NORRIS and DOHL: BEHAVIOR OF THE HAWAIIAN SPINNER DOLPHIN 



and A. trigonura were common in the stomach 

 samples but rare in collections of squid from 

 Hawaiian waters. Richard Young" described A. 

 trigonura as being uncommonly taken in Hawaii, 

 but being a vertical migrant occuring from 500 m 

 depth during the day to the upper 100 m at night. 

 This species made up the majority of our samples. 

 As for A. astrosticta, Young stated that it is known 

 in Hawaii from only a few captures, and that most 

 were taken on the bottom in trawls, while small 

 individuals were sometimes taken in midwater. 

 Our samples were adults. Young commented as 

 follows: "It is a displaced midwater faunal ele- 

 ment, or an animal having the distinctive adapta- 

 tions of a midwater animal but which seems to 

 migrate along the bottom. TheHistioteuthis is also 

 a vertical migrator that stays below about 150 

 meters." (See Table 3). John Walters (see footnote 

 6) commented that the shrimp Sergio /u/gens is an 

 enigmatic form known only in the adult form (ours 

 were adults) from night tows. 



Morning Shoreward Movement 



After nighttime feeding, spinner dolphin 

 schools turn toward shore, ultimately congregate 

 in certain sheltered locations where the schools 

 subside into the rest pattern. In the case of the 

 radiotracked animal, this movement toward 

 shore seemed to begin at about 0300 and to con- 

 sist of a gradual movement that zigzagged ever 

 closer to shore. 



The directions from which schools come into 

 Kealakekua Bay suggest that the movement to- 

 ward the coast may be a general one and not neces- 

 sarily pointed precisely at a rest cove. Some enter- 

 ing schools first swim along the coast, round 

 Palemano Point at the south tip of the bay, and 

 enter the bay over the shallows near Keei and 

 Napoopoo (Figure 1), while others enter the bay 

 directly from the open sea, coming in,at various 

 angles to the trend of the coast. Still others enter 

 from the north, once again after a traverse of un- 

 known length along the shore to the north of the 

 bay. More schools enter along the southern limb of 

 the bay than from the north or center. The true 

 figure for south entry may be even higher than the 

 figures indicate (58% for south entry vs. 14.5% for 



'Richard Young (Professor of Oceanography, University of 

 Hawaii) examined and identified stomach samples from our 

 Hawaiian spinner porpoise in 1973 and provided notes on the 

 occurrence of squids in the samples, while John Walters (Uni- 

 versity of Hawaii) provided identifications of shrimps. 



north entry: 27.5% entered in the middle sector), 

 since some first sightings were made close to the 

 cliffs at the back of Kealakekua Bay and, because 

 of their location, were placed in the second sector 

 records. It is likely that some of the schools entered 

 from the south or north prior to the beginning of 

 observation. 



These congregation patterns suggest that the 

 bays and coves used for rest periods may not neces- 

 sarily be the direct target of daily inshore move- 

 ment. The bays seem simply to collect schools that 

 accumulate along the coast after a night's feeding. 

 The fact that more schools arrive from the south 

 than from the north may reflect the nearby pres- 

 ence of adequate resting areas over the rather 

 extensive shallow- water areas immediately north 

 of the bay between Keikiwaha Point and 

 Keauhou. Waters to the south of Kealakekua Bay 

 are deep close to shore and only very modest sized 

 shallow coves exist at Honaunau and Hookena. 

 Farther south, along the 20 km stretch of coast 

 between Hookena and Milolii, no spinner dolphins 

 were seen although both flights and ship searches 

 were made. Nonetheless, data from marked ani- 

 mals show movement between the populations on 

 each side of this gap. Unless rest areas are encoun- 

 tered, dolphin schools remain transient. This does 

 not preclude the possibility that the animals may 

 be familiar with the various rest coves or actively 

 seek them when nearby. 



Arrival times (Figure 12) concentrated between 

 0600 and 0950 h, though some schools arrived 

 much later in the day. The early arrivals typically 

 subsided into rest and spent the majority of the 

 day in the bay. Later arrivals (those entering be- 

 tween 1100 and 1700 h) tended not to form resting 

 schools and often moved out of the bay after a brief 

 stay. The late afternoon arrivals may have com- 

 pleted a rest period elsewhere and then entered 

 the bay as part of a longshore movement prior to 

 going to the feeding grounds. Dolphins engaged in 

 such longshore movements have been followed out 

 to sea. In one such case a school rested, left the bay 

 to the south, traveled slowly very close to shore 

 until the small cove at Honaunau was encoun- 

 tered, and then turned out to sea as dusk ap- 

 proached. 



Not all dolphin schools encountering 

 Kealakekua Bay enter it. We occasionally saw 

 schools crossing the bay mouth and swimming on 

 in either direction. Our impression is that this 

 occurred when other schools were deep in the bay, 

 but unfortunately, adequate records to document 



837 



