Francis and Duffy Length at maturity in three pelagic sharks 



497 



Pregnant females (n=40) 

 Uterus width index (n=650) 

 Percentage mature (direct) 

 Percentage mature (fitted curve) 



■8 _Q -08 



125 150 175 200 



Fork length (cm) 



Figure 8 



Maturation of female blue sharks iPrionace glauca): variation in uterus 

 width index, direct maturity estimation from a suite of maturity indicators, 

 and length-frequency distribution of pregnant females are shown. 



Table 4 



Summary of length at maturity indicators in porbeagle, shortfin mako, and blue sharks, and estimates of median length at 

 maturity. Table entries are fork lengths in centimeters. Direct maturity estimates were derived by examination of a suite of 

 maturity indicators. Italics indicate estimates based on small sample sizes over the maturation length range. " — " indicates that 

 an estimate was not possible. 



Sex 



Maturity indicator 



Porbeagle shark 



Shortfin mako shark 



Blue shark 



Males 



Females 



50% with spermatophores 



Rapid clasper elongation complete 



Direct maturity estimate 



Median length at maturity 



Rapid expansion of uterus begins 

 First females pregnant 

 Direct maturity estimate 



Median length at maturity 



152 

 143 



140-150 



145 

 167 



170-180 



Only one pregnant female (290 cm FL) has been recorded from New Zealand. 



some female shortfin makos in which the membrane 

 was very thin and partially perforated, but had clearly 

 not been damaged by copulation. We believe that the 

 hymen disintegrates naturally with growth in makos; 

 the same possibility was proposed for blue sharks by 

 Pratt (1979). 



Using a combination of our direct maturity estimates, 

 and other indicators of maturity based on larger sam- 

 ples of sharks, we generated overall estimates of me- 

 dian maturity for both sexes of the three pelagic sharks 

 (Table 4). 



Porbeagle shark 



In male porbeagles, the length at which 50% of sharks 

 had spermatophores (152 cm) was longer than the length 



at which clasper elongation was complete (143 cm) 

 (Table 4). However the percentage of males having sper- 

 matophores did not reach 100% in the longer length 

 groups (Fig. 2), indicating that some mature males were 

 reproductively inactive. This finding is consistent with 

 reports from the western North Atlantic that male por- 

 beagles have a seasonal cycle of spermatophore produc- 

 tion, with a minimum in winter-spring (Jensen et al., 

 2002). If some mature males lacked spermatophores, the 

 length at which 50% of males had spermatophores in our 

 study was probably greater than the median maturity. 

 The lack of a direct maturity estimate limits our ability 

 to estimate the median maturity, but it is likely in the 

 range 140-150 cm. 



Similarly, we have no direct estimate of female por- 

 beagle maturity. There was a considerable gap between 



