Research Article: Choudhary, S., Dey, S., Dey, S., Sagar, V., Nair, T., & Kelkar, N. (2012, January). River dolphin distribution in regulated river systems: implications for dry-season flow regimes in the Gangetic basin. Aquatic Conservation: Marine and Freshwater Ecosystems, 22(1), 11–25. https://doi.org/10.1002/aqc.1240 

Blog Author: Simran Prasad

Key Takeaways: 

  • Large dams present in the Ganges river basin have impacted natural flow processes, especially in the dry season. The different flow processes have negatively affected endangered Ganges river dolphin populations within the basin.
  • The authors investigated habitat use by river dolphins in the Gandak river of the Ganges river basin.
  •  Dolphin presence was indicated in 40% of the segments within the Gandak river .
  • Adult dolphins showcased similar habitat preferences across regulated and unregulated rivers. However, dolphin absence was noted within river segments that had low flow rates.
  • The authors exhibit the importance of conservation efforts for river dolphins, to ensure appropriate river habitat availability and connectivity for dolphins. 

 

River flow processes are especially important for the maintenance of freshwater ecosystems in dynamic riverine conditions. Large scale infrastructure, i.e., embankments, dams and hydroelectric machinery, threaten freshwater biodiversity at multiple scales. These manufactured developments can result in the disruption of habitat connectivity along river segments. Many freshwater species have become endangered, due to these increasing threats to gene flow and movement pathways. These negative impacts can be further exacerbated by continuous dry seasons over multiple months, affecting species such as the river dolphin. During this period, river flow slowly decreases until the monsoon floods. This can cause substantial resource depletion for riverine species. 

In this study, scientists conducted boat-based surveys of river dolphins across the Gandak river in India, which stretches across 332 km, from the Gandak barrage to Patna. Field observations, i.e.number of unique dolphin sightings, GPS locations, dolphin age-classes, etc. were recorded. Field observations, such as barrages (water dams) upstream and downstream, historical distribution of river dolphins, and dolphin sightings from the barrage were made across the river. Dolphin presence was recorded in 40% of the total number of segments observed (332 segments), with 257 recorded as the best count of individuals. The study also indicated that dolphin habitat use across the river was influenced by factors like channel depths.

The research paper exhibits that river dolphin distribution is positively influenced by factors such as river depth, and that the flow-regulated Gandak river has clustering at smaller locations within the river. In addition, dolphin habitat preferences were also identified as being similar across different rivers. However future research is needed to understand the emigration patterns during pre- and post-water release periods of the basin. The study provides a fundamental baseline for future monitoring projects that can look at river dolphin distribution patterns across multiple spatial scales, as well as substantially quantifying dolphin-habitat dynamics. The paper also highlights the threats that dry-season river flow can create, such as decline in freshwater biodiversity, and the need to maintain ecological flow processes during different seasons in order to secure river dolphin populations in the future. In tandem with this aspect of research, authors highlight the necessity to account for local livelihoods at these spatial scales, as public support and provision of viable river flows is essential for averting threats to freshwater species. To execute this, a multi-scale plan that focuses on monitoring agriculture, industry and fisheries sectors is crucial, as this can secure ecological flow while working toward conserving endangered species. 

You can access the original article here.

Keywords: flow regulation; Ganges river dolphins; river depth; channel morphology; Bayesian zero-inflated spatial models; Gandak River; Gangetic basin