| Abstract: |
The three-striped roofed turtle (Batagur dhongoka), a Critically Endangered geoemydid endemic to the Ganga–Brahmaputra system, has contracted sharply across its historical range, yet evidence linking its persistence to water quality in the middle Ganga remains scarce. This study quantifies the abundance, demography and habitat association of B. dhongoka along a 452 km stretch between Bithoor (Kanpur) and Barwan (Bhadohi), Uttar Pradesh. Eight segments were surveyed over nine campaigns spanning three seasons and three years (2023–2025), yielding 2,402 sightings across 2,160 km of boat-based strip transects and 72 paired water samples analysed for ten variables. A weighted arithmetic Water Quality Index (WQI) ranged from 27.8 (Good) at Bithoor to 115.0 (Unsuitable) at Jajmau, downstream of the Kanpur tannery and sewage outfall. Encounter rates collapsed from 2.24 individuals km⁻¹ upstream of Kanpur to 0.02 individuals km⁻¹ at Jajmau, recovering to 2.14 individuals km⁻¹ in the Bhadohi reach. Encounter rate correlated positively with dissolved oxygen (r = 0.797, p < 0.001) and negatively with BOD (r = −0.678), faecal coliform (r = −0.787) and WQI (r = −0.673). Multiple regression explained 65.9% of variance (adjusted R² = 0.644, F₃,₆₈ = 43.84, p < 0.001), dissolved oxygen dominating (β = 0.763). Hatching success fell from 86.8% to 68.5% and juvenile representation from 32.1% to 20.0% along the same gradient, indicating recruitment failure rather than adult displacement. The corrected population estimate is 622 ± 148 individuals. Water quality, acting principally through oxygen availability, is therefore the proximate determinant of B. dhongoka distribution. |
