The Extremely Severe Threat the Freshwater Ecosystems of Kerala Face due to the Introduction of Exotic Species of Fishes in the Reservoirs
There is the often repeated assertion that the State of Kerala is blessed with an abundance of freshwater. An annual average rainfall of more than 3000mm, the north-south alignment of the Western Ghats with its crest rising up to an average elevation of 1800m above the mean sea level, the intense seasonal rainfall running off this steep hard rock mountain creating a large number of distinct river basins and the humid tropical vegetation cover have all created an extraordinary array of freshwater and brackish water ecosystems in the State of Kerala. The Western Ghats as a whole forms a refugia for a very large assemblage of biota. The complex topographical conditions each river basin is endowed with results in unique physico-chemical and biological characteristics not replicated even in the adjacent basins. Some sections of the Western Ghats have the distinction of harbouring the highest percentage of endemic species both in the plant as well as animal world. Simultaneously Western Ghats also has the dubious distinction of extensive and rapid habitat degradation. Hence it is considered a globally important hot spot as far as its biodiversity is concerned.
It is the quantum of available water and the characteristics of the hydrological cycle that makes the Western Ghats such an exceptional refugia of flora and fauna. Naturally moisture demanding plants, aquatic insects, fishes and amphibians constitute a large percentage of the RET (Rare, Endangered and Threatened) species recorded from this landscape unit. It is the human manipulations specifically adversely affecting the hydrological cycle that is posing the severest threat to this biodiversity. Deforestation and unsuitable landuse practices have already curtailed the perennial nature of the rivers. Excessive application of agro chemicals has drastically affected the chemical quality of the surface water discharge everywhere in the State. All the major rivers have been repeatedly dammed and some diverted to other basins. Downstream of all the dams for considerable lengths the river channels remain totally dry for practically round the year. The coastal brackish water systems have suffered drastic modifications including extensive reclamation, reduced freshwater inflow during the lean season and sea water ingress during summer apart from widespread urban sewage accumulation. In short practically all the rivers and backwaters in Kerala are imperilled.
The extraordinary diversity of freshwater fishes in Kerala is illustrated by the fact that a relatively small basin, Chalakkudy covering less than 1700sq km has more than 100 species of fishes recorded from it so far. The upper reaches of most of these basins are within forests and have not been exhaustively surveyed for their biota. This year the world has been celebrating as the Year of Biodiversity to highlight the significance of all other species sharing Planet Earth along with us. The celebration is also to draw attention to the fact that the intricate web of life supporting human existence also is suffering irreparable damage by our species.
Yet it is ironical that in this State of Kerala claiming high literacy standards and environmental consciousness we are simultaneously doing the most irresponsible of activities endangering our rich biodiversity and fragile ecosystems. The ongoing official programme of introducing exotic fishes in all the reservoirs in the State is a classical example of human folly. Already our natural habitats are extensively threatened by exotic species of plants and animals, some intentionally introduced and many accidental invasives. Weed species such as mikania, aggressive plant feeders such as the Giant African Snail, African fishes such as catfish are taking over habitats and drastically undermining them.
The present move to introduce exotic fishes into the reservoirs should be halted immediately. This move is supposed to be for enhancing the availability of freshwater fishes. But excepting a few, most of our reservoirs practically dry up in summer, especially during the years when there is a failure of the retreat monsoon. The introduced fishes would be aggressive, prolific breeders which would move out of the reservoirs and expand their range along the river courses, both upstream as well as downstream. They would easily push out of their niches the indigenous species and prey upon the local species of fishes, their fingerlings or spawn. They would voraciously feed on the aquatic biomass and successfully compete with all the indigenous species of freshwater fauna. Most of our reservoirs are in the Western Ghats and the catchment areas upstream of the reservoirs are Reserved Forests. At least twenty large reservoirs in the State are within National Parks and Sanctuaries where the primary objective of management of the area is wildlife protection. Introducing exotic species is obviously violation of the Wildlife Protection Act. Another seven reservoirs are inside wet evergreen forests with very high biodiversity potential where the species richness remains inadequately documented.
The very economic viability as well as sustainability of this dubious venture should be questioned. In spite of the long history of introducing fish fry into reservoirs such as Neyyar, Malampuzha etc the actual returns need to be assessed objectively. With very inadequate data base on the primary as well as secondary productivity in our man-made reservoirs, the carrying capacity of these unstable water bodies to support large fish populations is to be questioned.
8 December 2010 S. Sathis Chandran