Pool Passes-Biological Aspects in Their Construction

摘要

The effect of an obstruction upon river fish, especially the migrant species, will vary according to its location along the river bed. The following three cases may be distinguished:a) the obstruction is set up above the main spawning grounds of a given species, and, there¬fore, its effect will be least harmful;b) the obstruction intersects the river in the area of the spawning grounds and its adverse effect will be considerably greater than in the previous case depending on the residual area of spawning grounds below the obstruction;and c) the most serious consequences arise when an obstruction completely bars the way to the main spawning grounds. In such a case, the failure to build a fishway at that place will cause a rapid extinction of the species.