International eel symposium, 2003 - Quebec August 11, 2003
Poster Session

Catch Decline Rates of Japanese Eel, Anguilla japonica, in Relation to Environmental Conditions in Rivers, Japan

Tatsukawa, K.* Ocean Research Institute, University of Tokyo, 15-1, Minamidai-1, Nakano, Tokyo 164-8639 Japan
Sakai, T. Ocean Research Institute, University of Tokyo, 15-1, Minamidai-1, Nakano, Tokyo 164-8639 Japan
Matsuda, H. Ocean Research Institute, University of Tokyo, 15-1, Minamidai-1, Nakano, Tokyo 164-8639 Japan

Presenter email address: tatukawa AT ori.u-tokyo.ac.jp

Abstract Text: Annual catch of Japanese eel, Anguilla japonica, over than 50 tons since 1965 have been recorded from eleven rivers in Japan. These eel catch curve profiles from 1967 to 1996 were divided in two river groups, ARG and BRG, by multiple regression analysis. The decline rate (Z) of catch during thirty years in ARG was higher than that of BRG. A relationship between Zs and river environmental factors such as COD, SS, DO, a number of colitis germs group, a coefficient of river regime, a catch of fish, an index of habitat limited area by dam construction (IHL) and an index of habitat destruction indicated as unit water volume caused by dam (IHD) was examined by multivariate analysis. Both IHL and IHD among these factors produced more powerful effects on Z. The eel stock in ARG might have been suffered severely from a dam construction as compared with that in BRG. It may be necessary that as stopping a tendency of catch decline and also increasing an eel stock in a river, rehabilitating and restoring eel habitats to a former state should be a task of great urgency for our country