Minimum legal size of commercially important groupers in the Coral Triangle Sulawesi Sea, Indonesia

Major challenges facing grouper fisheries in Kwandang Bay within the Coral Triangle include declines in potential spawners and as well as in the abundance of juvenile fish. One measure that can be taken to maintain valuable fisheries stocks such as groupers is to regulate the minimum legal size (MLS). The aim of this research was to identify and analyse the mean size at first maturity (Lm₅₀) as a basis for setting an MLS for three grouper species of commercial importance. A total of 525 grouper specimens (307 Variola albimarginata, 90 Variola louti, and 128 Plectropomus leopardus) were collected from January to October 2022 from grouper traders, traditional markets, and the Kwandang Fishing Port. The Lm₅₀ for each species was calculated using the Spearman-Karber formula. The Kwandang Bay catch was dominated by immature juvenile fish and the size class contributing the most individuals was below the Lm₅₀ for all three grouper species. The MLS should be at least 32 cm for V. albimarginata, 33 cm for V. louti and 35 cm for P. leopardus in order to enable sufficient fish to spawn at least once, increase the number of spawners, and thereby maintain stock abundance.