Gillnet selectivity for swimming crab Portunus trituberculatus in the East China Sea

To explore the gillnet selectivity for swimming crab Portunus trituberculatus, six mesh sizes (100, 110, 120, 130, 140 and 150 mm) were tested to determine the optimal mesh size for swimming crab. The experiments were conducted in the traditional area for fishing crab in the East China Sea from 25 to 29 July 2018. Four kinds of selectivity curves were used for fitting, and the maximum likelihood method was used to estimate the model parameters. In this experiment, 436 swimming crabs were caught with six different mesh sizes. The carapace length range was 46.2–83.7 mm, and all crabs were caught by entanglement (i.e. body or limb). When the mesh size was larger than 100 mm, the proportion of juvenile crab (carapace length < 60 mm) was less than 20% of the total catch. A linear relationship was observed between the carapace width and height and the carapace length of the crab. Gillnet selectivity for swimming crab was well described by the normal model based on the smallest Akaike information criterion value. The optimal lengths calculated by the normal model were 49.8, 54.8, 59.8, 64.8, 69.8 and 74.8 mm for the six mesh sizes, respectively.