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Site description (2004 baseline)
Vembanad, one of the declared Ramsar site, is a coastal lagoon (Nameer 1993). It has a single, relatively narrow opening to the sea and must have been formed by the detritus dumped by six perennial rivers forming a narrow sand bar in the sea further west of the seashore. These six rivers (Achankoil, Pamba, Manimala, Meenachil, Moovatupuzha and part of Periyar) originating in the Western Ghats, with an annual rainfall of 4,000 to 5,000 mm and with extremely steep gradients in the channel, bring down considerable quantum of detritus. So over a period of time the sand bar in the coastal sea consolidated and stretched from near Kayamkulam in the south to Kochi in the north. The only mouth of the enclosed shallow water body is at Kochi. The lagoon thus formed is called the Vembanad backwater. In addition, during the rainy season, from July to October, the surplus discharge extends the waterbody by an additional 100-150 sq. km. Vembanad extends north-south, parallel to the shoreline, and is widest at its southern extremity, forming a bowl located about 3 m below msl. During summer, when the freshwater discharge in the rivers is reduced, water in the 100-150 sq. km flooded area recedes. Seawater flows inland through the Kochi mouth and gradually moves inland. By February-March, salinity reaches all parts of Vembanad. However, the salinity has a gradient with the highest levels near the northern sea mouth, gradually reducing southwards. All the six rivers emptying into the backwaters form braided channels, which fuse and split repeatedly, forming a delta-like configuration, which gets flooded during the rains. As Vembanad has been under human occupation for a long time, the natural vegetation has all but disappeared, except in the sacred groves of temples. A tiny portion of the once extensive Lowland Wet Evergreen Forest survives in a few sacred groves. Detailed literature on the vegetation of Vembanad Lake is not available to us. Sreekumar (2002) lists six species of mangrove (Avicennia officinalis, Bruguiera gymnorrhiza, Rhizophora apiculata, R. mucronata, Sonneratia cascolaris and Kandelia candel), 17 species of marshy and mangrove associates, eight nonmangroves, 15 hydrophytes, 18 weeds and garden escapes, and 12 species of plants under cultivation. In Pathirammal area of the lake, the endangered and endemic plant Aponogeton appendiculatus is seen (Red Data Book of Indian Plants, Botanical Survey of India, p. 31).

Key biodiversity

AVIFAUNA: The Nature Education Society, Trichur (NEST) was perhaps the first to bring out a comprehensive checklist of birds of Vembanad Lake (Nameer 1993). During their surveys coordinated along with the Asian Waterfowl Census (AWC), NEST identified 149 species of birds in January 1993. The total number of birds seen was 36,500 of 32 waterbirds and three raptors. About 57% of the species seen belonged to Anatidae, followed by Phalacrocoracidae (19%) and Ardeidae (17%). Many species of birds were much above their 1% biogeographic population threshold (see Wetlands International, 2002 for latest population thresholds). For example, 4,562 Little Cormorants Phalacrocorax niger were counted in 1993, while their 1% threshold is only 1,500 (Wetlands International 2002). Garganey Anas querquedula concentrates at Vembanad in large numbers. More than 8,000 were counted while the 1% population threshold is only 2,500. The Indian Whiskered Tern Chlidonias hybridus also concentrates here in large numbers, sometimes up to 1,700 individuals are seen (Nameer 1993). The Department of Forests and Wildlife, Government of Kerala with the help of Kottayam Nature Society conducted a survey after a period of eight years in 2001. This survey recorded 15 species not seen earlier in 1993. Although the number of bird species increased to 171, there was 45% decline in the bird population (Sreekumar 2001). But more alarming than the fall in the total number, was certain changes in the species composition in some important habitats. For instance, the un-reclaimed portion of Vembanad Kayal between Pathiramanal and Kumarakom had been the most important roosting site for migrant ducks and teals. Flocks totalling 25,000 were observed earlier. During 2001, only hundred odd ducks were seen here. The greatest loss in the recent past has been of the Northern Pintail Anas acuta (2,000 in 1993, but only 39 in 2001), Garganey (8,000 in 1993, none in 2001), and Common Teal Anas crecca (1,000 in 1993, none in 2001). However, at the same time, some species showed an increase. For example, the Lesser Whistling Duck Dendrocygna javanica increased from 5,000 in 1993, to 10,464 in 2001 and the Little Cormorant increased from 4,562 in 1993, to 6,058 in 2001(Sreekumar 2001). The population of the Indian Whiskered Tern remained almost same – 1,779 in 1993 and 1,888 in 2001. In 2002, Kottayam Nature Society conducted the AWC again with the help of the Department of Forests and Wildlife (Sreekumar 2002). The figures were alarming. A total of 13,276 birds were counted, almost half of the 2001 figures. This included land birds such as the Greater Grey-headed Fish-eagle Ichthyophaga ichthyaetus, Black Kite Milvus migrans and Black-winged Kite Elanus caeruleus. A general decrease in the number of almost every species was seen, except for few such as the Black-headed or White Ibis Threskiornis melanocephalus (Near Threatened) which increased from 1 in 2001 to 20 in 2002, Cotton Teal or Pygmy Goose Nettapus coromandelicus from 156 in 2001 to 631 in 2002. Northern Pintail showed some increase from 39 in 2001 to 1,700 in 2002. The Whiskered Tern also increased from 1,888 in 2001 to 3,483 in 2002. The greatest fall was seen in the number of Lesser Whistling Duck: only 962 were counted in 2002. Some species were not seen at all in 2002. While the Pheasant-tailed Jacana Hydrophasianus chirurgus disappeared in 2002, the Bronze-winged Jacana Metopidius indicus was seen for the first time. However, the overall trend was not good. The decline was mainly due to decrease in the number of ducks. The so-called Bird Sanctuary of the Kerala Tourism Development Corporation showed a decline in the number of birds. This is extremely significant as this is the only breeding area of waterbirds in this region (Sreekumar 2002). Despite the decrease in duck numbers due to increased disturbance by motorboats, Vembanad Lake still has great potential to bring them back to their former numbers, once motorboat movement is controlled. We have included this lake in the IBA list as it still has great potential to attract large numbers of waterbirds, once corrective measures are undertaken.

OTHER KEY FAUNA: Vembanad Lake is famous for its fisheries. A list prepared by Dr. K. G. Padmakumar (Sreekumar 2002), enumerates 58 species of fish, including many commercial fish such as Catla catla, Labeo rohita, Ctenopharyngodon idella, Wallago attu, and Channa punctatus. Shellfish Macrobrachium rosenbergii, M. idella and Metapenaeus dobsoni, and Lamellidens sp. Villorita cyprinoides, Meretrix meretrix and M. casta are the molluscs reported from this lake.

Acknowledgements
Key contributors: P. O. Nameer and B. Sreekumar.

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Recommended citation
BirdLife International (2024) Important Bird Area factsheet: Vembanad Lake (India). Downloaded from https://datazone.birdlife.org/site/factsheet/vembanad-lake-iba-india on 23/12/2024.