Severe Overexploitation of the Mud Spiny Lobster (Panulirus polyphagus) Revealed by Length-Based Assessment in Gresik, East Java, Indonesia

A critical lack of local biological and population data continues to undermine sustainable management of lobster fisheries in Indonesia. This study aims to assess the population dynamics of lobsters caught by the fishers through the identification of the lobster species, describe their life history traits, and evaluate their exploitation status. The data collected included morphological characteristics, carapace length (CL), body weight, Gonad Maturity Level (GML), East Java fisheries production data, and sea surface temperature (SST). Length-frequency data were analyzed to estimate growth parameters (using ELEFAN I) and to assess exploitation status using the length-based spawning potential ratio (LB-SPR) approach. The study identified three lobster species: Panulirus polyphagus, Panulirus ornatus, and Panulirus versicolor. Species composition was dominated by P. polyphagus (95%) with a total of 467 individuals (237 males and 230 females). The length-weight relationship of P. polyphagus exhibited a negative allometric growth pattern. The estimated length at first maturity (Lm) was 86.49 mm, while the length at first capture (Lc) was 69.5 mm, indicating that the average size of caught P. polyphagus individuals did not reach gonadal maturity (Lc < Lm). The asymptotic length was 92.18 mm with a growth coefficient of 1.5/year. The LB-SPR value for P. polyphagus was 3%, which falls under the overexploited category. Therefore, a reduction in fishing effort for lobster is recommended in the northern waters of Gresik.