal distribution of 
prey. A study that combines both the tagging methods 
used by Arranz et al. (2011) and survey data of the 
prey field documented with the use of scientific echo- 
sounders and by direct capture of voucher specimens 
would be particularly profitable. The regular occur- 
rence of Sowerby’s beaked whales in and near the can- 
yons on the southern margin of Georges Bank, where 
the whale specimens we studied were captured, offers a 
promising field opportunity for such research. 
