Performance of constructed fish spawning and rearing channels : development of the Imatra City Brook in Finland

Freshwater habitats and species have been lost because of river constructions, particularly regarding hydropower plants. Such losses may be mitigated, for example, by providing compensatory habitats. We present a case which had the objective to promote reproduction of a key species. Imatra City Brook in Finland was constructed in 2014 at a hydropower dam as a new reproduction area for brown trout (Salmo trutta L.). In the planning phase, the objective was to maximize suitable habitat types and areas with limited discharge. Monitoring shows promising densities of brown trout juveniles within only three years, inspiring hope for high smolt production in the main river. The increase in total macroinvertebrate abundances and taxa numbers in the second year of monitoring showed that species richness was comparable to that in natural rivers, and the brook was in a good ecological state. This case confirms the expected high potential of spawning and rearing channels to improve migratory fish stocks and compensate for lost habitats in constructed rivers.