• TESTES WEIGHT - lOOq N - It 

 A TESTES WEIGHT >350q. N - 6 



Figure 8— The body length/weight ratio as related to body 

 length in male Delphinus delphis. Individuals with combined 

 testes weights of 350 g are considered to be undergoing sper- 

 matogenesis. The shading designates the weightylength ratio in 

 which males apparently are sexually mature. 



BODY LENCTI 



FIGURE 9, — Relationship of the body length/weight ratio to body 

 length in female Delphinus delphis. Triangles represent indi- 

 viduals with at least one ovarian corpus. The shaded area de- 

 notes length/weight ratios in which sexually mature dolphins 

 predominate. 



Discussion 



The data indicate that sexual development is 

 better correlated with parameters which indicate 

 the individual's proximity to physical maturity 

 than with fixed morphometric values. A large in- 

 crease in combined testes weight from <80 g to 

 almost 400 g corresponds with rapid skeletal 

 growth in the individual dolphin (Figure 6). Con- 

 sequently, the FI is better correlated with sexual 

 maturity in males than dentine layers or body 

 length. Robustness is also highly correlated with 

 sexual development in males but the sample size is 

 small. 



For unknown reasons, ovulation is better corre- 

 lated with the length/weight ratio than with body 



length, dentine layers, or flipper bone develop- 

 ment. Similarly, in studies of humans, it was 

 found that girls who attained early menarche also 

 had greater weight for height than their 

 chronological peers who attained maturity at a 

 later time (Simons and Greulich 1943). Data from 

 S. attenuata (Perrin et al. 1976) also show ovarian 

 corpora to be poorly correlated with age and 

 length. 



Induced ovulation is a distinct possibility for D. 

 delphis. Harrison and Ridgway (1971) concluded 

 that ovulation in Tursiopa truncatus is induced 

 but the mechanism is unknown. The present data 

 imply that someD. delphis females never ovulate, 

 supporting the findings of Harrison et al. ( 1972). 



Oliver's' examination of Delphinus from the 

 eastern tropical Pacific showed that the smallest 

 testes with spermatogenesis weighed 140 g. For 

 the present study, specimens with combined testes 

 weights >350 g were collected in March, April, 

 July, September, October, November, and De- 

 cember. The large testes weights throughout the 

 year indicate that there is no seasonal rut, sup- 

 porting the findings of Harrison et al. ( 1969). 



Gaps in the data occur immediately prior to 

 maleD. delphis sexual maturity: FI scores 85-105 

 (Figure 6), body lengths 158-177 cm (Figure 4), 4-8 

 dentine layers (Figure 2). These gaps appear to be 

 the prepuberty ranges for those indicators. Be- 

 havior patterns may account for the absence of 

 data in these regions. Young males of Physeter 

 catodon (Ohsumi 1971) and Tursiops truncatus 

 (Evans and Bastian 1969) frequently herd sepa- 

 rately from the rest of the population. Alterna- 

 tively, these animals may have a greater capacity 

 to escape nets. Female specimens also are lacking 

 in the length, age, and FI ranges just prior to the 

 demonstration of ovarian scars. Preadolescent 

 females, like the males, may easily escape nets, or 

 have a social structure separate from the main 

 herd. 



Acknowledgments 



Mary F. P. Rieger and Linda J. Harrington pro- 

 vided assistance with the statistics and ovary 

 examination, respectively. G. A. Bartholomew, F. 

 G. Wood, W. E. Evans, W. F. Perrin, and J. C. 

 Quast offered helpful suggestions on the manu- 

 script. 



'C. W. Oliver, Inter-American Tropical Tuna Commission, La 

 JoUa, CA 92037. Unpubl. data, 



299 



