Guidelines for coastal fish monitoring.

Abstract

Coastal fish communities are influenced by a plethora of impacting variables, including human-induced pressures related to overexploitation, climate change, eutrophication, contaminants, habitat degradation, effects of trophic interactions and competition with non-indigeneous species (HELCOM 2018c). Although there is a general understanding on the influence of these pressures, little is known about their relative importance and local patterns. Because of the locality of the fish communities, variability between locations regarding which variables are the most important may also be expected. The aim of the current monitoring strategy is to monitor overall changes in coastal fish communities in relation to local and regional changes in the environment, and to support an indicator-based assessment of the status of coastal fish, reflecting potential effects of pressures such as climate, eutrophication, habitat degredation, trophic interactions and fishing. In relation to the effects of climate change, species of freshwater origin generally respond positively to increased water temperatures and decreased salinity levels, whereas marine species and those sensitive to higher water temperatures tend to respond negatively (Olsson et al. 2012a). The abundance of cyprinids in the coastal zone is considered to be indicative of coastal eutrophication in the Baltic Sea, whereas the abundance of coastal piscivores is considered to also reflect coastal fishing pressure (Bergström et al. 2016ab, Bergström et al. In press, HELCOM 2018c). To that end, in being in the center of the food web, all coastal fish species are impacted by trophic interactions and other changes in the ecosystem structure and function as well.