Studies on relations among ecosystem components for lake ecosystem management

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We examined the population dynamics of lacustrine sockeye salmon and pond smelt, and fauna and distribution of benthos in LakeTowada. The lacustrine sockeye salmon showed the scramble type of density-dependence as the population dynamics. Estimated parameters indicated that the survival of salmon juveniles suddenly decrease when released fish increase more than 2 million individuals. Pond smelt did not show density-dependent mortality in their spawner-recruitment relations. Results of stepwise multiple regression analysis showed that the salmon abundance was negatively correlated with Daphnia longispina abundance, and that pond smelt abundance positively correlated with abundance of D. longispina and copepod larvae. These results suggest that salmon would be in competition with pond smelt for the food. We conclude that the population dynamics of lacustrine sockeye salmon is affected by their population density and abundance of pond smelt in the Lake Towada.Fifty-three taxa of benthos were found. The lake basin was divided into 4 parts according to the benthos fauna. 1) littoral zone below 20m depth with a high biodiversity, 2) sublittoral zone between 20-60m depth with 22 taxa of Oligochaeta and chironomids, 3) profundal zone excluding the deepest part Naka-ko with only 4 taxa and 4) Naka-ko profundal zone with 9 taxa of macroinvertebrates. The bottom of the littoral zone changed from cobbles, sand and mud along a transect line from shore to sublittoral zone. The macroinvertebrates communities only in cobbles and sand showed a high biodiversity, mainly composed of lotic species, but those on mud showed a low biodiversity composed of mostly Oligochaeta and Chironomidae. The biomass of macroinvertebrates was highest at 12-15m depth almost, but the peak shifted to the shallower sites during the winter. This phenomenon and the fish distribution in the littoral zone might suggest that the fish predation controls the distribution of the macroinvertebrates community.