Jensen et a\ The reproductive biology of Lamna nasus in the western Noith Atlantic Ocean 



731 



90 110 130 150 170 190 210 230 250 270 290 



Fork length! (cm) 



0) 1 



0.8 - 



B 



0.6 



0.4 



0.2 



.' Male 



50% 



8 1 years 



13.1 years 



2 



10 12 14 16 18 20 



Age (years) 



Figure 4 



Maturity ogives for male and female porbeagle sharks: (A) ogives based on length, (B) 

 ogives based on age. Fifty percent maturity is indicated. 



and greater, spermatophores appear in the ampulla epidid- 

 ymis. By 162 cm FL fully calcified claspers were observed. 

 Individual variation exists in body length and the order in 

 which these developments take place. All males observed 

 were mature by 185 cm FL based on clasper calcification 

 and the ability of the rhipidion to open. The presence of 

 spermatophores may be used in addition; however, absence 

 of spermatophores can be attributed to season as well as 

 to maturity. Each clasper bears a sharp, conical, calcified 

 spur near the tip which folds out of the distal surface as the 

 rhipidion opens. In adults, the sharp spur tip was either 



covered by an epidermal membranous sheath, or naked. 

 A naked spur is an indicator of mating activity because 

 mating ruptures the sheath. The FL at which 50% of the 

 male population is mature, based primarily on clasper con- 

 dition, was estimated as 174 cm FL (Fig. 4A). 



Both testis size and the amount of spermatophores 

 in the ampulla epididymis showed distinct fluctuations 

 related to the mating season. From November through 

 mid December, the testis lobes were noticeably reduced 

 in diameter, the testes were smaller, and the epigonal 

 organ had infiltrated the space previously occupied by the 



