Endangered raakku populations decline in Finland due to high water temperatures and habitat challenges

A hot summer and elevated water temperatures have taken a toll on the northern populations of the freshwater mussel species, known as raakku. Researcher Aune Veersalu has monitored water temperatures over the summer in areas like Kaldoaivi and Utsjoki, noting that this year, Utsjoki recorded a peak temperature of 23 degrees Celsius, which is quite high for raakku, potentially affecting their health.

The most significant populations of endangered raakku can be found in the rivers of Central Finland. The most well-known raakku river in the north is Lutto, located in the Urho Kekkonen National Park in Inari, where numerous raakku populations thrive. Veersalu has specifically studied raakku in the Inari and Utsjoki regions, reporting that while some rivers are in good condition with young mussels, others are suffering and only host older individuals.

Other rivers in the Tenojoki water system also contain raakku populations. Inarijoki has historically been a productive raakku river, even yielding pearls in the past, but today, raakku are no longer found there, according to Veersalu.

Recently, raakku gained media attention due to reports of thousands of them dying after logging machinery crossed the protected Hukkajoki in Kainuu, an area significant for endangered species like the freshwater pearl mussel.

The future of raakku planted in Lutto, where hundreds were introduced a few years ago, remains uncertain. Although they survived their first year in controlled vessels and later transitioned to the river, it will take several more years to assess their progress. Veersalu explains that raakku have not reproduced in Lutto for the last 60 years, primarily due to the absence of host fish, as salmon have not been able to ascend from the Russian side of the river for decades. Raakku’s life begins as a tiny larva that attaches to a host fish’s gills before dropping into the river to mature, potentially living for up to 300 years.