Influence of the Kuroshio path on the catches of Japanese butterfish Hyperoglyphe japonica in waters around Hachijyo-jima Island in central Japan

Abstract

We examined stock abundance trends and the influence of the Kuroshio path on catches of Japanese butterfish (Hyperoglyphe japonica) in waters around Hachijyo-jima Island in central Japan. The results of a selected generalized linear model (GLM) using Akaike’s information criterion indicated that year, month, and changes in the Kuroshio path influenced catches of Japanese butterfish. The number of fishing boats per half month and the Kuroshio path were also found to influence fishing efficiency (catch per fishing boats per half month). Assuming that the coefficients of the year of the selected GLM indicated the stock abundance trend, no decrease in the stock abundance of Japanese butterfish was detected. Moreover, fishing efficiency improved with an increase in the number of fishing boats per half month, which can be attributed to the improvement in effective searching for fishing grounds. In addition, the effect of improvement in fishing efficiency with an increase in the number of fishing boats was generally higher in the C-type than in the except C-type of the Kuroshio path. In the case of the number of fishing boats per half month exceeding 13.3, it was predicted that the catches were higher in the C-type of the Kuroshio path than in the except C-type. In the case of the C-type, the depth of suitable water temperature for Japanese butterfish was shallower than that of the except C-type because of cooling of deep waters. Therefore, in the case of the C-type, fishing grounds may form in shallower depths. Therefore, fishing efficiency may improve because of a decreased influence of current and increased operation frequency per day due to a reduction in operation time.