FISHERY BULLETIN: VOL. 83, NO. 3 



morning and a lower level during midday, but we 

 have no direct evidence of this in bowheads. 



Although underwater blows seem to occur more 

 often in shallow water when whales may be feeding, 

 we have not included this behavior as a definite part 

 of feeding. There is only a general similarity to 

 bursts of bubbles associated with feeding humpback 

 whales in the North Atlantic (Hain et al. 1982), and 

 the bubble nets reported for humpbacks by Jurasz 

 and Jurasz (1979) are very different. 



Social Behavior 



Behavior was termed social when whales appeared 

 to be pushing, nudging, or chasing each other, or 

 when they were within half a body length of one 

 another. Whales within half a body length almost 

 always stayed close to each other, and oriented 

 towards each other or interacted in some manner. 

 Thus, our use of proximity as an indication of social- 

 ity was appropriate. Interactions between mothers 

 and calves, and between whales skim feeding in close 

 proximity, were not included as social interactions in 

 this analysis. Whales may, of course, communicate 

 by sound, and thus may socialize over far greater 

 distances than those described here. Our sonobuoys 

 often detected bowhead calls while socializing was 

 underway. However, we could not verify whether 

 acoustic communication was occurring between any 

 particular whales, so we restricted our definition of 

 socializing to visible behavior. Synchronous diving 

 and surfacing over areas many kilometers in 

 diameter (see below) may represent a different form 

 of social interaction from what we discuss in this sec- 

 tion. Because groups of whales usually could not be 

 reidentified positively from one dive to the next, we 

 treated observations of social behavior at intervals of 

 > 5 min as independent for the purpose of counting 

 number of interactions. Conversely, we did not score 

 social behavior by one group more than once in 5 min 

 when counting frequency. 



Frequency of Socializing 



Social behavior was seen less frequently in late 



August-early September than in early August, both 

 in 1980 and 1981 (Table 2). Rugh and Cubbage 

 (1980) and Carroll and Smithhisler (1980) reported a 

 higher incidence of social interactions during the 

 spring migration around Alaska than we saw at any 

 time. The apparent waning of social activity from 

 early to late August may be part of a continuing 

 decrease from a higher level in spring. 



Little socializing was observed in 1982. In presum- 

 ably undisturbed whales, we observed only seven 

 cases, all on 8, 19, and 23 August. Throughout 

 August 1982, most whales were alone and making 

 long dives. The overall socializing rate for each year 

 (Table 2) demonstrates the dramatic decrease in 

 socializing in 1982 compared with the two previous 

 years. This decrease may be related to the increase 

 in 1982 in the average distance from shore and depth 

 of water at locations where bowheads were studied. 

 However, we found no consistent trend for social- 

 izing to occur more often in shallow water than in 

 deep water within 1 yr. 



There was some indication of hour-to-hour vari- 

 ation in amount of social activity in all 3 yr (Fig. 5). 

 In 1980 and 1981, it peaked around 1400-1600 MDT, 

 the noon period by sun time. In 1982, the few (7) 

 cases were recorded from 1600 to 2000 MDT, some- 

 what after solar noon (Fig. 5). In both 1980 and 

 1981 , there was another peak after 2000 MDT. Why 

 whales should engage in more social activity around 

 noon (and possibly in the evening) than at other 

 times is unknown. However, diel rhythms are well 

 known in several mammals (e.g., Saayman et al. 

 1973 for bottlenose dolphins; Matsushita 1955 for 

 sperm whales; Schevill and Backus 1960 for hump- 

 back whales). The increased level of socializing 

 around noon may reflect a lowered level of feeding at 

 that time, which Nemoto (1970) suggested for baleen 

 whales in general. 



Physical Interactions 



During surface interactions with nearby whales, 

 socializing whales often turned. In contrast, non- 

 socializing whales often surfaced and dove again 

 without changing direction. In the 3 yr, turns oc- 



Table 2.— Number of social interactions per aerial observation hour, divided 

 into about 10-d periods, in 1980, 1981, and 1982. Only presumably undisturbed 

 periods are included. 



Year 1-10 Aug. 11-20 Aug. 21-31 Aug. 1-10 Sept. 



1980 28/7.0 = 4.0 



1981 14/4.3 = 3.3 



1982 1/1.5 = 0.7 



6/2.9 = 2.1 



12/5.5 = 2.2 



3/7.6 = 0.4 



8/7.7 = 1.0 



9/3.3 = 2.7 



3/12.8 = 0.2 



4/4.0 = 1.0 



Overall 



42/17.6 = 2.4 



39/17.1 = 2.3 



7/21.9 = 0.3 



362 



