FISHERY BULLETIN: VOL. 74, NO. 2 



1,800 



1400 - 



1200 



tl 1000 - 



800 



400- 



200- 



• • 



 ^■^■i^- ^-i» T>t!»-».*if» 



1 2 3 4 5 6 7 8 9 10 II 12 13 14 15 16 17 18 19 

 LAYERS (number) 



Figure 19. — Scatterplot of testes weight on number of postnatal 

 dentinal layers in Stenella attenuata. 



100 120 140 160 ISO 



BODY LENGTH (cm) 



220 



Figure 20. — Scatterplot of average diameter of seminiferous 

 tubules on body length in Stenella attenuata. 



Q I 2 3 4 5 6 7 8 9 10 M 12 13 14 15 16 17 IB 19 



LAYERS (number) 



Figure 21. — Scatterplot of average diameter of seminiferous 

 tubules on number of postnatal dentinal layers in Stenella 

 attenuata. 



248 



Sperm in the epididymis were scored as "ab- 

 sent," "present in small numbers," or "copious" 

 (easily seen in the histological sample without 

 searching). The shortest individual with large 

 numbers of sperm in the epididymis was 179 cm 

 long. This animal weighed 62 kg. In animals 

 larger than 180 cm and heavier than 58 kg, pres- 

 ence or absence of sperm in the epididymis bears 

 little relationship to total length. Thirty-six large 

 adults (>200 cm) were equally distributed among 

 the three categories of no sperm, some sperm, and 

 copious sperm. 



The smallest testes bearing epididymis with 

 sperm weighed 200 g, and the smallest testes 

 with copious sperm weighed about twice as much. 

 Some animals with testes heavier than 1.5 kg, 

 however, had no sperm in the epididymis. The 

 same pattern of wide variation is apparent in the 

 relationship between epididymis code and layers. 

 The youngest male with sperm in the epididymis 

 had 9 layers. The youngest animal with copious 

 sperm had 10 layers. After about 10 layers, there 

 appears to be no relationship between age and 

 presence or absence of large numbers of sperm. 



In summary, the onset of puberty, as indicated 

 by a rapid increase in diameter of seminiferous 

 tubules and increase in testes weight, is at 7 to 12 

 layers (average ~-9 layers; an estimate of ages at 

 puberty) and at lengths of 155 to 170 cm and 

 weights of 40 to 50 kg. Sexual maturity is at- 

 tained about 2 to 4 layers later, at 10 to 14 layers, 

 ^180 cm, and &58 kg. The midpoint of the range 

 of 10 to 14 layers, or 12 layers, may be taken as an 

 approximation of average age at attainment of 

 sexual maturity. Whether or not males at this 

 point are "socially mature" (sense of Best 1969) 

 can be determined only through behavioral 

 studies. Average length of males 12 layers old is 

 about 195 cm, and average weight is about 75 kg. 



The Female 



Attainment of Sexual Maturity 



Harrison et al. (1972) described and figured the 

 ovaries of S. attenuata (as S. graffmani). The 

 ovaries weigh less than 0.5 g each at birth. 

 Weight increases gradually to about 1.5 g at 

 about age 6 to 8 layers (average ~7 layers; an 

 estimate of age at puberty), when there is a sud- 

 den increase in average ovary size and weight 

 due to presence of corpora of ovulation and/or 

 pregnancy (Figure 22). This change comes at an 



