Long term changes of river structure around the middle and lower reaches of the Jinzu River [Japan]
2005
Tago, Y. (Toyama-ken. Fisheries Experiment Station, Namekawa (Japan)) | Yokogoshi, J.
Based on data available from 1868 to 2004, changes in river character around the middle and lower reaches of the Jinzu River were investigated. The aim of the study was to clarify the effects of the changes on the fishing areas for masu salmon, Oncorhynchus masou, and ayu, Plecoglossus altivelis, and on the local fishery. Before 1900 the flow of the Jinzu River meandered greatly toward the right at a site 6 to 10 km from the mouth of river. But the meandering flow was then straightened in 1921 by river conservation works. The loss in fishery grounds caused by this straightening was estimated to be about 1.4 km long. Fugan Canal, which connects with the Jinzu River, was constructed from East Iwase Port to Toyama Station on the north in 1935. In 1965, the lowest line of pebbles (0.24 square km) that existed was at a site 3.2 km from the mouth of river, but the pebbles were completely lost and the lowest line of pebbles moved back to a site 5.9 km from the mouth in 1984. The lowest lines of fishing grounds for masu salmon and ayu were at sites 0.6 km and 2.6 km, respectively, from the mouth of river in 1965, but they were reduced to sites 3.5 km and 5.6 km, respectively, from the mouth in 1984. It is considered that these changes in river character were largely caused by river conservation works such as dam construction, bank stabilization for low water and gathering gravels, and they have affected masu salmon and ayu fishery negatively through the loss of fishing and spawning grounds.
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