736 



Fishery Bulletin 100(4) 



Grand Banks 





^ 



Map of the capture locations of al 

 Grand Banks are indicated. 



Figure 11 



I gravid female porbeagles by month of capture. Approximate locations of Georges Bank and the 



(Kohler''). The largest embryos in our study from one litter 

 in April were 49-60 cm FL (59-72 cm TL). 



Discussion 



In the NW Atlantic, male porbeagles mature between 

 166 and 184 cm FL, and 50'^^^f maturity was at 174 cm FL, 

 which corresponds to an age of 8 years (Fig. 4B; Natanson 

 et al., 2002). The most accurate means of determining 

 male maturity is clasper length and calcification. Because 

 of the distinct seasonal variability, the presence of seminal 

 products alone, is not a good indicator of maturity. Clasper 

 rotation occurred at all sizes, eliminating it as a maturity 

 indicator. Our estimate of length at maturity substantially 

 refines Aasen's* estimate of 150 to 200 cm TL (146-193 

 cm FL) for this population. Aasen^ based his estimates on 

 clasper length in relation to dorsal length. 



Female NW Atlantic porbeagle sharks mature between 

 210 and 230 cm FL and 50':{ maturity was at 218 cm FL, 

 at an age of 13 years (Fig. 4B; Natanson et al., 2002). The 

 sizes of all female reproductive organs measured showed 

 a definitive inflection at maturity in relation to body size 

 and are good indicators of maturity. Aasen^ estimated fe- 

 male maturity between 2.0 and 2.5 m TL ( 193-240 cm FL) 

 based on uterus length. Our estimates compare well to the 

 upper part of his range; however our data do not support 

 his lower size at maturity. 



The seasonality of spermatophore production, observa- 

 tions of females with fresh mating scars, and observations 

 of males and females on the same longline indicated that 



« Kohler, N. K. 2000. Unpubl. data. NMFS Apex Predators 

 Program, 28Tarzwell Dr. Narragansett, RI 02882. 



porbeagles mate in the fall, primarily between September 

 and November. In an earlier study, sperm in the shell 

 gland of a female, and the presence of a male caught on 

 the same longline set in October, also suggested a fall 

 mating period (Pratt, 1993). Aasen (1963) proposed a fall 

 mating season (September-October) based on an increase 

 in the amount of sperm present in the males "towards 

 the end of August." This period agrees with the sugges- 

 tion of a long mating season in the SW Pacific porbeagle 

 population (Francis and Stevens, 2000). During this time, 

 females have fresh external mating scars, internal vaginal 

 scars, and spermatophores in the uterus. Gauld (1989) 

 suggested that mating occurs during December-January 

 in the northeast Atlantic on the basis of fresh mating scars 

 on the pectoral fins. 



Mating injuries have been documented for many spe- 

 cies of sharks. Bite marks on females during mating have 

 been documented in the blue (Pnonace glaitca), nurse 

 iGinglymostoma cirratum), sandtiger, (Carcharias taii- 

 rus), blacknose iCarcharhinits acronotus) finetooth iC. 

 isodon ), blacktip (C. limbatus), sandbar (C plumbeus), and 

 Atlantic sharpnose {Rhizoprumodon terraenovae) sharks 

 (Stevens, 1974; Gilmore et al., 1983; Schwartz, 1984; Cas- 

 tro, 1993, 1996, 2000). Fresh bite marks may coincide with 

 insemination and ovulation, marking the approximate 

 beginning of the gestation period (Parsons, 1983; Castro, 

 1996). Matthews ( 1950) noted lacerations in the vagina of 

 the basking shark iCetorhinus maximus) from the clasper 

 spur. Pratt ( 1979) also observed abrasions from claspers in 

 the vagina of female blue sharks. 



Gravid females typically carry single-ovum capsules 

 from September to November, and developing embryos 

 from October to April. Aasen (1963) reported no gravid 

 porbeagles from July to September 1961, in the NW At- 



