Lapväärtin-Isojoen taimenen poikastuotanto: Jokipoikastiheydet ja vaelluspoikastuotanto

River Isojoki trout populations have been affected by a multitude of anthropogenic activities such as building of migratory obstacles, declining water quality and high fishing pressure. River Isojoki trout populations have been maintained by long term stocking programs, but the management measures have been broadened in the past few years. Measures have been taken to improve the regulation of fishing, to improve migration conditions and to restore key life history habitats. Trout populations inhabiting the river system seem to have reacted positively to the management measures, as the production of juvenile trout has increased in several river sections based on long term electrofishing data. Parr (0+) densities are close to reaching or have already reached a good status (25 parr/100 m2) in several areas in the central and upper reaches of the river. The juvenile production development in the lower sections of the river have been positive, regardless of the relatively low quality of available habitats. The highest juvenile densities in recent years have been observed in Karijoki and Heikkilänjoki tributaries. A smolt migration monitoring program was conducted in 2019-2021 to estimate the smolt production of the river system. Smolt production was estimated to be 3500-7300 smolts per year, which is higher than previously estimated. However, there is not enough long term reference data on the smolt production development for River Isojoki to draw conclusions regarding the condition of the population. The positive developments in production of trout in the river system enable ending of the population supporting stocking program. Resources should instead be redirected to measures aiming to strengthen and increase the natural reproduction and distribution of trout. One key measure is to implement an extensive fishing regulation both in river and at sea. In addition to fishing regulations, measures could be taken to improve habitats for key life stages by restoring spawning and rearing habitats, and by improving water quality. There are still some deficiencies in migration connections as well, for example at the Perus hydropower dam but also at a number of other dams. As the trout populations continue to recover, fishing regulations may be eased and might also allow moderate fishing of wild trout. River Isojoki has the potential to become one of our country´s best destinations for trout fishing.