Stability in genetic diversity and rising gene flow among short mackerel, Rastrelliger brachysoma, populations in the Gulf of Thailand: A decadal perspective

Short mackerel ( Rastrelliger brachysoma ) is a migratory marine fish of significant commercial importance to Thailand’s fisheries. Despite a peak catch of 130.8 thousand tons in 2014, annual catches have steadily declined since 2015, primarily due to overfishing, hitting a historic low of 17.7 thousand tons in 2018. Although recent management strategies, including area closures, have fostered a partial recovery, production levels remain below pre-decline levels. To inform sustainable fisheries management, this study evaluates the genetic diversity and population dynamics of short mackerel in the Gulf of Thailand over a decade. We analyzed 256 recent samples from five spawning grounds --Trat, Samut Songkram, Prachuap Khiri Khan, Surat Thani and Pattani-- in the Gulf of Thailand between 2022 and 2024, comparing them with preceding samples from 2011 to 2018 using eleven microsatellite loci. Our results revealed moderate genetic diversity across populations and showed relatively stable diversity indices over time. Notably, immigration rates between populations have significantly increased in the past decade, suggesting enhanced gene flow. These findings highlight the effectiveness of area closures in maintaining genetic stability and promoting short mackerel population resilience. Stable genetic diversity and increased gene flow among populations underscore the importance of continued genetic monitoring and adaptive management to sustain short mackerel resources in the Gulf of Thailand. By leveraging genetic insights, fisheries management can further optimize strategies to ensure the recovery and long-term sustainability of the short mackerel populations.