Ganges River Dolphins (Platanista gangetica gangetica): Effect of Dams and their Conservation

by Rohan Nath

Introduction

Considering the rate with which many landscapes, including freshwater ecosystems, around the world is being converted by humans; it is important to understand the evolutionary  potential of endangered species. The race between the surrounding countries to harness water  extraction and hydropower propels the South Asian Rivers into a threat. The most endangered  freshwater river dolphin in the world- the Ganges River dolphin (Fig. 1) is found in the  Ganges-Brahmaputra-Meghna and Karnaphuli River Basin (Fig. 2) in India, Nepal and  Bangladesh. However, several human development projects and activities like dams and  barrages as well as natural factors hamper the ecology of the Ganges dolphin and alter their  habitat. Numerous factors are likely to put the population of Ganges dolphin at risk of  destabilization and extinction.  

Dams and water-related projects in the main branch and the tributaries of the Ganges Brahmaputra-Meghna and Karnaphuli River Basin create a flow-regulating barrier that obstructs the movements of the dolphin population. This results in small, local  subpopulations that disrupt the potential of the dolphin population for evolution. 

Fig. 1. The Ganges river dolphin (Platanista gangetica gangetica).  Image Source: Mansur / WCS Bangladesh / Braulik et al., doi: 10.1111/mms.12801.

Fig. 2. The Ganges-Brahmaputra-Meghna and Karnaphuli River Basin in South Asia and  the location of the major dams that isolate the dolphin population into several small  groups. Image Source: Paudel, S., & Koprowski, J. L. (2020). Factors affecting the  persistence of endangered Ganges River dolphins (Platanista gangetica gangetica). Ecology and evolution, 10(6), 3138-3148.

Why is evolution important for the Ganges dolphin? 

Under the serious threats of extinction, the dolphin population needs to adapt to changing  environmental conditions which may threaten their existence. Therefore, evolution is the  mean by which the population can cope up with environmental stresses. 

Effects of Dams on the Population of Dolphins 

i. Modification of Physical Habitat  

The dams lead to habitat loss and fragmentation resulting in the isolation of small groups of  Ganges dolphin with limited geographic range. Disturbances in any hydrophysical habitats  like required depth can potentially reduce or eliminate the reproductive success of the Ganges  dolphin. Further research is necessary to identify the other hydrophysical habitats to increase  the conservation and survival of the dolphin population. The rate of local extinction has  increased in the upstream range of the Ganges River. Considering the high risk in these small  isolated populations, it is important to develop a plan to work on the conservation of these  endangered species. 

The government of India declared the Ganges dolphin as the national aquatic animal and  developed the Conservation Action Plan for the Ganges dolphin. However, the government  also constructed dams and structures at international borders leading to an alteration in the  Ganges-Brahmaputra-Meghna and Karnaphuli River Basin, risking the population of the  species they declared as the national aquatic animal.  

WCS dolphin conservation project in Bangladesh and Vikramshila Gangetic Dolphin  Sanctuary, Bhagalpur District of Bihar in India are some of the river dolphin-based  conservation projects.

ii. Genetic 

The Farakka Barrage in West Bengal divides the Ganges dolphin global population into  several local subpopulations. The geographical limitation of the subpopulation of the Ganges  dolphin puts them at a higher risk of extinction. This usually occurs through phenomena like  reduction of genetic variability and inbreeding depression that decreases the genetic diversity  and fitness of the population. The number of small local subpopulations is further increased  with an addition of a new dam. Considering that the extinction of species occurs quicker in  freshwater than in terrestrial ecosystem, the increase in inbreeding and decrease in genetic  heterozygosity makes the local extinctions of Ganges dolphin seem inevitable.  

iii. Behavioural ecology of the Ganges dolphin 

Anthropological influences are likely to affect the specialized circadian rhythm of the Ganges  dolphin concerning habitat selection like depth profile selection for foraging and  reproduction. This in turn can affect the life-history stages and functional ecology of these  species. The Ganges dolphin uses the cyclic range of water levels and seasonally moves  between the mainstream and tributaries. For example, the Ganges dolphin is stimulated to  migrate to other tributaries when there is a high-water flow in the mainstream. Anthropogenic  structures like hydropower dams or development structures can regulate the water level and  present as a false environmental cue, leading to a dysfunction of the functional ecological  behaviour of the dolphin.  

iv. Human-dolphin conflicts 

The primary cause of endangerment and extinction of the Ganges dolphins is due to their  interactions between artisanal fisheries in the Ganges-Brahmaputra-Meghna and Karnaphuli  River Basin. The endangerment of the Ganges dolphin can be attributed to the dietary and  diel activity and spatial and temporal overlap with the fisheries. The factors leading to the  fisheries and Ganges dolphin interaction needs to be assessed for effective management.  Therefore, the driving factors like spatial overlap, dietary competition and behavioural  distractions need to be further researched both qualitatively and quantitatively to manage the  coexistence between the river dolphin and fisheries.

v. Implications for future management 

Genetic tools cannot be applied to explore the viability of the Ganges dolphin population in  the Ganges-Brahmaputra-Meghna and Karnaphuli River Basin because of the limitation of  resources and conservative policies. It is essential to develop a regional intergovernmental  project that promotes the investigation of genetic viability and factors associated with the risk  of extinction using genetic-based research. For genetic monitoring, it is important to consider  the use of non-invasive tools, like environmental DNA. It is suggested to integrate census  data with genetic data for the accurate prediction in the population trend of the Ganges  dolphin. Proper capture and handling techniques might make it possible to improve the  genetic stability by translocation of individuals among subpopulations.  

It is tremendously difficult to predict the extinction using a single ecological factor due to the  synergistic effect of several other factors. A better understanding of management purposes  and conservation could be reached if we integrate demographics, genetics, and environmental  factors in future studies. Restoration and preservation of essential surfacing and foraging  habitats and maintenance of minimum stream flow can prevent the further decline in the  population of the Ganges dolphin.

Reference 

1. Paudel, S., & Koprowski, J. L. (2020). Factors affecting the persistence of endangered  Ganges River dolphins (Platanista gangetica gangetica). Ecology and evolution, 10(6),  3138-3148.

Published by LakesOfIndia

Lakes of India is an E.F.I initiative aimed at sensitizing the larger public on freshwater habitats across the country. A blog platform where one can read about lakes across India. You can become a guest blogger to write about a lake in your hometown and initiate an action to protect that lake.

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