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



II. One and one-half layers in the first year 

 and one per year thereafter, or 



III. One and one-half layers per year until pu- 

 berty (at about nine layers in males and five 

 to six layers in females) and one per year 

 thereafter. 



There is a rapidly increasing body of evidence 

 (Perrin et al. 1976; Best 1976) that most del- 

 phinids accumulate growth layers at the rate of 

 1/yr, making Hypothesis II the most likely true of 

 the three, but some uncertainty still exists, espe- 

 cially for tropical forms. We therefore express the 

 conclusions of all age-based analyses below in 

 terms of the three hypotheses. Other, more com- 

 plex hypotheses can be suggested, but these three 

 in our view probably include the truth. 



Reproduction 



The Male 



Spermatogenesis is histologically evident in 

 50% of (right) testes weighing 94 g or more (weight 

 of epididymis included) (Figure 17). A perhaps 

 better criterion of sexual maturity is presence of 

 sperm in the epididymis (Figure 18). Combined 

 testis-epididymis weight at which half the males 

 possess "some" or "copious" sperm in the epididy- 

 mis is approximately 150 g. Another epididymal 

 criterion can be defined, namely, the testis- 

 epididymis weight above which the proportion of 

 males having "copious" sperm in the epididymis 

 does not increase, in this case above 50% at about 

 400 g. The three testis-epididymis weight criteria 

 of 94 g (50% spermatogenic), 150 g (50% with 



?. 100 



I- 80 



z 



UJ 



(n 



UJ 



£ 60 



100 



40 - 



o 

 o 



< 



rr 



a. 



C/5 



20 



20 40 80 120 160 



WEIGHT OF TESTIS + EPIDIDYMIS (g) 



200 



FIGURE 17. — Linear regression analysis of relationship between 

 proportion of males spermatogenic and testis-epididymis weight 

 in the eastern spinner dolphin. Sample sizes in parentheses. 



100 200 300 400 500 600 



WEIGHT OF TESTIS + EPIDIDYMIS (a) 



700 



FIGURE 18. — Presence of sperm in epididymis in relation to 

 testis-epididymis weight in the eastern spinner dolphin. Sample 

 sizes in parentheses. 



sperm in epididymis), and 400 g (asymptotic 

 weight with respect to proportion with copious 

 sperm) are considered below in relation to body 

 length and age (in dentinal growth layers). 



Testis-epididymis weight on the average in- 

 creases precipitously with body length between 

 160 and 170 cm (Figure 19), but is only weakly 

 correlated with body length beyond 175 cm. Males 

 of any length above 160 cm can be mature or im- 

 mature under each of the three criteria defined 

 above. The proportion of males mature under the 

 three criteria stabilizes at about 170 to 175, 175 to 

 180, and 180 to 185 cm body length, respectively 

 (Figure 20). The average length of adult males 

 under the three criteria ranges from 174 to 176 cm 

 (Table 4). 



■5 600 



400 





T 



-400? - 



-ISO? 



- 94, - 







140 150 160 170 

 BODY LENGTH (cm) 



i_± i 



ieo 



FIGURE 19.— Relationship between testis-epididymis weight 

 and body length in the eastern spinner dolphin. Circled dots are 

 sample means. Vertical bars are ranges. Sample sizes in 

 parentheses. 



739 



