Kolkata: Born under captivity in Patna Zoo, a young critically-endangered gharial who was released into the wild has now lost her freedom once again after swimming 1000 kilometres into the neighbouring West Bengal.

The nine-year-old sub-adult female gharial was released in the Gandak river near Valmiki Tiger Reserve last year along with 24 other crocodiles by the Bihar forest department as part of a conservation program.

For reasons best known to nature, the gharial swam over 1000 km over the next few months to reach Mahananda river which flows in the northern part of West Bengal. Gandak and Mahananda are both interconnected through the river Ganga as its tributaries.

In Malda district local fishermen raised an alarm after spotting the gharial as they felt threatened by the carnivorous mammal, which is rarely spotted in the river. West Bengal forest department officials then captured it and kept it at Rasik Bill in Cooch Behar last October. The release of the crococodile has now become complicated since it is a trans-state issue.

"This is not good for the animal. It has survived so long in nature after being in captivity for eight years. Now it is a wild animal and if it is forced to return to captivity then you are spoiling its life. We had released it in the wild so that biodiversity increases in the river," Wildlife Trust of India (WTI)'s Samir Kumar Sinha told PTI.

He is working along with the Bihar forest department to save the gharials from extinction as it is estimated that only about 200 breeding individuals of the species, listed as critically endangered, survive in the wild today.

WTI has already appealed to the West Bengal forest department to release the gharial at a safe wild location. "We will take necessary action after we receive a letter from the Bihar forest department," Bengal's chief wildlife warden Pradip Shukla told PTI when asked about the future of the mammal.

The reason for the migration of the gharial from Bihar to the neighbouring state remains a mystery. "Travelling over a range of around 200 km is a known phenomena for the gharials but what made this particular
gharial travel for 1000 km is a mystery to us. Floods during the monsoon may be one of the reasons but we are not sure." Sinha said.

What was more intriguing to wildlife experts is that she swam against the current for over 100 km to reach Bengal. "It first went upstream and crossed the barrage near the Nepal border and then it came downstream to Mahananda. When our field biologist went to the spot after hearing the news we identified it as we have done a unique marking system on all the ones we released from our stock," the WTI official said.

Gharials, which feed on fish, need fast flowing rivers and good sand banks for laying eggs. "This wasn't a fully adult individual so there is no question of she migrating in search of a mate. The mating season anyways starts from February," Sinha said. Finding a suitable place to release the gharial in the wild in West Bengal will be a tough task.

"The species is rarely found in the state. It needs a place where there isn't fishing pressure as fisherfolks feel threatened by the presence of the aquatic reptile," he said. Lister under Schedule I' of the Indian Wildlife(Protection) Act, gharials are endemic to the Indian subcontinent.

Under the program for restocking of gharials, WTI and Bihar forest department has so far released 30 captive-bred individuals into the wild. "We are monitoring their movements. Some of them may have crossed over to Nepal. We will soon do a survey to get more details," he said.