Assessment of horseshoe crab [Tachypleus tridentatus (Leach, 1819)] by catch in artisanal fish corrals of Palawan, the Philippines

Abstract

Importance of the work: Incidental capture in small-scale fisheries is an increasingly recognized threat to marine megafauna, yet quantitative assessments remain limited in data-poor tropical regions, particularly for stationary fishing gear. This study has provided the first fishery-wide baseline estimate of horseshoe crab bycatch in artisanal fish corrals in Palawan, the Philippines. Objectives: to provide the first fishery-wide baseline assessment of horseshoe crab [Tachypleus tridentatus (Leach, 1819)] bycatch in artisanal fish corrals in Palawan, the Philippines. Materials and Methods: A full census was conducted of fishers (n = 60) from nine coastal villages in Puerto Princesa City, complemented by spatial mapping of 155 fish corrals. Interview-derived catch per unit effort (CPUE) was used to estimate annual bycatch by scaling weekly catches across reported months of operation, with median values applied where data were unavailable. Results: The weekly bycatch was in the range 0–20 individuals/trap/wk, with median values of 2–3 individuals/trap/wk. Annual bycatch was estimated at approximately 14,300–28,600 individuals. Bycatch hotspots were concentrated in Honda Bay and Ulugan Bay. Although spawning was reported throughout the year, observations were strongly associated with periods of active trap operation, suggesting observation bias rather than distinct seasonal spawning. No respondents reported intentional killing, consumption, or sale of horseshoe crabs. Main finding: Artisanal fish corrals exert substantial incidental bycatch pressure on horseshoe crabs, despite the absence of targeted exploitation. These findings have established the first quantitative baseline for this fishery and have identified priority areas for spatially targeted management and community-based conservation.