NORMS and DOHL: BEHAVIOR OF THE HAWAIIAN SPINNER DOLPHIN 



belly below. The white of the belly extends up the 

 flanks to about the level of the eye. The beak, or 

 rostrum, is dark gray, tipped prominently with 

 black; the lip margins are dark; and the ventral 

 surface of the beak is white. The pectoral fins are 

 dark gray, and a dark flipper band connects its 

 anterior insertion to the eye, which is surrounded 

 by a black eyepatch. Flukes and dorsal fin are 

 dark gray. These color pattern components have 

 been described in more detail by Perrin (1972), 

 and they have been compared with the patterns of 

 geographical forms of spinner dolphins living in 

 the eastern tropical Pacific. In nature, against the 

 blue or turquoise backdrop of tropical water, the 

 dark pattern components of spinner dolphins ap- 

 pear in shades of brown, but the effect is usually 

 lost when the animals are removed from the wa- 

 ter. The white and other pattern marks are often 

 suffused with pink, from superficial blood flow in 

 the blubber, which may also contribute to the 

 overall brownish cast of pattern components in 

 living spinners. 



Systematics 



In recent years a worldwide picture of the dis- 

 tribution and systematics of tropical odontocetes 

 has begun to emerge. Well-documented collec- 

 tions, often with measurements and photographs, 

 have been made from all oceans, especially where 

 dolphins are involved in fishery operations 

 (Kasuya et al. 1974; Perrin 1975). A special bene- 

 ficiau-y of this work has been the once chaotic genus 

 Stenella. It now seems reasonably clear that the 

 genus is composed largely of three major species or 

 species complexes: the spinner dolphins, allied to 

 S. longirostris of the Hawaiian Islands; the striped 

 dolphin, S.coeruZeoo/6a,- and the spotted dolphins, 

 allied toS. attenuata of the Hawaiian Islands. All 

 are tropical or subtropical. All are often found far 

 offshore or near islands. 



In the eastern and central Pacific, Perrin ( 1975) 

 discerned four geographical forms of spinner dol- 

 phins: 1) a Costa Rican long-snouted form occur- 

 ring close to the Central American coast, 2) an 

 eastern form occupying the open sea from the 

 American coast out to long. 115° W, 3 ) a whitebelly 

 form occupying the open ocean both south and 

 west of the eastern form (and overlapping with it 

 to some extent) to about long. 145° W and nearly 

 to lat. 5° S, and 4) an Hawaiian form localized 

 around the Hawaiian island chain. Perrin ( 1975) 

 stated that Hawaiian spinner dolphins are most 



closely related to the adjacent whitebelly form, 

 differing from them by being somewhat more 

 robust, by having a larger area of white belly col- 

 oration, and by lacking the speckled margins of 

 the white belly field. He places the complex tenta- 

 tively in the species S. longirostris. 



Most of the races of spinner dolphins from 

 around the world are quite similar to the 

 Hawaiian form. Only the Costa Rican and eastern 

 forms are strikingly different, being nearly uni- 

 form gray, with faint hints of pattern components 

 found in other races. These aberrant forms also 

 show remarkable sexual dimorphism, which is 

 otherwise rather subtle throughout the species. 

 Fully adult males of these two races often possess a 

 dorsal fin that is canted sharply forward, "like it 

 was stuck on backward," and a very heavy post- 

 anal protuberance. The fin of Hawaiian spinner 

 dolphins is either triangular or very slightly fal- 

 cate, and only a subtle postanal protuberance can 

 be noted in adult males. 



METHODS 



A camp was established on the Green well Ranch 

 at the edge of the cliff overlooking Kealakekua 

 Bay (Figure 1). Two observation sites were used 

 for recording and observation by telescopic means. 

 Observer teams kept regular watches during day- 

 light hours. 



Several vessels were used for observations at 

 sea, or to provide an anchored platform in the bay, 

 including the brigantine Westward and the motor 

 sailers RV Hikino and the RV Imua. A trip 

 through the northwest Hawaiian chain was made 

 on the U.S. Coast Guard buoy tender Buttonwood. 



Fourteen spotting flights were made through- 

 out the main Hawaiian chain, mostly from small 

 fixed wing aircraft. 



Underwater observations were made in a spe- 

 cially built underwater observation vehicle or 

 mobile observation chamber (MOC) 6 m long, 

 which looked like a small submarine (Figure 2) 

 but did not submerge. It consisted of a float made 

 from an auxiliary aircraft gasoline tank and a cen- 

 tral observation chamber. The viewer in this 

 chamber below water obtained ventilation from a 

 squirrel cage blower and was surrounded by a 

 band of Plexiglas^ windows at eye height. Controls 

 for turning or tilting the craft were at hand, and a 



^Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service. NOAA. 



823 



