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

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 between-haul variations model. The mean L50values 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 L50 values for all three meshes are higher than the minimum landing size (13 cm TL). For hake and greater forkbeard, the L50 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, L50 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.