Francis and Duffy: Length at maturity in three pelagic sharks 



499 



has also been reported elsewhere (Pratt, 1979; Hazin et 

 al., 1994). Thus clasper length was not useful in estimat- 

 ing length at maturity. Our direct maturity estimate 

 was similar to the length at which 50% of sharks had 

 spermatozeugmata and indicated that median maturity 

 occurs at about 190-195 cm (Table 4). 



In females, maturation occurred over a wide length 

 range, as reported elsewhere (Hazin et al., 1994). Taking 

 into account the length distributions of pregnant females 

 and females with low UWI values (Fig. 8), we believe 

 median maturity is likely in the range 170-190 cm. 



In other blue shark studies, estimation of the length 

 at maturity has also been hindered by small sample 

 sizes, or even a complete absence of immature or mature 

 sharks. In the western North Atlantic, males mature at 

 about 178 cm, and females at around the same length, 

 although few mature females have been available (Pratt, 

 1979). In the Gulf of Guinea, Atlantic Ocean, 50% of 

 females were pregnant at 180 cm (Castro and Mejuto, 

 1995). In Australian studies, a lack of immature sharks 

 made it impossible to estimate maturity adequately (Ste- 

 vens, 1984; Stevens and McLoughlin. 1991). In the North 

 Pacific Ocean, 50% of males had spermatozeugmata at 

 166 cm and 50% of females were pregnant at 174 cm 

 (Nakano, 1994). Thus worldwide estimates of maturity 

 in blue sharks are similar to ours from New Zealand, 

 except perhaps for a smaller length at maturity of males 

 in the North Pacific. Unlike females in most species of 

 sharks, female blue sharks do not appear to mature at 

 a length greater than that for mature males. 



Acknowledgments 



We thank the Ministry of Fisheries for funding this 

 study under research project TUN2002/01, and provid- 

 ing access to data collected by observers. Lynda Griggs 

 (NIWA) assisted with data extracts and interpretation, 

 and Chris Francis (NIWA) carried out the probit analy- 

 ses. Lisa Natanson, Wes Pratt, Steve Campana, and 

 Henry Mollet kindly provided unpublished data and 

 advice on their interpretation. 



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