Three decades of Swedish experience demonstrates the need for integrated long-term monitoring of fish in marine coastal areas

The first attempts to monitor coastal fish in Sweden were made in the 1960s and 1970s. Ecological, physiological, biochemical and environmental chemistry data were collected in separate projects. When the National Marine Monitoring Programme was revised in 1992, a new strategy was introduced for assessments of long-term trends in coastal fish communities. Annual integrated monitoring of contaminants, biomarkers and population and community indicators of ecosystem health was started in selected areas using common sentinel species. Data from one monitoring area at the coast of the Baltic proper are analyzed in this paper. The results have shown a shift in fish community structure indicating changes in ecosystem productivity. Trends have been detected in growth rate (positive) and relative gonad size (negative) in perch (Perca fluviatilis), suggesting a metabolic disturbance according to the predictive response model developed for interpretations. One factor which may have contributed to the reduced GSI was a decrease in mean age of sampled fish during the period of study. Chemical exposure was indicated by a 3-fold increase of EROD activity during the monitored 15-year period. However, concentrations of most measured contaminants in perch have decreased during the same period. The experience of the integrated approach has shown that a tentative analysis of cause and environmental significance could be made, improving the assessment, but there still remain unsolved questions to be answered in follow-up studies. The analysis has also shown the importance of long-term monitoring at several levels of biological organization to distinguish between natural variation and low-level effects on ecosystems.