Effects of mesh size, fishing depth and season on the catch and discards of short mackerel Rastrelliger brachysoma gillnet fishery at the mouth of Pattani Bay, Thailand

Abstract

This study evaluates the impacts of mesh size of the net, fshing depth and season on the catches of target, non-target and discarded species for short mackerel Rastrelliger brachysoma gillnet fshery in the vicinity of Pattani Bay, Gulf of Thailand. The catches were examined for species composition, catch efciency and size of catch. Samples were obtained monthly from February 2019 to February 2020 at three fshing depths (2.0, 4.0 and 6.0 m) using gillnets with three diferent mesh sizes (3.0, 4.0 and 4.5 cm). Including the target species, 112 species were collected, the majority of which were non-targeted fshes and crustaceans. The target species, Rastrelliger brachysoma, contributed only 6.0% by number and 8.76% by weight to the total catches. The 111 non-target species were classifed into fve categories based on potential sale prices. A total of 18 species, equivalent to 3.04% by weight of the total catches, were considered to be of negligible value and discarded or sold for the production of fsh meal. Temporal variability was observed for number of individuals and biomass of total catches; the compositions of the catches clustered to two distinct seasons from December to March and from April to November, respectively. Spatial variability in this study focused on the depth profle which was found to signifcantly infuence species richness and sizes of some fsh species. For 12 species, mesh sizes of the gillnets signifcantly afected the number of individuals caught, as well as their weight and sizes. The novel fndings of this study provide essential information that can be used for the sustainable management of the Rastrelliger brachysoma fshery in the Gulf of Thailand.