Work

Water depth and human disturbance drive occupancy of endangered softshell turtles ( Nilssonia spp.) in eastern Nepal

Year: 2026

Type: article

Abstract: Freshwater turtles play vital roles in maintaining the health of aquatic ecosystems by supporting ecological balance, nutrient cycling and regulating prey populations. Unfortunately, they are among the most threatened species worldwide. Habitat fragmentation, illegal trade, overharvesting for meat, and use in ethnomedicinal practices have severely endangered freshwater turtle populations, including softshell turtles Nilssonia spp. We investigated environmental and anthropogenic factors influencing the occupancy of three endangered softshell turtle – N. gangetica , N. hurum and N. nigricans – in the eastern lowlands of Nepal. We conducted 95 site surveys between March and September 2024, recording detection histories across four replicate visits. Using single‐season occupancy models, we assessed the effects of water depth, pH, biological oxygen demand (BOD), habitat type (river, pond, wetland), connectivity, and a human disturbance index (HDI) on turtle occupancy while accounting for imperfect detection. Detection probability was significantly higher at night (0.48 ± 0.08) than during the day (0.22 ± 0.06), confirming nocturnal behavior and justifying time‐dependent detection in all models. Among 17 candidate occupancy models, three received strong support (ΔAIC ≤ 2), cumulatively accounting for 88% of AIC weight. Model‐averaged estimates revealed that occupancy was positively associated with water depth (β = 2.87, 95% CI: 1.33–4.42) and negatively associated with HDI (β = −1.66, 95% CI: −2.75 to −0.57). Occupancy increased with water depth across all HDI levels, with the strongest response at low disturbance sites, and declined sharply with increasing HDI, particularly in shallow waters. Potential habitats for these species in eastern Nepal are deteriorating due to intense human pressures such as electrocution, poisoning, overexploitation of aquatic resources, and habitat modification, which signifies the need for immediate and effective conservation actions.

Source: Wildlife Biology

DOI: 10.1002/wlb3.01531