Demographic survey of the yellow-phase Japanese eel Anguilla japonica in Japan

Catch statistics and biological data of the Japanese eel Anguilla japonica from 12 river systems in nine prefectures of Japan (36A degrees N, 140A degrees E-31A degrees N, 130A degrees E) during 1999-2004 were analyzed in order to evaluate the demography of A. japonica in Japan. Significant differences in biological characteristics of 6388 eels were found among the river systems. Fishery catches of eels in all locations have declined, but the magnitudes or patterns of decline seem to be different. Of sex-identified eels, mean total lengths +/- A SD (mm) of females (n = 3776) and males (n = 962) were 495.6 +/- A 104.3 and 412.9 +/- A 80.7, respectively, and overall sex ratio (% female) was 79.6 %. Mean age (years) and growth rate (mm year(-1)) were 5.0 +/- A 1.9 and 96.7 +/- A 38.6 for females (n = 3643) and 3.6 +/- A 1.7 and 120.5 +/- A 65.4 for males (n = 907), respectively. This study highlights the demographic heterogeneity of the A. japonica among the studied river systems, which suggests that it is important to conserve a variety of habitats in multiple river systems as an inclusive management target in addition to restoration of the diversity of habitats for eels in a single river system.