At least 50 critically endangered reptiles known as gharials have been found dead recently in a river sanctuary in central India, officials announced this week.
Conservationists and scientists are now scrambling to figure out what killed the crocodilelike animals.
The bodies, measuring between 5 and 10 feet (meters) long, have been found on the banks of the Chambal River, one of the few unpolluted Indian rivers.
In early December officials found the bodies of at least 21 gharials over three days. The bodies continued washing ashore in subsequent weeks.
The precise number of gharials that have died remains unclear, with the nonprofit Gharial Conservation Alliance saying 81 bodies have washed up so far.
D.N.S. Suman, chief wildlife warden for the Indian state of Uttar Pradesh, puts the number of dead animals at 50.
Parasite or Pollution
The gharial, one of the largest of the crocodilians, was on the verge of extinction in the 1970s.
An Indian government breeding program met moderate success by releasing several hundred into the wild.
But conservationists believe only about 1,500 gharials remain.
Many of the reptiles live in a sanctuary based along the Chambal, which contains the largest of three breeding populations in the world.
The latest possible clue to what's killing the gharials is an unknown parasite that scientists found in the dead animals' livers and kidneys, according to A.K. Sharma of the Indian Veterinary Research Institute.
"We can say that [the] liver and kidney of these gharials were badly damaged," Sharma said. "They were swollen and bigger than their usual size."
Other experts believe the gharials may have gotten sick and died after eating contaminated fish from the polluted Yamuna River, which joins the Chambal.
Pathological tests confirmed lead and cadmium in the bodies of the dead gharials, said Suman, the wildlife official.
"The Chambal River has clear water free from heavy metals," Suman said.
"The only possibility seems that these gharials might have migrated from heavily polluted Yamuna River, where they might have eaten fish."
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