EASTERN PAC. 



WESTERN PAC. 



PRESENT STUDY 



1 1 r 



1:0 2.0 



ESTIMATED AGE(yrs) 



Figure 11. — Comparison of growth curves for skipjack tuna 

 from the Pacific. Growth in the eastern Pacific (dashed line) was 

 recalculated from various tagging studies by Josse et al. (1979); 

 in the western Pacific from tagging (Josse et al. 1979, broken 

 line) and modal progressions (present study, line). All are ad- 

 justed to a common base age of 12 mo at 40.0 cm FL. Data from 

 Josse et al. (1979) were calculated by them using Tomlinson's 

 (1971) least squares procedure. 



be 60.0 cm, the value used in the present compar- 

 ison. 



Growth estimates of yellowfin tuna from the 

 eastern Pacific (Davidoff 1963), central Pacific 

 (Moore 1951), and western Pacific (Yabuta et al. 

 1960) were recalculated by Le Guen and 

 Sakagawa (1973) using Fabens' (1965) method and 

 are compared with the results of the present study 

 (Figure 12). The recalculated lengths-at-age were 

 in all cases similar to those obtained by the origi- 

 nal authors. Although the above studies were car- 

 ried out on large fish within the 47-170 cm FL 

 range, their L^ values were only slightly higher 

 (188.4-200.3 cm) than that obtained in the present 

 study. The major difference lies in rate of growth, 

 and, although extrapolation of the present results 

 beyond 71 cm is dangerous, these results and those 

 of Yabuta et al. (1960) imply that growth of yellow- 

 fin tuna in the western Pacific may be substan- 

 tially slower than in the central and eastern 

 Pacific. Marcille and Stequert (1976a) studied 

 growth of pole-and-line caught yellowfin tuna of a 



140 



i 100 



oc 



2 60' 



20- 



FISHERY BULLETIN: VOL. 79, NO. 3 

 CENTRAL PAC. 



EASTERN PAC 



PRESENT STUDY 

 WESTERN PAC. 



ESTIMATED AGE(yrs) 



Figure 12. — Comparison of growth curves for yellowfin tuna 

 from the Pacific. Eastern Pacific (Davidoff 1963, dashed line); 

 central Pacific ( Moore 1951, broken line); western Pacific ( Yabuta 

 et al. 1960, dotted line); and present study ( line). All were recal- 

 culated using Fabens' (1965) least squares procedure. Vertical 

 bar indicates limits of data used to derive the present curve; 

 extrapolation beyond this range is for comparison purposes only. 



similar length range (45-75 cm FL) in the equato- 

 rial western Indian Ocean. Their reported growth 

 rate of 17-19 cm/6 mo for this size range of fish is 

 similar to the results of the present study. A 

 further possible explanation for this apparent dis- 

 parity between growth in large and small yellow- 

 fin tuna may be simply that the von Bertalanffy 

 function does not adequately describe yellowfin 

 tuna growth, and that yellowfin tuna may undergo 

 changes in growth pattern, due to movement into 

 deeper water, for example. 



A point of ecological importance is the great 

 difference in growth rate between skipjack and 

 yellowfin tunas of the same size. Yellowfin tuna 

 grow to over 180 cm FL, over twice the length of 

 skipjack tuna and almost 20 times the body 

 weight. Studies on skipjack and yellowfin tunas' 

 bioenergetics (Kitchell et al. 1978), although indi- 

 cating a qualitative similarity between the two 

 species, demonstrated that the metabolic rate of 

 adult skipjack tuna, unlike that of yellowfin tuna 

 and most other fishes, is independent of body 

 weight. This may reflect the apparently less effi- 

 cient hydrodynamics of skipjack tuna, a conse- 



530 



