Individual assignment and mixed-stock analysis of short mackerel (Rastrelliger brachysoma) in the Inner and Eastern Gulf of Thailand: Contrast migratory behavior among the fishery stocks

Abstract Short mackerel (Rastrelliger brachysoma) is a pelagic-neritic and the most economically important fish in Thailand with the value reached 190 M USD in 2013. The short mackerel is however classified as data deficient in IUCN Red List. In particular, short mackerel resource in the Gulf of Thailand is recently drastically decreased due to overfishing. In this study, we applied the individual assignment (IA) and mixed-stock analysis (MSA) based on microsatellite loci to short mackerel fishery catches in the Inner and Eastern Gulf of Thailand. We found contrast migratory behavior among the fishery stocks. The majority (55.51%) of fully grown mackerel caught from the Inner Gulf of Thailand was sedentary mackerel in the fishing area, Samut Songkhram spawning ground. In contrast, almost all fully grown short mackerel (85.58%) caught from Eastern Gulf of Thailand were migrant from Southern Gulf of Thailand, Pattani spawning ground (>600 km of migration distance). This information strongly indicated that distinct management strategies are required to sustain fishery catches in the two large fishing areas. The seasonal closure on significant spawning grounds of short mackerel, including limit the number of vessels and the ban of destructive fishing gears are highly recommended for fishery management in the Gulf of Thailand.