Monitoring of the impact of Muuga Port activities on fish communitiesand fishery in Muuga Bay in 1994-2004: difficulties in results definition and needs for method improvement

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The changes in size/species structure of the fish communities as well in catch dynamics in the Muuga Bay have been monitored using experimental gill nets settled along the western coast of Bay within the area of potential impact of the Port of Muuga – the one of the largest and multifunctional port in the Baltic Sea, in 1994-2004. Possible rate of impact, potentially caused by different activities of the Port, such as dredging, navigation intensity and pollution, were studied in conjunction to the natural changes in the ecosystem of Muuga Bay. Also the fish communities and catch dynamics in neighbouring bays as controls were studied. It has been found that the clearly defined effects of Port activities on fish communities are very heavy to be estimated because of large number of natural ecosystems factors affecting, and also due the influence of fishery. Furthermore, the additional uncertainties were obtained due to peculiarities of used monitoring gears. Especially the necessity of accounting the size/species selectivity of monitoring gears should be pinpointed.