NOTE Murphy: Occurrence and group characteristics of Balaenoptera acutorostrata 



583 



of sightings were singletons it is possible that sex or 

 age class has little or no effect on group size in this 

 area, unless one sex or class is disproportionately 

 represented here. The apparent predominance of 

 immature whales among stranded specimens may 

 reflect a similar overrepresentation of juveniles in 

 the general population; if this is the case, the abun- 

 dance of singletons would agree with the finding of Kato 

 et al. (1990b) that immature animals along with ma- 

 ture males tend to be solitary, whereas mature females 

 usually form schools, especially near the pack ice. 



lar to that reported from other areas such as the 

 western coast of North America where minke whales 

 appear to act independently of each other even 

 though several individuals may be present in the 

 same area while feeding (Hoelzel et al., 1989; Dorsey 

 et al., 1990). According to many studies (Ivashin and 

 Votrogov, 1981; Bushuev, 1991, Sears et al. 3 ), minke 

 whales tend to group together when food is abundant, 

 but it was unclear whether these animals were feed- 

 ing cooperatively or were drawn to the same area by 

 the availability of food and were feeding independently. 



Feeding behavior 



In this study less than one percent of all minke whale 

 sightings involved confirmed feeding behavior. The 

 CeTAP study (1982) also reported relatively few 

 sightings of surface feeding. The lack of surface feed- 

 ing in the study area is odd given that sympatric 

 confamilials are commonly observed feeding (e.g. 

 humpback whales [Payne et al., 1986]; fin whales 

 [Overholtz and Nicolas, 1979]). In other areas of the 

 North Atlantic, minke whales are observed feeding, 

 displaying surface lunges and rolling (Sears et al. 3 ; 

 Haycock and Mercer 4 ). Near the San Juan Islands, 

 off the west coast of North America, minke whales 

 also exhibit lunging and rolling behavior during feed- 

 ing (Hoelzel et al., 1989; Dorsey et al., 1990). 



Off the San Juan Islands minke whales appear to 

 prey mainly on small schooling fish (juvenile herring, 

 Clupea harengus; sand lance, Ammodytes spp.) 

 (Dorsey, 1983; Dorsey et al., 1990), which are also 

 the principal food source for minke whales off the 

 Mingan Islands (Sears et al. 3 ). Both humpback and 

 fin whales feed primarily on herring or sand lance in 

 the southern Gulf of Maine (Overholtz and Nicolas, 

 1979; Payne et al., 1990); many observers assume 

 that these fish also represent a principal prey of 

 minke whales, a belief which is strengthened by the 

 scarcity of minke whales in Massachusetts Bay dur- 

 ing 1986 and 1987 when the local sand lance popula- 

 tion crashed (Payne et al., 1990). However, it is not 

 understood why these minke whales rarely exhibit 

 feeding behavior at the surface, unless whales in this 

 area either exploit fish schools at greater depths than 

 do whales recorded for other feeding grounds or em- 

 ploy a foraging technique that does not utilize the 

 surface for catching prey. 



Nearly all minke whales observed feeding during 

 this study were singletons, a finding which is simi- 



4 Haycock, C. R., and S. N. Mercer. 1984. Observations and notes 

 on the abundance and distribution of cetaceans in the Eastern 

 Bay of Fundy near Brier Island, Nova Scotia, in August and 

 September 1984. Unpubl. Rep. 



Conclusion 



In general, both the yearly and seasonal distribu- 

 tion of minke whales in Massachusetts Bay and Cape 

 Cod Bay is similar to that found for other popula- 

 tions of this species. The data in this study also gen- 

 erally agree with other published information per- 

 taining to group size, feeding behavior, and the oc- 

 currence of mother-and-calf pairs. Unfortunately, 

 because the social structure and group composition 

 of the minke whales observed in this study are un- 

 known, it is impossible to determine whether or not 

 the minke whales of Massachusetts and Cape Cod 

 bays exhibit the same segregational patterns that 

 have been suggested for other populations of this 

 species in both the northern and southern hemi- 

 spheres. It would also be valuable to explore whether 

 individual minke whales return to the same area 

 from year to year as documented off the west coast 

 of North America, or whether the minke whales seen 

 here represent transient individuals from one or more 

 populations. Continued study with an emphasis on 

 photographic identification of individuals is greatly 

 needed as well as continued work in the biopsy of 

 individuals throughout the year in order to gain some 

 insight on the sex ratio, genetic structure, and group 

 composition of this and other populations. 



Acknowledgments 



This manuscript would not have been possible with- 

 out the help and support of many. I thank Phil 

 Clapham for his insight and time, without whom sta- 

 tistical analyses would not have been so much fun. 

 In addition, I thank the researchers at the Center 

 for Coastal Studies for their suggestions and all 

 around interest in minke whales, the naturalists 

 aboard the Dolphin Fleet whalewatch vessel for their 

 great (and much appreciated) effort in collecting in- 

 formation on this species, and lastly, the Dolphin 

 Fleet captains and crew for acknowledging that 



