The estimation of the number of hatches of migratory fishes has hitherto been made by summing up the yearly catches of the fishes which belong to a certain year class. In applying this procedure the age composition of catches must be detected and, therefore, considerable amount of work is demanded for obtaining the result required. In this paper, the writer gives a new method for treating this problem, which, though essentially the same as is the case with the above mentioned method, deals with the problem in the form of integral equation. According to this method, the result required can be arrived by using merely the successive data of the total number of annual catches of the fish under considera-tion and the computations are carried out graphically instead of lengthy arithmetic calcula-tions. The theory is applied to the case of the spring herring in the Hokkaidõ waters, resulting good, agreements in general characters with the results already been obtained by the older schemes.