WI'RSIOETAL.: BEHAVIOR (IF HOWIIKADWHALKS 



by industrial activity in nearshore waters is also a 

 possibility (see footnote 12). The fact that predomi- 

 nant feeding modes shifted from year to year is con- 

 sistent with the "variable food supply" explanation. 

 In 1980, whales in shallow water exhibited bottom 

 feeding and skim feeding, while whales in slightly 

 deeper water apparently fed in the water column. In 

 1981, most feeding appeared to be water-column 

 feeding and skim feeding. In 1982, whales made long 

 dives and presumably were often feeding in the 

 water column. 



Bowhead whales have finely fringed baleen, the 

 longest of any whale species, and are adapted to 

 strain small zooplankters from the sea. Stomach con- 

 tents indicate that, at least in Alaskan waters, bow- 

 heads feed mainly on copepods. euphausiids, and 

 amphipods (Marquette et al. 1982). Summering bow- 

 heads tend to occur at locations where copepod abun- 

 dance is above average (Giiffiths and Buchanan foot- 

 note 7). Lowry and Burns (1980) examined five 

 whales killed off Barter Island, AK, in autumn and 

 found about 60% copepods and about 37% euphau- 

 siids in their stomachs. However, all five whales may 

 have fed at least partially near the sea floor; about 

 3% of the stomach contents consisted of mysids, 

 amphipods, other invertebrates, and fish. Durham 

 (1972) also suggested, based on stomach content 

 analyses showing mud-dwelling tunicates, vegeta- 

 tion, silt, and small pebbles, that bowheads feed at 

 times near the bottom. Lowry and Burns concluded 

 from stomach content analyses that "... a feeding 

 dive probably involves swimming obliquely from sur- 

 face to bottom and back, feeding the entire time." 

 Although this may be true at times, there is no direct 

 information on underwater feeding behavior. We 

 suspect that bowheads can detect concentrations of 

 prey and open their mouths when appropriate. The 

 bowhead whale is perhaps a more catholic feeder 

 than once thought, capable of taking advantage of 

 many different types of prey items at various posi- 

 tions in the water column and near the bottom. Year- 

 to-year changes in distributions and availability of 

 prey may account for the distributional changes that 

 we have observed, but data on yearly changes in 

 prey are lacking. 



During spring migration around Alaska, bowhead 

 whales appear to do little feeding; their stomachs 

 usually are nearly empty (Marquette et al. 1982). On 

 the other hand, feeding continues in autumn after 

 bowheads have moved from the Canadian to the 

 eastern part of the Alaskan Beaufort Sea (Lowry 

 and Burns 1980; Marquette et al. 1982). Some 

 feeding occurs in autumn as far west as the Point 

 Barrow area (Lowry et al. 1978; Braham et al. 1984), 



and perhaps farther west off the Soviet coast 

 (Johnson et al. 1981). 



Feeding is not the only activity of bowheads in 

 summer. Socializing, perhaps with occasional sexual 

 activity, is also important. In 1982, however, there 

 was less socializing than in 1980-81. Whales were in 

 close proximity to each other less in 1982. This year- 

 to-year difference in proximity may be related to the 

 difference in type of feeding. While skim feeding at 

 the surface, whales are often in close echelons. The 

 proximity necessary for echelon feeding offers more 

 chance for socializing, and socializing before or after 

 feeding in echelon may be important to that mode of 

 feeding. When whales appear to feed in the water 

 column, however, they usually do not stay as close 

 together. Thus, this type of feeding may neither re- 

 quire nor stimulate aggregations of animals, and the 

 suspected predominance of water-column feeding in 

 1982 may explain the low socializing rate that year. 

 Even when there is no close socializing, however, 

 animals are often in a dispersed group within which 

 acoustic communication is probably possible. Our 

 observations of surfacing and dive synchrony by 

 whales spread over distances of several kilometers 

 indicate that they may have been in touch by acoustic 

 communication. 



The primary mating period of bowhead whales 

 occurs in spring, including the spring migration 

 (Everitt and Krogman 1979; Carroll and Smithhisler 

 1980; Johnson et al. 1981; Nerini et al. 1984). We 

 saw some evidence for sexual activity in the Cana- 

 dian Beaufort Sea in both 1980 and 1981, but not in 

 1982. Even the active rolling at the surface that we 

 observed in 1981, however, was not as boisterous as 

 observed by Everitt and Krogman in spring. Also, 

 we found an indication of less social activity in late 

 August-early September than in early August. This 

 apparent waning in social activity may be a contin- 

 uation of the waning of sexual activity that started in 

 late spring. 



Many calves are born in winter or spring before 

 the whales reach Point Barrow, although some may 

 be born in early summer (Davis et al. footnote 9). 

 During summer, the activities of female bowheads 

 with accompaning calves are closely coordinated 

 with those of their calves, and differ in some details 

 from the activities of other adult bowheads (this 

 study; Wursig et al. 1984). At least some calves re- 

 main with their mothers for the fall migration (Davis 

 and Koski 1980). We know of no information con- 

 cerning the age of weaning of bowhead calves, but in 

 the closely related right whale, at least some calves 

 remain with their mothers for 1 yr and ultimately 

 separate from their mothers after returning to the 



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