Population status of thresher shark listed in Appendix II CITES of Southern Java Seas, Indonesia

Abstract

This study aims to determine the population status of species listed in Appendix II CITES, Alopias pelagicus and Alopias superciliosus, in the Southern Java Seas. 571 A. pelagicus and 449 A. superciliosus were measured for fork length, weight, and male sexual maturity during February-December 2022. Their total catches data (2009–2021) were obtained from the Cilacap Ocean Fishing Port Statistical Report. The total sustainable catch was analyzed using the Catch-based Maximum Sustainable Yield (CMSY) method. The catch of A. pelagicus had a length range of 143–152 and 163–178 cm for A. superciliosus. For combined sex, the size at first capture and first sexual maturity of males was 137 and 149.8 cm for A. pelagicus and was larger for A. superciliosus (153 and 160.8 cm). The von Bertalanffy's growth analysis revealed a growth coefficient K of 0.11 years-1 and an asymptotic length (L∞) of 288 cm. While for A. superciliosus, K and L∞ were 0.41 years-1 and 306 cm. The CMSY of A. pelagicus and A. superciliosus was 48.6 and 42 tons. Their exploitation rate in 2021 was 1.8 and 3.38, which exceeded the maximum allowable limit. Therefore, size limits and maximum catch quota regulations are urgently needed for their conservation.