Some aspects of trawl induced unaccounted mortality

Modern fishing practices call for the use of size selective gears to ensure the survival of juveniles until they reach an appropriate size for harvest. This implicitly assumes the survival of escapees. Previous survival studies have focused on the escapem ent through codends meshes. However, recent observations have identified several other areas as potentially important sources of unaccounted mortality in trawl fisheries. In regions with concentrated fishing activity, fish may be subjected to repeated her ding and escape through the trawl. This may have a cumulative effect on levels of stress and physical injury, It is proposed to use PIT tags to assess the degree of repeated encounter and to conduct a small-scale survival experiment to quantify its effect . Video evidence has shown that a considerable number of fish escape under the trawl; may of these are subsequently hit by the ground-gear. This project will quantify the escape ratio and assess injury frequency and resulting mortalit The generation of sa nd clouds in areas of high trawling activity results in suspended material remaining in suspension. The effect on the physiology of escaped fish is unknown. It is proposed to assess the physical characteristics of sand clouds and their impact on stress, r espiration levels and subsequent survival of fish.