Wenzel et al.: Food habits of Mesoplodon Dicers in the western North Atlantic 
385 
Table 2 
Analysis of fish prey identified in stomachs of Sowerby’s beaked whales (Mesoplodon bidens ) taken in the pelagic drift 
gillnet fishery for Swordfish ( Xiphias gladius ) in the western North Atlantic between August 1989 and July 1996. %FO= 
percentage of frequency of occurrence; %N=percentage of number of otoliths. Unidentified means that the structure of the 
otoliths was distinct for identification but the otoliths were not identified. Unidentifiable otoliths were worn or digested and 
not identifiable. 
Family 
Species 
Common name 
Occurrence 
(no. of 
stomachs) 
%FO 
Number 
of 
otoliths 
%N 
Minimum 
number 
of fish 
Alepocephalidae 
Alepocepkalus cf. agassizii 
Agassiz’s Smoothhead 
4 
50 
10 
0.1 
6 
Diretmidae 
Diretmus argenteus 
Spinyfin 
1 
13 
2 
0.0 
1 
Gonostomatidae 
Gonostoma elongatum 
Longtooth Anglemouth 
2 
25 
6 
0.1 
4 
Macrouridae 
Coelorinchus sp. 
Grenadier 
1 
13 
4 
0.0 
2 
Macrouridae 
Coryphaenoides sp. 
Grenadier 
3 
38 
39 
0.4 
21 
Macrouridae 
Nezumia bairdii 
Marlin-spike 
8 
100 
1019 
10.8 
515 
Melamphaidae 
Poromitra capita 
Ridgehead 
1 
13 
3 
0.0 
2 
Melamphaidae 
Scopelogadus beanii 
Bean’s Bigscale 
7 
88 
344 
3.6 
178 
Merlucciidae 
Merluccius albidus 
Offshore Hake 
1 
13 
1 
0.0 
1 
Merlucciidae 
Merluccius bilinearis 
Silver Hake 
2 
25 
311 
3.3 
156 
Moridae 
Gadella imberbis 
Beardless Codling 
3 
38 
65 
0.7 
33 
Moridae 
Laemonema barbatulum 
Shortbeard Codling 
8 
100 
3332 
35.3 
1672 
Moridae 
Unidentified morid 
Codling 
1 
13 
178 
1.9 
89 
Myctophidae 
Bentkosema glaciale 
Glacier Lanternfish 
3 
38 
5 
0.1 
3 
Myctophidae 
Bolinichthys supralateralis 
Stubby Lanternfish 
1 
13 
2 
0.0 
1 
Myctophidae 
Ceratoscopelus maderensis 
Horned Lanternfish 
7 
88 
75 
0.8 
40 
Myctophidae 
Hygophum hygomii 
Bermuda Lanternfish 
4 
50 
6 
0.1 
4 
Myctophidae 
Lampadena speculigera 
Mirror Lanternfish 
7 
88 
36 
0.4 
19 
Myctophidae 
Lampanyctus spp. 
Lanternfishes 
8 
100 
797 
8.4 
403 
Myctophidae 
Lobianchia gemellarii 
Cocco’s Lanternfish 
8 
100 
1222 
12.9 
613 
Myctophidae 
Nannobrachium cf. atrum 
Dusky Lanternfish 
5 
63 
15 
0.2 
8 
Paralepididae 
Arclozenus risso 
White Barracudina 
8 
100 
90 
1.0 
49 
Paralepididae 
Unidentified paralepidid 
2 
25 
4 
0.0 
2 
Paraliehthyidae 
Paralichthys oblongus 
Fourspot Flounder 
1 
13 
1 
0.0 
1 
Phycidae 
Phycis chesteri 
Longfin Hake 
7 
88 
634 
6.7 
321 
Phyeidae 
Urophycis chuss 
Red Hake 
2 
25 
30 
0.3 
15 
Phycidae 
Urophycis tenuis 
White Hake 
2 
25 
8 
0.1 
4 
Scorpaenidae 
Helicolenus dactylopterus 
Blackbelly Rosefish 
7 
88 
350 
3.7 
179 
Serrivomeridae 
Serrivomer beanii 
Stout Sawpalate 
1 
13 
3 
0.0 
2 
Sternoptychidae 
Polyipnus clarus 
Slope Hatchetfish 
1 
13 
2 
0.0 
1 
Stomiidae 
Chauliodus cf. sloani 
Sloan’s Viperfish 
4 
50 
15 
0.2 
9 
Unidentified otoliths 
8 
100 
215 
2.3 
114 
Unidentifiable otoliths 
8 
100 
627 
6.6 
318 
Total otoliths 
9451 
Stomiidae 
Ckauliodus spp. 
Viperfish jaws 
2 
25 
18 
3 
Total fishes 4789 
A second potential bias arises because hard parts 
of different prey may pass through the gastrointesti- 
nal tract at different rates. For example, squid beaks 
are resistant to digestion and often accumulate in 
stomachs of marine mammals, but the soft tissue 
and bones of fishes are more readily digested (Bigg 
and Fawcett, 1985). The complex structure of beaked 
whale stomachs (Mead 1989, 1993, 2007) makes it 
likely that relatively indigestible squid beaks are re- 
tained for prolonged periods. Therefore, the results 
reported here may overestimate the already low im- 
portance of cephalopods in the diet of the Sowerby’s 
beaked whale. 
A third possible bias arises from the secondary in- 
gestion of prey, in which recovered hard parts enter 
whales in the stomachs of prey and are not consumed 
directly by whales themselves. It is difficult to evalu- 
ate this potential source of bias. It is possible, for ex- 
ample, that the Horned Lanternfish ( Ceratoscopelus 
maderensis) we recovered could have been secondarily 
introduced into the stomachs of the Sowerby’s beaked 
whales that we examined, given the small size of the 
