Fish community in Lake Suwa: Based on the fishery statistics report of the Lake Suwa Fishery Cooperative.
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概要
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Changes in the fish community in Lake Suwa after World War II were analyzed based on fishery statistics data describing the amount of fish landed on an annual basis reported by the Lake Suwa Fishery Cooperative. The total amount of fish landed in Lake Suwa increased from 1946, reached a peak in 1970, and then decreased and recorded its lowest amount in 1999. Resource species caught in the fisheries were basically categorized into fish, shellfish and shrimp. During the period of increasing catches in Lake Suwa prior to 1970, pond smelt Hyposesus transpacificus nipponensis and crucian carp Carassius carassius were the major species, although there were some years when shellfish species accounted for a ratio of 1/2 to 1/3 of the total catch. It should be especially noted that diverse fish species were caught during the years when the fishery catch was increasing. During the period after 1970, most of the species caught were smelt fish, and the catch of shellfish decreased drastically while that of crucian carp was constantly decreasing. Fish species other than smelt, crucian carp and common carp were rarely caught in recent years, and the catch of common carp was catching up with the amount of crucian carp, which was the 2nd highest catch following smelt. The recent annual catch from Lake Suwa was about 1/4 of that in the 1970s, and the catch of pond smelt has decreased to 1/10 of that in the 1970s. One of the reasons for the decrease in the amount of fish landed since 1970 may be a decrease in the aquatic plant area along the coastline due to the reclamation and dredging of the littoral zone. The decline in fishing due to the aging of fishermen and the reduction in fish prices could be other reasons. As there are some situations that cannot be explained only by the decline in the fishing conation of fishermen, the reduction of the fish catch should be discussed also in the context of the influence of changes in the aquatic environment of Lake Suwa. Regarding changes in the composition of fish fauna, alien fish species such as largemouth bass and bluegill as well as ukigori (floating goby) are also increasing in recent years. Such changes should be carefully observed in future.
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