Sex Ratio and Sexual Dimorphism 



Data on sex ratio and sexual dimorphism (i.e., 

 differences in size between the sexes) are adequate 

 only for the blue marlin. In Honolulu, the commercial 

 catch of blue marlin consists of males and females in 

 about equal numbers. A random sample of 694 blue 

 marlin taken between 1960 and 1962 consisted of 48 

 percent males and 52 percent females. On a short- 

 term basis, however, one sex may dominate the catch. 

 The following sex ratios were obtained at recent 

 Hawaiian International Billfish Tournaments, which 

 were held at varying times from June through August: 



The sex ratio approached the expected 1:1 condition 

 only in 1964; in the other years the fish were either 

 segregated by sex or the males were more suscepti- 

 ble to the fishing gear and techniques used. 



There is a marked difference in the size attained 

 by male and female blue marlin. Over a 3-year 

 period in which 694 blue marlin were examined, 

 nearly all of the males weighed between 100 and 200 

 pounds, whereas most females were between 200 and 

 500 pounds. Furthermore, males never became as 

 heavy as females. The largest male sampled weighed 

 only 293 pounds; females have been taken at weights 

 greater than 1,600 pounds. As a rule of thumb, a blue 

 marlin heavier than 300 pounds is a female. 



Although the data are few, the black marlin resem- 

 bles the blue marlin in its sexual dimorphism. The 

 largest known male weighed only 322 pounds, whereas 

 the world's record black marlin, a female, weighed 

 1,560 pounds. In the striped marlin the weight dis- 

 tributions of the sexes are about the same; 400 pounds 

 is about the upper limit. 



Weight 



The blue marlin not only displays fluctuations in 

 sex ratio and great sexual differences in weight; fish 



