Trammel net size selectivity and determination of a minimum legal size (MLS) for the haffara seabream, Rhabdosargus haffara in the Gulf of Suez

The size selectivity of trammel nets used in the Suez Bay in small-scale fishing operations was calculated for the haffara seabream Rhabdosargus haffara using length-frequency distributions of the catch from three different mesh sizes (34, 37 and 40 mm) of the inner layer of the trammel net. Three experimental fishing trials were conducted in the Suez Bay during October 2018, and January and September 2019. The SELECT method has been used to estimate selectivity parameters using five major models (log-normal model, normal location model, normal scale model, gamma model, and bi-normal model). The bi-normal was assessed as the most appropriate model for the haffara seabream. Modal sizes were estimated as 11.8, 12.1, 16.1 cm for 34, 37 and 40 mm mesh sizes, respectively. The calculated lengths at first maturity (L_m) were 13.67 cm for males and 14.15 cm for females. Our findings revealed that the fish lengths caught by the inner layer 34 and 37 mm mesh sizes were less than the length at first maturity, while, those caught with 40 mm were more than the length at first maturity. The minimum legal size (MLS) for R. haffara was fixed at 14.15 cm. Finally, the results revealed that increasing the mesh size of the trammel nets, especially the inner layer mesh, can lead to significant improvements in size selectivity and allow the protection of this valuable fish resource.