664 



Fishery Bulletin 89(4), 199! 



Figure 14 



Mean monthly hepasomatic index of the school shark Galeo- 

 rhinus galeus, from Rio Grande do Sul, Brazil, in different 

 reproductive stages. GR, gravid; NGR-1, 1st year nongravid; 

 NGR-2, 2d year nongravid. 



Ripley (1946) concluded that in eastern North Pacific 

 animals, gestation lasts 12 months during which there 

 is no vitellogenesis and that parturition occurs in sum- 

 mer. Data on the female cycle in this population were 

 obtained from a single sampling area where, in a sam- 

 ple of J3747 females, 88% were gravid, 11% had large 

 ovarian follicles, and 1% were resting. The percentages 

 reflect the situation at a certain point of the migration 

 route of the gravid females, but the data indicate the 

 simultaneous presence of three categories of adult 

 females. In winter, Olsen (1954) observed two types 

 of nongravid Australian females: one with the largest 

 ovarian follicles ranging from 4.0 to 5.0cm in diameter, 

 and the other with maximum follicle diameters of 

 1.0-2. 0cm. These two categories occurred simulta- 

 neously and in similar numbers. Parturition took place 

 in November-December, and size at birth was about 

 31cm TL. Olsen (1954) assumed that gestation starts 

 immediately after mating in winter and lasts 6 months. 

 The presence of the two nongravid categories was ex- 

 plained by a period of 18 months for the production of 

 the mature follicle, giving a cycle of 2 years. However, 

 in view of the data on gestation in western South Atlan- 

 tic and eastern North Pacific animals, it is unlikely that 

 this phase lasts only 6 months in Australian animals. 

 Therefore, we conclude that the duration 

 and timing of the reproductive cycle are 

 similar in these three populations of 

 school shark. 



The observed increase in body size of 

 embryos from the anterior to the poster- 

 ior end of the uterus has also been noted 

 in eastern North Pacific and Australian 

 animals. This may partly reflect duration 

 of the ovulation process, during which 

 eggs enter the oviducts in pairs at inter- 

 vals of 24-48 hours in the smooth dog- 

 fish, in the skates, Raja brachyura and 

 Raja erinacea, and in the sand shark 

 (TeWinkel 1950, Holden 1974, Gilmore et 

 al. 1983). Assuming an interval of 36 

 hours in the school shark, the duration of 

 ovulation for all eggs would range be- 

 tween 10 and 40 days, depending on 

 fecundity. The size difference between 

 the first and the last embryo in the uterus 

 would then reflect the growth of the first 

 embryo during the ovulation period, 

 although the possibility of a correspond- 

 ing difference in yolk reserve remains to 

 be investigated. 



In spring, liver weight as a proportion 

 of total body weight (HSI) of the eastern 

 North Pacific adult female NGR-2 was 

 14%, and about 4% in GR females. In the 



