VOLUME 19 (Supplement)

Population dynamics of blue swimming crab (Portunus pelagicus) in Samar, Philippines

The blue swimming crab (Portunus pelagicus) is an economically and ecologically important species in Indo-Pacific coastal fisheries. In Samar, Philippines, declining catches have raised concerns about the sustainability of this resource due to increasing fishing pressure and habitat disturbance. This study assessed the population dynamics of P. pelagicus from February to November 2023 across three municipal fishing grounds in Samar. A total of 4,131 crabs were sampled from artisanal landings, and their carapace width (CW) was measured. Length-frequency data were analyzed using the Bhattacharya method and the ELEFAN I routine in FISAT II, using the von Bertalanffy Growth Function, to estimate growth, recruitment, and mortality parameters. Results showed that the population was dominated by intermediate size classes (81–110 mm CW), while larger individuals (>120 mm CW) were relatively scarce, indicating a truncated population structure. Growth analysis estimated a growth coefficient K = 0.92 yr⁻¹, suggesting rapid growth. Recruitment occurred year-round with distinct peaks in June (16.43%) and September (13.44%). Mortality estimates were Z = 2.93 yr⁻¹, M = 1.08 yr⁻¹, and F = 1.85 yr⁻¹ (R² = 0.8932), resulting in an exploitation rate (E) of 0.63. Because E exceeded the commonly used optimal threshold of 0.50, the results indicate substantial fishing pressure on the stock. These findings emphasize the need for management interventions, including seasonal closures during peak recruitment periods, enforcement of minimum size limits, and improved gear selectivity, to maintain reproductive capacity and ensure the long-term sustainability of P. pelagicus fisheries in Samar.