Abundance and Prey Availability Assessment of Ganges River Dolphin (Platanista gangetica gangetica) in a Stretch of Upper Ganges River, India

Abstract: 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/km2 (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/km2 and a total average biomass of 5.36 kg/km2. Dolphin density showed a significant positive relationship (R2 = 0.587) with density of Reba fish (Cirrhinus reba) (β = 0.31, p = 0.00) and Baam fish (Mastacembelus armatus) (β = 0.50, p = 0.04) and also with water depth (β = 0.17, p = 0.03). Presence of dolphins varied across different water depth categories (χ2 = 106.38, df = 3, p < 0.01) and different parts of the river (χ2 = 21.68, df = 2, p = 0.00) with more than 50% of dolphin sightings occurring in confluences, indicating their preference for deep water pools.

Key Words: Ganges River dolphin, Platanista gangetica gangetica, Cirrhinus reba, Mastacembelus armatus, confluence, deep water pool, line-transect

Document Type: Research article

DOI: 10.1578/AM.36.1.2010.19

Page Numbers: 19-26

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