An interview with Professor Hiroshi Hakoyama about the decline of invasive fish in the mid-stream of the Chikuma River was broadcast on NHK Kanto Koshinetsu and Evening Shinshu!
On November 1, 2022, NHK Kanto Koshinetsu Morning News, Evening Shinshu, NEWS WEB, and NEWS WEB Shinshu reported the results of a study showing that the number of smallmouth bass in the midstream of the Chikuma River has declined and that native fish such as dace and minnows have increased. Professor Hiroshi Hakoyama believes that the difference in the nature of native and non-native fish, especially the difference in movement between small water systems (such as irrigation canals) and the main stream, may have affected their survival during typhoon flooding. During the breeding season, native fish such as crucian carp jump over small weirs and enter small water bodies such as canals to spawn, and then return to the main stream as adults. Therefore, it is possible that individuals of native fish that lived in waterways less affected by typhoons returned to the Chikuma River and increased in number. On the other hand, smallmouth bass, which are native to the Mississippi River in North America, may not be fully adapted to the flood disturbance of Japanese rivers.
This research was conducted by the Nagano Prefectural Fisheries Experimental Station as part of the Chikuma River River Ecology Group of the Ministry of Land, Infrastructure, Transport and Tourism, led by Professor Hiroshi Hakoyama of the Institute of Freshwater Biology. We will work together as a research group to advance river ecological engineering research in the Chikuma River and Shinano River basins and contribute to flood control in the river basins.