- A keystone species in India’s freshwater river ecosystem, the gharial is critically endangered because of extensive fishing, sand mining, the presence of feral dogs and cattle as well as dams and barrages.
- Gharials are piscivorous reptiles whose preference for undisturbed habitats and specialised diet make them particularly vulnerable to habitat degradation and fishing pressures.
- A new study of population dynamics and conservation status of gharials in the Gandak river highlights the need to extend conservation efforts to unprotected rivers like the Gandak.
The population of gharials, the only surviving crocodilian member of the genus Gavialis, is in decline. Listed as Critically Endangered on the IUCN (International Union for Conservation of Nature) Red List, the global population of gharials, endemic to India, has been reduced from 5000 in the 1940s to a few hundred individuals in the wild. Researcher Ashish Panda of Wildlife Institute of India attributes this decline largely to their specialist nature, especially of their habitat, and multiple anthropogenic pressures stacked against their conservation.
A recent study conducted by Panda and his team to understand the population status and distribution of gharials (Gavialis gangeticus) in the Gandak river, reveals that the species avoid human presence and prefer to occupy undisturbed riverine habitats with deeper pools. The study documents that the presence of human settlements near the riverbank poses a threat to the gharials as they reduce their basking time, potentially affecting their physiology. Other threats in the form of fishing, fishing nets in the river, the presence of feral dogs and cattle in the human-dominated landscape across the length of the river, river braiding and changes in river flow due to damming are reasons severely threatening the small but robust population of gharials in the Gandak river, a transboundary tributary of the Ganga that flows through the Indian states of Bihar and Uttar Pradesh.
Other than the gharials in Gandak river, most of the population is distributed in the Ganga and its tributaries, notably Chambal, Girwa and Son.
Surviving in unprotected habitats
What makes the Gandak river and its gharials special is its unprotected status, unlike the Chambal river which is a notified sanctuary, says Panda, which makes survival more challenging for the animal. Researchers also believe that the river is home to the second-largest population of gharials in India and the only breeding population in a non-protected area. A 2020 survey by the Wildlife Trust of India (WTI) recorded 259 individuals in the river, a claim contested by experts like Tarun Nair, from the Wildlife Conservation Trust, who is also a member of the IUCN Crocodile Specialist Group. He expresses doubt as many individuals are often hard-released into the river as a conservation effort. “They can’t be considered residents. They don’t stay put and are capable of travelling long distances in the rivers that act like conveyor belts,” he says. Nair mentions a case where a tagged individual was found to have travelled over 1000 kilometres from where it was released. He, however, lauds the researchers’ effort to study the conservation challenges in the Gandak river as most of the riverscape is unprotected and human-dominated except for Valmiki tiger reserve and Sohagi Barwa wildlife sanctuary.
The gharial, or long‐nosed crocodile, is a large piscivorous reptile that historically occurred across the riverine systems of India, Pakistan, Bangladesh and southern part of Bhutan and Nepal, from Indus in the west to the Irrawaddy river in Myanmar in the east. Today they survive only in the waters of India and Nepal. The adult male can reach a size of seven metres while the females are often between four to five metres. They are considered keystone species in freshwater river systems.
Fishing and mining threats
Also known as the fish‐eating crocodile, gharial gets its name from the Hindi word ghara or pot, alluding to a distinct morphological character — the bulbous knob, a cartilaginous mass — at the tip of a breeding male’s snout. The snout and rows of uniform sharp teeth, supported by a strong muscular neck, make the gharial an excellent fish catcher. The adult gharials eat only fish, making extensive fishing in their habitats a cause for concern as it could impact food availability. Fishing nets across the rivers endanger the animal as they get entangled in them and incidents of drowning have been reported. The study notes that gharials have been seen avoiding fishing boats, perhaps as an adaptive mechanism.
Sand and boulder mining, especially in the southern tributaries of the Ganga, have been found to be disturbing the nesting patterns and sites of the species. There is also the threat of feral dogs preying on gharials’ eggs. They are not natural predators and are an outcome of human presence, says Panda. Nair says such predators are not controlled by ecological factors and hence pose a larger threat.
The biggest population decline of the species occurred between 1950 and 60s, notes the paper, primarily due to poaching. Conservation efforts picked up in the mid-70s that helped the population to rebound but the species continues to remain endangered due to more modern threats like dams and barrages.
Changing river flow dynamics
Maintaining the natural riverine system is paramount to its survival, according to Panda. This, however, is not the case in most Gangetic rivers where gharials are present. Dammed or barraged, the water flow often alters seasonally as per irrigation needs. The authors say that during the survey of the Gandak, they encountered river braiding because of the river’s inclination to flood and the barrages’ sudden discharge of water for irrigation purposes. This braiding may cause the river to split into several separate channels, notes the paper, affecting the accuracy of gharial population estimates. River braiding also impacts the survival of yearlings and hatchlings which are unable to withstand the change in water currents. Nair highlights that river interlinking is a potential threat that is often overlooked.
When the researchers divided the river into segments for study, they found certain segments of the river to be more affected by these pressures than the others. As a conservation outcome, Panda hopes that the human interference in the Gandak river is minimised and better protection is offered throughout the course of the river.
Banner image: A gharial basks on the Gandak river. The decline in the population of the species is largely to their specialist nature, especially of their habitat and multiple anthropogenic pressures. Photo by Ashish Panda.