PRATT REPRODUCTION IN BLUE SHARKS 



Blue shark claspers exhibit these characteris- 

 tics (Figure 8) in a gradual transition with body 

 growth rather than the abruptness noted by Clark 

 and von Schmidt (1965) for thecarcharhinids. It is 

 therefore difficult to distinguish maturity in sub- 

 adult blue sharks based on external organs. 



Another valid index of sexual maturity is the 

 presence or absence of sex products such as eggs 

 and sperm. Several authors have used the pres- 

 ence of male sexual products as indicators of 

 maturity. Kauffman (1950) working on the tiger 

 shark observed ". . . the release of milt from the 

 gonoduct when pressure was applied." Matthews 

 (1950) stated that a basking shark of 622 cm 

 ". . . was just approaching sexual maturity, for 

 though the testis was showing incipient activity, 

 the ampullae of the ductus deferentia were rather 

 small, completely empty of spermatophores and 

 showing no signs of having contained any." Olsen 

 ( 1954) recognized that maturity took place over a 

 fairly extensive size range. He noted that in the 

 school shark, Galeorhinus australis, seminal fluid 

 flows freely from the cut surface of the enlarged 

 testes and the seminal vesicles contain active 

 spermatozoa in early summer. In borderline cases 

 Olsen histologically sectioned the testis. He 

 considered those fish to be mature that had ". . . 

 enlarged seminiferous tubules [sic] which carried 

 bundles of ripe spermatozoa . . . ." Bonham et al. 

 (1949) and Templeman (1944) working on the 

 spiny dogfish, Squahis acanthias. combined clas- 

 per length with the presence of spermatozoa in the 

 seminal vesicles to determine maturity. 



In the blue shark, two organs which enlarge as 

 the male matures are the testes and the epididy- 

 mides. Unfortunately, testes length ( Figure 9) and 

 epididymis width (Figure 10) follow the same 

 gradual size increase as the claspers (Figure 8). 

 Because they do not exhibit major inflections, 

 these relationships are of little use for determin- 

 ing the onset of sexual maturity. 



The most reliable method that I have found for 

 determining maturity in the difficult subadult to 

 adult sizes is to assess the ability of a shark to 

 produce spermatophores. Many sharks with clas- 

 pers that appear mature lack spermatophores and 

 have small ductus deferentia. The spermatophore 

 is the last tissue to mature and it develops 

 abruptly in blue sharks. 



Of 193 male blue sharks examined, 74 (38. 3*^) 

 contained some quantity of spermatophores. The 

 sharp increase in spermatophore occurrence be- 

 tween 175 and 205 cm body length is the transition 



80 100 t20 140 160 160 200 2Z0 240 260 



FORK LENGTH (cm) 



Figure 8. — Clasper-body length relationship compared with 

 spermatophore development in the blue shark. 



o o o <t 



a o 



80 100 120 140 ISO 180 200 220 240 260 



FORK LENGTH (cm) 



Figure 9. — Testes length-body length relationship in the blue 

 shark. 



o c^ o o o 



eo 100 120 140 160 160 200 220 240 260 



FORK LENGTH (cm) 



Figure lO. — Epididymis width-body length relationship in the 

 blue shark. 



451 



