489 



Abstract— Reproductive data col- 

 lected from porbeagle, shortfin mako. 

 and blue sharks caught around New 

 Zealand were used to estimate the 

 median length at maturity. Data 

 on clasper development, presence or 

 absence of spermatophores or sper- 

 matozeugmata, uterus width, and 

 pregnancy were collected by observers 

 aboard tuna longline vessels. Direct 

 maturity estimates were made for 

 smaller numbers of sharks sampled 

 at recreational fishing competitions. 

 Some data sets were sparse, par- 

 ticularly over the vital maturation 

 length range, but the availability 

 of multiple indicators of maturity 

 made it possible to develop estimates 

 for both sexes of all three species. 

 Porbeagle shark males matured at 

 140-150 cm fork length and females at 

 about 170-180 cm. New Zealand por- 

 beagles therefore mature at shorter 

 lengths than they do in the North 

 Atlantic Ocean. Shortfin mako males 

 matured at 180-185 cm and females 

 at 275-285 cm. Blue shark males 

 matured at about 190-195 cm and 

 females at 170-190 cm: however these 

 estimates were hampered by small 

 sample sizes, difficulty obtaining rep- 

 resentative samples from a popula- 

 tion segregated by sex and maturity 

 stage, and maturation that occurred 

 over a wide length range. It is not yet 

 clear whether regional differences in 

 median maturity exist for shortfin 

 mako and blue sharks. 



Length at maturity in three pelagic sharks 

 (Lamna nasus, Isurus oxyrinchus, and 

 Prionace glauca) from New Zealand 



Malcolm P. Francis 



National Institute of Water and Atmospheric Research 



301 Evans Bay Parade 



Greta Point 



Wellington, New Zealand 



E-mail address m francisifi'niwa co nz 



Clinton Duffy 



Department of Conservation 

 Private Bay 68908 

 Auckland, New Zealand 



Manuscript submitted 20 April 2004 to 

 the Scientific Editor's Office. 



Manuscript approved for publication 

 30 March 2005 by the Scientific Editor. 



Fish. Bull. 103:489-500 (2005). 



The attainment of sexual maturity in 

 sharks is a major developmental mile- 

 stone which has a large impact on their 

 distribution, behavior, and biology. 

 Immature sharks often associate with 

 each other regardless of sex, but after 

 maturity sexual segregation is the 

 norm. Mature males and females may 

 come together only to mate, resulting 

 in movements that may range from 

 small-scale aggregation of dispersed 

 individuals to long-range migra- 

 tions over thousands of kilometers. 



The process of maturation, and the 

 subsequent need to channel energy 

 into reproduction, affect the growth 

 rate of at least some shark species. 

 Immature male and female porbea- 

 gles grow at the same rate, and the 

 growth rate of both sexes slows at 

 maturity; however females mature at 

 a greater age than males and there- 

 fore their period of fast immature 

 growth lasts longer and they grow 

 larger than males (Natanson et al., 

 2002). 



The maximum reproductive lifes- 

 pan of a shark species is the time 

 elapsed between the age at maturity 

 and the maximum age. In conjunction 

 with the duration of the reproductive 

 cycle, the reproductive lifespan deter- 

 mines the maximum number of litters 

 a female shark can produce in her 

 lifetime. Population modeling indi- 

 cates that shark species that mature 

 at a young age have a greater capac- 

 ity to recover from exploitation than 



sharks that mature later (Smith et 

 al., 1998). Thus age at maturity is a 

 crucial factor influencing the produc- 

 tivity of a species. 



Age at maturity can be estimated 

 directly from paired age-and-matu- 

 rity estimates taken from the same 

 shark, but often such data are not 

 available, or are too few to provide 

 precise estimates. Consequently it is 

 often necessary to estimate age at 

 maturity indirectly from length at 

 maturity and a growth curve. 



In the present study we estimate 

 the length at maturity for three spe- 

 cies of large pelagic sharks in New 

 Zealand waters: porbeagle (Lamna 

 nasus (Bonnaterre, 1788)), shortfin 

 mako (Isurus oxyrinchus Rafinesque, 

 1810), and blue (Prionace glauca 

 (Linnaeus, 1758)) sharks. These spe- 

 cies are commonly caught by tuna 

 longliners fishing around New Zea- 

 land (Francis et al., 2001). Longline 

 fishing effort declined from a high 

 of over 25 million hooks per year 

 in the early 1980s, to a low of 2—4 

 million hooks in 1995-98, largely 

 because of a reduction in the number 

 of foreign licensed vessels (Francis 

 et al., 2001). Since then, the do- 

 mestic longline fleet has expanded, 

 and fishing effort exceeded 10 mil- 

 lion hooks in 2001-02 (Ayers et al., 

 2004). Because of concern over the 

 sustainability of the catches of both 

 target and nontarget species in this 

 fishery, the New Zealand Ministry 



