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Fishery Bulletin 103(3) 



system. The presence or absence of spermatophores or 

 spermatozeugmata is a good indicator of the ability of 

 a male to produce viable sperm, but it is not infallible: 

 such structures sometimes lack viable sperm (Pratt 

 and Tanaka, 1994). Furthermore, male reproductive 

 products may not be present year-round: blue sharks 

 appear to have a seasonal cycle of spermatozeugmata 

 production in the western central Atlantic (Hazin et 

 al., 1994), although Pratt (1979) found no evidence of a 

 cycle in the western North Atlantic. Thus the presence 

 of spermatophores and spermatozeugmata does not 



necessarily confirm reproductive viability, and their 

 absence does not confirm immaturity. Similarly, fully 

 calcified claspers that can be rotated, splayed open, 

 and possess an anchoring mechanism may confer an 

 ability to mate, but they do not necessarily confirm an 

 ability to deliver viable products; however the lack of 

 fully developed claspers presumably does prevent suc- 

 cessful copulation. 



In the present study, either the length at which 

 clasper development was completed in half the male 

 population, or the length at which 50% of males pos- 

 sessed spermatophores or spermatozeug- 

 mata, whichever was higher, provided 

 an estimate of the lower bound of the 

 median maturity. The actual median 

 maturity may be higher than this es- 

 timate if some males had reproductive 

 products that lacked viable sperm, or if 

 some other feature of the reproductive 

 system (e.g., the siphon system) was in- 

 sufficiently developed to enable delivery 

 of sperm to the female. 



An analogous argument applies to fe- 

 male sharks. Full development of the 

 uterus and oviducal gland, and produc- 

 tion of vitellogenic ovarian ova, are all 

 required for successful reproduction. 

 Expansion of the uterus, as measured 

 here by UWI, may not be a sufficient 

 condition by itself. Thus the length at 

 which half the female population had 

 expanded uteri places a lower bound on 

 the median maturity. 



The smallest length at which females 

 were pregnant, and the length-frequency 

 distributions of pregnant females, are 

 not by themselves good indicators of me- 

 dian maturity. A better indicator would 

 be the length at which half the females 

 in a population first become pregnant, 

 but this is impossible to determine. Fur- 

 thermore, pregnancy estimates could be 

 confounded by unrepresentative sam- 

 pling of a population that may be seg- 

 regated by reproductive status and by 

 nonparticipation of some females during 

 breeding because they are "resting" be- 

 tween pregnancies. Nevertheless, preg- 

 nancy absolutely confirms maturity; 

 therefore it is a useful adjunct to other 

 measures of maturity. 



The presence or absence of a hymen 

 has been used in some studies to indi- 

 cate maturity. However it should not be 

 used for that purpose because adolescent 

 (premature) mating occurs in at least 

 some species of sharks, including blue 

 sharks (Pratt, 1979). Furthermore, the 

 absence of a hymen may not even be a 

 good indicator of mating: we observed 



