Stock assessment of Japanese sardine in the waters off the southeast coast of Hokkaido using line transect method.

Abstract

Recent attempts to assess a stock quickly have been actively carried out. Two types of surveys may be suitable as methods, namely, ship-and air-borne observation. In this paper, we use the aerial observation for the reasons described later. The aerial observations were performed four times around the areas where big catches of sardine have been taken. In the surveyed area, schools of Japanese sardine can be sighted and counted easily. It is, therefore, very advantageous to use aircraft for assessing sazdine stock quickly. The line transect method was applied on the basis of the data and the assumption, such as dimensions of schools, weight of a school, and density in a school. Although the method used here has many problems to be solved, this method for pelagic fish is useful and satisfactory. So we think this method may be used widely in future.