REPRODUCTION IN THE BLUE SHARK, PRIONACE GLAUCA 



Harold L. Pratt, Jr.' 



ABSTRACT 



In the male blue shark. Prionace glauca, paired testes produce spermatozoa year round which are 

 stored first in the epididymides, then as spermatophores in the lower ductus deferentia. Spermatazoa 

 are transferred to the female through paired claspers employed singly. Spermatozoa are injected into 

 the upper vagina and pass through the uterus and isthmus into the shell (oviducall gland, where they 

 are stored until the female is ready for fertilization. Male blue sharks reach maturity at 183 cm fork 

 length when 5(K^ possess spermatophores. Females pass through a subadult phase (145-185 cm), when 

 the organs for copulation and sperm storage are developed but the ova are undeveloped. During this 

 phase females receive numerous toothcuts in their thickened dermis as a prelude to mating and 

 frequently copulate. 



I examined reproductive organs from 160 subadult female blue sharks, caught in shelf waters off 

 southern New England during summer months, by histological sectioning to determine if spermatozoa 

 were present. Of these females, 79 had spermatozoa in the oviducal gland, establishing successful 

 copulation. Inseminated females then emigrate offshore where fertilization occurs the following spring 

 during ovulation. Blue sharks are viviparous and bear young after 9 to 12 months gestation. Thirty- 

 eight new or unpublished accounts of gravid females are investigated, as well as one 192 cm hermaph- 

 roditic blue shark. 



In shelf waters during the summer the sex ratio for subadults is nearly equal while males dominate 

 the adult sizes due to the emigration of inseminated females. 



The blue shark, Prionace glauca, is the most 

 abundant of the larger oceanic sharks in the At- 

 lantic (Bigelow and Schroeder 1948). It is fre- 

 quently among the incidental catch of tuna and 

 swordfish longliners in temperate, subtemperate, 

 and tropical parts of the world ocean. Nichols and 

 Murphy (1916) reported seeing "hundreds, even 

 thousands" of them swimming free and attracted 

 by the activity of the sperm whale fishery in the 

 tropical Atlantic. Longline fishing operations con- 

 ducted by National Marine Fisheries Service 

 biologists in the offshore areas between Cape Cod, 

 Mass., and Cape Hatteras, N.C., reveal the blue 

 shark to be more numerous in this area than any 

 other large shark or big game fish (Casey and 

 Hoenig^). 



Like other elasmobranchs, blue sharks have a 

 complex reproductive cycle which contributes to 

 their success as a species. Suda (1953), Strasburg 

 ( 1958), Aasen ( 1966), and Stevens ( 1974) have all 

 contributed information about blue shark repro- 



'Northeast Fisheries Center Narragansett Laboratory, Na- 

 tional Marine Fisheries Service, NOAA, Narragansett, RI 

 02882. 



^Casey, J. G., and J M. Hoenig. 1977 Apex predators in 

 deepwater dumpsite 106. In Baseline report of environmental 

 conditions in deepwater dumpsite 106. NOAA Dumpsite 

 Evaluation Report 77-1, p. 309-376. 



duction, but many of the details concerning 

 anatomy, maturity, and the sexual cycle were in- 

 complete. New information is presented on the 

 mechanism of spermatozoa storage in the male 

 and female blue sharks and adaptations for mat- 

 ing in the female. 



In this study, the reproductive systems of west- 

 ern North Atlantic blue sharks have been investi- 

 gated to better understand the life history of this 

 important apex predator. 



MATERIALS AND METHODS 



Blue sharks sampled from October 1969 to April 

 1977 came from two sources: 1) longline catches 

 made by research and commercial vessels and 2) 

 anglers' catches landed during shark fishing tour- 

 naments. The area sampled extended from Cape 

 Hatteras to east of Georges Bank, both on the 

 continental shelf and in the Gulf Stream. Three 

 fish were also collected north of St. Thomas, V.I. 



Throughout this paper I use fork length (FL), a 

 straight line measurement from the tip of the 

 snout-to the fork of the tail. Measurements involv- 

 ing the upper caudal (such as total length, TL) are 

 variable due to its flexibility. Fork length is an 

 easier and more accurate measurement for one 

 person to make at sea. Many authors cited use 



Manuscript accepted November 1978 

 FISHERY BULLETIN: VOL. 77. NO. 



445 



