AGE AND r.ROWTH OF YELLOWFIX TUNA 



137 



Figure 3. — Weight-frequency distributions (in pereentagej 

 of long-line anrl live-bait catches of yellowfin tuna 

 landed at Honolulu. Smoothed data of 1948 and 1949. 

 Monthly frequenc}' distributions are shown by fine line, 

 and mean monthly frequency distributions by heavy 

 line. Po.sitive deviations from the mean are shaded. 



Initial examination of the plotted data in 

 figures 1 and 2 shows the presence of a modal 

 group of fishes which can be followed through most 

 months of both 1948 and 1949. The group was 

 designated .V for reference. In the 1948 data the 

 progression of the modes representing this group 

 indicates gradual growth until June, followed by 

 a 5-month period in which no growth is indicated. 

 Following this there appears to be a short period 



of rapid growth from October through December. 

 From January through December, modal group A^ 

 shows a gain in weight from 75 to i;}5 pounds, a 

 gain of 60 pounds in 1 year. Also present in the 

 plotted data is a smaller size group which becomes 

 evident in the long-line fishery in October 1948 

 and in December 1 949. This suggests the entrance 

 of a modal group 1 year younger than group A'^. 



The 1949 data (fig. 2) presented a similar trend 

 in modal progression, except for the last 3 months 

 of the year where rather erratic modal peaks were 

 evident. Because the catches for these months 

 were not large in comparison to catches of the 

 summer months (table 1) any unusual distribu- 

 tions of weights of fish landed would cause erratic 

 modal peaks to appear in the percentage frequency 

 distributions. 



Table 1. — Xumbers of yellowfin liina taken by long-line 

 fishing and auctioned at the Kyodo Fishing Company, 

 Ltd., Honolulu, in 1948 and 1949 



Month 



January 



February... 



March 



April 



May 



June 



July 



August 



September. 



October 



November. 

 December.. 



Total 



1948 



2,488 



1»49 



2,181 



For a more detailed study of the combined data 

 of the 2 years, a criterion was set up to determine 

 what should be designated a mode and to designate 

 its position. . Modal peaks of positive deviations, 

 evident in the combined 2-ycar data, when plotted 

 as deviations from the mean curve (fig. 4) which 

 met either of the two following conditions were 

 treated as modes in this study: 



(1) Any positive deviation of a class which 

 shows a difference of 0.5 or more from values of 

 both adjacent classes (fig. 5-A). 



(2) Wlum the difl'erence between frequency 

 values of positive deviations of two adjacent 

 classes is less than 0.5, and when the frequency 

 values of the classes above and below these two 

 adjacent values are at least 0.5 less than the 

 adjacent values, the intersection of the extrapola- 

 tion of the lines connecting the two classes with 

 the adjacent classes was considered the position 

 of the mode (fig. 5-B). 



