Ladoga salmon reach Hiitolanjoki spawning grounds after 115 years

Ladoga salmon have reached the furthest point ever recorded in Finland’s Hiitolanjoki River, where they form the country’s only wild lake salmon population, Yle reports. Salmon fry were found last week at Uudensillankoski, upstream of Highway 6 in Rautjärvi.

The Southeast Finland Centre for Economic Development, Transport and the Environment found the fry during an electrofishing survey. The fish were stunned with electricity, counted and released back into the river.

Waterways manager Matti Vaittinen said the finding was historic. Ladoga salmon last reproduced at Uudensillankoski 115 years ago.

Three hydropower dams downstream from Uudensillankoski have been removed in recent years. The dams had prevented Ladoga salmon and Ladoga trout from reaching spawning grounds further upstream on the Finnish side.

Possible transfer to the Torsanjoki

The Torsanjoki River lies further upstream from Uudensillankoski. The final dam blocking salmon and trout from reaching the extensive Torsanjärvi water system was removed in December last year.

No Ladoga salmon or Ladoga trout have yet been observed in the Torsanjoki. Vaittinen said the migratory fish may still be avoiding the river because its water is slightly more acidic than that of the Hiitolanjoki.

The Southeast Finland Centre is considering transferring salmon and trout from the Hiitolanjoki to the Torsanjoki, a few kilometres away, to help the fish adapt to the new river environment. The transfer would require permission from the fisheries authorities.

According to Vaittinen, the Torsanjoki has a strong flow and good water quality. Its waterways contain tens of kilometres of new river and stream habitat where Ladoga salmon and, in particular, trout could reproduce.

Hot summers pose the biggest threat

Vaittinen said increasingly hot summers are currently the greatest threat to migratory fish populations in the Hiitolanjoki water system. Rising water temperatures can become too high for salmon and trout.

The Torsanjoki has already experienced serious fish deaths caused by heat. The first extensive deaths occurred in 2010, when almost all the trout died. Fish have also died during at least two subsequent hot summers.

Vaittinen said an unobstructed water system extending to Lake Ladoga provides a reserve of large spawning fish. If fish die during a hot summer, he said, these fish can return to repopulate the rivers.