FISHERY BULLETIN: VOL 77, NO ■> 



ovarian eggs are reaching maturity (Figure 18) 

 and the greatest number of females are becoming 

 inseminated (Figure 27). Larger females are 

 caught in decreasing numbers on the mating 

 grounds on the shelf. Their absence probably indi- 

 cates a successful insemination and offshore mi- 

 gration. Since courtship and copulation are not 

 without peril to the female, it is reasonable that 

 they should move offshore at this time. The sex 

 ratio remains between 5 and 10% female, from 200 

 to 230 cm where a second peak occurs. These are 

 mostly postpartum and gi-avid females in their 

 first pregnancy. They have probably followed the 

 main population inshore for its summer feeding 

 migration. It is possible that since their eggs are 

 ripe they may also need to supplement the amount 

 of spermatozoa in the oviducal gland. 



CONCLUSION 



The blue shark's success as a species is partly 

 dependent on a highly evolved system for repro- 

 duction. The blue shark differs from other car- 

 charhinids in having a steady growth rate for the 

 sexual organs, a lack of seasonality in the genera- 

 tion of sex products, and a distinct female subadult 

 stage. A different approach has been necessary to 

 discern the size at sexual maturity for both sexes: 

 an analysis of spermatophore development for the 

 male, and an examination of the seminal recepta- 

 cle present in the female oviducal gland. 



There are many stages between the generation 

 of sexual products (sperm, eggs, embryosi and the 

 time of their delivery. Elaborate capabilities have 

 been developed by both sexes for lengthy storage 

 and nourishment of spermatozoa, first in the 

 epididymis, then as spermatophores in the ductus 

 deferens, and finally in the oviducal gland of the 

 female where they are retained for months and 

 possibly years. 



Sexual maturity occurs for both sexes at a simi- 

 lar body length when they are together on the 

 continental shelf for the summer season. 



While the details of mating and copulation are 

 obscure, it is highly successful since not a single 

 female of age was observed without evidence of 

 mating activity and 49% were inseminated. 



With the exception of the strays examined op- 

 portunistically during this study gravid females 

 occupy a niche that is different from the continen- 

 tal shelf population. The release of young and 

 their early development apparently occur in 



oceanic areas. Little is known of this important 

 period in their life history. 



SUMMARY 



Males 



The internal anatomy of the male blue shark is 

 similar to other carcharhinids. The vas deferens is 

 enlarged and convoluted for the storage of sperm 

 and spermatophores. The clasper lacks a spur and 

 resembles that of the basking shark and tope. 

 Juvenile and small mature males 4 and 5 yr old 

 ( 153-180 cm) are the most commonly encountered 

 size group on the continental shelf off southern 

 New England from June to October. Male blue 

 sharks reach maturity at 180 cm and probably 

 copulate frequently through the summer. Only 

 about 2'7( of all males caught have claspers swollen 

 and discolored by mating. 



Females 



The internal anatomy of the female blue shark 

 is similar to other species of placentally viviparous 

 carcharhinids. The single right ovary delivers ova 

 up to 20 mm in diameter to paired oviducts. They 

 are fertilized as they pass through the oviducal 

 gland by stored spermatozoa and develop in paired 

 uteri. 



Female blue sharks can be grouped into imma- 

 ture, subadult, and adult categories based on size, 

 behavior, and development. 



1 . Immature females range from 46 cm (birth) to 

 a maximum of 145 cm long. The ovary is small 

 with many undeveloped follicles. The oviducal 

 gland and uterus are undifferentiated from the 

 oviduct. The vagina is sealed by a membrane 

 which may persist to a fork length of 135 cm. 



2. Subadult females range from 145 to 185 cm 

 long and possess differentiated though not com- 

 pletely functional reproductive organs. The ovary 

 contains follicles between 2 and 6 mm. Externally, 

 the oviducal gland is heart shaped and roughly 

 twice the diameter of the oviduct. The uterus is 

 differentiated from the oviduct but not >2 cm in 

 diameter and never contains embryos. The skin 

 begins to thicken to receive the courtship wounds 

 of the males. There are several reasons for consid- 

 ering these females as a separate group. Fish in 

 this condition are the most common group of 

 females on the continental shelf from Hudson 



468 



