Forecasting of fishing condition of ayu [Plecoglossus altivelis] in lake Biwa [Japan]

Methods for forecasting fishing conditions and for resource management of ayu Plecoglossus altivelis in Lake Biwa was investigated. The annual catch in number was predicted by the number of larvae sampled by net survey. Since the growth of ayu seems to be influenced by water temperature and population density, mean body weight over the year of landed fish was estimated by the number of days of snowfall and the number of larvae sampled. The number of days of snowfall is an index of the minimum water temperature. Annual catch in weight can be estimated by the number of days of snowfall. The commercial value of ayu reaches its maximum at an appropriate body weight, therefore resource management was discussed; in other words, how many larvae should be released depending on the number of days of snowfall. It is expected that mean body weight will be kept suitable if the larval density is increased in years when there is little snowfall, and vice versa.