382 



Fishery Bulletin 94|2). 1996 



et al., 1994). Approximately 99% of the contents ( 145 

 g wet weight) comprised partially digested remains 

 of a single species of lanternfish, Ceratoscopelus 

 maderensis. Other prey were represented only by 

 hard parts, such as otoliths and squid beaks. Cepha- 

 lopod prey remains included 7 upper and one lower 

 beak of Selenoteuthis scintillans and 2 lower beaks 

 of Loligo pealei. In total, 1,994 otoliths from at least 

 8 fish species were recovered from the stomach (Table 

 1). The state of digestion of stomach contents sug- 

 gested that the porpoise had been feeding mostly at 

 night and in the early morning on small-bodied fish 

 and squid. 



Of the prey items we identified from this porpoise, 

 only silver hake, Merluccius bilinearis, are common 

 prey of harbor porpoises in the Gulf of Maine. In sum- 

 mer, harbor porpoises in the Bay of Fundy and Gulf 

 of Maine feed primarily on Atlantic herring, Clupea 

 harengus, augmenting this with silver hake and other 

 demersal species (Smith and Gaskin, 1974; Recchia 

 and Read, 1989 ). Recent analyses of the stomach con- 

 tents of harbor porpoises from the southern Gulf of 

 Maine indicate a shift to smaller-bodied prey, such 

 as pearlside, Maurolicus weitzmani, during autumn 

 (Readet al. 2 ). 



These observations lead us to suggest that harbor 

 porpoises in the northwest Atlantic are not tied to 

 shallow nearshore waters during winter. The stom- 

 ach contents of this specimen indicate that porpoises 

 can forage successfully on midwater prey in deep 

 water. Similar prey remains have been recovered 



Read, A.J. , J. E. Craddock, and D. Gannon 1994. Life his- 

 tory of harbor porpoises and pilot whales taken in commercial 

 fishing operations off the Northeast United States. Northeast 

 Fisheries Science Center, Natl. Mar. Fish. Serv., Woods Hole. 

 MA 02543. Final Contract Rep. 50-EANE-2-00082. 



from the stomach of a harbor porpoise taken in Irish 

 waters (Rogan and Berrow ;i ). Porpoises can dive to 

 depths of more than 225 m (Westgate et al., 1995), 

 although deep-feeding excursions would not be nec- 

 essary if mesopelagic prey are taken at night when 

 they migrate toward the surface. Adult Cerato- 

 scopelus maderensis, for example, are found at depths 

 of 33-250 m at night (Scott and Scott, 1988). If por- 

 poises are able to use the shelf edge and slope wa- 

 ters during winter, a large expanse of suitable habi- 

 tat is available from the Grand Banks to Cape 

 Hatteras. This hypothesis is supported by the obser- 

 vations of Stenson and Reddin, 4 who reported the 

 incidental capture of harbor porpoises in experimen- 

 tal drift nets set during winter and spring off the 

 slope of the Grand Banks outside the 1,000 m isobath. 



A largely offshore winter distribution of harbor 

 porpoises would explain the paucity of sightings of 

 this species outside the summer and fall months. The 

 Gulf of Maine population of harbor porpoises is be- 

 lieved to number more than 45,000 individuals 

 (Palka, in press); such a large number of animals 

 would have been detected in coastal waters, even 

 during winter. We hypothesize that the population 

 disperses to the south during winter and is found in 

 low densities over the shelf and slope waters, possi- 

 bly mixing with porpoises that summer in the Gulf 

 of St. Lawrence and Labrador. Molecular genetic 

 techniques are being used to address the question of 

 stock mixing during winter ( Rosel 5 ). The many young 

 porpoises that strand along the mid-Atlantic coast 

 during this season, most of which are less than a 

 year old, may have been segregated from the remain- 

 der of the population after they were weaned from 

 their mothers. 



We recognize that it is difficult to test this hypoth- 

 esis of offshore dispersion during winter. Traditional 

 visual census techniques are ineffective with very 

 low densities of harbor porpoises, particularly given 

 the weather conditions that prevail during this sea- 

 son. Few fisheries that might capture harbor por- 

 poises are operative during this season; pelagic drift- 

 net fishing effort is currently limited to only a few 



1 Rogan. E., and S. D. Berrow. 1995. Aspects of the biologj of 

 the harbour porpoise. Phocoena phocoena, in Irish waters 

 Paper SC/47/SM40 presented at the 47th meeting of the Scien- 

 tific Committee of the International Whaling Commission, 

 Dublin, Ireland. 



1 Stenson, G B., and D G Reddin. 1991. Incidental catches 

 of small cetaceans in drift nets during salmon tagging experi 

 ments in the Northwest Atlantic In Harbor porpoise in east- 

 ern North America: status and research needs; workshop held 

 5-8 Mav 1992 at Northeast Fish. Si i Cenl Natl Mar Fish. 

 Serv. Woods Hole, MA 02543. 



Rosel. P. 1995. Department of Zoology. Univ. New Hamp- 

 shire. Durham NH 03824 Personal commun. 



