VII. DISCUSSION, RECOMMENDATIONS, 

 AND CONCLUSIONS 



A. INTRODUCTION 



In this section we review and 

 present our conclusions on the aspects 

 of the life history of the Atlantic blue- 

 fin tuna. Since the fisheries in each area 

 have been described and their trends 

 have been summarized in Section IV, 

 we shall not refer to them further ex- 

 cept as necessary to elucidate the life 

 history of the species. Our opinions on 

 stock identity will conclude our discus- 

 sion of the material in the preceding 

 sections. 



Although much information on the 

 biology of the Atlantic biuefin tuna has 

 been compiled in this work, we have 

 not attempted to cover all of the aspects 

 of its life history, nor have we been 

 able to cite all of the works on the 

 topics which we have discussed. We 

 shall point out the areas in which the 

 existing information seems to be defi- 

 cient, and make recommendations in 

 regard to future research. 



B. AGE AND GROWTH 



There has been good agreement 

 on the sizes of Atlantic biuefin tuna at 

 ages 1-11 (Table 1 ). There is less con- 

 fidence in determinations for older ages. 

 Caddy et al. ( 1 976) extended estimated 

 age determinations to 25 years, and 

 also provided separate von Bertalanffy 

 growth curves for males and females. 

 These authors noted that earlier age 

 determinations had ascribed fish smaller 

 than 245 cm to age group 1 3, whereas 

 their own determinations indicated that 

 245 cm was roughly equivalent to ages 

 14-15 for males and age 18 for fe- 

 males. 



They also asserted that apparent 

 underestimates of the ages offish more 

 than 240 cm long had resulted in esti- 

 mates of L4, based primarily on data 

 from fish less than 12 years old, which 

 were in excess of any sizes recently 

 recorded for Atlantic biuefin tuna. If 

 their results should be validated, con- 

 siderable revisions of recent estimates 



of the age composition of the Atlantic 

 biuefin tuna stocks (Sakagawa and 

 Coan 1973) would be required. Berry 

 et al. (1977), however, questioned pre- 

 vious age determinations for Atlantic 

 biuefin tuna. They concluded that me- 

 dium size tuna (defined as fish weigh- 

 ing between 56.7 and 136.1 kg) might 

 have been overaged by one or two years, 

 and that giant fish might have been 

 overaged by from one to 1 years. They 

 attributed this alleged overaging to the 

 counting of double or multiple mark- 

 ings on vertebrae or otoliths as repre- 

 senting two or more years' growth 

 rather than a single year's. 



It is most important that the actual 

 age composition of the "relict" popula- 

 tion (as described by Caddy et al . 1 976) 

 of giant Atlantic biuefin tuna be deter- 

 mined with certainty. ' 



It is also important that the linear 

 growth rate of the larval, postlarval and 

 early juvenile stages of biuefin tuna be 

 determined for the various spawning 

 areas. This information is needed in 

 terms of length, rather than weight, to 

 permit better estimates of spawning 

 dates and localities fi-om the collecrion 

 data for these very small biuefin tuna. 



Seasonal variations in the growth 

 rates of biuefin tuna up to 4 years old 

 are reasonably well known (Mather and 

 Schuck 1960, Fume.stin and Dardignac 

 1 962) but the data now available should 

 permit extension of this knowledge to 

 older ages. Information on this subject 

 could be greatly increased by more sys- 

 tematic and extensive collections of size 

 fi-equency data and biological material, 

 especially fi^om catches of the oceanic 

 longline fisheries. 



The possibility that the growth rate 

 of the Atlantic biuefin tuna has in- 

 creased as the size of the stock has 

 decreased should also be investigated. 

 This possibilit>' is suggested by the re- 

 markable number of extremely large 

 biuefin caught since 1970 (see Section 

 IV). 



C. DISTRIBUTION, 

 MIGRATIONS, AND 

 SPAWNING 



I. Introduction 



Although there are differences in 

 details, the general patterns of distribu- 

 tion, migrations and spawning on the 

 two sides of the Atlantic fit the hypo- 

 thetical migratory model presented in 

 Section VIB3, which may be summa- 

 rized as follows: 



a Very Small Fish (<50 cm, 

 < 1 year old) 



Convergence from various spawn- 

 ing areas to concentrate in nursery and 

 feeding areas. 



b. Small Fish (50 cm-120 cm, 

 1 to 4 years old) 



1. Immature Individuals 



Two-way migrations between 

 warm season nursery and feeding areas 

 and cold season wintering areas. 



ii. Mature Individuals 



Three-way migrations between 

 warm season feeding areas, cold sea- 

 son wintering areas, and late spring- 

 early summer spawning areas. 



c. Medium Fish (120 cm -185 

 cm, 5 to about 8 years old) 



More extensive three-way migra- 

 tions between warm season feeding ar- 

 eas, cold season wintering areas, and 

 spring-early summer spawning areas. 



d. Large Fish (> 185 cm, > 8 

 years old) 



Maximum three-way migrations 

 between warm season feeding areas, 

 cold season wintering areas, and spring- 

 early summer spawning areas. 



Except in certain situations related 

 to the reproductive cycle and/or the 

 configuration of the coasts, the biuefin 

 migrations are not confined to narrow 

 routes but spread over wide areas. The 

 species is very widely distributed, and 

 capable of long and rapid movements 



133 



