Preliminary study on minimum mesh size of gillnet for Scomberomorus commersoni in the South China Sea

To maintain sustainable development of gillnet fishery for Scomberomorus commersoni and to protect fisheries resources, we conducted the fishery survey and selectivity experiments in 2012 and 2015. The index of relative importance (IRI) was used to evaluate the fished species of the gillnet fisheries. Based on the SELECT (share each length catch total) method, both Normal and Bi-normal models were used to calculate the selectivity of gillnets for S.commersoni. Finally, with consideration of the minimum landing size of S.commersoni, we determined the minimum mesh size of the gillnet for S.commersoni. The results reveal that S.commersoni is the most important catch species for the fishery. Its IRI was 9 472.00 and 14 363.02 in 2012 and 2015, respectively. A total of 295 specimen of S.commersoni were caught. In 2012, the modal fork length groups of S.commersoni were 751 ~800 mm (accounted for 32.52%). In 2015, the first and second modal fork length groups of S.commersoni were 501 ~550 mm and 701 ~750 mm, respectively. The modal relative length of Normal model was 6.961. The first and second modal relative length of Bi-normal model was 4.440 and 6.728, respectively. The result of model deviance indicates that Bi-normal model is the best-fit model. Suppose that the minimum landing size of S.commersoni was 380 mm, the minimum mesh size of the gillnet for S.commersoni would be 120 mm.