Estimates of towing time in surveys
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To decide the start and stop time for a survey haul the current method used in Norwegian sampling are the data from the door sensors and height sensors of the trawl. When the trawl has achieved its right geometry, the start time for the haul is recorded. A multisampling device was used for separating catches in a survey for three different time periods: the time before the trawl had the right geometry, when sampling, and after the haul was defined to be at the end, when the haulback started. Significant differences were found in mean length of saithe between the periods of sampling, but for cod, capelin, haddock and Norwegian pout no significant change in mean length was found. A bottom contact sensor showed that the trawl had bottom contact several minutes both before and after the sampling period was defined. A change in sampling strategy and use of bottom contact sensors and MultiSampler may reduce variance in survey towing time.
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