Environmental changes and the dynamic response of biological community along the shore of Lake Biwa

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There are about 70 species of fishes in the present Lake Biwa. They include fishes which have been speciated in the lake by expanding their habitat into deep and open offshore of the lake, and also the exotic species like the largemouth bass the bluegill. There are also about 50 species of molluscs, a half of them are endemic to the lake.Many of these fishes and molluscs, however, utilize the shallow shore of the lake and inland waters through or during a part of their life. The survey on the historical changes in human activities along the lake shore revealed ; the most areas along lake shore and inland waters had been developed into paddy fields from old ages, however, the environment of these area has been changed again within this two or three decades. Such environmental changes might cause the changes in biological community in shallow waters along lake shore, inland waters and paddy fields. The land development far from the lake mightalso affect on the freshwater biological community around lake shore, especially on the fishes migrating between rivers and the lake.On the other hand, the underwater direct observation with the aid of SCUBA on the community structure of benthic animals along the lake shore revealed that many benthic animals depends on not only the lake bottom structure but also the condition of aquatic vegetation though the most of aquatic vegetation is occupied by exotic species. In another case, the decrease in lake water level causes the separation of fish population into riverine and lacstrine populations by blocking their upstream migration, though the water level of Lake Biwa is basically depends on the weather condition but also largely by human management.