Bypass Channels Can Serve As Compensative Reproduction Habitat For Salmonids

Even though connectivity of rivers may be restored by fishways, there is still in many cases a crucial lack of suitable spawning and rearing habitats for the species of concern. In Finland, these species are usually salmon (Salmo salar L.) and brown trout (Salmo trutta L.). Traditionally, technical (e. g. vertical slot, denil, borland) and also nature-like fishways are constructed for these species and research is focused on species' abilities to find the entrance, swim upstream, and on the time spent in passing through the fishway. In fish pass projects, attention should be paid also to possibilities for habitat construction. In this prefacing work, we collected some basic physical information from potentially suitable habitats, especially for spawning of salmonids. Existing bypass channels and natural streams seemed to have equivalent physical features. These features were further evaluated in light of known preference values for salmon and brown trout reproduction habitat. Results show that good quality habitat values are found in diverse streams and channels. Discharge variability and an option for flow regulation have a clear impact on habitat quality. These advantages should be taken into account during the planning process in order to maximize the reproductive potential for the target species and also to compensate habitats and ecosystem functions comprehensively. In most cases it would be feasible to switch from compensation stockings towards natural reproduction and replenishment -and here bypass channels may play a fundamental role.