422 



Fishery Bulletin 89(3), 1991 



150° 140° 130* 120* 110* 100° 90° 80° 70° 



150° 140" 130° 120° 110° 100° 90° 80* 70*, 



Figure 17 



Average body length of adult male and female spinner 

 dolphins, by area. For males, cells with length > 180 cm are 

 hatched; for females, cells with length > 176 cm are hatched 

 (adult males are about 4 cm longer than adult females on 

 average; Perrin et al. 1985 and present data). 



125°W for males (Fig. 14A) and 10°N and 120°W for 

 females (Fig. 15 A). It was absent in the cells south of 

 5°N and east of 120°W and in the cells west of 135°W. 

 The extreme pantropical combination reached only 

 34% in males, in the southernmost region (Fig. 14C), 

 and 44% in females (Fig. 15C). It was absent (except 

 for one female) from the cells in which the eastern com- 

 bination predominated (north of 10° N and east of 

 120-125°W). It was present only at low levels in the 

 southwestern region, about the same as just to the 

 south and west of the core eastern region. Except in 

 the core eastern region, the majority of dolphins were 

 intermediate (combined scores of 4-9 for males and 5-9 

 for females (Figs. 14B, 15B); in some cells between 0° 

 and 15°N, over 95% of the adults were intermediate. 

 Even in the core eastern region, about one third were 

 intermediate. The degree of intermediacy was not 

 uniform, however. For both sexes, there was a very 

 steep latitudinal gradient in average scores of inter- 

 mediate animals at about 10°N (Fig. 16). There was 



also a steep longitudinal gradient, at about 125°W for 

 males and 115°W for females. Outside this sharply 

 bounded core "eastern" region, variation in interme- 

 diate scores was very much less, with only slight N/S 

 and E/W gradients and most animals relatively close 

 to the pantropical extreme. 



Proportionately more adult females than adult males 

 in the westernmost cells (west of 140°W) were of the 

 extreme pantropical combination (Fisher's exact test, 

 P<0.01), whereas this was not as true in the southern- 

 most cells (P>0.10). 



Body length 



The major shift in average adult length of both males 

 and females (Fig. 17) was at about 5°N, rather than 

 at about 10°N as for the other characters (e.g., com- 

 pare with Figs. 14-16). The region of smaller animals 

 extended south along the coast of northern South 

 America to about 5°S. Animals from the far west were 



