Size selectivity and catch efficiency of diamond-mesh codends in demersal trawl fishery for conger pike (Muraenesox cinereus) of the South China Sea

Size selectivity and catch efficiency of six diamond-mesh codends with different mesh sizes, 25–54 mm (termed as D25-D54), for conger pike (Muraenesox cinereus) were tested and compared using the covered codend method in the South China Sea (SCS). In order to address the present minimum mesh size (MMS) regulations of the trawl fishery for conger pike in the SCS, we quantified the selective properties of two legal codends, D25 and D40, which followed the MMS regulations in the studied area, and used them as baseline to compare with other codends. Our results demonstrated that the catch efficiency decreased with the increment of mesh sizes in codends. The D25 codend was insufficient to protect juvenile conger pike. For this legal codend, 54.31% of conger pike below the Market Reference Size (MRS, 22.4 cm) was retained, and more than 93% of conger pike retained would have to be discarded. Applying the other legal codend, D40, the problem of capturing juvenile fish was significantly mitigated. In this codend, only 9.61% of conger pike below the MRS was retained. However, the loss of commercial-sized fish was considerable, as about 50% fish above the MRS would escape from it. Our study will be beneficial to the enforcement and reform of the MMS regulations in China's fisheries management