Mapping of deep pool habitats in the rivers of water deficit Bundelkhand region: a novel approach for fish conservation and sustainable management.

Deep pools are perennial habitats in riverine systems that serve as feeding and breeding grounds for diverse aquatic biota, including threatened and endemic fishes. Mapping and understanding the dynamics of deep pools are vital for conservation planning and management, especially in water deficit ecoregions. This study was conducted to assess the temporal trend in the climatic variables and map deep pools in four rivers, viz., Ken, Betwa, Dhasan, and Yamuna, in the water-stressed Bundelkhand region of Uttar Pradesh, part of the Ganga Basin. The temporal trend of climatic variables (1974-2023) recorded in the Bundelkhand region showed a decreasing trend (p > 0.05) for rainfall, an increasing trend in mean annual temperature-max (p > 0.05) and temperature-min (p < 0.05). The deep pool habitats were mapped using a Sentinel-2 satellite imagery-based normalized difference water index map for pre-monsoon seasons, 2021-2023 through a Google Earth Engine approach. A high number of deep pool habitats was reported in Betwa (> 5000) followed by Yamuna (> 3400), Ken (> 900), and Dhasan (> 700) Rivers. Most deep pools (> 65%) fall within the size range of 100-500 m². The field verification and observations based on experimental fishing revealed that the identified deep pools support rich fish diversity and sustain critical life forms. However, unsuitable water quality conditions in the deep pools in the Betwa and Yamuna rivers necessitate habitat restoration and water quality management. The potential of deep pools as "refugia" for native and threatened fishes in water-scarce regions and measures to sustain optimal habitat conditions are discussed. This study lays the groundwork for future initiatives to safeguard vital aquatic habitats and associated fish genetic resources amidst ongoing water stress and environmental changes.