Underwater Long-Term Observation at the Largest German Artificial Reef in the Baltic Sea

The Baltic Sea is one of the most frequented regions in the world. The Baltic neighbouring states more and more see the need to adapt their economic interests to the given ecological conditions. This can not always be done sufficiently, which can be seen at the example of coastal fishery in some of these countries. Owing to the critical condition of economically important fish stocks, selective fishing and fish-stock saving measures have become main fields of research. Supported by the European Union and by the federal state government we have tried in Mecklenburg-Vorpommern during the last four years to investigate the effects of an artificial Baltic reef with respect to fishing. For this purpose more than 1300 reef elements — made of a special sort of concrete and having different shapes and size — have been arranged on an area of 200 × 200 m at a water depth of 12 m about 1.5 m away from the coast. Over a period of almost four years different methods and techniques have been applied to observe and record the effects of these structures on the natural environment in a long-term investigation. Continuous video-optical underwater observation using up to nine simultaneously controlled underwater cameras proved to be a special technical challenge. Important results have been gained from a monitoring with research divers and from a defined test and comparison fishing done once every month. Various fishing methods have been applied — also those which are normally not common in that region. A special low-cost variant of a remote controlled underwater stereo photo camera has been developed and built in order to get biometric data of the fish without catching it.