22 



Fishery Bulletin 89(1), 1991 



JUN 



N391 



JUL 

 N697 



83 93 103 113 123 133 143 153 163 TL (cm I 



Figure 3 



Length-frequency distribution of male Galeorhinus galeus by 

 month. 



during cruises 4/80, 9/81, and 3/82. Smaller length 

 classes were more frequently caught during cruises 

 4/84 and 3/85, but did not form a marked mode in the 

 length-frequency distribution. 



Techniques for enhancing vertebral rings 



Rings were visible in all the attempted methods, but 

 because of the large number of rings and marginal 

 crowding in the centra of older sharks, only detailed 

 microscopic observations were successful in providing 

 comprehensive readings and measurements. The 

 graphite method was an easy and simple technique that 

 provided good results in enhancing rings of vertebrae 

 of younger sharks. However, the large number of rings 

 near the margin of vertebrae of older sharks was dif- 

 ficult to determine using this technique, and the 

 number of rings was always underestimated compared 

 with results by other techniques. 



Stained sections of vertebrae provided good results 

 in enhancing rings both in calcified and decalcified 

 material. In the latter, no measurements were taken 

 because of shrinkage and distortions observed after the 

 decalcification procedure. The matrix shrank in the 

 space formerly occupied by the mineral, and this zone 

 became narrower than in the calcified state. 



380 



JUN 



480 

 JUL 



780 



SEP 



781 



SEP 



981 

 SEP 



382 



JUL 



1083 



AUG 



383 



NOV 



484 

 JUN 



285 

 JUN 



385 



JUL 



480 



JUL 



33 133 143 153 163 



Figure 4 



Length-frequency distribution of female Galeorhinus galeus 

 by cruise. 



The most satisfactory technique for enhancing and 

 counting rings was microradiography. With this 

 method, the more calcified zones appeared white while 

 the less calcified appeared dark (Figs. 6, 8). Direct 

 observations of the sections showed that the former 

 more mineralized zones were translucent and the latter 

 less-mineralized zones were opaque when observed 

 under transmitted light (Figs. 7, 8). Sections of various 

 thickness were examined. The best contrast between 

 zones was obtained from sections between 250 and 



