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This study investigates the catch components of a commercially used demersal trawl cod end in Izmir Bay, and reveals some of the morphological characteristics of nine commercial ¢sh species; red mullet (Mullus barbatus), hake (Merluccius merluccius), whiting (Merlangius merlangus euxinus), poor cod (Trisopterus minutus capelanus), tub gurnard (Trigla lucerna), common pandora (Pagellus erythrinus), axillary sea bream (Pagellus acarne), picarel (Spicara smaris) and annular sea bream (Diplodus annularis) in relation to mesh size and shapes. Furthermore selectivity of 40-mm polyethylene netting cod end for red mullet, hake, common pandora, axillary sea bream, picarel and annular sea bream is presented. The results are discussed in a way to understand the probable e¡ects of ¢sh body shape on mesh selectivity.

Weight-length relationships are presented for 60 fish species captured from Izmir Bay, Central Aegean Sea. Samples were collected using bottom trawls (mesh sizes 24 mm at stretched cod-end). The b values W ¼ aL b showed a mean value of 3.027 (SE ¼ ±0.03) and more than 50% of the values ranged between 2.912 and 3.189. One species, Cepola macrophthalma, showed strong negative allometric growth.

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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.