Avoidance reactions of herring to a survey vessel, studied by scanning sonar
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The behavioural response of a shallow herring layer to a steaming vessel has been studied by the use of a high-resolution scanning sonar technique. When the vessel was completely darkened, no significant reaction important for biomass estimation was observed, either at three or at nine knots speed. With usual deck lights, however, the reaction was severe, and the integrator system strongly underestimated the true herring density.