Utredning av fisktärna, strandskata och skarv som indikatorer för miljögiftsövervakning

Bird eggs are a good matrix for the measurement of environmental contaminants, especially those contaminants that biomagnifies through the food web. The purpose of this report is to create an overview of the usefulness of three species (Eurasian oystercatcher, common tern and great cormorant) as indicator species for (local) contaminant monitoring within the Swedish National Monitoring Programme for Contaminants in Marine Biota. Eurasian oystercatcher and common tern has been part of the monitoring programme since 2011. No monitoring of the great cormorant has taken place in Sweden. We present data that show that the great cormorant is placed at the highest trophic level (~4) followed by common tern (~3.5) and the Eurasian oystercatcher (~3). This is reflected in higher contaminant concentrations for the great cormorant. Great cormorant and common tern thus better reflect the trophic level suggested for monitoring of marine systems (4.5-5).and suggests that this species might be a good choice as an indicator species. The Eurasian oystercatcher and the great cormorant are represented in both freshwater and marine environments, but while the great cormorant population is increasing that of the Eurasian oystercatcher is declining in Sweden. However, long time series for Eurasian oystercatcher and common tern within another European network (TMAP) means that there with these species are a possibility of conducting comparative studies across multiple European sites. We find that the contaminant fingerprint seem more comparable between Eurasian oystercatcher and common tern than guillemot eggs from the Baltic Proper and that the pattern of both species in general compare to the local food web. For the temporal trends on the other hand, the fat soluble contaminants in Eurasian oystercatcher show increasing trends opposite to that of common tern. Such an increase is not observed at other European stations. The contaminant levels also indicate some unexplained deviations from the trophic levels between Eurasian oystercatcher and common tern. Thus, while both Eurasian oystercatcher and common tern seem to represent the local food web to some extent, there are several unexplained patterns that suggest a need to continuously monitor both species