Status of coastal fish communities in the Baltic Sea during 2011-2016 - the third thematic assessment

Abstract

Coastal fish, the fish assemblages in relatively near-shore and shallow (< 20 m depth) coastal areas, in the Baltic Sea harbour a mixture of species with marine and freshwater origins. Typical species are perch, pikeperch, pike, roach and breams, which are of freshwater origin and confined to coastal areas, as well as marine species like flounder, cod and herring, which often have seasonal migrations between nearshore and outer sea areas. Coastal fish populations and communities provide important ecosystem services, contributing to ecosystem functioning and high socio-economic and cultural values. They represent key elements for assessing environmental status in relation to environmental objectives within the Baltic Sea Action Plan (BSAP) and the Marine Strategy Framework Directive (MSFD). The main aim of this report is to provide a comprehensive assessment of the status of coastal fish in the Baltic Sea during 2011-2016, in support of the second holistic assessment of HELCOM (HOLAS II). The results are included in summary in the State of the Baltic Sea report. The report contains the latest status assessment of coastal fish in the Baltic Sea using two Baltic-wide CORE indicators and an agreed assessment approach (Chapter 3). The report also includes a review of major pressures acting on coastal fish communities (Chapter 2), and of potential measures to restore and support coastal fish communities in the Baltic Sea (Chapter 4). The report ends with future recommendations for continued work on coastal fish monitoring and assessment in the Baltic Sea in relation to the BSAP and MSFD (Chapter 5). The status assessments presented in this report includes data from Finland, Estonia, Latvia, Lithuania, Poland, Denmark and Sweden. Experts from Russia and Germany have also participated in the HELCOM work on coastal fish during recent years, but data from these countries are not included in the current assessment. Status is assessed based on the two HECLOM core indicators ‘Abundance of key species’ and ‘Abundance of key functional groups’, of which the latter is composed of a component assessing the abundance of piscivores and one on the abundance of Cyprinids/mesopredators. The results show that the status of the coastal fish communities varies between areas, regions and indicators, but the general status based on the two core indicators appears weak. Only approximately half of the assessed areas and assessment units are classified as being in good status. The more northern areas, where perch is used as the key species, are more often assessed to be in good status than more southern areas, where flounder is recognised as the key species. For the two functional group indicators, the status of piscivores follows a similar pattern of the key species indicator, with relatively better status in more northern areas. The other important functional group, cyprinids, shows insufficient status also in more north-eastern areas of the Baltic Sea as a result of too high abundances. The current monitoring network for coastal fish is rather extensive, but does still only support an assessment in half or less than half of the 42 listed assessment units for coastal fish in the Baltic Sea. The confidence of the assessment is moderate to low, depending on area and indicator, mainly as a result of short time-series, poor spatial representation, and data quality issues. The review of pressures acting on coastal fish communities show that a multitude of natural and human-induced pressures potentially affect coastal fish communities simultaneously. These include for example fishing, habitat exploitation, climate change, eutrophication and natural interactions within the coastal food-web. Whereas a few pressures are strong and often explain a large proportion of the variation in fish abundance and distribution, the effects of others can only be observed locally or under certain conditions and vary across areas and among communities. The potential for generalizations across areas is hence limited, and evaluations of which pressure is of key importance should be undertaken for each individual case separately considering the ambient local conditions in each area together with the range of potential human induced pressures. As a result, measures to restore and protect coastal fish communities should also be developed with a local perspective, and different measures might be relevant in different geographic areas. In general, however, scientific evidence on the effectiveness of different measures is poor, as only few thorough evaluations of implemented measures have been undertaken in the Baltic Sea. The few measures that have been scientifically evaluated with proven effects includes actions aimed at reducing the mortality of fish (e.g. no take areas). There is also partial supportfor temporary fishing closures and gear and catch restrictions. Among measures that aim at improving the production of fish, habitat protection and restoration have proven to be effective. For many other potential measures there is a general lack of scientific support, including biomanipulation, nutrient and substance abatement, as well as stocking of hatchery-reared fish. The assessment results and reviews presented in this report show that coastal fish assessments and monitoring in the Baltic Sea have taken noteworthy steps forward since the last thematic assessment. For example, Baltic-wide CORE indicators on coastal fish have been agreed on, as well as a regionally agreed concept for assessing the status of coastal fish communities. Knowledge has improved on the key pressures impacting on coastal fish communities, and on measures that are potentially most effective for supporting and restoring coastal fish communities. In spite of this, there are still several knowledge gaps and development needs, which should be considered in the future. There is a need to safeguard existing monitoring programs and to initiate new monitoring programs for coastal fish in geographic areas that are currently poorly covered or not possible to assess at all. There is also a need to continue harmonizing assessment approaches to enable comparisons across monitoring programs and data sources, and to further develop common indicators and assessment methods. This concerns the further evaluation and development of current indicators, as well as the development of new generic indicators, focusing on aspects of size-structure in the assessed fish communities. Finally, it is clear that initiatives to strengthen the evaluation measures must be undertaken. It is recommended that the results presented in this report should be used as the basis for following up on the objectives of the BSAP and MSFD, as well as for the development of national management plans and coastal fish assessments in the Baltic Sea.