PERRIN ET AL.: GROWTH AND REPRODUCTION OF THE EASTERN SPINNER DOLPHIN 



600 



x 



S? 400 



< 



(X. 



in 



200 



50 



70 



90 



110 130 



BODY LENGTH (cm) 



150 



170 



190 



FIGURE 13. — Scatterplot of brain weight on body length for 77 specimens ofStenella longirostris 

 from the eastern Pacific. The sample of fetuses and neonates ( <100 cm) includes 1 1 eastern 

 spinner dolphins, 9 whitebelly spinner dolphins, and 9 specimens (mostly fetuses) unidentified to 

 race. Triangles are fetuses, open circles are sexually immature postnatal specimens, shaded 

 circles are sexually adult specimens ( by criteria explained in text below). Length at attainment of 

 adult cranium size based on data in Perrin ( 1975b). The linear regression to estimate brain 

 weight at birth is based on 22 near-term fetuses and neonates 63 to 88 cm long. 



_ 600 



I 



§ 400 



rr 



CO 



Ave In at birth 

 I 



Attainment of adult cranium size 



i * ? 



i 



i ,  



~  Y = I0 259X -535 3 

 .* '.. ' (n = l5, r = 0.820) 



i Ave brain weight at birth = 311 g 



o* 



?? <f 



o* 

 d-d 1 



V 



9 







r 



<f% 



Adult ave - 726 g 

 9 (n = 40d"+429,sd=64l) 



» 



130 150 



BODY LENGTH (cm) 



170 



FIGURE 14. — Scatterplot of brain weight on body length for 133 eastern spinner dolphins from the offshore 

 eastern tropical Pacific. Triangles are fetuses, open circles are sexually adult specimens. Linear regression 

 to estimate brain weight at birth based on near-term fetuses and neonates, 73 to 91 cm long. Criteria for 

 sexual maturity and basis for length at attainment of adult cranium size from Perrin (1975b). 



1,475 g, compared with the 1,600 g reported by Lilly based on an 

 unknown sample size. Twelve nonneonatal brain weights (prob- 

 ably including some of juveniles) published by Morgane and 

 Jacobs ( 1972 ) ranged from 1 ,260 to 1 ,950 g and averaged 1 ,536 g. 

 Thus, deviation of the estimate of Sacher and Staffeldt for Tur- 

 siops (396 days, or 13.08 mo) from the more directly obtained 

 estimate of 12 mo ( Sergeant et al. 1973 ), an overestimate of about 

 10%, is of unknown significance and probably reflects statistical 

 error as well as possibly deductive error. 



therefore applied the equation to brain data for the 

 spotted dolphin, S. attenuate (Figure 14 — 

 neonatal brain weight = 3 1 1 g, adult brain weight 

 = 726 g). The estimate of gestation time obtained 

 is 304 days, or 10.03 mo, as compared with 11.5 mo 

 (rounded off) estimated by a more direct method 



735 



