Vanishing act | Humans to blame for 80% drop in three-striped roofed turtle numbers

New Delhi: The three-striped roofed turtle, once found in numbers in the Ganga and Brahmaputra rivers, has now largely disappeared with a government-funded study detecting an over 80 per cent drop in its population in half a century, largely due to habitat loss, illegal trade and pollution.

The study, supported by the National Mission for Clean Ganga, has revealed an alarmingly low genetic diversity in the rescued population of the freshwater reptile species, raising concerns over its long-term survival.

Underscoring the urgent need for science-backed conservation efforts, the study called for long-term genetic tracking, stricter enforcement against poaching, and efforts to restore the semi-aqautic turtle's habitat, especially in its last stronghold -- the National Chambal Sanctuary.

The sanctuary is located on the Chambal river near the tri-point of Rajasthan, Madhya Pradesh and Uttar Pradesh.

"The population of Batagur dhongoka (three-striped roofed turtle) has experienced a substantial decline due to entanglement in fishing nets, the construction of major hydrological projects affecting river flow dynamics and nesting beaches, water pollution, and the detrimental effects of illegal trade," the study said.

Researchers from the Wildlife Institute of India analysed genetic samples from the turtles housed at two Turtle Rescue and Rehabilitation Centres -- TRRC in Varanasi and GARRC in Narora -- part of a captive care initiative under the Namami Gange programme.

Using mitochondrial DNA and microsatellite markers, the study found that the population exhibit low levels of genetic variation, a warning sign for any species on the brink.

The genetic data showed only weak structuring between the two populations, one from TRRC in Varanasi and the other from GARRC in Narora, suggesting past intermixing but also indicating the danger of inbreeding. The average heterozygosity was under 50 per cent and many individual turtles carried similar genetic markers.

Moreover, the demographic pattern estimated by the Bayesian skyline plot (BSP) analysis indicates historical stability followed by growth in the effective population size, with a recent reduction in population size from 2,000 years ago.

The study flagged a major concern for the ongoing rehabilitation programme -- a lack of clarity around the geographic origin of some rescued turtles. This not only makes it harder to plan successful reintroductions but also raises the risk of outbreeding depression if genetically mismatched turtles are placed with wild populations, it said.

"Gathering information on the geographic origin of individual (turtles) is sometimes difficult and the release of these unknown origin rescue individuals in the wild is often accompanied by high initial losses of released individuals.

"Hence, while a small number of individual (turtles) are released locally, genetic monitoring is vital to understand the wider and long-term contemporary genetic diversity for effective management and conservation interventions," the research said.

In order to ensure the effective protection and conservation of the three-striped roofed turtle, the government has taken a proactive measure by incorporating it into Schedule I of the Wildlife (Protection) Act, 1972, as amended in 2022. Species under this schedule enjoys the highest level of protection.

The research from last year was among several key documents unveiled on a new portal launched by the Ministry of Jal Shakti to promote access to ecological data and conservation insights. The study was initially published in the National Library of Medicine - PubMed Central.