there are minor shifts. During July, 1950 and 

 August and September, 1951 there is some change 

 in the prominent modes, and in the December, 

 1950 sample the large mode is displaced 15 cm, 

 to the left. This last anomaly probably reflects 

 the location of the catch, for this sample was 

 taken farther west than the others. 



While it is sonnewhat surprising not to 

 find modal progression in equatorial yellowfin, it 

 is not difficult to propose a hypothesis to account 

 for its absence. Perhaps any given area (consid- 

 ering only the restricted ecological niche sampled 

 by the longline) is occupied by yellowfin of a re- 

 stricted size because there is constant ingress of 

 snnaller fish and egress of larger fish. This 

 would obscure evidence of growth of the donninant 

 size groups and in fact occasionally produce what 

 appears to be negative growth, found to some ex- 

 tent in almost all time series data from equatorial 

 waters. This may not apply in the Hawaiian area, 

 where the seasonal presence of a population of 

 deep-swimming yellowfin and the scarcity of 

 small fish (Murphy and Ikehara 1955) suggest that 

 major recruitment to the deep-swimming popula- 

 tion (the group sampled by the longline) takes 

 place elsewhere. 



COMPARISON OF SIZE DISTRIBUTIONS FROM 

 THE CENTRAL AND WESTERN PACIFIC 



Although there is no evidence that the 

 donninant size groups present represent age 

 classes of fish at the Equator, it is of interest 

 to compare the size distributions of longline- 

 caught yellowfin fronn all areas in the central 

 and western Pacific. Samples with a mid-date 

 during or near February are compared because 

 this is the only time of year for which data are 

 available from all areas and it is necessary to 

 relax the definition of amode for this connpari- 

 son as there are relatively few measurennents. 

 Samples from different years are used, but it 

 has been shown that there is little difference in 

 modal positions from year to year in a given 

 area. (The Hawaiian size distribution for 

 Febr usury 1948- 1953 was converted from pounds 

 to centinneters for ready comparison with the 

 other data. ) 



Figure 10 shows these distributions 

 with the modes indicated by arrows. There are 

 four modal sizes, two or nnore of which appear 

 in each locality. This agreement in nnodal po- 

 sition is also shown in table Z, and it can be 

 seen that the distances between modes are 



nearly identical, except for the central 



o o 



equatorial Pacific (155 W.-165 W. longitude). 



no 120 130 140 



LENGTH IN CENTIMETERS 



Figure 10. --Comparison of yellowfin size distributions 

 from the central and western Pacific. 



10 



