Occurrence and group 

 characteristics of minke whales, 

 Balaenoptera acutorostrata, 

 m Massachusetts Bay and 

 Cape Cod Bay 



Margaret A. Murphy 



Cetacean Research Program, Center for Coastal Studies 

 Provincetown, Massachusetts 02657 



The minke whale, Balaenoptera 

 acutorostrata, is one of the small- 

 est of the baleen whales. Despite 

 exploitation by the whaling indus- 

 try in recent years, comparatively 

 little is known about the biology 

 and behavior of this species. The 

 minke has a cosmopolitan distribu- 

 tion, although recent biochemical 

 studies suggesting large genetic 

 differences between oceanic popu- 

 lations (Amos and Dover, 1991; 

 Hoelzel and Dover, 1991; van Pijlen 

 et al., 1991; Wada and Numachi, 

 1991; Wada et al., 1991) have cast 

 some doubt on the long-held belief 

 that all populations constitute a 

 single species. As is the case for 

 most baleen whales, minke whales 

 appear to migrate to high latitudes 

 in the summer for feeding and to 

 travel to tropical waters in the win- 

 ter for birthing (Horwood, 1989; 

 Mitchell, 1991). However, specific 

 breeding grounds have yet to be 

 unequivocally identified, and it is 

 unknown whether both sexes and 

 all age classes in a population un- 

 dertake the migration to low lati- 

 tudes. In some temperate, subtropi- 

 cal, and tropical areas, minke 

 whales are observed throughout 

 the year (Ivashin and Votrogov, 

 1981; Best, 1982; Gong, 1987; 

 Stern, 1990), although it is unclear 

 whether these sightings represent 

 year-round residency on the part of 

 particular individuals or a more 



general movement through the 

 area by members of one or more 

 populations. 



In recent years, much has been 

 learned about other mysticetes 

 through long-term studies based on 

 the identification of individual 

 whales (see Hammond etal., 1990). 

 Unfortunately, minke whales lack 

 the great variability in natural 

 markings that have facilitated de- 

 tailed investigations of larger 

 confamilials (such as humpback 

 whales, Megaptera novaeangliae). 

 This, together with the difficulty of 

 photographing them owing to their 

 small size and great speed, has hin- 

 dered studies based on photo- 

 graphic identification, although 

 studies of small localized popula- 

 tions have been possible (Dorsey, 

 1983; Dorsey et al., 1990; Stern et 

 al., 1990). In general, however, 

 studies of free-ranging minke 

 whales have been few, and their 

 population structure, social organi- 

 zation, and migratory movements 

 remain poorly understood. 



Minke whales are commonly ob- 

 served in the waters of Massachu- 

 setts Bay and Cape Cod Bay in New 

 England, and since 1979, sightings 

 of this species have been routinely 

 recorded from both commercial 

 whalewatching vessels and dedi- 

 cated surveys. In this paper, sight- 

 ing records are examined in an ef- 

 fort to describe the temporal distri- 



bution, seasonal abundance, and 

 feeding behavior of minke whales 

 in this region. These data are then 

 compared with information re- 

 ported for this species from other 

 areas, notably within the North 

 Atlantic. 



Methods 



Study area 



The study area includes the coastal 

 region dominated by Cape Cod Bay 

 and Massachusetts Bay along the 

 northeastern coast of the United 

 States (Fig. 1). Cape Cod Bay is a 

 semi-enclosed sandy basin with a 

 maximum depth of 60 m. Massa- 

 chusetts Bay lies north of Cape 

 Cod; depths range from 40 m to 100 

 m except on Stellwagen Bank, an 

 elongated glacial feature of sand 

 and gravel approximately 25 km in 

 length, which has a minimum 

 depth of 18 m. 



Effort 



Data were collected between 1979 

 and 1992. The total number of 

 cruises conducted during this pe- 

 riod was 10,249 (this figure excludes 

 those made in certain weather con- 

 ditions, as noted below); of these, 

 9,728 (94.9%) were made from 30- 

 m commercial whalewatching ves- 

 sels operating between April and 

 October of each year from Province- 

 town, Massachusetts. Additional 

 cruises («=374) were made from a 

 12-m diesel-powered research ves- 

 sel beginning in the autumn of 

 1983, and 77 cruises were made 

 from a 14-m auxiliary ketch begin- 

 ning in the autumn of 1985. The 

 remaining non-whalewatch cruises 

 were made primarily from a 5-m 

 inflatable boat. Because virtually 

 all of the whalewatching trips were 

 approximately four hours in length, 



Manuscript accepted 15 December 1994. 

 Fishery Bulletin 93:577-585 (1995). 



577 



