Selectivity of diamond, square and hexagonal mesh codends for Atlantic horse mackerelTrachurus trachurus, European hakeMerluccius merluccius, and greater forkbeardPhycis blennoidesin the eastern Mediterranean

Abstract

Knowledge on selectivity is considered essential for an adequate management of the trawl fishery. This paper compares the selectivity of conventionally used codends of 44 mm diamond mesh, 40 mm square, and hexagonal mesh for Atlantic horse mackerel, European hake and greater forkbeard in the eastern Mediterranean. Data were collected using the covered codend method and analyzed using the logistic equation with the maximum likelihood method. Mean selection curves were analyzed and compared using the betweenhaul variations model. The mean L 50 values of diamond, square and hexagonal mesh codends are 14.7, 15.9 and 17.1 cm total length (TL) for horse mackerel, 10.4, 14.4 and 11.0 cm TL for hake and 12.2, 15.8 and 12.7 cm TL for greater forkbeard, respectively. For horse mackerel, the differences among the codends are statistically significant (P < 0.05); however, the L 50 values for all three meshes are higher than the minimum landing size (13 cm TL). For hake and greater forkbeard, the L 50 value for the square mesh codend is significantly different from the values for diamond and hexagonal meshes (P < 0.01), whereas there is no significant difference between diamond and hexagonal meshes (P > 0.05). Regardless of the mesh shape, L 50 values were substantially lower than the minimum landing size or size at first maturity for hake and greater forkbeard. To enable more effective solutions, research on species-selective trawls is required for the Mediterranean demersal trawl fishery.

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“…Compared to the other studies, L50 value of 40 mm square mesh codend (15.3 cm) is very close to Aydın and Tosunoğlu (2010) value (15.9 cm). However, present study gave higher L50 value with D44 codend than Aydın and Tosunoğlu (2010). This situation may be caused by using narrower codend in our study (300 meshes) according to other studies (400 meshes).…”

“…Studies have proved that the conventional diamond mesh codend selectivity is rather poor for many commercially important species in the Mediterranean (Özbilgin and Tosunoğlu, 2003;Tokac et al, 2004Tokac et al, , 2010Özbilgin et al, 2005, 2012, 2015Guijarro and Massuti 2006;Ordines et al, 2006;Bahamon et al, 2006;Luchetti, 2008;Sala et al, 2008;Aydın and Tosunoğlu, 2010;Sala and Luchetti, 2010;Aydın et al, 2011). Thus, researchers have suggested for improving selectivity using larger mesh size in the codend for reducing discards of the Mediterranean demersal trawl fleet (GFCM, 2007).…”

Effect of shortening the length of codend on brushtooth lizardfish caught in square mesh codend of otter trawl in Eastern Mediterranean

“…Thus, selectivity of fishing gears needs to be improved in order to assure sustainable fishery. Recently, several studies have focused on improving selectivity of this fishing method used for exploiting deep sea fish (Aydin and Tosunoglu, 2010;Aydin et al, 2011;Ozbilgin et al, 2011;Aydin et al, 2014;O'Neill et al, 2016). European Union based legal arrangements, suggest the use of square mesh trawl fishing nets with minimum mesh size of 40 mm and rhombic mesh nets with minimum mesh size of 50 mm in the Mediterranean (E. C. Council Regulation, 2006).…”

Selectivity of 40 mm square- and 90º turned-mesh codend for the deepwater rose shrimp, Parapenaeus longirostris (Crustacea), and greater forkbeard, Phycis blennoides (Actinopterygii: Gadiformes: Phycidae), in the eastern Mediterranean

“…On the other hand, Ragonese and Bianchini (2006) suggested that the range of 50.2-70.3 mm is a "biologically-sound mesh size" referring to the size at 50% maturity ranges of 20-22 mm for rose shrimp for Italian waters. Guijarro and Massutí (2006) (Aydın et al 2010); and 16.9 cm (42.9 mm) (Ozbilgin et al 2012). On the other hand, a T90 L 50 value determined in the course of the presently reported study (12.2 cm) is comparable to the previously reported value of 12.5 cm (Tokac et al 2010, Ozbilgin et al 2012, determined for diamond-mesh codend of 42.4 and 42.2 mm, respectively.…”

“…In this study, 40S had 165 square meshes in circumference, 90º turned meshes (40T90) had 330 meshes in circumference. There were several selectivity studies conducted on 40 mm and 44 mm PE diamond-mesh codend in the Mediterranean (Petrakis 1997, Lucchetti 2008, Sala et al 2008, Aydın and Tosunoglu 2010. The selectivity of 40 mm diamond-mesh codend has been reported to be rather poor because a large proportion of the codend catch is immature and smaller than the minimum landing size or fi rst maturity size.…”