Abstract.- Age and growth of 

 the school shark Galeorhinus galeus 

 was studied from rings in the verte- 

 bra and length-frequency data. Sam- 

 ples were collected by trawling off 

 the southern Brazilian coast from 

 June 1980 to September 1986. Histo- 

 logical studies were also conducted 

 on the characteristics of the verte- 

 bra. Standard histological techniques 

 and microradiography were used to 

 determine the pattern of vertebral 

 calcification. The vertebrae of G. ga- 

 leus are composed of calcified carti- 

 lage. Chondrocytes in calcified zones 

 remain alive, probably nourished 

 through vascular channels extending 

 from the perichondrium into the car- 

 tilage matrix. A narrow zone of un- 

 calcified matrix at the outer edge of 

 the centrum indicates that calcifica- 

 tion is preceded by initial develop- 

 ment of hyaline cartilage. The verte- 

 bra presents a pattern of alternating 

 heavily and less heavily mineralized 

 zones, narrow and wide, respective- 

 ly. The narrow zones were named 

 rings, which are translucent under 

 transmitted light and white to the 

 microradiograph. These rings are 

 probably laid down yearly in a slow- 

 growing phase extending throughout 

 the four winter months of June to 

 September. Lengths at age were 

 back-calculated and the von Ber- 

 talanffy growth parameters are: 

 males-K = 0.092, L„ = 152 cm, and 



to 



-2.69; females-K = 0.075, L„ 



= 163 cm, and tn = -3.00. ELEFAN 

 software was used to determine the 

 growth curve best fitted to length- 

 frequency data, but results overesti- 

 mated the growth rate due to the 

 slow growth and modal overlap. 



Age, Growth, and Structure 

 of Vertebra \n the School Shark 

 Galeorhinus galeus (Linnaeus, 1 758) 

 from Southern Brazil 



Beatrice Padovani Ferreira 



Fundacao Universidade do Rio Grande. Rio Grande, RS. 96200, Brazil 

 Present address: Marine Biology Department 

 James Cook University of North Queensland, Townsville Q481 I, Australia 



Carolus Maria Vooren 



Departamento de Oceanografia, Fundacao Universidade do Rio Grande 

 Rio Grande, RS, 96200, Brazil 



Manuscript accepted 12 October. 

 Fishery Bulletin, U.S. 89:19-31 (1991). 



The elasmobranch skeleton consists 

 of calcified cartilage. In most elasmo- 

 branchs, vertebrae are the only avail- 

 able structure that display periodic 

 rings, which are useful for determin- 

 ing age. These rings result from dif- 

 ferent ratios of organic matrix/min- 

 eral, making the zones optically 

 distinct (Casselman 1974). Since the 

 description by Ridewood (1921), sev- 

 eral techniques have been developed 

 for enhancing the visibility of these 

 rings thus making the counts easier 

 and more accurate. However, infor- 

 mation about the histology of elasmo- 

 branch vertebral rings is limited, and 

 statements about their chemical com- 

 position and optical properties are 

 contradictory (Casselman 1983). 



The school shark Galeorhinus ga- 

 leus is one of the principal species in 

 the shark fishery in southern Brazil 

 (Vooren and Betito In press). With 

 the purpose of providing information 

 for management decisions, age and 

 growth of the Brazilian school shark 

 were determined from rings in the 

 vertebrae and length-frequency data. 

 A histological study was conducted to 

 investigate the structure of the verte- 

 brae and to determine variations in 

 their composition. 



Materials and methods 



The study area was the continental 



shelf and upper slope off southern 

 Brazil, between latitudes 34° and 

 30° S, at depths between 10 and 500 

 m. Data used for size-frequency anal- 

 ysis were obtained during trawl fish- 

 eries of this area from June 1980 to 

 September 1986 (Table 1). All fishes 

 were sexed and their total length 

 (TL, cm) was measured from the tip 

 of the snout to the extremity of the 

 upper lobe of the tail, which was 

 stretched back to be aligned with the 

 body axis. Vertebrae were collected 

 during the cruises listed in Table 1, 

 and samples were chosen to include 

 both sexes and the full size-range 

 available. Sexual maturity and repro- 

 ductive stage (Table 2) were deter- 

 mined according to size criteria es- 

 tablished for this species by Peres 

 (1989). 



The data were processed on the 

 Statistical Package for the Social 

 Sciences, SPSS (Nie 1975). Length- 

 frequency distributions for both sexes 

 were plotted by cruise, by month, and 

 also by a selected combination of the 

 two largest samples. The ELEFAN 

 (Electronic Length Frequency Anal- 

 ysis) software (Pauly and David 1981) 

 was used to determine growth param- 

 eters (k and L m ) from length-fre- 

 quency data. The goodness of fit was 

 given by the index Rn. 



Vertebrae for age determination 

 were dissected in the field from the 



19 



