Biologisk recipientkontroll för Ringhals kärnkraftverk: årsrapport för 2025

Ringhals nuclear power plant is one of Sweden’s main producers of electricity. Due to intake and discharge of seawater that cools the condenser process in the reactors of the power plant, there is an impact on the surrounding coastal environment. This impact is monitored and analysed in a biological recipient control program. This annual report presents the result of the surveys within the control program for 2025. It focuses on the communities of fish and crustaceans, losses of fish eggs, larvae and fry in the cooling waterways as well as the presence of invasive alien species. During spring, 2025, two types of annual sampling were carried out in the cooling water intake channel to monitor the losses of different life stages of fish in the power plant. A Bongo net was used to monitor eggs and larvae, where large flatfish eggs (plaice) and cod were the most common eggs, while shorthorn sculpin and herring were the most common larvae. Sampling in the cooling water intake for juvenile fish and fry is largely focused on the catches of glass eel and is carried out using a modified Isaacs-Kidd-trawl. Transparent goby dominated the catches, followed by sprat and glass eel. In general, catches were low during 2025 and constituted only about a fourth of the catches from the previous year. The effect of the release of cooling water into the sea is monitored by yearly fyke net surveys in three locations: The recipient area of Ringhals, which is directly affected by the cooling water, Vendelsö, used as a reference area unaffected by cooling water, and Norra Horta, which is affected to some extent. To include seasonal variations in water temperature, two surveys are conducted, one in April and one in August. In 2025, the most common fish species was corkwing wrasse with the highest catches during August in the partly affected area. During April, cod was the most common species at the Ringhals area and Norra Horta, while goldsinny wrasse was most common in the reference area. In general, the occurrence of warm-water species was higher in the recipient area, and the occurrence of cold-water species was higher in the reference area. The total catch of shore crab was relatively high in all areas and fishing periods, with a peak in the reference area in August. The area around the outlet of the water sieving stations exhaust pipe was examined with a ROV (Remotely Operated Vehicle) to visually inspect impact on the sea floor. Discharge and sedimentation of shell parts of mussels and crabs was observed like previous years. To investigate the presence of marine invasive alien species, a scuba diving survey was conducted in two locations outside of Ringhals: The recipient area of Ringhals, and the reference area Vendelsö. The survey could not be conducted at Norra Horta because of strong winds. Two species of algae alien to the west coast were found during the survey: (Sargassum muticum) and (Dasya baillouviana), as well as one alien animal species, (Magellana gigas). All species have previously been observed along the Swedish west coast. Additionally, brush-clawed shore crab (Hemigrapsus sanguineus) was found in April in the fyke net survey at the recipient area, which makes it the sixth observation during the fyke net surveys.