580 



Fishery Bulletin 93(3). 1995 



Group-size frequency 



A total of 5,806 minke whale sightings were recorded 

 for which the group size could be reliably determined. 

 Observed group-size frequency ( x=1.06, SD=0.315) 

 for singletons (rc=5,536) was 95.3%, for pairs (n=223) 

 3.8%, and for trios (n=46) 0.8%. With the exception 

 of a single group of five whales, no groups larger than 

 three were observed during this study. 



Feeding behavior 



A total of only 27 (0.4%) of 6,266 sightings involved 

 confirmed feeding at the surface. These sightings 

 occurred in all months between May and October 

 inclusively. In 24 of the 27 sightings of feeding, group 

 size was recorded: single animals accounted for 21 

 (87.5%) of these, two sightings involved pairs, and 

 one sighting a group of three whales. 



7 - 

 6 



Q- 



a 

 a. 



i/i 4 



3 



2 H 

 1 



* 



-f- 



] I I f 

 \ i i i 



Jan Feb Mar Apr May Jin Jul Aug Sep Oct Nov Dec 



Month 



Figure 3 



Observed variations in occurrence (mean and standard error) 

 of minke whales, Balaenoptera acutorostrata, in Massachusetts 

 Bay and Cape Cod Bay by month for all years (1979-92) of the 



study. 



Discussion 



Temporal occurrence 



Minke whales appear to arrive in the waters of 

 Cape Cod Bay and Massachusetts Bay in the 

 early spring and in some years occurred as late 

 as December. The considerable interannual 

 variability in the abundance of minke whales 

 probably reflects variation in effort (see Table 

 1) or fluctuations, or both, in the abundance and 

 distribution of prey That it may be linked to 

 the latter is suggested by the very low sighting 

 rates recorded in 1986 and 1987, two years in 

 which the local abundance of sand lance (Am- 

 modytes spp. ) is known to have been at a mini- 

 mum and when other piscivorous mysticetes 

 were largely absent from the study area (Payne 

 et al., 1990). However, the concentration of ef- 

 fort on other mysticetes (and consequently on 

 areas preferred by them) may have introduced 

 a bias against minke whale sightings if these 

 whales exhibit significant differences in habi- 

 tat preference (this is currently unknown). 

 Interannual variability in abundance has also 

 been reported in other areas and has been simi- 

 larly linked to prey availability, as well as to 

 effort and, in Arctic areas, distribution of sea 

 ice (Sigurjonsson, 1982; Larsen and 0ien, 1988). 



There was also considerable variation in 

 abundance from month to month. The data re- 

 ported here indicate a distinct peak in abun- 

 dance beginning in July and continuing through 

 September. No minke whales were observed in 

 January or February: although this may have 

 been due to the markedly decreased sampling 

 effort during these two months, this appears 

 unlikely given the dedicated (i.e. non-whale- 

 watching) nature of the surveys conducted at 

 this time and the frequently calm conditions 

 which were a prerequisite for such cruises. 



This general pattern of occurrence (abundant 

 in summer, scarce or absent in winter) is simi- 

 lar to that reported for other high-latitude 



