separated fisheries (Hawaiian and Japanese), there is also complemen- 

 tary alternation of modes for a given year. Finally, it appears that 

 once a dominant modal group enters a fishery (e.g. Hawaiian) it may 

 be followed in that fishery for several years. Taken as a whole, these 

 phenomena suggest that the bigeye undertake poorly understood, re- 

 current, and probably complex migrations. 



GROWTH 



Incomplete knowledge of sonne aspects of the life history of 

 bigeye tuna results in a lack of understanding of the usual behavior of 

 the dominant modes in the western and central Pacific. Hence any in- 

 terpretation of the modes as year groups and interpretation of the 

 movement of those modes as groAvth must be very tentative. 



It is readily apparent from the weight frequency curves cover- 

 ing the period November 1947 through December 1954 in the Hawaiian 

 fishery that clear-cut modal progression is displayed by bigeye tuna 

 (figs. 4-11, table 2). Figure 13, which shows these dominant modes 

 fitted with straight lines, indicates the apparent rate of growth. 

 Table 4 lists the average annual weight increase of these groups as 

 determined from the "growth lines. " Assuming that the progression 

 of the nnodes represents growth, these size groups increase as much 

 as 40-50 pounds in one calendar year. Judging from the slope of the 

 growth curves (fig. 13) and the maximum sizes attained by Hawaiian 

 bigeye, about 6 or 7 years would seem to be a fair estimate of the life 

 span of the species in Hawaii, 



However, in the equatorial region the description of growth by 

 the modal progression method is not feasible, since it appears that 

 dominant modes in the size distribution do not progress. 



25 



