Long-term changes in fish abundance and environmental indices in the Black Sea

Hydroclimatic, biological and anthropogenic data-series (1915-1993) were analysed to determine and compare main trends and fish stock-environment relationships in the Black Sea. Long-term patterns were studied on different temporal scales: interdecadal, decadal and interannual variation. The results showed evidence of coherent patterns across different indices. Temperature, atmospheric pressure, wind and river run-off series were significantly correlated with most of the biological, anthropogenic and fish stock indices. Anthropogenic factors such as eutrophication and hypoxia were responsible for degradation of the coastal ecosystems, but they can also have negative impacts on open-sea populations. The correlations established allow formulation of hypotheses on the causal links between the abiotic environment, productive processes and population dynamics. The physical environment was recognised as being the main factor driving the biological productivity and essentially influencing all processes in the sea. Other factors responsible for a great part of the observed variability in marine data were biological interactions and anthropogenic impact. The rise in overall productivity after 1970 might be explained by several factors acting simultaneously: a favourable climatic regime, increased eutrophication, and the effect of trophic cascades attributable to overfishing of predators. The indices and relationships studied can be useful for integrating environmental information in fisheries and ecosystem management.