Biologisk recipientkontroll vid Ringhals kärnkraftverk: årsrapport för 2020

Ringhals nuclear power plant is one of Sweden's largest electricity producers. Due to the intake from and discharge of cooling-water into the sea, that cools the process in the plant, there is an impact on the surrounding coastal water environment. This impact is monitored and analyzed in the ongoing biological recipient control program. This annual report presents the results in the surveys within the control program for 2020. It focuses on the communities of fish and shellfish, losses of eggs, larvae and fry in the cooling waterways and the presence of alien species. During the spring, annual sampling of fish eggs and fish larvae with Bongo net is carried out in the intake channel for cooling water to monitor the losses in the power plant. Flatfish larvae were the most frequent catch among fish larvae in sampling during 2020. Sampling in the cooling water intake after juvenile fish and fry is largely focused on the catches of glass eels (Anguilla anguilla) and is carried out by using a modified IsaacsKidd-trawl. Glass eel catches have declined strongly since the 1980s. The decline in abundance has been similar throughout the distribution area (Europe, northern Africa and western Asia) and is not a result of the losses in cooling water intake. The effect of the cooling-water released into the sea is monitored by yearly fyke net surveys in the recipient area of Ringhals, affected by the cooling water, in the reference area at Vendelsö, unaffected by cooling-water, and in the area at Norra Horta, which is partly affected. To include seasonal variations in water temperature, the surveys were conducted yearly at twice, in April and in August. In 2020, corkwing wrasse was the most common fish species in test fishing. In general, the occurrence of hot water-favored species was higher in the recipient area and the occurrence of cold-water-favored species was higher in the reference area. The total catch of shore crab was quite high in all places and fishing periods with the peak in the recipient area in August. To investigate the presence of marine invasive alien species, yearly scuba diving surveys were conducted outside the power plant's cooling water discharges. In 2020, five species alien to the west coast were found during the diving inventory, all of which have previously occured along the Swedish west coast. In addition to these five species in the inventory, another alien species, the Asian blue crab (Hemigrapsus sanguineus), was caught during the fyke net fishery in the recipient area in both April and August.