Population dynamics of three Epinephelus groupers in the Sulawesi Sea, Indonesia

Abstract

Groupers of the genus Epinephelus play important roles in coastal ecosystems and small-scale fisheries. Market demand has driven intensive exploitation, threatening stock status and coastal community livelihoods if these valuable fisheries are poorly managed. This research on grouper population dynamics in Kwandang Bay, on the Sulawesi Sea coast of Gorontalo Province, Sulawesi, Indonesia, focused on three Epinephelus species: E. fasciatus, E. faveatus, and E. ongus. The mean length at first maturity (Lm50) was estimated using the Spearman-Karber formula, and population dynamics parameters were estimated through Response Surface Analysis using the ELEFAN I suite in FISAT II. Catches of all three species were dominated by juveniles with total length TL < Lm50. The respective asymptotic lengths (TL?) for E. fasciatus, E. faveatus, and E. ongus were 47.52, 53.50, and 52 cm, with von Bertalanffy growth coefficient K values of 0.49. 0.54 and 0.53, respectively. Natural and fishing mortality estimates were 1.01/year-1 and 1.23/year-1 for E. fasciatus, 1.05/year-1 and 2.00/year-1 for E. faveatus, and 1.04/year-1 and 2.44/year-1 for E. ongus. The Beverton and Holt yield per recruit analysis indicates overexploitation with respective exploitation rates (E) of 0.55/year-1, 0.66/year-1, and 0.70/year-1, all exceeding Emax = 0.37/year-1. Recommendations include setting minimum legal size limits (above 25 cm for E. fasciatus and E. faveatus, 26 cm for E. ongus), as well as reductions in fishing effort of 31% for E. fasciatus, 42% for E. faveatus, and 46% for E. ongus.

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