In a first, the Zoological Survey of India (ZSI) has published an compendium of animal species in the Indian Sundarbans, estimating that there are 2,626 of them in the fragile island ecosystem. The listing includes a diverse 25 phyla, as they are biologically classified.

The Indian segment of the Sundarbans, part of a UNESCO World Heritage site, forms part of the Ganga-Brahmaputra delta across 9,630 sq. km, distributed among 104 islands.

The region hosts 2,487 species that come under the zoological kingdom of Animalia, and 140 under the more primitive Protista.

“The publication titled Fauna of Sundarban Biosphere Reserve is the first consolidated and updated information of the faunal diversity of the Sundarbans. It lists over 2,600 species, including the new species described from the mangrove ecosystem as well as threats faced by them due to climate change,” ZSI Director Kailash Chandra told The Hindu.

Biswajit Roy Chowdhury, secretary of Nature Environment and Wildlife Society, a non-governmental organisation and one of the authors of the publication, says it is encyclopedic in its scope.

“When we talk about Sundarbans we refer to only a few major species in the reserve forest area in about 4,260 sq. km. The publication catalogues the entire faunal diversity of Sundarban Biosphere Reserve covering 9,630 sq. km spread over 19 blocks in South 24 Parganas and North 24 Parganas of West Bengal,” Mr. Roy Chowdhury said.

Gone missing

The researchers document the famous tigers of these islands, which have adapted to aquatic conditions around, the human-tiger conflict, and behaviour of the big cat. The fortunes of 50 mammalian species including the Asian small-clawed Otter, Gangetic Dolphin, Grey and Marsh Mongoose and the wild Rhesus Monkey, the only primate here, are also documented.

“Due to pressure on habitat from people and natural threats that have shrunk the mangrove swamp habitat, mammal numbers are declining,” the authors say. Two Rhinos, Swamp deer, Barking deer and Hog deer and Asiatic Wild Water Buffalo are not found in Sundarbans anymore, they say.

There are 356 species of birds, the most spectacular being raptors, or birds of prey, that occupy the highest canopies of the forest. Osprey, Brahminy Kite and White-Bellied Sea Eagle are dominant, while Rose-ringed parakeets, flycatchers and warblers are also found in the middle tier, while in the lower tier, kingfishers abound — and the Sundarbans has nine of them.

There are 11 turtles, including the famous Olive Ridley and Hawskbill sea turtles and the most threatened freshwater species, the River Terrapin.

A crocodile, 13 lizards including three species of Monitor Lizards and five Geckos are found here. The rivers, creeks channels and the islands together harbour about 30 snake species, led by the King Cobra, considered vulnerable by IUCN.

Others documented are the Monocellate or monocled cobra, Russell’s viper, common and banded kraits. Besides, ten species of frogs and toads are found.

Cartilaginous fish

The mangrove ecosystem covers about 350 species of fish. Cartilaginous fish, which have skeletons of cartilage rather than bone, make up 10.3%. The IUCN conservation status shows 6.3% fish are near-threatened and 4.85% are threatened. Also, there are 173 molluscs.

In another indication of its richness, 753 insect species are encountered in the Sundarban Biosphere Reserve. Of these, 210 are butterflies and moths. Moreover, Crustaceans — crabs, shrimp and prawns — constitute 334 species.