Fisheries Bycatch in a Tropical Mangrove Forest, with a Focus on Gobies: a Case Study in Xuan Thuy National Park, Vietnam

The goby fish is dominant in tropical mangrove estuaries like Xuan Thuy National Park in Vietnam, where fishing is allowed in the core area, but the lack of regulations targeting specific species and landing sizes contributes to bycatch issues. To address this, we conducted a one-year survey to investigate non-target and undersized fish bycatch. Based on collections using a series trap nets from March 2018 to February 2019, it revealed a relatively diverse goby community consisting of 28 species, with the most abundant being Glossogobius olivaceus and Bostrychus sinensis in the study site. Among the captured species, 16 (57.14%) had no economic value and were bycatch. Additionally, between 5.46% and 92.31% of individuals from each species had a standard length below the optimum length, including the three primary target species, B. sinensis, G. olivaceus, and G. giuris, with 88.81%, 90.95%, and 92.31% of individuals being smaller than the optimum length. The goby community in the study area faces severe bycatch issues concerning both non-target species and undesired size. As the body depth – standard length relation model estimated the optimum body depth of target species to be larger than 15 mm when the optimum length is used, we propose using fishing gear with a mesh size of 15 mm for sustainable fishing.