46 



FISHERY BULLETIN OF THE FISH AND "WILDLIFE SERVICE 



60 



40 



20 









 40 



20 













 X 220 

 en 



u- 200 



o 180 



^ 160 



§ 140 



^ 120 



100 



80 



60 



40- 



20 



















NONE MEASURED 1950 i 







H- 



-A. 



n nr 



1951 - 



n m 



NONE MEASURED 



1952- 

 1953 



1954 



m J955 



W~ 1957 



Vf 



H- 



• ' 



20 30 40 



FORK LENGTH-INCHES 



50 



Figure 7. — Frequency distribution by 1-inch groups of 

 lengths of bluefin tuna taken August 17-31, by years. 



years. Although length data on older ages are 

 not sufficient for analysis, we believe that counts 

 of annuli are useful for estimating the age of 

 older fish despite the decreasing reliability of 

 readings with increasing age. 



We find also that the analysis of length-fre- 

 quency curves is consistent with age determina- 

 tions h\ counts of annuli on scales and vertebrae. 

 Such discrepancies as exist probably result from 

 the fact that the samples for age readings were 

 smaller and less uniformly distributed through the 

 seasons than were those taken for length measure- 

 ments. For example, most of our samples for 

 counts of annuli of 3-year-olds were collected in 

 early summer or fall rather than in midsummer. 

 Even so, correspondence in conclusions reached 

 from the two kinds of data is close. 



20 30 40 



FORK LENGTH-INCHES 



50 



Figure 8. — Frequency distribution by 1-inch groups of 

 lengths of bluefin tuna taken September 1-15, by years. 



20 30 40 



FORK LENGTH-INCHES 



Figure 9. — Frequency distribution by 1-inch groups of 

 lengths of bluefin tuna taken September 16-30, by years. 



Weight frequencies of landings of medium- 

 sized bluefin tuna in Cape Cod Bay and Nova 

 Scotia in the years 1948-51 (fig. 13) show a ten- 

 dency for modal weights to coincide with sizes 

 determined by counts of annuli for ages 5-7. 

 Most clear cut cases are the 5-year-olds in Cape 

 Cod Bay and 6-year-olds in Nova Scotia in 1948, 



