Analysis of catch composition of two shrimp beam trawls in South China Sea

We carried out an investigation during 2012-2015 to analyze the structural characteristics and catch composition of one-beam trawl and two-beam trawl in the fishing grounds of the northern South China Sea. The index of relative importance (IRI) was used to evaluate the catch composition. The ratio of by-catch to shrimp by mass and the percentage of un-matured fish were also calculated. The results indicate that major difference of structural characteristics existed between one-beam trawl and two-beam trawl. The average ratio of by-catch to shrimp by mass was 12.68±14.52 and 1.79±1.02 for one-beam trawl and two-beam trawl, respectively. For both shrimp beam trawls, the dominant target species were Metapenaeus ensis,  M.joyneri, Marsupenaeus japonicus and M.affinis; the dominant by-catch species were Cynoglossus trigrammus, Saurida tumbil,  Sillago japonica, Caranx (Atule) kalla, Siganus oramin, Thrissa dussumieri, Portunus sanguinolentus, P.trituberculatus and P.pelagicus. The percentages of un-matured fish were high for both shrimp beam trawls. Furthermore, the potential impact of shrimp beam trawl on fishery resources is discussed.