Changes in the strategy of a small-scale jigging fishery for Japanese flying squid Todarodes pacificus off northeastern Japan

Abstract

Long-term fluctuations in the strategy of a small-scale squid jigging fishery for Japanese flying squid Todarodes pacificus off northeastern Japan were evaluated based on time series data for nine variables derived from the catch obtained by Iwate’s fishing boats, the total catch and the income from the waters off Iwate, the number of licenses issued by Iwate Prefecture, and crude oil prices from 1970 to 2008. Upon applying principal component and change-point analyses, the first three principal components were found to explain 80.4% of the total variance, and eight temporal change points were detected. A multiple sequential t-test analysis of regime shifts detected significant shifts in the time series for each variable. A decrease in the total catch obtained by Iwate’s fishing boats was delayed with respect to the decline in catch from off Iwate in the 1970s, which can be explained by adaptive migration, as the fishers shifted grounds to exploit more abundant resources. In the 1980s, the number of licenses for fishing boats from Iwate remained high as the fishers again adapted to better exploit the reduced resources available without migrating to different fishing grounds. In the 1990–2000s, the number of licenses for fishing boats from Iwate declined for economic reasons (high running costs and low squid prices), but the remaining fishers adapted yet again in the mid-2000s to increase the catch off Iwate by operating in daylight.