Butler and Myklevoll were the 

 first investigators to estimate the ages 

 of significant numbers of bluefm tuna 

 more than 14 years old. 



Berry et al. (1977) discussed in 

 great detail the techniques of aging 

 bluefin tuna by reading annuli on 

 vertebrae and otoliths. They de- 

 scribed methods of storing, staining 

 and examining vertebrae, and their 

 interpretation of the markings on 

 them. They found that immediate 

 freezing and freezer storage produced 

 better results than the other methods 

 of preservation which they tested. Im- 

 mediate staining and reading, how- 

 ever, was probably the most satisfac- 

 tory procedure. They noted that stain- 

 ing time varied with the size of fish, 

 and that the inner rings, particularly 

 in large fish, stained before the outer 

 ones. 



Their interpretation of marks on 

 vertebrae was complex. It involved 

 ridges, grooves, fimbriated lines, and 

 stained and unstained rings. They 

 noted that several stained rings might 

 occur early in the staining process 

 within an annular zone, and that these 

 might coalesce in various ways as 

 staining progressed. 



Berry et al. (1977) did not in- 

 clude size-for-age data or age data 

 for individual fish, but they presented 

 extreme and average vertebral ages, 

 determined from readings of verte- 

 bral annuli, for bluefin tuna in vari- 

 ous weight ranges. They tentatively 

 recommended the use of vertebrae 

 for estimating ages up to about 10 

 years for this species. 



From 1932 until 1974, counting 

 vertebral annuli was generally re- 

 garded as the most satisfactory 

 method of aging large Atlantic blue- 

 fin tuna. 



c. Otoliths 



The use of otoliths in determin- 

 ing ages of T. Ihvnnus ihynnus was 

 first investigated in the 1920s, bul 

 important results did not appear until 

 1975. 



Despite the fact that F. de Buen 

 (1925) had been discouraged by the 



difficulties encountered in extracting 

 otoliths, Frade ( 1 925) described pro- 

 cedures for their relatively rapid re- 

 moval, and the nature of the growth 

 zones on them. These descriptions, 

 accompanied by excellent illustra- 

 tions, suggested that this was a prac- 

 tical method of age determination. 



At the "Conference of experts" 

 (Anonymous 1 932b), however, Frade 

 reported that, although he had found 

 zones of growth in thin sections of 

 otoliths, he was not sure that these 

 sections included all of the years of 

 growth. He attributed his uncertainty 

 to the irregular shape of the otoliths. 

 The experts concluded that growth 

 zones were laid down on otoliths, but 

 that it was difficult to assign absolute 

 ages by counting these zones. They 

 therefore recommended that this tech- 

 nique be used mainly to confirm age 

 determinations obtained by other 

 means. 



Frade and Vilela ( 1 962) referred 

 to age determinations from otoliths 

 by Frade (1950), but we have not 

 seen the latter work. No further ref- 

 erences to Frade's early work with 

 otoliths have come to our attention. 



The next attempt to determine 

 ages of bluefin tuna from otoliths 

 was by Nichy (Nichy and Berry 

 1 976). They developed techniques for 

 estimating the ages of bluefin tuna 

 similar to those of Frade ( 1 925). They 

 used otoliths from large individuals 

 caught off Prince Edward Island in 

 the Gulf of St. Lawrence, Canada, in 

 1974. Caddy and Butler (1976) clas- 

 sified large bluefin tuna taken in Ca- 

 nadian waters in 1974 and 1975 by 

 yearclasses, using Nichy and Berry's 

 techniques and some of their deter- 

 minations in addition to their own. 

 They did not report the sizes of these 

 fish. 



Caddy et al. (1976) present the 

 most complete study available on the 

 growth of bluefin tuna as determined 

 from otoliths. They used this method 

 to determine the ages of large indi- 

 viduals (age 10 and over) caught in 

 Canadian waters during the summer 

 and fall of 1975. They calculated pa- 



rameters for von Bertalanffy growth 

 equations for males and females, us- 

 ing their data for fish of ages 10 or 

 greater and Mather and Schuck's 

 (1960) results for fish of ages 1-4. 



Their work was the first to indi- 

 cate different growth rates for the 

 two sexes. Butler et al. ( 1 977) repro- 

 duced the above material with the 

 addition of preliminary age data from 

 the otoliths of 60 large bluefin taken 

 in Canadian waters in 1976, and pre- 

 sented some modifications of the 

 Nichy and Berry (1976) and Caddy 

 and Butler ( 1 976) techniques. 



Berry et al. ( 1 977) discussed the 

 removal, storage, measuring, mount- 

 ing and sectioning of otoliths. They 

 described the sections and their in- 

 terpretation of the markings on them. 

 They found that, at ages greater than 

 10 or II, hyaline bands occurred in 

 pairs which represented a single an- 

 nular zone. 



They discussed definitions of annuli 

 on vertebrae and otoliths, and pro- 

 posed the following tripartite hypoth- 

 esis: 



a) Major discernible markings on ver- 

 tebrae and otoliths of Atlantic blue- 

 fin tuna do nol have to be pre- 

 sumed to be annuli. 



b) Within each year of life, multiple 

 markings are successively formed 

 on vertebrae and in otoliths. These 

 multiple markings may appear in 

 prepared specimens of vertebrae 

 and otoliths as irregular combina- 

 tions Single markings that repre- 

 sent the end of a year of life (an- 

 nuli) may be distorted by varia- 

 tions of the within year multiple 

 markings. 



c) Annuli may he deciphered by con- 

 sidering the nature in which they 

 form and by interpreting the varia- 

 tions that may exist within and be- 

 tween individual prepared samples. 



Berry et al. ( 1 977) did not present 

 age data based on readings of annuli 

 on otoliths. 



3. Release-Recapture Data for 

 Tagged Fish 



When size data at release and 

 recapture of a given fish are avail- 



