Biologisk recipientkontroll vid Ringhals kärnkraftverk: årsrapport för 2015

Abstract The use of cooling water at the Ringhals nuclear power plant affects the marine environment. The fish and shellfish community is affected in two steps. In the first step, fish eggs, larvae and larger fish that are transported into the nuclear power plant with the cooling water may face unnatural mortality. In the second step the heated water is released back into the sea, where the fish and shellfish are affected by the increase in temperature. The presence of heated water could also contribute to alien invasive species establishing in the coastal area. Reactors R1, R3 and R4 at Ringhals nuclear power plant produced electricity during the major part of the year 2015, with exceptions for the annual audits and shorter stops in production. Reactor R2 was closed down for the whole year. Fish eggs and fish larvae are sampled in the incoming cooling water using a modified Bongo net to monitor losses of eggs and larvae in the nuclear power plant. The most abundant larvae are shorthorn sculpin larvae ( flounder ( ( Kidd midwater-trawl is used. This sampling is mainly focused on glass eels ( The abundance of glass eels have declined strongly since the beginning of the 1980´s. The decline of the glass eel abundance is most probably due to a general decrease in recruitment and not to a local effect caused by the nuclear power plant. The effects of the cooling-water released into the sea are monitored by fykenet surveys in the recipient (Ringhals) as well as in a reference area (Vendelsö). These areas are compared in two seasons to reveal effects of the cooling water emissions. The diversity of the fish community has developed differently in the two areas during the cold season, where Ringhals showed a decrease in diversity and Vendelsö was stable. This is possibly an effect of the warm water emissions from the power plant. Species that prefer warm water have been observed to concentrate in the recipient area. Eel ( melops) stable or increasing catches in the area. Species that prefer cold water, such as shorthorn sculpin and eelpout (Zoarches viviparous), were less abundant in the recipient area. Only the European flounder showed an increasing trend in both Ringhals and Vendelsö. To investigate the presence of marine alien invasive species a scuba diving survey was conducted in five shallow areas in a gradient from the outlet of cooling water. No new alien species were found in the 2015 survey, but three species already established on the Swedish west coast were found. The species found were the Japanese oyster ( species of red algae muticumMyoxocephalus scorpius) followed by EuropeanPlatichtys flesus). The abundance of the third most abundant rock gunnel larvaePholis gunnellus) have decreased since 1979. To sample juvenile fish a modified Isaacs-Anguilla anguilla).Anguilla anguilla), corkwing wrasse (Symphodusand shore crabs (Carcinus maenas) are three examples, which show eitherCrassostrea gigas), oneDasya baillouviana and one brown algae, Japanese wireweed (Sargassum).