Selectivity of Codend Mesh of Beam Trawl in Laizhou Bay in Autumn

Abstract:

The beam trawl is a common fishing gear in the Bohai Sea area and is associated with significant by-catch rates because of its poor selectivity. To improve the selectivity of codend mesh, the authors conducted selective experiments on the codend mesh of beam trawls in the Laizhou Bay during September 2017. A cover net method was used and five kinds of codends (mesh sizes of 15, 25, 35, 45, and 55 mm) were studied. Results show that beam trawls had a poor selectivity for catch species, capturing most of the benefic species in the operating area. Escape rates of the catch in weight, number, and value increased with codend mesh size. The 50% selectivity body length (L0.5) and selection range of Cynoglossus joyneri, Oratosquilla oratoria, Trachypenaeus curvirostris, and Alpheus japonicas linearly with mesh size. The L0.5 of O. oratoria and T. curvirostris appeared to exhibit a linear relationship with codend mesh size (m). Linear regression equations of L0.5=1.472m+12.63 (R2=0.934) and L0.5=1.394m+ 0.724 (R2=0.920), were derived for the respective species. To protect economically valuable species such as O.oratoria, T. curvirostris, the authors suggest enlarging the minimum mesh size for beam trawls to 45 mm, which would maintain production efficiency and protect juvenile fish resources.