Gillnet selectivity in Hake Merluccius merluccius and Red mullet Mullus surmuletus in the Mediterranean Sea.

Investigations on selectivity of Hake and Red mullet gillnets have been carried out in the Gulf of Lions (Western north Mediterranean sea). Species diversity index and size selectivity parameters have been calculated in relation to meshes sizes and 2 different net height. Shannon index inferior to 0.2 and Evenness index inf. to 0.6 demonstrate the high selectivity of these two gears. Catch mode give explanation in the diversity in the catch size for Hake gillnetting. By-catch proportion increase with the mesh size whatever the gillnet type. Estimation of optimal ratio (fish length / stretched mesh length) by SELECT method give a value of 4.8 for Red mullet and 6.5 for Hake whatever the net height. Comparison with other selectivity studies in Mediterranean Sea on same species and suggestions for the reduction of the impact of bottom static nets on the environment are commented in conclusion.