Wenzel et al.: Food habits of Mesopiodon bidens in the western North Atlantic 
383 
Table I 
Origin and description of Sowerby’s beaked whales (Mesopiodon bidens) obtained in the western North Atlantic between Au- 
gust 1989 and October 2003. Most whales were retained as bycatch in the pelagic drift gillnet fishery for Swordfish (Xiphias 
gladius). One whale was collected stranded in Kennebunk, Maine. Latitudes and longitudes are given in decimal degrees. 
NA=not available; M=male; F=female. 
Wt. of 
stomach 
Whale contents 
identification 
Latitude 
Longitude 
Depth (m) 
Year 
Month 
Day 
Source 
Sex 
Length (cm) 
(g) 
D00253 
40.23 
67.90 
1050 
1989 
10 
10 
Drift gillnet 
M 
491 
1816 
D00341 
40.02 
68.80 
1200 
1995 
6 
24 
Drift gillnet 
F 
485 
5830 
D01369 
40.87 
66.42 
1600 
1994 
6 
10 
Drift gillnet 
M 
462 
5897 
D01380 
40.97 
66.32 
1900 
1994 
6 
3 
Drift gillnet 
F 
460 
4082 
D03070 
40.03 
68.77 
1350 
1996 
7 
4 
Drift gillnet 
F 
476 
2700 
D03202 
40.35 
67.35 
1350 
1996 
7 
6 
Drift gillnet 
M 
470 
2650 
D03458 
40.03 
68.63 
1600 
1996 
7 
4 
Drift gillnet 
F 
471 
NA 
D03486 
40.97 
66.40 
750 
1994 
7 
10 
Drift gillnet 
F 
495 
4082 
D06061 
40.78 
66.57 
1250 
1990 
8 
9 
Drift gillnet 
F 
274 
Empty 
F00120 
40.87 
66.48 
1150 
1989 
8 
26 
Drift gillnet 
M 
473 
Partial 
MH03-604 
43.33 
70.52 
NA 
2003 
10 
2 
Stranding 
M 
442 
Empty 
counted the maximum number of either right or left 
otoliths for each fish species. We assessed relative prey 
importance by frequency of occurrence (FO) and pro- 
portion of numerical abundance (%N). FO is the pro- 
portion of stomachs that contained a particular type 
of prey, %N is the proportion that each prey type rep- 
resented of the total number of prey items recovered, 
and the minimum number of fish, is determined by the 
number of paired otoliths found in each stomach, with 
any odd numbered otolith raising the minimum num- 
ber of fish by one (Table 2). We measured whole undi- 
gested otoliths from abundant fish prey with a stage 
micrometer or vernier calipers and estimated prey 
sizes with linear regressions derived from the WHOI 
reference collection (Table 3). We estimated the num- 
ber of individual cephalopod prey from the maximum 
number of either upper or lower beaks (Table 4). 
Results 
One of the 10 stomachs which we examined was from a 
calf and contained only mucous or milk, and the stom- 
ach of the stranded individual was completely empty. 
In addition to the 10 stomachs examined for this study, 
another stomach was dissected and examined at sea 
by a NEFOP observer who retained only 14 otoliths: 9 
Marlin-spike ( Nezumia bairdii) and 5 Cocco’s Lantern- 
fish ( Lobianchia gemellarii). Because of the incomplete 
examination of the stomach contents of this individual, 
we did not include it in the quantitative analysis of 
food habits. The remaining 8 stomachs were intact and 
contained prey; therefore we used the contents of these 
stomachs in our quantitative analysis of the frequency, 
numerical abundance, and size of prey. Genetic analy- 
sis confirmed that these stomachs were all from Sow- 
erby’s beaked whales. 
Fishes dominated the diet of these whales; in to- 
tal, we recovered 9451 otoliths of fishes and jaws of 
18 Sloan’s Viperfish (Chauliodus sloani ). The only 
prey represented by more jawbones than otoliths was 
Sloan’s Viperfish, The mean number of otoliths per 
stomach was 1196 (range: 327-3452). The recovered 
otoliths represented at least 31 species from 15 fami- 
lies of deepwater fishes (Table 2). Fishes from the fami- 
lies Moridae (%N=37.9% of prey), Myctophidae (22.9%), 
Macrouridae (11.2%), and Phycidae (7.2%) were pres- 
ent in all 8 stomachs. Most (74.1%) prey were from the 
following 5 taxa, ordered by proportion of numerical 
abundance: 1) Shortbeard Codling ( Laemonema bar- 
batulum), Moridae, 35.3%; 2) Cocco’s Lanternfish, Myc- 
tophidae, 12.9%; 3) Marlin-spike, Macrouridae, 10.8%; 
4) lanternfishes ( Lampanyctus spp. ), Myctophidae, 
8.4%; and 5) Longfin Hake ( Phycis ehesteri), Phycidae, 
6.7%. In each stomach, 12-19 different fish taxa were 
present, with a mean of 15. The estimated standard 
lengths of fish prey ranged from 4.0 cm to 27.7 cm (Ta- 
ble 3). In its esophagus, whale DO 1380 had 13 whole 
Cocco’s Lanternfish, ranging in length from 8.0 to 10.0 
cm (mean: 9.2 cm), similar to lengths of fish estimated 
from otoliths of this species found in the other 7 stom- 
achs examined (Table 3). 
Squid remains were found in 7 of the 8 analyzed 
stomachs, but they were represented by only 123 beaks 
(minimum 73 individuals) of 3 identified taxa (Table 
4); cephalopods accounted for only 1.5% of total prey. 
The mean number of squid beaks per stomach was 15.4 
(range: 0.0-35.0). 
