able, its growth during the period at 

 liberty is established. If age at the 

 time of release can be determined, 

 age at the time of recapture can like- 

 wise be calculated. Positive age and 

 growth information thus obtained can 

 provide a valuable check on estimates 

 based on indirect methods (Mather 

 1980). 



C. RESULTS 



1. Sizes of Fish at Determinable 

 Ages 



The first objective of most age 

 and growth studies is to determine 

 the mean sizes offish at each year of 

 age for which this is possible. Ideally 

 the sizes should be determined at one 

 year intervals after the date of spawn- 

 ing. This was done by Sella (1929a) 

 and Rodriguez-Roda (1960, 1964a), 

 but most other investigators have 

 been limited to seasons in which suf- 

 ficient material was available. 



Sella (1929a) presented the first 

 important study of the age and growth 

 of bluefin tuna. This was based on 

 counts of annuli on veilebrae from 

 more than 1,500 bluefin tuna caught 

 in June, during the spawning season. 

 The individuals whose ages were as- 

 sessed as 3 or more years had been 

 taken off Tripolitania (western 

 Libya). Sella noted that these results 

 did not differ noticeably from those 

 for bluefin tuna taken in other parts 

 of the Mediterranean. He assessed 

 ages of 1 and 2 years for individuals 

 which had been captured in the 

 Adriatic Sea, since fish of these sizes 

 were not available off Libya. He pre- 

 sented his results in terms of mean 

 length and mean weight for each year 

 of age from 1 through 14. 



Westman and Gilbert (1 94 1 ) and 

 Westman and Neville (1942) pro- 

 duced the first important informa- 

 tion on the growth of bluefin tuna 

 taken in the western Atlantic. Their 

 works provided well supported 



LnielhtKenb7S«lb(192»a) 



Wdghl given b;SeUi(l»2»a) 



• LrngtbglvMib; WMta>aniDdCUb»r1(l»4l) 



O Lcagtbtlv«b7Hamn(l9C0) 



X Uopb given b7VUd*«taL(l9tO) 



2S0-, 

 2*0- 



220 



200- 



190- 



160- 



liO 



120- 



m- 



eo- 



60- 



E 



% 



O L*iiglligtvenb]>TI<w* (1960a) 



7 Lengtb given bjRsdrlgiui-Rada (19(0) 



•«- Length given b^Malbef and Scfauck (1 9tO) 



^ Wetghl given b; Mather and Schuck (1 9(0) 



-300 



-250 



-200 



-ISO 



100 



9" 



so 



- 



II 12 13 li 



information of the sizes of fish of 

 ages 1-4 taken during the summers 

 of 1938 and 1941 off Long Island, 

 New York, and sizes based on small 

 samples or individual specimens, for 

 young of the year and for various 

 ages of 5 years or more. 



Several additional works on the 

 age and growth of bluefin tuna taken 

 in various parts of the Atlantic Ocean 

 were published between 1958 and 

 1962. Tiews (1963) plotted the sizes 

 for ages obtained by Sella (1929a), 

 Westman and Gilbert ( 1 94 1 ), Hamre 

 (I960), Vilela et ai. (I960), Tiews 

 I960), Rodriguez-Roda (1960), and 

 Mather and Schuck (1960) (Figure 

 4). As Tiews observed, the results of 

 these studies, using material from sev- 

 eral widely separated areas, are re- 

 markably similar. 



Rodriguez-Roda (1960, 1964a) 

 presented the following formula for 

 back-calculating the fork length of a 

 bluefin tuna at ages previous to that 

 of its capture: 



1= 17.88 +V^(L- 17.86) 



where: 



L = fork length in cm of the fish, 



V = radius in mm of the fourth or fifth 



precaudal vertebra, 



1 = fork length in cm of fish at age x, 

 and 



V = radius (mm) of vertebral ring cor- 



responding to age X. 



The back-calculated lengths were 

 considerably less than those obtained 

 directly for fish of the same ages. 

 This was due in part to the fact that 

 the vertebral rings were laid on dur- 

 ing the winter, but the direct age de- 

 terminations were made from mate- 

 rial collected in late spring and early 

 summer. 



Rodriguez-Roda presented re- 

 vised size-for-age data (1969c) and 

 the following von Beilalanffy equa- 

 tion for the relation between age and 

 size: 



1, = 355.84(1-6"'""""*'") 



Figure 4. Sizes for ages as estimated by various authors (Tiews 1 963). 



