A terrapin is a turtle and the one found in the Sunderbans, about 60 centimetres in length, is called the northern river terrapin. It is critically endangered and a few surveys in the past to detect wild terrapin populations fell apart as scientists could not trace them. It can be told apart from other turtles of its family by two features — its pointed, upward tilting nose and its four-clawed forelimbs. Earlier it was thought that the terrapins found in Malaysia and Thailand and those found in the Sunderbans were of the same species. But through genetics it was ascertained that they were two different species — the southern river terrapins or Batagur affinis (found in Malaysia and Thailand) and the northern river terrapins or Batagur baska (found in the Indian and Bangladeshi Sunderbans).
During the breeding season, the colour of the pupils of the femaIe is brown whereas the pupils in the males become yellowish-white. Their neck and head have a dark brown pigmentation and the base of the neck and forelimbs have a reddish pigmentation. This reddish pigmentation is absent in Batagur affinis, making the Sunderban’s river terrapins a unique species. Earlier these terrapins were found aplenty in the wild and were collected by fishermen for their meat and eggs. But recent surveys in turtle meat markets could find no river terrapin meat. This is not good news as dearth of terrapin meat in the market denotes a severe decline in the population. As the scientific community became concerned with the rarity of this species in the wild, they tried to carry out captive breeding programmes for freshwater terrapins. A captive breeding programme is where adult terrapins from the wild are bred in captivity. A successful breeding programme is one in which the offspring, once they manage to survive into adulthood, are released into the wild.
On June 12, 2012 the Forest Department’s efforts paid off when the critically endangered Batagur baska, was bred successfully in captivity at Sajnekhali, Sunderbans, India. The Forest Department had been trying to breed the mature terrapins kept in the forest headquarters in Sunderban Tiger Reserve for four years without success, till the unfortunate jinx was broken this year. Twenty five hatchlings were born. In neighbouring Bangladesh, similar news was awaiting researchers as northern river terrapins in the Bhawal National Park laid eggs in captivity and 20 hatchlings were born.
Without conservationists having an estimate of how many Batagur baska remain in the wild, breeding populations in captivity has a very important role in conserving the species. There are about 39 Batagur baska in captivity (two males, eight females, one juvenile) in Sajnekhali, Sunderbans, 17 terrapins (five females and 12 males) in Bhawal National Park, Bangladesh and two females in the Madras Crocodile Bank Trust, India, which were rescued from a market in Calcutta. Vienna Zoo, Austria, houses nine (three males, three females and three juvenile/sub–adult females) Batagur baska and will soon send one male to the Madras Crocodile Bank Trust to round up a small breeding group. Vertebrate species with very small effective population sizes of even less than 10 females can recover if they are bred through proper scientific protocols.
The turtles mainly prefer freshwater habitats and go up to river mouths or estuaries in the breeding season. River terrapins in the Indian Sunderbans travel from freshwater rivers to sandy beaches of islands near the Bay of Bengal to lay their eggs covering about 80 kilometres. After laying eggs they return back to the freshwater. But salinity level in the Sunderbans has risen over the years, even in freshwater rivers like Raimangal. Are these turtles suffering because of that? Has a rise in salinity upset the natural migration of the turtles? Even if captive breeding programmes work, scientists will have to find a way to mitigate this problem.