Distribution of artisanal fishing gears with impacts on sedimentation and benthic macroinvertebrate assemblages in Songkhla Lake, the largest lagoon in Thailand.

The present study investigated the distribution and diversity of stationary fishing gears in Songkhla Lake and assessed the effects of the most abundant gear in the lake, the standing trap, on sedimentation and the abundance of benthic macroinvertebrates. Our survey revealed that six types of fishing gear were used: standing traps, fyke nets, fish aggregating devices, seabass net cages, small traps and stationary lift nets. The type of fishing gear used depended on the depth of water. The density of installed standing traps reached a maximum of 357 traps/km, which was the highest density of any fishing gear installed on the lake. They were mainly set in the middle part of the lake, where the water was less than 2 m deep. Sedimentation was examined inside and outside the areas influenced by standing traps. Sediment samples were collected with sediment traps in the northeast and southwest monsoon seasons. Sedimentation rates inside and outside the areas influenced by standing traps differed at some sites but the pattern was not consistent across seasons. Sedimentation rates were higher in the northeast monsoon season with the average rate 1132.32 ± 43.73 (mean ± SE) g mday when precipitation and run-off were higher and 323.98 ± 10.68 g mday in the southwest monsoon or dry season. Moreover, the proportion of finer clay particles was greater in the sediment from the areas influenced by traps. Benthic macroinvertebrate communities between the two areas were different. A bivalve, Potamocorbula sp., which dominated benthic macroinvertebrate assemblages, had a higher abundance in areas influenced by traps. The effects of stationary fishing gears on sedimentation and benthic macroinvertebrates highlighted in this study suggest that the long-term deployment of these gears may affect food chain dynamics in this lagoon system. Ultimately, a proper regulation of the use of these gears may be needed.