Seasonal variation in mortality of red mullet (<em>Mullus barbatus</em>) escaping from codends of three different sizes in the Aegean Sea

Abstract

Summary:This study was performed off the southern coast of Yassıca Island in the İzmir Bay on the Turkish coast of the Aegean Sea to investigate the mortality of red mullet (Mullus barbatus, Mullidae) escaping through 40-mm square-mesh and 44-and 50-mm diamond-mesh codends attached to a conventional demersal trawl net. In total, 48 replicate experimental hauls were performed in the summer and winter of 2011 and 2012. Mean escape mortality for all hauls in winter (33.2%±6.51) was significantly higher (p<0.0001) than that in summer (26.5%±6.19). Furthermore, mortality was also highest among the smallest fish, particularly during winter. Irrespective of season, the escape mortality of red mullet was lowest from the 40-mm square-mesh codend (mean, 25.5%±4.58). These observations emphasize the importance of investigating the survival potential of escaping fish when considering the benefits of different selective devices in the management of a fishery.Keywords: escape mortality, bottom trawl, size-related mortality, seasonal variation, mesh size, mesh shape, Aegean Sea.Variación estacional en la mortalidad post pesca del salmonete (Mullus barbatus), capturado con arrastre de fondo en el mar Egeo Resumen: El estudio se llevó a cabo frente a la costa sur de la isla de Yassica en la Bahía de Izmir, costa turca del mar Egeo para investigar la mortalidad post captura del salmonete (Mullus barbatus, Mullidae) que escapa de las redes de pesca con copos de malla cuadrada de 40 mm, y romboidales de 44 y 50 mm acoplados a una red tradicional de arrastre demersal. En total, se realizaron 48 lances experimentales durante el verano e invierno de 2011 y 2012. La media de la mortalidad post captura para todos los lances en invierno (33.2%±6.51) fue significativamente mayor (p<0.0001) que en verano (26.5%±6.19). Además, la mortalidad fue más alta entre los individuos más pequeños, especialmente en invierno. Independientemente de la estación, la mortalidad post captura del salmonete fue inferior con el copo de luz de malla cuadrada de 40 mm (media, 25.5%±4.58). Estas observaciones ponen de manifiesto la importancia de la investigación de la supervivencia potencial de los peces que escapan de las redes de pesca a la hora de considerar los beneficios de distintos dispositivos selectivos en la gestión de una pesquería.Palabras clave: mortalidad post captura, arrastre de fondo, mortalidad dependiente de la talla, variación estacional, luz de malla, forma de la malla, mar Egeo.Citation/Como citar este artículo: Düzbastilar F.O., Breen M., Aydin C., Özbilgin H., Özgül A., Ulaş A., Metin G., Gül B., Lök A. 2017. Seasonal variation in mortality of red mullet (Mullus barbatus) escaping from codends of three different sizes in the Aegean Sea. Sci. Mar. 81(3): 339-349. doi: http://dx

Mortality of Common pandora (Pagellus erythrinus Linnaeus, 1758) escaping from demersal trawl codends: Water temperature effect

“…Conversely, the results of condition factor did not affect the mortality rate between winter and summer. Likewise, Düzbastılar et al (2017) determined that in terms of K factor, there was no significant difference between dead fish and survivors (p>0.01) of the escapees of red mullet for all the hauls in summer and winter seasons. In experiments, average total lengths of fish passed through the codend meshes were 9.9 cm (min, 5.6 cm and max, 13.9 cm) and 10.3 cm (min, 5.6 cm and max, 14.9), in winter and summer respectively.…”

“…The escape mortality depends on many factors such as fish species and size, mesh size and shape, catch size and composition, water temperature, fishing gear properties (Sangster et al, 1996;Suuronen, 2005;Broadhurst et al, 2006;Ingólfsson et al, 2007;Düzbastılar et al, 2017). We focused on the effects of mesh size and shape by considering water temperature and condition factor, which are accounted to be seasonal effects, on the escape mortality for common pandora.…”

“…Higher mortalities (up to 75%) were determined when the observation cages were held at higher temperatures because of the cover-cage method as described by Lehtonen et al (1998). Düzbastılar et al (2017) found that mean escape mortality of mullet for all trawl hauls in winter (33.2%±6.51) was higher than that in summer (26.5%±6.19). Likewise, Düzbastılar (2014) reported higher mortality rates (between 61.3-95.3%) for red bandfish at higher seawater temperatures (<13ºC and compared to >24.9ºC).…”

“…), and having extremely complicated and problematic structure (Metin et al, 2004;Suuronen, 2005;Düzbastılar et al, 2010a, c). A small number of fish species escaping from trawl codends was investigated (Metin et al, 2004;Düzbastılar et al 2010a, b, c;Düzbastılar, 2014;Düzbastılar et al, 2016Düzbastılar et al, , 2017 while more than 50 species were captured by trawlers in Turkish waters (Tosunoğlu et al, 2003).…”

“…One of the major factors causing mortality of trawl-caught fish is water temperature influencing physiological activities and fish behaviours (Özbilgin and Wardle, 2002). However, a few investigations about the water temperature effect on the escape mortality were conducted and most of these so far have not reflected the commercial trawl fishery (Suuronen et al, 2005;Düzbastılar et al, 2010a;Düzbastılar, 2014;Düzbastılar et al, 2017). Nevertheless, the effect of seawater temperature, which is a key factor affecting fish condition, swimming performance (Özbilgin and Wardle, 2002), spawning stage (Özbilgin et al, 2007), healing of gear-induced wounds (Suuronen, 2005;Suuronen et al, 2005;Düzbastılar et al, 2015) etc., must be studied in order to understand its function in the escape mortality In this study, the escape mortality of common pandora, which is targeted species by commercial trawls in the Aegean Sea and the effect of water temperature on the mortality of fish escaping from trawl codends was reported.…”