Acta Ichthyologica et Piscatoria 45(1): 75-83, doi: 10.3750/AIP2015.45.1.08
Determining the severity of skin injuries of red mullet, Mullus barbatus (Actinopterygii: Perciformes: Mullidae), inflicted during escape from trawl codend
expand article infoF.O. Düzbastılar, T. Laleli, A. Özgül, G. Metin
Open Access
Background. The authors suggest that skin injury, particularly scale loss, during the capture may be one reason of the escape mortality. However, skin and fin damages are not responsible for all of the observed mortalities occurring during the fish passage through the mesh of the trawl codend. Nevertheless, physical damages may expose escapees to secondary infections from bacteria and fungi. This study investigated the types and occurrence of deformation for red mullet escapees to better understand the cause of their death. Improving the survival rate by using alternative gear modifications require detailed information on assessments of escape mortality including trawl gear-induced injuries. Therefore we aimed to determine the damages of body parts among the escaped red mullet from trawl codends. Materials and methods. Injuries and mortalities sustained by red mullet, Mullus barbatus Linnaeus, 1758, escaping from three different trawl codends were investigated in the Aegean Sea within 10–18 February 2012. The fish were held captive in fish cages and their behaviour was observed by divers three times per day for a period of 9 days. During the observation, dead fish were removed and immediately transferred to the laboratory for measurement and post-mortem examination. Results. The rates of escape mortality of red mullet penetrating through 40 mm square mesh codend, 44 mm diamond mesh codend, and 50 mm diamond mesh codend were 26.3%, 46.3%, and 27.4%, respectively. In total, 323 red mullet died after escaping from codends. Two of these could not be examined because of post-mortem decomposition and 21 others were defined as undamaged. Scale loss was the most common injury (300 fish, 93.5%) in red mullet individuals that died due to post escape mortality. The second most common injury was tissue loss (34.6%) followed by skin loss (19.9%). The majority of scale damage cases was around the abdomen and on either side of the caudal peduncle. In general, the frequency of the scale loss increased towards the tail. The frequency of different fin injuries of escaped fish were: 58.6% (torn), 44.5% (broken), and 6.2% (loss), respectively. Conclusion. Red mullet escape mortality was highly correlated to fish length (P < 0.001), however, we identified no clear relation between fish size and scale loss.
fish, damage, scale loss, escape mortality, Aegean Sea, codend