DNA study found 27 different species of fish at Olkiluoto

TVO’s water permit requires regular fish stock analyses. The purpose of a new fish monitoring project that started in September is to analyse the type and number of fish carried into the plant units. The analysis will also consider fingerlings of less than one centimetre in length.

According to Tammela, catching the fingerlings has proved challenging. So far, net fishing has been attempted from the walking bridge on the inlet water channel, the piers and from a boat, but the results have been underwhelming.

Observations indicate that small fingerlings actively swim in the water’s surface layer and will not be carried with the stream in the inlet water channel, says Tammela.

The Centre for Economic Development, Transport and the Environment has approved the research plan for the fish monitoring performed by Tammela.

New eDNA method

According to the Finnish Environment Institute, the eDNA method has been piloted globally in biodiversity studies in recent years. The results have been promising.

eDNA refers to DNA that organisms spread into their environment. eDNA samples are taken from a water or land environment, snow or the air. The DNA contained in the samples is isolated in a laboratory.

At Olkiluoto, the first samples were taken from the power plant’s cooling water in June 2023. During analyses, 27 species of fish and 5 species of clams were identified from the DNA in the water samples. Only these two types of organisms were analysed in the first stage, as they are important indicators of the sea’s diversity.

The eDNA result confirms an earlier view on clams. For fish, however, the variety is higher than indicated by earlier studies. In total, there are slightly more than 60 species of fish in the areas of the Baltic Sea that belong to Finland. 

– During the time of the eDNA sampling, the most abundant species at Olkiluoto were the Baltic herring, three-spined stickleback, bleak, pike and bream, Tammela says.

TVO has also participated in an invasive alien species project that surveys the organisms growing in the power plant’s structures that are in contact with sea water. During the annual outage, samples were taken from the sea water systems inside the plant units, such as the heat exchangers. The analysis will be different from before, as it will determine the species of invertebrates, for example. The analysis will be performed by a laboratory company in Finland, and the project involves several power plants from Finland and Sweden.

In the spring, we told about the species of fish that were discovered among the cooling water screenings. Will eDNA replace screenings studies going forward?

– eDNA and screenings studies complement each other nicely and also verify the results. eDNA tells us which species are found in the cooling water, while studying the screenings allows us to determine the number, length and weight of the fish, Tammela points out.

A dream job

Tammela graduated from the University of Jyväskylä, majoring in Aquatic Sciences and specialising in fishery biology and fisheries. He is a fish researcher whose job description has broadened at Olkiluoto.

- Yes, this is my dream job. New tasks related to life cycle analyses, annual greenhouse gas release calculations and CSRD sustainability reporting provide interesting new challenges, Tammela says.

In addition to studying screenings and eDNA, TVO is also performing test fishing, age and growth determinations for fish, fishing for record-keeping purposes and surveys among professional and recreational fishermen in the waters near Olkiluoto, as well as surveys of water quality and benthic fauna.

Indeed, the island of Olkiluoto is one the most researched areas in Finland, and its diverse nature has been charted in detail.

Story by Juha Poikola
Photo by Tapani Karjanlahti