Role of learning in mesh penetration behaviour of haddock (Melanogrammus aeglefinus)

If fish that have passed through the meshes of a fishing net are capable of escaping more easily on subsequent encounters, there may be important implications for the efficiency and selectivity of fishing gears in heavily fished populations. Here we report on the effect of learning on mesh penetration of haddock (Melanogrammus aeglefinus) under laboratory conditions. Ten haddock were trained using a classical conditioning procedure (with food) to race between two alternately flashing light emitting diodes (LEDs) positioned at the ends of a 6-m-long oval swimming pool. Once the fish were conditioned to race between the LEDs, their penetration ratios in netting barriers of 200-mm and 100-mm bar length, square-mesh curtains in their path on each food presentation were calculated. Fish were reluctant to penetrate mesh barriers of 200 mm at the beginning of the experiment, but all the experimental animals did manage to penetrate. The ratio of these fish in penetrating the smaller mesh size of 100 mm decreased in the first two presentations, but then increased again with experience. The potential consequences of these findings in relation to gear efficiency and gear selectivity studies are discussed. (C) 2004 International Council for the Exploration of the Sea. Published by Elsevier Ltd. All rights reserved.