Rovajärvi military range shelters 30,000 endangered freshwater mussels

Yle reports that Metsähallitus has found around 30,000 highly endangered freshwater pearl mussels in Rovajärvi, a military shooting range in Finnish Lapland. The survey has covered only two small rivers, making the number significant.

Rovajärvi is the scene of frequent military exercises, including large international NATO drills. Heavy artillery is fired in the area, and armoured vehicles are used there.

However, Metsähallitus special conservation adviser Jari Ilmonen said he had not observed any harm to the mussels from the exercises. The activities are concentrated elsewhere, and tanks do not cross the rivers, he said.

“If waterways, especially those containing mussels, are avoided, then there is no problem,” Ilmonen said.

The Finnish Defence Forces said restrictions related to protected areas and groundwater zones are taken into account during exercises. The protection of aquatic species is considered when planning bridges, other water construction and crossing points, said Lieutenant Colonel Petri Sipilä, chief of staff at the Jaeger Brigade.

Sipilä said there is currently no need to change military activities because of the mussel populations.

Young mussels hide in the gravel

Ilmonen said the mussel populations at Rovajärvi appear promising and may be viable. Small mussels have been found, indicating that the species is reproducing at least to some extent.

Under a Nordic assessment method, at least one tenth of a population should consist of young mussels for it to remain viable. Young freshwater pearl mussels have been found at Rovajärvi, but not in sufficient numbers so far.

They may be difficult to detect because they hide in gaps between stones and in gravel on the riverbed, Ilmonen said. Mussels are measured and their ages estimated from growth rings before they are returned to the water.

The species requires clean, oxygen-rich water

Freshwater pearl mussels can live for more than 200 years. They are demanding and their presence indicates that a waterway is in good condition, as they require a clean, oxygen-rich riverbed.

Large mussel populations also help keep water clean by filtering it as they feed.

Metsähallitus is investigating freshwater pearl mussel populations and their distribution more broadly across Lapland. The agency has records of mussels in about 100 rivers, and Ilmonen said dozens of undiscovered populations may still exist.

About five rivers or streams containing mussels have been identified at the Rovajärvi range. Ilmonen said more could be found and estimated that the area may contain six to ten populations in total.

Finland has about 160 freshwater pearl mussel populations, according to Ilmonen. Sweden has more than 600.

The research is funded by forest company Stora Enso. In 2024, thousands of freshwater pearl mussels were killed by forestry machinery at a Stora Enso logging site in Suomussalmi.