The species, declared endangered by International Union for Conservation of Nature, may have been done in by sand mining, the scientists said.

Principal investigator Archana Bahuguna said the team chanced on the missing turtles while researching fresh water turtles in the Ganga. A report in the matter has been sent to the Zoological Survey of India in Kolkata.

Explaining possible reasons why the turtles are vanishing, Bahuguna said, "Freshwater flow in the river has been hindered by mining and construction of barrages, and this is fatal to fresh water turtles. Also, people have been poaching them for medicine and meat. Cultivation of sugarcane near the river and its tributaries, Baan Ganga and Solani, could also have had an adverse effect on the turtles. Planting sugarcane requires clearing broad-leafed plants that grow on the river bank. Without these plants, the turtles have no cover under which to lay their eggs, which are then at the mercy of humans and animals like jackals."

Bahaguna said the habitat of the turtles is near the Jhilmil Conservation Reserve, and forest officials in the reserve must take steps for conservation of the species.

The turtles are also threatened by climate change. The warmer the water, the greater the likelihood eggs will hatch as female turtles. "Like with crocodiles, the gender of hatchlings changes with temperature. Low temperature yields males, while high temperature leads to females. Since temperatures have been rising over the last five years, most species turn out to be female, creating gender imbalance," Bahaguna said.

Freshwater turtles, unlike their marine counterparts, do not migrate over long distances. As such, it becomes difficult for females to seek out males for mating, putting the species in real danger of extinction. Bahaguna said her team was also surprised to find freshwater turtle species, Morenia Petersii and Pangshura Tentorai circumdata, which are not native to Uttarakhand but were last seen in Bihar in 2010.