Table 6. Factors derived from the length-weight formula for Area 1 (north of 

 latitude 35°N and west of longitude 50° W) and Area 2 (Straits of Florida and 

 adjacent waters). 



Area 2 



May-June 



• 4.8070 



2.9044 



185-260 



Atlantic. Area 1 comprised waters 

 north of latitude 35°N and west of 

 longitude 50°W. Area 2 included the 

 Straits of Florida and adjacent wa- 

 ters. Factors derived from the fol- 

 lowing length-weight formula are 

 shown in Table 6; 



W = A + B Log L 



where: 



W is the live (whole) weight of the 

 fish (kg), and 



L is the fork length (cm) 



Unpublished data collected by 

 Schuck and Mather showed that al- 

 though there was a marked increase 

 in the length-weight ratio of large 

 bluefin from June through October, 

 the length-weight ratio of individu- 

 als less than 100 cm long did not 

 change noticeably from month to 

 month during the summer. 



5. Differential Growth of Males 

 and Females 



Although some authors noted 

 that male bluefin tuna attain larger 

 sizes than females, only two studies, 

 those of Caddy et al. ( 1 976) and But- 

 ler et al. (1977). showing a consis- 

 tent difference in growth rate have 



come to our attention. Few of the 

 publications on the growth of the spe- 

 cies present data in terms of sex of 

 fish. Hamre (1960) found no signifi- 

 cant difference in growth between 

 males and females. 



Tabulations of age determina- 

 tions by sex offish (Rodriguez-Roda 

 1 964) indicate that males attain larger 

 sizes than females. The data suggest, 

 however, that this difference is due 

 to greater longevity for males, rather 

 than a difference in growth rates. 

 Rivas (1976) reported that, on the 

 average, the males in samples of large 

 bluefin taken off the Bahamas and in 

 the Gulf of Mexico in various years 

 were 4 % longer and 13 % heavier 

 than the females. 



As noted in part 1 of this subsec- 

 tion. Caddy et al. (1976) found con- 

 sistent differences in length for age 

 between large male and female blue- 

 fin caught in Canadian waters in 1975 

 (Figure 5). These authors also found 

 differences in the length-weight rela- 

 tionship between males and females 

 in the period July-November (Fig- 

 ure 10). Males are heavier than fe- 

 males of the same length. Since, as 

 this figure shows, there is very little 

 difference in maximum girth between 



the sexes, the males must be consid- 

 erably heavier posteriorly than the 

 females. 



6. Ultimate Length 



The asymptotic or ultimate 

 length (L_^) of Atlantic bluefin tuna 

 has been estimated from some growth 

 studies. Rodriguez-Roda (1964a, 

 1971) presented an L^ of 355.8 cm, 

 derived from his age determinations 

 for bluefin tuna collected off the 

 southern Atlantic coast of Spain. 

 Caddy et al. (1976) derived an L^of 

 447.88 cm from the age-size data of 

 Mather et al. (1974), an average of 

 several previous works, and an L of 

 286.64 cm for males and 277.3 15 cm 

 for females from their own determi- 

 nations for fish taken in Canadian 

 waters. The longest bluefin tuna en- 

 tered for record consideration by the 

 International Game Fish Association 

 as of December 1976, weighed 540 

 kg and was 312 cm long (FL) (the 

 method of length measurement used 

 was not specified) (E. K. Harry, per- 

 sonal communication). Larger blue- 

 fin tuna have been reported in the 

 literature. For example. Hamre et al. 

 (1971) reported an individual in the 

 310-315 cm range measured at the 

 Istanbul (Turkey) fish market in Janu- 

 ary 1967. Unfortunately, the weights 

 of many large bluefin are reported 

 without any information on their 

 length. Sara (1969) mentioned blue- 

 fin tuna of 625 and 685 kg taken in 

 traps off Sardinia in 1969 and 

 Scaccini et al. (1975) cited fish weigh- 

 ing up to 600 kg taken in the 

 Favignana trap off western Sicily in 

 June 1974. 



7. Discussion 

 There has been good agreement 

 on the size for age of Atlantic bluefin 

 tuna for ages 1-11 (Table 4). There 

 is less confidence in determinations 

 for older ages. Caddy et al. (1976) 

 extended estimated age determina- 

 tions to 25 years, and also provided 

 separate von Bertalanffy growth 

 curves for males and females (Fig- 

 ure 5). These authors note that ear- 



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