FISHERY BULLETIN: VOL 77. NO 4 



prophylene lines ('A in; 0.6 cm) 18 m long (Figure 

 15). With this insubstantial barrier we were able 

 to encircle whole schools of spinner dolphins in 

 20-40 m of water and to crowd them severely. In 

 one case when the hukilau was reduced to a sur- 

 face area of 6 x 10 m, a school of 40-60 animals 

 refused to leave through the wide openings but 

 continued to mill inside (Figure 15). Even when 

 two of the thin vertical lines were removed, leav- 

 ing a "door" 6 m wide, the school continued to 

 circle, "eyeing" the opening but not passing 

 through it. Only when the area was further re- 

 duced did the majority of the animals pass through 

 the wide opening. They had been held captive for 3 

 h 50 min in this fashion. 



Although large and small schools may become 

 quiescent, sporadic low intensity aerial behavior 

 may continue. The impression given is that very 

 small schools (ca. 6-12 animals) maintain a degree 

 of individual wariness, perhaps related to the un- 

 certain protective effectiveness of their few mem- 

 bers, while very large schools may always contain 

 some alert animals. For instance, based on a small 

 number of observations in the large ( 100-150 ani- 

 mals) schools seen at Keahole Point, we have 

 never noted deep quiescence. It is as if the mem- 

 bers of the small school were afraid, and that some 

 activity always occurred somewhere in the larger 

 schools. Only schools of about 20-40 animals seem 

 to achieve the most complete quiescence. 



Even though aspects of diurnal behavior se- 

 quences were recorded on 83 days, complete se- 

 quences were recorded on only 13 days. Based on 

 these observations, rest periods ranged from 41 

 min to 6 h (mean = 3.62 h). 



Once quiescent, resting schools are rather 

 difficult to disrupt. Several times cruise boats or 

 water skiers went through resting schools during 

 our observations. The usual result was a brief 

 flurry of low-level aerial behavior, for example, a 

 desultory headslap, an imperfect spin, and then 

 the school would subside into complete quiescence 

 again (Figure 13). 



Arousal 



Arousal, unlike descent into rest, is abrupt, both 

 in terms of school dispersion and aerial activity. In 

 a completely quiescent spinner dolphin school, 

 arousal was marked by sudden active aerial 

 behavior — a complete spin or headslap, for in- 

 stance. Within 10 min of such initial aerial activ- 

 ity the school was often fully alert, with aerial 



Figure 15. — An Hawaiian "hukilau" composed of a cork line 

 and hanging vertical weighted lines, showing a school of spin- 

 ner dolphins held inside. Vertical lines are 3 m apart and 20 m 

 long. See text. 



activity high throughout the school. In fact, the 

 highest levels of aerial activity recorded occurred 

 at arousal, and later, during feeding (Figure 13). 



Zigzag Swimming 



At arousal the pace of the spinner school quick- 

 ens. Group structure suddenly becomes obvious 

 again. At arousal the school moved back and forth 

 across the bay, or sometimes in and out from the 

 bay center to the cliff base. In either case the 

 school often began to traverse deep water. Typi- 

 cally, it swam toward the bay mouth beginning 

 with a flurry of activity and speed, often with ani- 

 mals rushing through the water, creating spray 

 and small bow waves as they raced along. As the 

 bay mouth was approached, usually the school 

 gradually slowed and flnally began to mill then 

 turned back into the bay. Sometimes the school 

 then subsided into further rest, or accelerated 

 again, often toward the opposite side of the bay. 

 This entire pattern is what we have termed "zig- 

 zag" swimming. These patterns, we suspect, are, 

 to some extent, influenced by the topography of 

 Kealakekua Bay, and may take somewhat differ- 

 ent expressions elsewhere. 



Spinner dolphins were observed moving in zig- 

 zag fashion at Kealakekua Bay, in and out and 

 from headland to headland. The longest bout of 



842 



