River Turkimusoja was restored this summer
River Turkimusoja is the most distinctive of the FPM rivers
In 2014, a local resident of H盲meenkyr枚 municipality found a freshwater pearl mussel (from this on FPM) in River Turkimusoja. Species identification was confirmed by the Central Museum of Natural Sciences. It was known that there were FPMs in the river decades before. According to one local resident, there were FPMs in the river in the early 1940s. However, over the decades, the population size has decreased to much that it was thought that FPM had already completely disappeared. Fortunately, this was not the case.
In 2018, a demarcation decision, delimiting the place of occurrence of a specially protected species, was made for River Turkimusoja to prohibit the destruction or weakening of the place of occurrence in accordance with 47. 搂 of the Nature Conservation Act (1096/1996). The purpose of the decision is to secure the conditions for the occurrence of the FPM population, as Turkimusoja is host to many different kinds of land use and extensive construction projects, such as the road improvement project of H盲meenkyr枚. This is Finland's first and only demarcation decision made for freshwater pearl mussel. Other FPM rivers in Finland are largely without protection for their habitat, except for Natura areas. Hopefully in the future, several other FPM rivers will also get the protection status they deserve.
Why does River Turkimusoja need to be restored?
The river's restorations are based on previous projects, restoration plans and monitoring results. Since the discovery of the population, the status of FPM and trout populations as well as water quality have been actively investigated in Turkimusoja. For example, FPM monitoring was done in 2015 (Valovirta 2016) and supplemented in 2016 (Alleco Oy 2017). The most recent surveys are from the year 2022 (Alleco Oy 2022), where the size of the population was estimated only 1200 individuals. The most amazing thing is, that according to the latest research data, Turkimusoja has an increasing population and its life cycle is working.
Despite the increasing population, FPMs in River Turkimusoja's are not doing well. The oxygen content of the gravel is a decisive factor in terms of the vitality of the juvenile stages of the FPMs, as the juveniles spend the first 5鈥�10 years buried inside the gravel. There are far too few habitats suitable for the juvenile phases. In addition, very poor results have been obtained from electrofishing of trout: it hardly occurs. FPM can reproduce only when there is a sufficient trout or salmon population in the stream. Also the river's water quality has abnormality, for example in terms of iron and solid matter.
In conclusion we can say that the in-stream habitat restoration is necessary.
Whistle while you work
In summer 2024, Centre of Economic Development, Transport and the Environment of Pirkanmaa started a long-awaited and dreamed-of in-stream habitat restorations in River Turkimusoja. The restorations belong to LIFE Revives project鈥檚 actions. The goal is to increase both the diversity and the number of suitable habitats for FPMs and its host fish, brown trout. Restorations were done by using wood material, restoring spawning beds, removing migration barriers, protecting riverbanks and establishing FPM kindergartens. Hy枚tyvuokraus Ltd. was selected as the contractor for the restorations.
Restoration by wood material is especially suitable for the sandy river Turkimusoja. Wooden structures were used to clean the bottom of the river and spawning beds and to attach solid matter. The effects of the wooden structures were immediately visible as better flow conditions and increased number of shelters. Of course, some of the effects will only be visible after the first flood, when the solid matter sorts and accumulates. When restoring by wood material, different methods, such as an underminers and current deflectors, as well as mechanisms that collect solid matter were used. Examples of these are shown below.
When restoring spawning beds, an effort was made to utilize the already existing spawning areas as much as possible. The surface structure of the river bed was mechanically broken and fine material was sorted out of the gravel. In some places, natural gravel brought from elsewhere had to be used.
In addition to the spawning beds, so called FPM kindergartens were established for the FPM juveniles. First a hole was dug with a shovel, after which stones or wooden material was placed as the bottom layer for drainage to ensure water flow through the gravel. After sorting out, the gravel and stone material was returned. Suitability of these kindergartens for natural settling of FPM juveniles is monitored in the LIFE Revives project.
This summer, 30 adult FPMs were transported from River Turkimusoja to the Konnevesi Research Station to reproduce in captivity. After captive breeding, when strong enough to survive alone in the river environment, the FPM juveniles will be returned to River Turkimusoja 鈭� first either in whole plates or in gravel boxes. Some years later, the juveniles will be released to the river bottom to live independent life.
In-stream habitat restoration in River Turkimusoja was completed in August. Next year, restorations will be made in Pirkanmaa's other FPM streams; In River Pinsi枚n-Matalusjoki and River Ruonanjoki.
We are looking forward to the monitoring results after the restorations of Turkimusoja. Keep your fingers crossed!
Author: Katja Vainionp盲盲, coordinator of LIFE Revives in Centre of Economic Development, Transport and the Environment of Pirkanmaa