*The "large" categoiy comprises fish of 5 kan weight and over [1 kan ; 



8,27 pounds] so according to Aikawa and Kato (^' it includes ^ ~ ^r Q „ ; .89 



6.-4 - -^.82 

 of the seventh-year fish and all of those of the eighth year and older. The 



njedium fish are from 3 to 5 kan in weight and include 1 - .39 r .11 of the 



seventh-year fish, all of the sixth-year fish, and h^ ' |*^ - ,19 of the 



fifth-year fish. Small fish comprise 1 - .4.9 s .51 of the fifth-year fish and 



all fish in their fourth year or younger. If the survival rate is represented 



,89p^4- -al 



by p, the ratio between large and medium fish is l-p This formula 



.49tp+.llp^ 

 gives a figure of .57 for 1934, 3.55 for 1935, ,6A for 1936, and .97 for 1937 



or an average of lo05 for the four years. The corresponding survival rates are 



,5A, ,^At .56, ,6a, and 0656 respectively, 



♦♦Among other tunas the natural mortality rate for the black tuna has been 



calculated at ,20 (see preceding article in this journal). The albacore 



probably does not differ \7idely in this respect, so if we assume a natural 



66 

 mortality rate of .20, we get a catch rate of 1 - 1^2726" ° *^^'' '^® catch 



rate for the black tuna is .10, but the catch rate for the young fish shows the 



high figure of ,55. For the yellowfin tuna the catch rate for the young fish is 



,06 vrtiile that for the mat'ire fish is .29. (See the two preceding articles in 



this journal.) 



7^837 



15 



