Development of method for estimation of 0 + fish abundance index of jack mackerel Trachurus japonicus by mid-water trawling and area-swept method in the southwestern Sea of Japan

Abstract

Japanese jack mackerel (Trachurus japonicus) is an important commercial fish which is distributed widely along the Japanese coast and for which a total allowable catch is designated. However, the 0 + fish stock can not be estimated by VPA. In this paper, a 0 + fish abundance index was examined using mid-water trawling (10 by 10 m trawl mouth, 7mm codend mesh) and the area-swept method. A total of 62,387 0 + fish jack mackerel were caught in the waters of the southwestern Sea of Japan during early summer (2003 to 2008). Jack mackerel were distributed in areas that were 50m depth at a temperature of 12.5-20,5°C, The 0 + fish abundance index was presumed by pattern A: divided into two sea areas (Tsushima area and Oki area), and by pattern B: divided into four sea areas in consideration of the water temperature distribution. The coefficient of variation of 0 + fish abundance index estimated by pattern B (13.8-48.5%) was lower than that by pattern A (19.4-50.3%). This indicates that the mid-water trawling method with area-swept method considering the water temperature can be used to estimate the 0 + fish abundance index of jack mackerel.