FISHERY BULLETIN: VOL. 71, NO. 1 



Table 3. — Estimates of parameters of the von Bert- 

 alanffy growth function for yellowfin tuna of unknown 

 age from the eastern Atlantic Ocean. 



Region 



Year 

 class 



K 



No. of 

 obser- 

 vations 



Range of 

 lengths (cm) 



In some instances, the estimates of K and L„ are 

 unexpectedly too high or too low, indicating that 

 the estimates are inappropriate for the entire 

 life span of the species. According to Knight 

 (1968) and Le Guen (1971), a possible cause of 

 variation in K and L« is lack of size measure- 

 ments for the entire life span of the species. This 

 appears to be the case in some instances for our 

 data. Length measurements for Dakar, for ex- 

 ample, were from catches made predominantly 

 by pole-and-line, or baitboats that generally catch 

 small fish, a characteristic that is well document- 

 ed (Pianet and Le Hir, 1971). Consequently, 

 large fish were underrepresented in the samples, 

 resulting in heavier weight on the lower size 

 groups. Estimates of L^ were therefore unrea- 

 sonably high, while those of K were unreason- 

 ably low. It should be noted that generally 

 L„ and K are inversely correlated (Beverton and 

 Holt, 1959). 



For some year classes, apparent growth ap- 

 pears to be exceptionally faster than for others. 

 Apparent growth of yellowfin tuna from Pointe- 

 Noire can best illustrate this point (Figure 6). 

 The 1965 and 1967 year classes grew at a faster 

 rate than the 1964 or 1966 year class. The re- 

 sult was an apparent convergence of the growth 

 curve for the 1964 year class with that for the 

 1965 year class, and the 1966 year class with the 

 1967 year class. In each case, there appears to 

 be no relation between the time of recruitment 

 and the rate of growth. 



Regional Differences in Apparent Growth 



For each region, the von Bertalanffy equation 

 was fitted to data for all year classes combined. 

 Apparent growth of yellowfin tuna from Abid- 

 jan, Gulf of Guinea, and Pointe-Noire was quite 

 similar for sizes (ranged from about 60 to 160 

 cm long) observed in the samples (Figure 7). 

 Apparent growth of Dakar fish, on the other 

 hand, seemed exceptionally faster, which is at- 



180 r 



160 



140 - 



120 - 



O 



100 - 



80 



60 



ABIDJAN- 



GULF OF GUINEA 



ALL REGIONS 



DAKAF! 



POINTE-NOIRE 



2 3 4 5 



APPARENT AGE (YEARS) 



Figure 7. — Growth of yellowfin tuna from the eastern 

 Atlantic Ocean. 



180 



