Many lake-resident fishes (e.g. crucian carp) migrate seasonally to irrigation waterway and paddy field for spawning. Recent habitat fragmentation by artificial barriers inhibits such reproductive migration of endemic fishes and increases the extinction risk of populations. Exotic fishes (preda- tors) is also a threat to the existence of endemic fishes. The timing and location of their predation and the relationship between the predation pattern and habitat fragmentation must be taken into account in the design of ecological networks. Our aim is to develop a method to assess the effect of alteration of the ecological network on extinction risk of endemic fishes. We examine the popu- lation dynamics, habitat suitability and habitat use of the endemic and exotic fishes in Lake Suwa to conduct a population viability analysis (PVA).

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