Restoration work seeks to save Karvianjoki pearl mussels

Restoration work has begun to save the endangered freshwater pearl mussel population in the Karvianjoki River, Yle reports. The river is the only one in the Satakunta region where the mussels still live, but their population is estimated at about 2,000.

Work began this summer at Rakennuskoski rapids as part of the LIFE Revives project, coordinated by the University of Jyväskylä. Practical work in the Karvianjoki area is being carried out by the Southwest Finland vitality centre.

Workers are creating spawning gravel beds for trout, as well as rocky areas where young trout can shelter during their first stages of life. The pearl mussel depends on a healthy trout or salmon population because of its host parasite relationship with trout.

The restoration is also increasing the area of rapids by moving rocks in the river channel. Gravel patches are being created where adult mussels can live and young mussels can burrow.

The mussels at Rakennuskoski have been moved upstream for safety during the work. The restoration is expected to continue for about three more weeks, after which the need for further improvements will be assessed.

The condition of the population is considered critical. Based on their size, some of the mussels in the Karvianjoki may be as old as 100 years.

The population is currently declining. These measures are genuinely needed to keep this mussel population here, said Lotta Mäkinen, a regional coordinator at the Southwest Finland vitality centre.

Wider watershed restoration also needed

The situation is even worse in the Kiskonjoki River in the Southwest Finland region. Pearl mussels have previously been found there, but the latest surveys did not locate any.

It is quite a critical situation there. They have either disappeared, or there are individual mussels here and there that have not been found, Mäkinen said.

She said broader watershed restoration is also needed. This would involve using environmentally friendly forestry methods, moderating the amount and depth of drainage, and introducing water protection measures in agriculture.

The Southwest Finland vitality centre is systematically monitoring the effects of the restoration. The trout population is being tracked through electrofishing, while the condition of the mussels is monitored through direct observations. The restored areas are being assessed using nail and redox tests.