Ecological insights and conservation strategies for the data-deficient Indian horseshoe crab Tachypleus gigas (Müller, 1785) along the Odisha coast, India

This study focuses on the conservation of Tachypleus gigas (Müller), a marine chelicerate of ecological significance, threatened by habitat degradation, pollution, and fishing activities along the Odisha coastline. Listed as ‘Data Deficient’ by the IUCN, T. gigas populations face severe risks, necessitating targeted conservation measures. The study objective is to (1) assess environmental factors influencing T. gigas distribution and survival, (2) evaluate the effectiveness of rescue and relocation efforts, and (3) engage local communities in conservation. A total of 483 individuals were rescued from fishing zones and relocated to protected areas to support population recovery. Field surveys (July 2023–March 2024) at ten stations (five rescue and five relocation sites) revealed that seasonal salinity variations, driven by monsoon influx and pre-monsoon evaporation, significantly influenced habitat suitability and reproductive success. Morphometric analyses indicated positive allometric growth in carapace length (R² = 0.79), width (R² = 0.79), and telson length (R² = 0.59), supporting locomotion, defense, and reproduction. Rescues varied seasonally and spatially, with lunar phases influencing distribution. Principal Component Analysis highlighted salinity, temperature, and sediment composition as key drivers of T. gigas distribution, with organic carbon levels correlating positively with T. gigas counts during the monsoon. Monsoonal shifts in sediment composition and water quality altered benthic ecosystems, impacting long-term habitat suitability. Despite these findings, ghost net entanglement remained a critical threat, with 40.7% of fishermen discarding trapped crabs. Community engagement, including educational outreach to 235 fisherfolk, was crucial in garnering support for protected no-fishing stations. Post-relocation monitoring indicated a 72.5% survival rate over six months, reinforcing the effectiveness of targeted conservation. This study underscores the need for an interdisciplinary approach integrating long-term monitoring, habitat restoration, stricter fishing regulations, and community participation to ensure T. gigas resilience.