Reducing catch efficiency of rabbitfish (Siganus oramin) in a shrimp beam trawl fishery of the South China Sea

The bycatch of unwanted fish species is a main concern in shrimp beam trawl fishery of the South China Sea. This study evaluated the effect of using combined square-mesh and diamond-mesh codends (CSDM codends) on catch efficiency of a shrimp trawl fishery with the catch comparison and catch ratio approach. The trouser trawl method was applied using the commercial 22-mm diamond mesh codend (D22) as the baseline. The target species, greasyback shrimp (Metapenaeus ensis), and main fish bycatch rabbitfish (Siganus oramin) were chosen as the referred species. The results demonstrated that there was no significant change for the target species but a significant reduction on the unwanted fish bycatch when the CSDM codends were used. Compared with the D22 codend, the CSDM codends would reduce the catch efficiency of greasyback shrimp by less than 18% on average, and the reduction was not statistically significant; whereas catch efficiency of rabbitfish would be significantly reduced by more than 45% and the reduction was length-dependent. The results also showed that the catch efficiency of fish bycatch would reduce as the mesh sizes of the diamond-section of the tested codends increased. These promising results demonstrate that the CSDM codends have a potential to be applied to fishery management for mitigating fish bycatch in the shrimp fishery of the studied area.