In view of this size difference it is of interest 

 sex ratio for possible variation throughout the year. 



I I I I I I 



I I I I I I I I I I I I 



I I MALE N-153 

 B FEMALE N=I03 

 ^ AREA OF OVERLAP 



209 229 249 269 289 



WEIGHT IN POUNDS 



Figure 1. --Weight frequency distributions of 

 bigeye tuna landed at the Honolulu market 

 from May to August 1951. 



(table 1), indicate that the sex ratio remained rather 

 60 percent males throughout the year. 



to examine the 

 Aside from in- 

 trinsic interest, 

 this is advisable 

 because a peri- 

 odic change in the 

 sex ratio could 

 shift the positions 

 of the nnodes of 

 unsexed samples 

 and make an anal- 

 ysis of growth 

 misleading. The 

 mean percentage 

 of males for Ha- 

 waiian bigeye for 

 the year 1949 was 

 59. 2 percent and 

 for 1951, 57.5 

 percent (Otsu 

 1954). The larg- 

 er samples (over 

 100 specimens) 

 from these same 

 years and Decem- 

 ber of 1950, when 

 tabulated by months 

 constant at about 



The possibility that the sex ratio changes as the fish grow re- 

 quires examination because this could affect the position of modes 

 based on unsexed samples. Otsu (1954) states ". . . . the sex ratio in 

 the catch /fifth Japanese mothership expedition/ below 80-90 pounds is 

 about equal, whereas the males predominate among the larger bigeye 

 and yellowfin. " However, if the female bigeye size frequency distri- 

 bution is shifted a distance equal to the average growth lag between 

 sexes, the apparent change in sex ratio with increase in fish size 

 disappears. 



Figure 3, lower panel, shows the sex ratios plotted by size 

 groups from the data used by Otsu (fig. 2). The proportion of males 

 increases with an increase in the size of the fish. (The small numbers 

 in the extreme groups connected with dashed lines are better ignored. ) 



