FISHERY BULLETIN: VOL. 70, NO. 3 



genus has been accomplished since True's work 

 on the Delphinidae published in 1889, when the 

 existence of spinner porpoises in eastern Pacific 

 and Hawaiian waters was not yet known. Evi- 

 dence presented below concerning geographical 

 variation in pigmentation supports the concept 

 of a single species, highly variable geographi- 

 cally, but taxonomic and nomenclatorial decisions 

 must be based on adequate review of osteological 

 characters, as well as on a broader range of ex- 

 ternal characters than is considered here. The 

 use of Stenella cf. S. longirostris therefore is 

 provisional pending the outcome of more exten- 

 sive studies underway by me and others. A si- 

 milar situation obtains for the spotted porpoises, 

 and use here of Stenella graffmani for the spotted 

 porpoise (s) of the eastern Pacific is also pro- 

 visional. 



DEVELOPMENT AND INDIVIDUAL 

 VARIATION 



This account of ontogeny is divided into two 

 parts, one describing development of color pat- 

 tern as inferred from specimens from the more 

 easterly, relatively nearshore population (s) of 

 spinner porpoise referred to below as the "east- 

 ern spinner," and another for specimens of the 

 "whitebelly spinner" of the more westerly, far- 

 ther offshore areas of the eastern Pacific (Fig- 

 ure 1). 



EASTERN SPINNER 



Length at birth is 75 to 85 cm (Harrison et al., 

 1969). The smallest specimen examined was 

 80 cm long. The smallest specimen photo- 

 graphed was 105 cm long (Figure 2). At this 

 size, the animal is predominantly dark gray. The 

 gray of the dorsum grades imperceptibly into 

 white around the genital region and in a smaller 

 area in the axillary region. A dark gray flipper 

 band from flipper base to the eye-gape region 

 is demarcated above by a narrow, very light line 

 running from behind the posterior insertion of 

 the flipper to the eye and below by a sharp 

 boundary with a light gray gular region. The 

 boundary between the two shades of gray runs 



forward between the eye and the end of the gape, 

 becoming obscure in the furrow at the base of 

 the melon. The very light gray below grades 

 anteriorly into darker gray, so that the upper 

 and lower sides of the snout are of about the 

 same shade as the dorsal field. The gape is edged 

 with very dark gray sharply delineated above 

 for about the last third of the gape and below 

 for about the last half of the gape but grading 

 distally above and below into the generally dark 

 gray of the snout. A small eye patch of similar 

 shade is present, and a narrow eye stripe, also 

 of dark gray, runs from the eye patch forward 

 to join the gape mark near the apex of the melon. 

 A similar mark extends from the blowhole to the 

 apex. The margin of a very faintly defined dor- 

 sal cape (not visible in the photographs) runs 

 from near the apex of the melon to behind the 

 dorsal fin, passing high over the eye and dipping 

 slightly below the fin to yield a saddle effect dis- 

 cernible only upon very careful scrutiny of a 

 freshly caught animal. Low on the side and 

 adjacent to the genital slit, an elongate, smudge- 

 like mark extends obliquely for several centi- 

 meters along a line that if extended in both di- 

 rections would run from the eye to behind the 

 anus. All appendages are on both surfaces the 

 same gray as the dorsum. The major point of 

 individual variation in animals of this and larg- 

 er size is in the extent of the ventral and ax- 

 illary white areas; in some individuals they are 

 larger and may even be confluent, with the dorsal 

 margin extending back from the axillary area 

 to run into the higher genital white area. 



The pattern persists as described into sub- 

 adulthood (subadult being defined as an animal 

 of adult or near-adult size but sexually imma- 

 ture) without change aside from overall dark- 

 ening (Figure 3) . In subadulthood the margins 

 of the ventral and axillary white areas begin to 

 become speckled, and in adults (Figures 4, 5, 6, 

 7, 8, and 9) the dorsal field, by now very dark 

 gray, appears to encroach on the white areas with 

 spots and blotches to yield a very speckled ap- 

 pearance below (Figure 10). As in younger 

 animals, the major feature subject to individual 

 variation appears to be the extent of the whrte 

 areas, although in no adult specimens examined 

 were the genital and axillary areas confluent. 



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