Fish Habitat Science and Management in Finnish Freshwaters

Abstract

The area of Finnish inland waters is 33,500 km². Forty fish species, eleven of them indigenous, have been encountered in the area. The annual catch from inland fisheries is around 40,000 metric tons. The largest changes in fish habitats in Finnish inland waters have been caused by hydropower construction and timber-floating in rivers, and eutrophication and water level regulation in lakes. River-spawning fish species have lost their spawning habitats or access to spawning sites. In many lakes, eutrophication together with selective gill-net fishing has shifted the fish assemblages towards dominance by cyprinids and other small-sized plankton feeders. Acid precipitation has affected fish stocks in ca. 1% of the 56,000 lakes. Acidification has decreased during the past decade. The management and use of water resources is regulated by the Water Act. To meet the requirements of the Act, e.g., in water construction works the use of the best available techniques (BAT) is required. Enhancement of fish habitats and natural reproduction is gaining importance in fisheries management instead of or together with stocking of young fish. Timber-floating has ceased in streams and rivers, and rehabilitation programs for fishery purposes have been carried out. Habitat-hydraulic models have been used to guide rehabilitation programs in rivers to meet the needs of juvenile salmonids. In lakes, eutrophication from point sources have been reduced. Reduction of non-point loads is now in the focus. Modelling of interactions in fish community, fishing and stocking has given promising results in fisheries management. Water level regulation practices that take into account the survival of fish eggs and larvae are considered in large reservoirs and lakes. In the future, the dynamics of ecosystems should be given more emphasis to mitigate the combined effects of anthropogenic influences on fish habitats and communities.