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During the project the available technology for ROV-based surveys of benthic biotopes has developed. By aid of laser markers and sonar equipment it became possible to measure exact areas of the bottom and to obtain quantitative assessments of the organisms. An acoustical underwater positioning system, in combination with detailed bathymetric information derived from modern acoustic techniques, made it possible to follow and log in detail the movements of the ROV in relation to benthic structures and geographic position. Consequently, positions of the video- recorded organisms and biotopes could also be obtained. A good overview of where to find habitats with specific biological values and characteristic species for the area, has been obtained. Some of these habitats and species are marked on maps in the report.

Different techniques were used to survey and classify both hard-bottom biotopes and sediment epifauna. During the ROV-survey of the Koster-Väderö trough, however, it quickly became obvious that existing classification systems were not detailed or developed enough to be appli- cable to the deeper biotopes of the area. Presumably new classification systems are needed, perhaps with special adaptations for ROV-technology. Even so, the survey studies of the area have generated valuable information, both about the distribution of species and biotopes and about the effects from trawl fishing on sediment epifauna. Realistic estimates of time and expenses needed for survey projects based on ROV-technology have been obtained.The conclusion is that ROV-technology for many types of surveys provide a more effecient method than the traditional ones.

Video and sonar documentation have supplied new information about current threats to the biological diversity of the surveyed area.Combined effects from eutrophication and sediment re-suspension in connection with trawl fishing, causes heavy sedimentation, sometimes suffocating the fauna of the deep hard bottoms. Mechanical damage has also been demonstrated, as trawling occurs immediately adjacent to especially sensitive biotopes, such as coral reefs.

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