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OBSERVATORY TECHNOLOGY IN FISH RESOURCES MONITORING

Marine resources are often monitored by means of standardized survey giving a snapshot picture of the state of the stocks. Comparisons of temporal variation in such snapshot pictures are used to evaluate present state and predict future development. To secure comparability and avoid variability such surveys are strictly standardized and keep away from periods and areas of high dynamics. However, the interesting processes and the most informative areas and periods to study is exactly the dynamic ones where the function and performance of the ecosystem is most apparent. We call such areas for “Ocean hubs” and we will in this paper describe an acoustic system using the observatory approach to monitor and extract detailed biological information as well as physicalbiological couplings of important to ecosystem function. The system is mounted in a Norwegian fjord opening and designed to monitor flux of herring to and fro the overwintering area. Two 38 kHz scientific echo sounder are mounted on the sea floor looking vertically to the surface and quantify fish density. An 18 kHz sonar insonifies a cross section of the fjord opening including the volume covered by the sounders and is used to evaluate how representative the sounder volume is. An upward looking Acoustic Doppler Current Profiler observes the same layers of herring as the echo sunders and is used to measure the relative speed of the fish compared to water. The system is cabled to land and data can be observed from the office settings adjusted according to needs. Some of the information is posted on the Internet. The results are promising showing that new knowledge and understanding about fish behaviour, migration speed, diurnal dynamics etc. can be obtained though observatory techniques.