Long term changes in the status of coastal fish in the Baltic Sea

Management for sustainable coastal ecosystems is benefited by coherent large scale status assessments to support the identification of measures, but these efforts may be challenged by both data availability and natural biogeographical variation. Coastal fish are a resource for commercial and recreational fisheries as well as significant contributors to coastal ecosystem functioning, by linking lower and higher levels of the food web. This study addresses long term changes in coastal fish communities at Baltic Sea regional scale, in order to identify overall trends and support the operationalization of large scale status assessments of marine biota. The study was focused on two indicators representing the functional groups of Piscivores, which are attributed to changes in food web processes including predation/fisheries, and Cyprinids, which are associated with eutrophication. The indicators were assessed for trends within ten-year intervals, using data combined from national monitoring programs during 1991-2013. The results showed predominantly declining trends in Piscivores and of increases in Cyprinids during the studied three decades, both indicative of a deteriorating status. The pattern was however reversed in the most recent years. Similar results among adjacent areas were identified in some cases, but overall differences at local scale were high, indicating strong influence of local processes. The results suggest that coordinated local measures in order to abate cumulative effects are a preferred way of improving the overall status of coastal fish. The latest studied time intervals were the overall most stable and could be considered as potential baseline years for upcoming regional assessments.