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Fishery Bulletin 111(4) 
as a result, direct observation of foraging is impossi- 
ble. Most insight into their feeding behavior has come 
from digital acoustic tags, which record the 3-D move- 
ment and acoustic environment of tagged individuals 
(e.g., Madsen et al., 2005). Application of these tags to 
individuals of the Blainville’s beaked whale ( Mesoplo - 
don densirostris) indicates that this species forages at 
depths of more than 1000 in in dives that may last for 
almost 1 h (Arranz et ah, 2011). To date, however, no 
Sowerby’s beaked whales have been studied with digi- 
tal acoustic tags. 
Given the challenges of studying live whales, all 
published information on the food habits of the Sow- 
erby’s beaked whale has been acquired from stranded 
specimens (Dix et al., 1986; Lien and Barry, 1990; Lien 
et al. 1990; Ostrom et al., 1993; Pereira et ah, 2011; 
Spitz et al., 2011; Santos et al. 1 ’ 2 ). Recent analysis of 
the stomach contents of 10 stranded Sowerby’s beaked 
whales from the Azores in the eastern North Atlan- 
tic (Pereira et al., 2011) provided evidence that small 
meso- and bathypelagic fishes constitute an important 
part of the diet of this species in this area. 
One largely untapped source of information on the 
biology of the Sowerby’s beaked whale comes from a 
sample of animals taken as bycatch in a pelagic drift 
gillnet fishery for Swordfish ( Xiphias gladius) that op- 
erated in the western North Atlantic between 1989 and 
1998. The pelagic drift gillnet fishery was monitored by 
observers from the Northeast Fisheries Observer Pro- 
gram (NEFOP); these observers documented bycatch 
consisting of more than 1100 individuals of 14 marine 
mammal species (Waring et al., 2000). This bycatch 
included 46 beaked whales taken in the “northern or 
summer stratum” of the fishery that operated along 
the continental shelf break along the southern side of 
Georges Bank (Waring et al., 2009). Pelagic drift gill- 
nets were prohibited after 1998 because of the large 
number of cetaceans taken during fishing operations 
that used them (Waring et al., 2000; 2002). Here, we 
describe the stomach contents of Sowerby’s beaked 
whales taken in this pelagic drift net fishery, and we 
provide the first detailed account of the food habits 
of Sowerby’s beaked whales from the western North 
Atlantic. 
Materials and methods 
We examined the stomach contents of 10 Sowerby’s 
beaked whales taken incidentally in the pelagic drift 
gillnet fishery for Swordfish in the Atlantic between 
August 1989 and July 1996 and a single dead stranded 
1 Santos, M. B., G. J. Pierce, H. M. Ross, R. J. Reid, and B. 
Wilson. 1994. Diets of small cetaceans from the Scottish 
coast. ICES Council Meeting (C.M.) document, 1994/N:11. 
[Presented as a poster.] 
2 Santos, M. B., G. J. Pierce, G. Wijnsma, H. M. Ross, and R. 
J. Reid. 1995. Diets of small cetaceans stranded in Scot- 
land 1993-1995. ICES Council Meeting (C.M.) document, 
1995/N:6. 
individual from Kennebunk, Maine (Table 1 and Fig. 
1). We obtained skin tissue from each bycaught speci- 
men and conducted DNA analysis at the NOAA South- 
east Fisheries Science Center to confirm that each ani- 
mal was in fact a Sowerby’s beaked whale. DNA was 
extracted from the tissue through the use of standard 
proteinase K digestion followed by organic extraction 
(Rosel and Block, 1996). The quality of the DNA was 
assessed through agarose gel electrophoresis, and DNA 
quantity was measured with a fluorometer (Amersham 
Biosciences 3 , now GE Healthcare Life Sciences, Little 
Chalfont, UK). 
To confirm field identifications on the basis of mor- 
phology, the 5’-end of the mitochondrial DNA control 
region was amplified and sequenced as described in 
Sellas et al. (2005). Resultant DNA sequences were 
identified to species through phylogenetic reconstruc- 
tion with an alignment that contained the new con- 
trol region sequences and the sequences obtained from 
the 5 species of beaked whales present in the western 
North Atlantic. Mesoplodont whales form strongly sup- 
ported clades in phylogenetic analyses of control region 
sequences; therefore, this method is well suited to spe- 
cies identification of unknown samples (Henshaw et al., 
1997; Dalebout et al., 2004). 
The unusual stomach anatomy of beaked whales has 
been described in detail by Mead (1989, 1993, 2007). 
We examined the contents of the esophagus and upper 
digestive tract, including the fore stomach, main stom- 
ach, connecting chambers, and pyloric stomach. We fol- 
lowed a standard protocol for analysis of stomach con- 
tents (see Craddock et al., 2009), separating hard parts 
from the remaining digesta by elutriation and then 
decanting them through a sieve with a 0.5-mm mesh. 
We then sorted, dried, and identified all hard parts to 
the lowest possible taxonomic level. Certain diagnostic 
bones of fishes (e.g., otoliths, dentaries, premaxillar- 
ies, and maxillaries) were stored separately from other 
hard parts. Squid beaks and all parasites were counted 
and preserved in 70% ethanol. We archived the con- 
tents of each stomach separately. 
We identified the hard parts of prey items through 
the use of published guides (Roper et al., 1984; Clarke, 
1986; Harkonen, 1986; Vecchione et ah, 1989; Campa- 
na, 2004) and the otolith and skeletal bone reference 
collection prepared by J. E. Craddock at the Woods 
Hole Oceanographic Institution (WHOI). This collec- 
tion is now part of the ichthyology collection of the 
Museum of Comparative Zoology, Harvard University, 
Cambridge, Massachusetts (http://www.mcz. harvard. 
edu/Departments/Ichthyology/researchcoIl.html, ac- 
cessed May 2013). 
We estimated the number of fish prey using half the 
number of otoliths when more than 50 otoliths were 
present. When fewer than 50 otoliths were present, we 
3 Mention of trade names or commercial companies is for iden- 
tification purposes only and does not imply endorsement by 
the National Marine Fisheries Service, NOAA. 
