Biologisk recipientkontroll vid Forsmarks kärnkraftverk: årsrapport för 2013

This report describes surveys conducted within the biological surveillance program of the Forsmark nuclear power plant in 2013. The planned power uprate at the power plant started in 2013 in Forsmark 2 and led to an increased use of cooling water. Impingement losses of fish at the cooling water intake in spring time were dominated by three-spined stickleback (Gasterosteus acelatus). In autumn the most common species were herring (Clupea harengus) and most of the sample was composed by larvae, which could indicate success of recruitment for the species in the Forsmark area. The loss of eels (Anguilla Anguilla) was low compared to last year’s sampling and consisted like previous periods of silver eels. The results of the gill net surveys in the Biotest basin during spring time showed high catches of perch (Perca fluviatilis) and roach (Rutilus rutilus) which indicates the importance of the area as a place for warm water species to spawn. However, the catches of juvenile perch and roach were low in the Biotest basin in the autumn. Fyke net surveys in 2013 confirmed a negative trend in eel catches in the Biotest basin since 2004, when the grids in the outlet were removed. Length distribution of eels indicated migration of young eels into the warmer water. A positive trend in catches of perch in the Biotest basin during autumn continued during 2013. The amount of young fish, from young-of-the-year to three years old, dominated the catches. Growth rate studies showed extremely high growth rate and some of the 0+ fry measured up to 18 cm. Young-of-the-year pikes (Esox lucius) were abundant, also showing high growth rates. Benthic macrofauna biomass and abundance at the Länsman station, temporarily affected by cooling water, showed a recovery from low numbers in the two preceding years. Digging activities and cable-laying in the area possibly contributed to the low levels in 2011 and 2012. In 2013, the macro fauna had recovered to normal numbers and biomass. The bird surveys in the Forsmark archipelago showed that the Biotest basin is the most important area for the species in the area covered by this study. During 2013 the Great Cormorant (Phalacrocorax carbo sinensis) for the first time established a breeding colony in Biotest basin. Due to frequent disturbance activities from the white-tailed eagles in the area the breeding failed. A positive trend of Common Goldeneye (Bucephala clangula) in the Biotest basin continued during 2013. It is possible that the alien species Conrad´s false mussel (Mytilopsis leucophaeata), recently established in the Biotest basin, currently serves as important food for the Common Goldeneye.