Factors of Catch Fluctuations of Skipjack Tuna in the North-eastern Waters of Japan and Its Forecasting

Abstract

In this paper, we attempt to develop a reasonable catch forecasting method for skipjack tuna caught in the north-eastern waters of Japan. In developing such a method, it is very important to find the main factors which control the catch fluctuations. The conventional method is based on the data of mean length and mean fatness of the fish harvested just before the fishing season, and the reproductive relationship estimated using the catch history. This approach, however, failed to forecast the catch in the years when the catch was extremely high. In this study, we therefore focused on the relationship between catches in the north-eastern waters of Japan and the following three variables; (1) catch caught in the waters off Chiba Prefecture, (2) the Kuroshio current pattern, (3) the first date of capture of skipjack tuna in the waters off Chiba Prefecture, and then forecasted the catch using regression analysis. The results showed that the accuracy of forecasting was very high almost every year including years when the catch was very high. It is considered that the method proposed here overcomes the problems of the conventional method. © 1995, The Japanese Society of Fisheries Science. All rights reserved.