1. Biologic monitoring at Barsebaeck nuclear power plant 1985-1997. 2. Biological monitoring at Swedish nuclear power plants in 1998. Annual report 1998

This report gives an account for two studies on the ecological effects of effluents to the aquatic environment from the Swedish nuclear power plants: 1. The results of biological monitoring at the Barsebaeck nuclear power plant during the period 1985-1997 are summarised. Comparisons are made with a previous report from 1969-1983. The fish community was studied by fyke net test fishing in the cooling water effluent area along a gradient out to unaffected sites. The loss of young eels in the cooling water intake was estimated annually. Damage on female grey mullet oocyte development was analysed on samples of cooling water exposed fish. 2. The biological monitoring at the Swedish nuclear power plants during 1998 was with minor exceptions performed according to the established programmes. The monitoring at Forsmark is running in the enclosed Biotest basin at the cooling water outlet and in the surrounding archipelago. Reference data are collected at Finbo, NW Aaland, and in the nearby Graesoe archipelago. In 1998 as in previous years the benthic macro fauna abundance within the Biotest basin showed strong variations. In the beginning of the year abundance and biomass were low, in the autumn though, higher than average. Oskarshamn: The monitoring is performed in the small effluent bay, Hamnefjaerden bay, in the waters surrounding the cooling water plume and in a reference area, Kvaedoe-fjaerden, 100 km north of the power plant. Perch and roach catches have been high in the Hamnefjaerden bay since the late 1980's. In 1998 catches of perch were on a higher level than in 1997, both in spring and in summer. The changes for roach were small. A moderate decrease in eel catches took place in 1997 and 1998, indicating a reduced effect of stockings in the late 1980's. Ringhals: The monitoring is performed in the area close to the cooling water outlet, which is located at an open coast, and in a reference area. An attraction of yellow eel to the effluent area has been demonstrated with fyke net test fishing in April and August. Eel catches decreased in August from 1997 to 1998 and a marked decrease took place in the recipient as well as in the reference area after 1994. In both areas the 1998 catches were the smallest observed since the early 1980's. The most evident attraction to the cooling water effluent has been observed for the shore crab (Carcinus maenas), the abundance of which did not change much in 1998 compared to recent years. Barsebaeck: Monitoring is performed in the vicinity of the effluent area and in a reference area and is focused on fishing with fyke nets in April and August. Yellow eel catches in April have been low since 1995 and remained so in 1998. Catches in August 1998 decreased at all stations and a negative trend is revealed after a peak in the mid 1990's. A negative trend also exists for eel-pout in the 1990's. In the same period cod has been more abundant than earlier. The August cod catches of 1998 were the highest recorded from 1985 onwards. The biomass of small yellow eel trapped in the cooling water intake of the power plant was estimated to 80 kg in 1998. No stockings for compensation of the losses was undertaken, due to previous over-compensation