The Baltic Sea is the world’s largest coherent brackish sea area. Its salinity is much lower compared to ‘true’ marine seas like the North Sea. Although these are unfavourable conditions for marine fish species, over thousands of years their populations have adapted to the specific hydrographic conditions in the different basins of the Baltic Sea. Marine fish species like cod, herring and sprat form the basis of productive fisheries. Flatfish like plaice, flounder, dab and turbot are commercially fished, too.
Changes in salinity, for example caused by irregular inflow events of North Sea water, have a direct influence on the offspring of important fish stocks. However, we need to know their recruitment situation to be able to make catch predictions that are of use. Therefore, we are investigating the live history of all commercially important fish species, as well as their interactions with fisheries and the environment. In addition, we continuously develop our fish stock assessment models further.
For example, to better forecast the future development of herring stocks, and to calculate the strength of a specific year class, we record the number of herring larvae in the Greifswalder Bodden near Rügen once per week over the entire spawning season.
Investigations like this help us to give scientifically sound advice to fishing managers and politicians for the yearly adaption of catch quotas.