666 



Fishery Bulletin 89|4), 1991 



The gradual decrease of the HSI in both sexes dur- 

 ing winter suggests that at that time, the population 

 invests little effort in feeding and lives mostly off its 

 lipid reserves. From interpolation in the observed HSI 

 pattern, it is concluded that during the first two sum- 

 mers after parturition, the female accumulates lipids. 

 During the third year of the cycle, HSI decreases 

 constantly from ovulation to parturition (Fig. 16). In 

 coastal waters of Uruguay, the species is caught by 

 bottom gillnets during winter and by bottom longlines 

 during summer (De Buen 1952). This is consistent with 

 the hypothesis of the endogenous periodicity of feeding 

 under hormonal control, as in Clupea harengus (lies 

 1984). It is suggested that in the school shark, feeding 

 during winter is reduced to the intake of proteins 

 necessary for the continuous production of urea. In the 

 liver of the female, a seasonal and a three-year cycle 

 are timed to store and metabolize lipid reserves, to 

 synthesize and transfer vitellogenin, and to control 

 buoyancy, in a sequence which corresponds with the 

 varying physiological needs during the reproductive 

 cycle. 



• - rf IMMATURE 

 A ' ADULT 



Figure 16 



Mean monthly hepatosomatic index during the reproductive 

 cycle of the school shark Galeorhinus galeus, from Rio Grande 

 do Sul, Brazil. NGR-1, 1st year nongravid; NGR-2, 2d year 

 nongravid; GR, gravid. Arrows indicate the hypothetical pat- 

 tern during periods when the population occurs outside the 

 study area. 



National Research Council (CNPq). and the Research 

 Institute Fund of the Banco do Brasil (FIPEC). 



Citations 



Acknowledgments 



The authors thank our colleagues, and Captain Jose 

 Anchieta Rios Pinto and his crew of the RV Atldntico 

 Sul, for the cooperation at sea and ashore. Special 

 thanks are due to Dr. Rosangela Lessa for ideas and 

 participation in all aspects of the work from 1980 to 

 1985; to the Laboratory of Histology of University of 

 Rio Grande (FURG) for valuable technical support; to 

 Mr. Brasilio Gibicoski Loureiro for graphical services; 

 to Beatrice Padovani Ferreira and Dr. Manuel Haimo- 

 vici for discussion of results and critical revision of the 

 manuscript. The study was financed by the Intermin- 

 isterial Comission for Marine Resources (CIRM), the 



Baldridge. H.D. Jr. 



1970 Sinking factors and average densities of Florida sharks 

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1988 Nouvelles donnees sur la reproduction du milandre, 

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1978 Plasma levels of vitellogenesis in the elasmobranch 

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