The third pillar of our work is the collection of long-term monitoring data series. These are the basis for our understanding of the functioning of ecosystems, und thus also for the sustainable use of theses ecosystems. Many of our monitoring data series are immediately used for assessing commercially important fish stocks. These assessments are conducted by scientists of Baltic Sea neighbouring countries under coordination of the International Council for the Exploration of the Sea (ICES). The timely collection and delivery of these data is required under international law, and the German Federal gouvernement has tasked us to fulfill this obligation. This requires significant funding and effort. We separate "fishery dependent" data (direct removals by commercial and recreational fisheries) and "fishery independent" data, usually collected from specialised research vessels during standard surveys.