FISHERY BULLETIN: VOL, 77. NO, 4 



posed of a mixture of open sandy bottom dotted 

 with coral formations. Coves may or may not be 

 present. All rest areas are close to deep water. 

 Usually water >500 m depth can be reached 

 within a few kilometers. Some schools, such as 

 those in the Waikiki (Oahu) or Manele Bay 

 (Lanai) areas, have access to considerably shal- 

 lower water than others. Schools living there may 

 be restricted to waters no deeper than about 600 m 

 since our observations on the Kona coast of Hawaii 

 indicate that schools do not move more than a few 

 kilometers from shore at night. Other schools, 

 such as at Keahole Point (Hawaii) regularly move 

 into water >2,000m depth. Ofcourse, the observa- 

 tions we have made on the island of Hawaii may 

 not hold elsewhere. 



Apparently spinner dolphins only occasionally 

 travel onto extensive shallow areas like that at 

 Lahaina Roads (Auau Channel), which is about 24 

 km long. Instead they typically congregate along 

 its margins, along the south shore of Lanai Island 

 and Kahoolawe Island, where deep water is 

 nearby. The areas most closely studied here are 

 Kealakakua Bay and Keahole Point, both have 

 deep water accessible within 1.5-2.5 km of shore. 

 The inference is that rest areas are chosen by 

 dolphins not only for physical characteristics such 

 as depth, bottom type, and perhaps calm water but 

 also for their accessibility to nighttime feeding 

 areas. 



Spinner dolphin schools also rest in atoll la- 

 goons. At Kwajalein Atoll, on 10 September 1973, 

 at 1630, a school of about 40 spinner dolphins was 

 noted about 1 km inside Bigej Pass. The school was 

 moving toward the pass, presumably on its way 

 out to sea. A local resident told us that the school 

 was regularly in this pass and not found in other 

 nearby passes into the central lagoon. Similar ob- 

 servations have been made at Kure Atoll, Midway 

 Atoll, and near Shark Island at French Frigate 

 Shoals. The animals (approximately 35), resting 

 quietly in a shallow channel not far inside Eastern 

 Island at Midway, were sighted from a helicopter. 

 Probably wherever atolls and spinner dolphins 

 occur together the animals use the atoll lagoons 

 for rest. 



In the eastern tropical Pacific a large spinner 

 dolphin population occupies oceanic areas far from 

 land. In view of the use of shore situations 

 elsewhere in the range of the species, one wonders 

 what, if any, substitution is made. Norris and Dohl 

 (in press) have speculated that the frequently ob- 

 served association between spinner and spotted 



dolphins in the eastern tropical Pacific (this as- 

 sociation does not occur in Hawaii) may hold the 

 answer. Spinner dolphins may seek the schools of 

 spotted dolphins for refuge during rest in the open 

 sea. We believe this may be true because spotted 

 dolphins feed during the day, while spinners are 

 nocturnal feeders, and spinner dolphin schools 

 have been observed to join spotted dolphin schools 

 in the morning (Norris et al.''). If such rest associa- 

 tion occurs, the spinner dolphins are associating 

 with alert animals in this oceanic area. Related to 

 this the yellowfin tuna seine fishermen chase and 

 encircle dolphins to catch tuna, most fish appar- 

 ently follow the spotted dolphins. Since the asso- 

 ciation between tuna and dolphin is probably food 

 based, the tuna may be following the dolphin 

 species that is actively searching for food. That is, 

 like the tuna, the spinner dolphin may follow ac- 

 tive dolphin schools. 



Spinner dolphins resting along shores maintain 

 a continuous but slow locomotion, and it seems 

 likely that the searching or feeding activities of 

 spotted dolphins would not greatly change these 

 requirements for rest. 



MARKED ANIMAL STUDIES 



Dolphin schools are seen frequently at the same 

 localities while other areas never seem to harbor 

 them. Are these schools of resident animals, or are 

 they composed of transients that for some reason 

 choose certain regions of the coast for rest? The 

 frequent observation of dolphin collectors that a 

 given school will avoid their vessel after animals 

 have been collected from it (Norris and Prescott 

 1961) indicates possible residency. On the other 

 hand, dolphin schools are not always in these rest 

 localities, and the number of animals using a 

 given cove may vary widely from day to day. This 

 indicates fluidity in school structure and variabil- 

 ity of school movement. Such fluidity has been 

 noted for other porpoise schools by Wiirsig and 

 Wursig (1977) and Saayman and Tayler (1979). 



Because we were concerned that the spinner 

 dolphins of the Kona coast of Hawaii should not 

 fear our vessel, we sought to recognize individu- 

 als by natural scars and marks rather than by 

 placement of tags. Ultimately we were able to 

 catalog 50 recognizable individuals and resight- 



"Norris, K. S., W, E. Stuntz, and W. Rogers. 1978, The 

 behavior of porpoises and tuna in the eastern tropical Pacific 

 yellowfin tuna industry-preliminary studies. Natl. Tech. Inf. 

 Serv,. Final Rep, No, MMC76/12 PB 283-970, xi + 86 p. 



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