Food Habits of Sowerby's Beaked Whales (Mesoplodon Bidens) Taken in the Pelagic Drift Gillnet Fishery of the Western North Atlantic
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Food habits of Sowerby's beaked whales (Mesoplodon bidens) taken in the pelagic drift gillnet fishery of the western North Atlantic Item Type article Authors Wenzel, Frederick W.; Polloni, Pamela T.; Craddock, James E.; Gannon, Damon P.; Nicolas, John R.; Read, Andrew J.; Rosel, Patricia E. DOI 10.7755/FB.111.4.7 Download date 04/10/2021 11:21:11 Link to Item http://hdl.handle.net/1834/30395 381 Abstract—We describe the food hab- Food habits of Sowerby’s beaked whales its of the Sowerby’s beaked whale (Mesoplodon bidens) from observa- (Mesoplodon bidens) taken in the pelagic drift tions of 10 individuals taken as bycatch in the pelagic drift gillnet gillnet fi shery of the western North Atlantic fishery for Swordfish (Xiphias gla- dius) in the western North Atlan- Frederick W. Wenzel (contact author)1 tic and 1 stranded individual from Pamela T. Polloni2 Kennebunk, Maine. The stomachs of 8 bycaught whales were intact James E. Craddock2 (deceased) and contained prey. The diet of Damon P. Gannon3 these 8 whales was dominated by John R. Nicolas1 (deceased) meso- and benthopelagic fishes that 4 composed 98.5% of the prey items Andrew J. Read found in their stomachs and cepha- Patricia E. Rosel5 lopods that accounted for only 1.5% of the number of prey. Otoliths and Email address for contact author: [email protected] jaws representing at least 31 fish taxa from 15 families were pres- 1 Protected Species Branch 4 Division of Marine Science and Conservation ent in the stomach contents. Fishes, Northeast Fisheries Science Center Nicholas School of the Environment primarily from the families Mori- National Marine Fisheries Service, NOAA Duke University dae (37.9% of prey), Myctophidae 166 Water Street Beaufort, North Carolina 28516 (22.9%), Macrouridae (11.2%), and Woods Hole, Massachusetts 02543 Phycidae (7.2%), were present in all 5 Protected Resources and Biodiversity Division 2 8 stomachs. Most prey were from 5 Biology Department Southeast Fisheries Science Center fish taxa: Shortbeard Codling (Lae- Woods Hole Oceanographic Institution National Marine Fisheries Service, NOAA monema barbatulum) accounted for Woods Hole, Massachusetts 02543 646 Cajundome Blvd. 35.3% of otoliths, Cocco’s Lantern- 3 Department of Biology Lafayette, Louisiana 70506 fish (Lobianchia gemellarii) contrib- Bowdoin College uted 12.9%, Marlin-spike (Nezumia 6500 College Station bairdii) composed 10.8%, lantern- Brunswick, Maine 04011 fishes (Lampanyctus spp.) accounted for 8.4%; and Longfin Hake (Phycis chesteri) contributed 6.7%. The mean number of otoliths per stomach was 1196 (range: 327–3452). Most of the fish prey found in the stomachs was quite small, ranging in length from (e.g., Waring et al., 2010). Waring et 4.0 to 27.7 cm. We conclude that the The Sowerby’s beaked whale (Meso- Sowerby’s beaked whales that we plodon bidens) is 1 of 4 species of the al. (2001) reported that off the north- examined in this study fed on large genus Mesoplodon (Family Ziphiidae) eastern coast of the United States, numbers of relatively small meso- in the western North Atlantic. The Mesoplodon beaked whales were and benthopelagic fishes that are Sowerby’s beaked whale is restricted encountered most frequently along abundant along the slope and shelf to the North Atlantic and the most the shelf break and north wall of break of the western North Atlantic. boreal species in its genus, with ob- the Gulf Stream. The habitat prefer- servations recorded as far north as ences of these animals overlap with 71°N (Carlstrom et al., 1997; Hook- the habitat preferences of the sperm er and Baird, 1999; McAlpine and whale (Physeter macrocephalus), but Rae, 1999; Lucas and Hooker, 2000; Sowerby’s beaked whales were con- Waring et al., 2010). There is also a centrated on the colder shelf edge single record of a stranded Sowerby’s (Griffi n, 1999; Waring et al., 2001). beaked whale from the Gulf of Mexi- MacLeod et al. (2003) reviewed co (Bonde and O’Shea, 1989). available information on the diet of Most information on the distribu- beaked whales and concluded that Manuscript submitted 4 February 2013. tion and abundance of beaked whales fi shes are important prey of 5 of the Manuscript accepted 30 August 2013. off the northeastern coast of the 10 (Family Ziphiidae) species for Fish. Bull. 111:381–389. United States has been derived from which diet information was avail- doi: 10.7755/FB.111.4.7 vessel surveys conducted by NOAA able. This conclusion stands in con- Fisheries. It is diffi cult to identify trast to earlier reviews of the diet The views and opinions expressed or implied in this article are those of the Mesoplodon beaked whales to species of beaked whales where the impor- author (or authors) and do not necesarily level at sea; therefore estimates of tance of squids was emphasized (e.g., refl ect the position of the National abundance are often reported at the Clarke, 1986). Beaked whales are Marine Fisheries Service, NOAA. generic level in stock assessments cryptic, deep-diving odontocetes, and, 382 Fishery Bulletin 111(4) as a result, direct observation of foraging is impossi- individual from Kennebunk, Maine (Table 1 and Fig. ble. Most insight into their feeding behavior has come 1). We obtained skin tissue from each bycaught speci- from digital acoustic tags, which record the 3-D move- men and conducted DNA analysis at the NOAA South- ment and acoustic environment of tagged individuals east Fisheries Science Center to confi rm that each ani- (e.g., Madsen et al., 2005). Application of these tags to mal was in fact a Sowerby’s beaked whale. DNA was individuals of the Blainville’s beaked whale (Mesoplo- extracted from the tissue through the use of standard don densirostris) indicates that this species forages at proteinase K digestion followed by organic extraction depths of more than 1000 m in dives that may last for (Rosel and Block, 1996). The quality of the DNA was almost 1 h (Arranz et al., 2011). To date, however, no assessed through agarose gel electrophoresis, and DNA Sowerby’s beaked whales have been studied with digi- quantity was measured with a fl uorometer (Amersham tal acoustic tags. Biosciences3, now GE Healthcare Life Sciences, Little Given the challenges of studying live whales, all Chalfont, UK). published information on the food habits of the Sow- To confi rm fi eld identifi cations on the basis of mor- erby’s beaked whale has been acquired from stranded phology, the 5’-end of the mitochondrial DNA control specimens (Dix et al., 1986; Lien and Barry, 1990; Lien region was amplifi ed and sequenced as described in et al. 1990; Ostrom et al., 1993; Pereira et al., 2011; Sellas et al. (2005). Resultant DNA sequences were Spitz et al., 2011; Santos et al.1,2). Recent analysis of identifi ed to species through phylogenetic reconstruc- the stomach contents of 10 stranded Sowerby’s beaked tion with an alignment that contained the new con- whales from the Azores in the eastern North Atlan- trol region sequences and the sequences obtained from tic (Pereira et al., 2011) provided evidence that small the 5 species of beaked whales present in the western meso- and bathypelagic fi shes constitute an important North Atlantic. Mesoplodont whales form strongly sup- part of the diet of this species in this area. ported clades in phylogenetic analyses of control region One largely untapped source of information on the sequences; therefore, this method is well suited to spe- biology of the Sowerby’s beaked whale comes from a cies identifi cation of unknown samples (Henshaw et al., sample of animals taken as bycatch in a pelagic drift 1997; Dalebout et al., 2004). gillnet fi shery for Swordfi sh (Xiphias gladius) that op- The unusual stomach anatomy of beaked whales has erated in the western North Atlantic between 1989 and been described in detail by Mead (1989, 1993, 2007). 1998. The pelagic drift gillnet fi shery was monitored by We examined the contents of the esophagus and upper observers from the Northeast Fisheries Observer Pro- digestive tract, including the fore stomach, main stom- gram (NEFOP); these observers documented bycatch ach, connecting chambers, and pyloric stomach. We fol- consisting of more than 1100 individuals of 14 marine lowed a standard protocol for analysis of stomach con- mammal species (Waring et al., 2000). This bycatch tents (see Craddock et al., 2009), separating hard parts included 46 beaked whales taken in the “northern or from the remaining digesta by elutriation and then summer stratum” of the fi shery that operated along decanting them through a sieve with a 0.5-mm mesh. the continental shelf break along the southern side of We then sorted, dried, and identifi ed all hard parts to Georges Bank (Waring et al., 2009). Pelagic drift gill- the lowest possible taxonomic level. Certain diagnostic nets were prohibited after 1998 because of the large bones of fi shes (e.g., otoliths, dentaries, premaxillar- number of cetaceans taken during fi shing operations ies, and maxillaries) were stored separately from other that used them (Waring et al., 2000; 2002). Here, we hard parts. Squid beaks and all parasites were counted describe the stomach contents of Sowerby’s beaked and preserved in 70% ethanol. We archived the con- whales taken in this pelagic drift net fi shery, and we tents of each stomach separately. provide the fi rst detailed account of the food habits We identifi ed the hard parts of prey items through of Sowerby’s beaked whales from the western North the use of published guides (Roper et al., 1984; Clarke, Atlantic. 1986; Harkonen, 1986; Vecchione et al., 1989; Campa- na, 2004) and the otolith and skeletal bone reference collection prepared by J.