Assessing habitat associations of critically endangered big-headed turtles to support grassroots river conservation

Mark Richard Herse, Wanlop Chutipong, Noppasorn Khuntong, Yik Hei Sung , George Andrew Gale

Modern wildlife conservation relies primarily on state-run protected areas and hunting regulations, whereas grassroots initiatives to protect ecosystems from various threats such as large-scale infrastructure development are underrecognized and receive limited scientific support. We studied critically endangered big-headed turtles (Platysternon megacephalum) to support a grassroots river conservation initiative in Southeast Asia’s rapidly developing Mekong region. The study area was a montane watershed in northern Thailand, including an ambiguous national park boundary, national forest reserve lands used and cultivated by local people, and a state-planned (currently suspended) large dam site. Local villages have opposed the planned dam project since 2021, warning that it could threaten the capture fishery and other aquatic biodiversity, including big-headed turtles, which have been seen by local fishers. We aimed to provide the initiative’s leading village council and government-mandated authorities with current information on the turtle population to support species and ecosystem conservation. We trapped for turtles at 250 river and stream pools (494 total trap-nights) above the planned dam site in 2024–2025 and assessed how species occurrence and observed body size varied with different pool features. We captured 24 individuals turtles (seven juveniles, four subadults, 13 adults) in 22 widely distributed river and stream pools, including three turtles within 500 meters of the planned dam reservoir. Species occurrence increased with pool width, depth, and boulder substrate (refugia). Body size was smaller in streams than in the river and correspondingly increased with water pH and decreased with forest canopy closure, possibly reflecting favorable conditions for nesting and/or juvenile survival in stream habitats. We recommend permanently canceling the dam project to avoid diminishing or isolating this breeding turtle population, in accordance with the National Biodiversity Action Plan. Local interventions to mitigate hazardous irrigation (e.g. diversion of stream water from nesting areas) and fishing practices (e.g. electrofishing, use of explosives) could further improve conservation. Amidst ongoing land-use intensification and habitat degradation, grassroots initiatives to halt undesirable development projects and improve environmental management are crucial for protecting threatened wildlife. Our study demonstrates the potential for scientists to contribute to such initiatives.