WI'KSK; KTAL.: BKIIA\1()K(»F HOWHKAI) whalks 



Table 1. — Dives preceded by a predive flex among noncalf 

 bowheads early and late August 1982. The frequency of 

 occurrence is significantly highier after 19 August (chi-square 

 = 4.29, df = 1, 0.025 < P< 0.05). 



7.465 min, n = 36; Mann-Whitney U = 97.5, P < 

 0.01). Five dives were preceded by two predive 

 flexes, with the flexes separated by a blow. Two 

 dives were preceded by three flexes. We have no 

 data on durations of dives following multiple flexes. 



During the dive, which can at times be predicted 

 by the predive flex, the whale makes its body convex 

 and pitches forward and down. If the angle of sub- 

 mergence is steep, the tail is usually raised above the 

 surface; if not, the tail may remain below or just 

 touch the surface. Rarely do bowheads sink down 

 without visibly arching the back. 



In 1982, 59 of 138 dives (42.8%) were preceded by 

 raised flukes. Of the 32 dives preceded by one or 

 more predive flexes, 21 also showed raised flukes. 

 These two predive behaviors tended to occur 

 together (x" = 3.94, P < 0.05, df = 1), and dives with 

 raised flukes were significantly longer than those not 

 preceded by raised flukes (18.67 ± SD 9.966 min, n 

 = 12, vs. 10.05 ± 6.956 min, n = 38; Mann-Whitney 

 U = 114, P< 0.01). 



There was no difference in durations of surfacings 

 concluded with and without raised flukes. However, 

 surfacings including predive flexes tended to be 

 longer than those without predive flexes (3.09 + SD 

 1.038 min, n = 14, vs. 1.79 ± 1.284 min, w = 52; i = 

 3.50, df = 64, P < 0.001), probably because dura- 

 tions of surfacings and dives are correlated (Wiirsig 

 et al. 1984). 



The function of the predive flex is unknown. 

 Flexes occur more often before longer dives (which 

 may take the whales deeper in the water column). 

 Raising the flukes before a dive appears related to 

 the steepness of the dive; whales that roll forward 

 while dropping the front of the body at least 30° 

 below the water surface usually raise their flukes. 

 The weight of the raised tail stock in the air must 

 help propel the animal downward (much as human 

 skin divers raise their legs above the surface during 

 the initiation of a steep dive). Although raised flukes 

 are common during steep dives in many whales, the 

 predive flex has not been reported in other spe- 

 cies. 



The Underwater Blow 



The underwater blow is a burst of air emitted 

 underwater. The bubble burst is circular and up to 15 

 m in diameter when it arrives at the surface. Release 

 of air underwater was recorded about 10 times via 

 nearby (< 1 km away) sonobuoys; the noise was 

 detectable for 3-4 s, but the white water and expand- 

 ing concentric wave were visible much longer. On 

 one occasion, we definitely saw that the air came 

 from the blowhole rather than the mouth, and we 

 believe that this is always true. We saw underwater 

 blows immediately after whales dove and just before 

 they surfaced, but more usually in the middle of the 

 dive, when the whales were out of sight. 



Underwater blows were most frequent in 1980 

 during periods of pronounced feeding in water < 14 

 m deep (see Feeding section). In 1980, we saw 158 

 underwater blows in 30.4 observation hours; in 1981, 

 57 blows in 30.8 observations hours; and in 1982, 

 only 6 blows in 36.5 observation hours. (The dif- 

 ference between years is statistically significant; x^ 

 = 189, df = 2, P < 0.001.) Concurrently, whales 

 tended to be found in progressively deeper water 

 from 1980 to 1982. 



Underwater blowing occurred more often in the 

 morning and evening than around solar midday in 

 both 1980 and 1981 (Fig. 4; solar noon occurs about 

 1500 MDT in the eastern Beaufort Sea). The midday 

 "lull" in underwater blowing coincided with a peak in 

 frequency of socializing, the main nonfeeding 

 behavior observed (see Social Behavior section 

 below). Nemoto (1970) suggested that baleen whales 

 in general show a high level of feeding activity in the 



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TIME OF DAY (MDT) 



Figure 4. - Number of underwater bowhead whale blows per aerial 

 observation hour in relation to time of day, 1980 and 1981 com- 

 bined. There were few underwater blows in 1982. The numbers at 

 the top of each column are number of blows seen/number of obser- 

 vation hours. 



361 



