490 



Fishery Bulletin 103(3) 



of Fisheries introduced individual trans- 

 ferable quotas for a number of pelagic 

 species, including the three sharks, in 

 October 2004. 



Despite the panglobal distributions of 

 porbeagle, shortfin mako, and blue sharks, 

 and their importance in the catches of 

 pelagic longline fisheries worldwide, com- 

 paratively little effort has been devoted to 

 estimating their length (or age) at matu- 

 rity. In the northwest Atlantic Ocean, the 

 length at maturity of male and female por- 

 beagles has been well determined (Jensen 

 et al., 2002), but preliminary data from 

 the southwest Pacific Ocean indicate that 

 females mature at a much smaller length 

 there (Francis and Stevens, 2000). Mol- 

 let et al. (2000) found significant differ- 

 ences in the length at maturity of female 

 shortfin makos between the Northern and 

 Southern hemispheres; however there is 

 little information on the length at matu- 

 rity of male makos (Stevens, 1983). Blue 

 sharks have been studied in a number 

 of regions worldwide (Pratt, 1979; Ste- 

 vens, 1984; Hazin et al., 1994; Nakano, 

 1994; Castro and Mejuto, 1995), but size 

 and sex segregation have made it difficult 

 to obtain representative samples of both 

 sexes from which to determine length at 

 maturity. 



In the southwest Pacific Ocean, esti- 

 mates of length at maturity are lacking or 

 uncertain for at least one sex of all three 

 species. Although all species make long 

 distance movements, and presumably have 

 wide-ranging stocks, the interhemispheric 

 differences in length at maturity reported 

 for female porbeagles and shortfin makos 

 indicate that it is not safe to transfer esti- 

 mates from one region to another. The aim 

 of the present study is to develop region- 

 specific estimates of length at maturity 

 for male and female porbeagle, blue and shortfin mako 

 sharks, and to determine whether this parameter var- 

 ies globally. These results will contribute to efforts to 

 determine the productivity and stock status of pelagic 

 sharks in New Zealand waters. 



i — i — TTri — i — i — i — i — i — i — i — i — i — i — i — r 



; 



D 



Norfolk/^ 

 Island M 



■3 





Figure 1 



Start-of-set positions of tuna longline sets during which observers 

 sampled porbeagle [Lamna nasus), shortfin mako (Isurus oxyrin- 

 chus), and blue [Prionace glauca) sharks. Also shown are the North 

 Island ports where sharks landed during fishing competitions were 

 sampled. 



Fisheries observers aboard commercial tuna longline 

 vessels (Fig. 1). Sharks obtained from fishing competi- 

 tions provided the opportunity to measure a wide range 

 of reproductive parameters on relatively small samples, 

 whereas sharks observed on tuna longline vessels pro- 

 vided large samples but limited reproductive data. 



Materials and methods 



Sharks obtained from fishing competitions 



Data sources 



Reproductive data were collected from two main sources. 

 The first consisted of sharks sampled by the authors at 

 recreational fishing competitions, or occasionally sharks 

 retained by commercial fisheries or research vessels. The 

 second source consisted of data and occasionally embryos 

 and female reproductive tracts collected by Ministry of 



Competition sharks consisted mainly of makos and 

 blue sharks sampled at fishing competitions around the 

 North Island (Fig. 1). Most sharks were sampled from 

 the Hawke Bay competition held annually in February 

 or March from the port of Napier. Other significant 

 competitions were sampled at Castlepoint, Raglan, and 

 New Plymouth. All except two of the competition sharks 

 were collected in summer (January-March) and samples 



