Danilewicz et al.: Reproductive biology of male Pontopona blainvillei from Rio Grande do Sul, southern Brazil 



585 



attainment of sexual maturity. The rate of 

 testes-mass gain was 0.05 g/cm for imma- 

 ture and 0.28 g/cm for mature dolphins. 

 All animals with combined-testes weight 

 higher than 5.0 g were sexually mature, 

 and this finding may indicate that this 

 parameter can be used as a reliable indi- 

 cator of sexual maturity in male fran- 

 ciscanas from Rio Grande do Sul (Table 

 1). However, the large variation in testes 

 weight after the attainment of sexual 

 maturity precludes a correlation between 

 testes mass and standard length. 



Although testes length increases pro- 

 gressively as standard length increases 

 (Fig. 6), there is no abrupt increase in 

 testes length at the moment of attain- 

 ment of sexual maturity, as observed in 

 the testes mass. A nonlinear regression 

 (exponential) best fits this relationship 

 (y =4. 5444 e0.0163.vi. As opposed to testes 

 mass, there is a considerable overlap in 

 the values of testes length of immature, 

 pubertal, and mature franciscanas (Table 

 1), which makes testes length a less reli- 

 able predictor of sexual maturity than 

 testes mass. 



Age, length, and weight at sexual maturity 



Forty-seven specimens in the sample pro- 

 vided information on age and reproduc- 

 tive status (35 immature or pubertal, and 

 12 mature). The oldest immature animal 

 was 5 years old and the youngest mature 

 was 2 years old (Table 1). Average age at 

 attainment of sexual maturity was esti- 

 mated to be 3.6 years by the DeMaster 

 method (SD = 0.47; 95% CI =2.7-4.5) and 

 3.0 years by the logistic equation Y = 1/(1+ 

 e o.74-2 23i) The a g e structure of the sample 

 studied is presented in Figure 7. 



Sexual maturity in relation to standard 

 length was estimated for 110 males. The 

 smallest mature and the largest immature 

 males were 120.5 and 137.5 cm long, respectively. The av- 

 erage length at sexual maturity was 128.2 cm (SD=1.49; 

 959r CI=125. 3-131.1 cm). Sexual maturity in relation to 

 total weight was estimated for 90 males. The lightest 

 mature and the heaviest immature males were 20.3 and 

 29.7 kg, respectively. The average weight at sexual matu- 

 rity was 26.4 kg (SD = 0.88; 95% 01=24.7-28.1 kg). 



Index of testicular maturity 



The differences of the mean index of testicular maturity 

 between immature (0.03), pubertal (0.04), and mature 

 (0.11) dolphins were statistically significant (ANOVA, 

 Fs=210.0 df=101, P<0.001). There was almost no overlap 

 in the values of this index between mature specimens 



5 g 



70 75 80 85 90 95 100 105 110 115 120 125 130 135 140 145 150 155 160 



itanoaro lentth (nm) 



Figure 4 



Relationship between standard length and mean diameter of seminif- 

 erous tubules in immature (open boxes), pubertal (filled boxesl. and 

 mature (trianglesi male franciscanas (Pontoporia blainvillei) in Rio 

 Grande do Sul l;i=91>. 



and immature and pubertal specimens (Table 1). All 

 males with an index value higher than 0.07 were sexu- 

 ally mature. These results indicate that the index of 

 testicular maturity is a very good indicator of sexual 

 maturity for franciscanas. 



Reproductive seasonality 



The null hypothesis that the combined and relative testis 

 weight would be higher in the months when the females 

 are reproductively active is rejected. No increase in the 

 testes weight was observed during the months when 

 most mating occurs (Fig. 8). There were no statistically 

 significant differences in the combined-testes weight 

 (ANOVA, Fs=2.28; df=34; P=0.48; n=35) and relative 



