The present study was conducted between January and June 2007 to assess the abundance and density of Ganges River dolphin (Platanista gangetica gangetica) and their prey in a 28-km stretch of the River Ganges between Narora Barrage and Anupshahar. Two different sampling methods were used to estimate dolphin densities. Estimated density was 2.58 +/- 0.40 individuals/km(2) (mean +/- 1 SE) using the direct count method and 4.97 +/- 0.60 individuals/km2 using the boat-based, line-transect distance methods, with an encounter rate of 0.52 +/- 0.068 individuals/km and detection probability of 0.647. No significant differences between the upstream and downstream counts (t = 1.29, df = 9, p > 0.05) were detected. The adult male to adult female ratio was 0.66: 1.00, whereas the calf to adult female ratio was 0.42: 1.00. We collected 16 fish species of length class varying from 3.5 to 20 cm (range of preferred size of dolphin prey) with a total density of 176.42 fish/km(2) and a total average biomass of 5.36 kg/km(2). Dolphin density showed a significant positive relationship (R(2) = 0.587) with density of Reba fish (Cirrhinus reba) (beta = 0.31, p = 0.00) and Baam fish (Mastacembelus armatus) (beta = 0.50, p = 0.04) and also with water depth (beta = 0.17, p = 0.03). Presence of dolphins varied across different water depth categories (chi(2) = 106.38, df = 3, p < 0.01) and different parts of the river (chi(2) = 21.68, df = 2, p = 0.00) with more than 50% of dolphin sightings occurring in confluences, indicating their preference for deep water pools.
