A research group led by Associate Professor Ichiro Koizumi of the Graduate School of Environmental Science, Hokkaido University announced that an estimated 4 or more fish had been introduced into a small tributary that dried up in the summer in early winter four months later. bottom.
Among the fish that spend their lives in the river, there are species that make good use of different environments such as tributaries and mainstreams, fast-flowing streams and slow-flowing pools according to the growth and seasonal changes of individuals.Especially in the harsh environment of winter, changes in habitat use can be seen, such as the gathering of hundreds of fish in a limited habitat, but field surveys are difficult in the northern regions where rivers freeze, so fish The current situation is that there are still many unclear points about the wintering ecology.
This time, when the research group was exploring the Tokachi River basin in Hokkaido, it was confirmed that a small tributary had dried up in the summer.When the water returned in September, only a few rainbow trout were caught, and almost no aquatic insects such as stoneflies, mayflies, and caddisflies were found.However, a large number of fish were caught when the survey was conducted at the end of November.Therefore, in order to investigate quantitatively, five fixed-point survey areas were set up from the confluence of the tributaries to the headwater area, and the population was estimated by the removal method, and the total number of fish inhabiting this tributary was estimated.
As a result of the analysis, it became clear that a total of more than 4 fish, mainly rainbow trout, dace, and stone loach, went up in less than four months after the fish disappeared.There were few mature parent fish or year-old fish (1-year-old fish) with weak swimming ability, and young immature fish accounted for the majority.Until now, it has been known that fish with high swimming ability such as rainbow trout and dace often make large-scale overwintering movements, but it is clear that even Fukudojo, which lives mainly on the riverbed and has low swimming ability, has such seasonal movements. It became.
The tributary surveyed this time is a waterway-like river of only 1 km.It has become clear that many fish use it even in places that seem to be unsuitable for habitat.The results of this research show that small artificial waterways can enhance the overwintering survival of fish even in rivers that have been rehabilitated, and provide an important perspective in river management.
