The present status of trolling of the Biwa salmon Oncorhynchus masou subsp. Lake Biwa,

Size at maturity of fluvial white-spotted charr, Salvelinus leucomaenis, was studied in small headwater tributaries of nine rivers around the Lake Biwa water system, Japan. Threshold size at maturity in both sexes showed significant positive relationships with water discharge, indicating that smaller threshold sizes at maturity of fluvial white-spotted charr occurred in smaller habitats. These results provide a link between size at maturity and habitat size and have important implications for the management of both habitats and white-spotted charr populations.

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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.