NORMS and DOHL; BEHAVIOR OF THE HAWAIIAN SPINNER DOLPHIN 



they are common on the throat, flanks, and espe- 

 cially on the belly and the region between the 

 flippers. 



DISCUSSION 



Instead of finding tightly knit schools of con- 

 stant size that habitually occupied a given cove, as 

 we had expected we found coves occupied by 

 schools of highly variable numbers and composi- 

 tion. These variable schools often merged with 

 other schools to form large feeding groups 

 offshore, and school members moved back and 

 forth between resting areas many kilometers 

 apart in what seemed a completely free fashion. 

 Rather than finding dolphins occupying a "home 

 cove" the tendency to gather in shallow waters 

 near shore seems to be related to a combination of 

 topographic factors including the presence of 

 adequate areas of shallow water and the proximity 

 to nearby deepwater feeding grounds. Further, the 

 population occupying such a cove during the daily 

 rest period seems limited in some fashion by this 

 same topography. Kealakekua Bay seems able to 

 hold only about 60-70 animals, and even this 

 number seems so large that rest may be inhibited. 

 Deep rest, without aerial behavior, seems only to 

 occur when relatively few animals, about 30-40 or 

 less, are in the cove. In contrast, Keahole Point 

 regularly holds >100 animals during daily rest. 



Instead of finding schools headed directly for 

 rest areas in the morning, we found schools mov- 

 ing toward the coast in the morning in a much 

 more general fashion, encountering the coast, 

 swimming alongshore, entering coves, sometimes 

 coalescing with schools already in occupancy, or 

 apparently sometimes passing by a cove filled with 

 animals, to move on toward other less occupied 

 rest areas. The entry and exit patterns of schools 

 relative to coves also suggests such opportunistic 

 use. At Kealakekua Bay, schools entered primar- 

 ily from the south perhaps because "rest areas 

 south of this bay are very restricted while much 

 more extensive areas exist to the north and in 

 effect this inhospitable shore "collects" but does 

 not hold incoming schools, Exit, on the other hand, 

 is primarily to the north, as if schools came into 

 the cove rested for a time, and continued on their 

 way toward offshore feeding grounds. The primary 

 feeding grounds seem to be to the north and west of 

 Kealakekua Bay, off the shallows of the island, 

 though our observations are sparse. To the north 

 of Kealakekua Bay are other rest areas, while to 



the south deep water adjoins the shore. Thus occu- 

 pancy or lack of same of a given rest cove and 

 arrival direction to it may be related to nighttime 

 feeding movements which leave animals offshore 

 at various locations after the scattering layer de- 

 scends with dawn. None of this, of course, indi- 

 cates that dolphins do not know where available 

 rest areas are, or know the features of them. 



What, then, is the true dolphin school? Are the 

 large offshore aggregations, formed of a coales- 

 cence of smaller resting groups, such a cohesive 

 unit? Or, should we focus our attention on school 

 subgroups of a few animals, which may habitually 

 swim together (though our evidence is inconclu- 

 sive in this respect), in the search for structure, 

 regarding the large groups as opportunistic as- 

 semblages? Or, can both be properly considered as 

 schools? 



The large offshore feeding assemblages have 

 clear structure in some respects. Such schools 

 often dive and surface more or less together, and 

 much social behavior is evident at times in them. 

 These schools swim in a common direction and 

 sometimes change course in a coordinated fashion. 

 We often noted age-related subgroups within 

 them; mothers and calves, or juveniles swimming 

 together. But, if such schools are followed, they 

 will sometimes split into parts that move in differ- 

 ent directions, and clearly, they fragment during 

 the day when smaller schools enter coves or shal- 

 lows to rest. 



Smaller schools exhibit most of the same be- 

 havior, though many times not all age classes will 

 be represented in them. Schools of less than about 

 30 animals are seldom split for long by a vessel. 

 These groupings we call schools, preferring to rec- 

 ognize that such schools change in size from time 

 to time. 



Clearly, from our marked animal information, 

 individuals utilize a rather extensive area of coast 

 for feeding, moving from group to group, and thus, 

 in aggregate the population of a given portion of 

 coast is a functional unit, in relation to its trophic 

 relations with the immediate environment. The 

 degree of discreteness of such populations from 

 those adjacent remains wholly unknown, as does 

 any possible intermixing between islands. 



Considering this high degree of fluidity, how is 

 directed movement of a school achieved and how 

 does the structure of schools come about? No 

 leader seems to exist in the standard sense of an 

 animal determining direction of movement by 



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