SKIN INJURY AND MORTALITY OF BALTIC COD ESCAPING FROM TRAWL CODENDS EQUIPPED WITH EXIT WINDOWS

Skin injury and mortality of Baltic cod (Gadus morhua L.) escaping fro m trawl codends equipped with two different types of 95 mm exit window were investigated between May and June 1994 in the southern Baltic Se a (ICES Subdivision 25). Fish escaping through the end of an open code nd extension (i.e. the trawl was towed without the codend) were also s tudied. Escaping fish were collected in a small mesh cage that was rel eased from the codend cover, closed and then slowly towed to the cage site. In total, nine valid hauls were completed, and 261 cod (24 to 50 cm long) were held in cages for a period of 10 to 14 days. Only two e scapees (34 and 36 cm) died during the experiment; both fish died duri ng the first caging day. The degree of skin injury of fish was examine d after cagings. Scale loss was the predominant visible skin injury; t he main area of injury for most specimens was the posterior half of th e body. Other skin injuries included lesions around the flank and snou t, and dark 'net marks' behind the head. Scale loss was observed in 29 of 109 (27 %) cod that had escaped through exit windows codends. The average injured area was 2.5 % of the total skin area. For the open co dend escapees, 48 of 139 (35 %) fish examined exhibited scale loss, an d the average injured area was 2.3 % of the total skin area. No clear relationship existed between the degree of skin injury and fish size. Most of the observed skin injuries were probably caused by mechanical abrasion while fish were inside the trawl.