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Sreekantha Energy & Wetlands Research Group, Centre for Ecological Sciences, Indian Institute of Science, Bangalore - 560 012. E-mail: sreekantha@ces.iisc.ernet.in

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The Western Ghats, extending for over a length of 1600km, lying parallel to the coast hardly 50km away, form one of the magnificent escarpments of late Tertiary age. Except for a short gap near Palghat, it is unbroken throughout its length. The marked diversity of landscape, the youthful character of the rivers, the precipitous escarpments, the narrow gorges and the relative high elevation of the plateau compared to the plains (Radhakrishna, 1991) are the key geographical features of these Ghats.

The Western Ghats, one among the 25 global hotspots of biodiversity, harbours very rich flora and fauna. There are records of over 4,000 species of flowering plants (38% endemism), 330 butterflies (11% endemic), 156 reptiles (62% endemism), 508 birds (4% endemism), 120 mammals (12% endemism) (Daniels, 2003), 290 fishes (41% endemism) (Dahanukar et al, 2004); (Babu and Nayar, 2004) and 131 amphibians (75% endemism) (Gururaja, 2004). The varied climate and diverse topography create a wide array of habitats that support unique sets of plant and animal species. The level of endemism is high and the region is considered one of the world's biodiversity hotspots (Menon and Bawa, 1997).

Fishes-most diverse, yet most neglected

Fishes are the most numerous vertebrates living on this earth and worldwide there are over 25000 species of fishes. Of this about 48% live in freshwaters that constitute just 0.01% of the earth's water. Freshwater fish diversity is unevenly distributed on this planet. The species richness is high in tropical region compared to other parts of the earth. Usually these regions are characterized by high levels of endemism. The world's major rivers like Amazon, Congo, Nile, etc. are some of the pristine rivers of the world with respect to freshwater fish diversity. I t has been estimated that the river Amazon and its tributaries may together harbour 3000 or more species of fishes. Such species-rich areas are called ‘hotspots' and dominate other patterns or trends. Probably the climatic conditions of the tropical region are more stable compared to the temperate regions of the world. This could be one of the favourable conditions for the growth, survival and evolution for the species in tropical regions.

While a great deal of attention has been given to the loss of biodiversity in tropical rain forests, or in coastal areas, the diversity of and within freshwaters has been widely neglected. There is little doubt that freshwater fishes represent the most threatened set of vertebrates (Leveque, 1997). In classifying the worlds' top 25 biodiversity hotspots, vertebrate group was considered excluding fish. This is mainly because of the poorly available data wherein the author (Myer et al 2000) predicts that there could be at least 5,000 species waiting to be discovered among fish, which is more than all mammals.

FRESHWATER FISH DIVERSITY OF WESTERN GHATS

Several attempts have been made to compile a checklist of freshwater fishes of the Western Ghats. These attempts mainly focused on evolving with a comprehensive checklist of freshwater fishes, which is an out come of the patchy (may be of a river basin, a region in the Western Ghats, an administrative boundary within the Western Ghats, etc) taxonomic information available on the diversity of freshwater fishes. Daniels (2001) has listed 218 species from the Western Ghats of which 114 (52%) are endemic to Western Ghats. However, this report lacks a detailed checklist of fishes found in the Western Ghats. The subsequent checklist (Shaji et al 2001) listed 287 fishes with names of individual species. This compilation considered certain estuarine fishes that are found to ascend freshwater for longer distances. The list highlighted the presence of 67% endemic species and 18 exotic or transplanted to the region. The most recent information available is by Dahanukar et al 2004 that lists 288 freshwater fishes, of which 118 (41%) are endemic to Western Ghats. The threat status of fishes found in Western Ghats suggests that at least 41% of fish fauna is threatened by either being vulnerable, endangered, or critically endangered. This study also necessitates the implication of potent conservation measures to conserve the fish fauna of Western Ghats.

Present scenario

Present compilation of the checklist (Annexure) of the freshwater fishes in Western Ghats region lists 318 species of which 42.8% (136 species) are endemic to the region. Of this about 27 species are critically endangered and 55 endangered while 128 are data deficient. Altogether, 39.1% (123 species) of the freshwater fishes come under the category of critically endangered, endangered and vulnerable (Figure 1). Of the 27 critically endangered species 24 are endemic to the region. Similarly, of the 55 endangered species, 37 are endemic. Yet 49 endemic species are data deficient. A comparison of IUCN status between endemic and non-endemic species has been made in figure 2, which clearly shows that the endemic species comprises more of threatened species and the non-endemic comprise more of generalist species in Western Ghats.

Figure 1. Species composition with respect to IUCN status

Figure 2. Comparison of the IUCN status between endemic and non endemic groups of fish species

DIVERSITY OF HABITATS IN WESTERN GHATS

The Western Ghats gifted with perennial streams outlines the unique habitats for the fishes. They run for about 1600 km from north to south and are drained by 38 east flowing and 27 west flowing major rivers. It is now identified that these pristine habitats are unique biological regions and ‘hotspots' of fish diversity. The river systems consist of mainly the running water habitat and lacustrine habitats. There are numerous small lakes and ponds throughout the Western Ghats, which form the standing water habitats. Apart from these, there are forest swamps, deep wells, estuaries, gorges, etc, which are responsible for diverse fish fauna of the region.

Lake habitats in the Western Ghats

It can be observed that the species composition in these different habitats differs significantly between each other. Hill-streams dominate with the species of Balitoridae, especially the species of the genus Schistura. The torrential habitats compose of the highly adapted species of Garra, Glypththorax, etc. Shallow gradually flowing streams are rich with most general and small species (Ex. Puntius, Danio, Rasbora, Aplocheilus, etc). Species composition in the lacustrine habitats is mainly influenced by human beings in terms of exotic species introduction and large-scale harvesting. In these types of habitats large and medium commercial fishes dominate along with native commercial fishes. The exotic fish in the Western Ghats are Cyprinus carpio, Carassius carassius, Tinca tinca, Oreochromis mossambicus and the rainbow trout Oncorhynchus mykiss (golden and ordinary strains). The estuaries are dominated with dadromous and secondary freshwater fishes. Some of the Wells in Kerala are recorded with the blind catfishes such as Horaglanis krishnai and H. alikunhi.

The freshwater ecosystems of the Western Ghats are characterized by their patchy nature. Due to which each freshwater ecosystem, say a river or lake can be considered as an island with its own environmental characteristics. This situation might have allowed to occur allopatric speciation and several species are known only from a drainage or a portion of the drainage system. This could be one of the important reasons behind, the exceptional fish diversity in Western Ghats and yet so endemic and threatened.

Connection between river basins

Natural inter-basin transfer of fish fauna takes place when the terrain is flat and receives heavy rainfall that inundates the entire region. In case of Western Ghats, although rainfall is of the range of 6000mm annually, undulating terrain and great slopes of the basin provides little scope for inter-basin transfer of the fish fauna. However, recent anthropogenic activities in the form of damming the rivers and inter-basin transfer of water are the possible pathway for fish fauna to exchange between river basins.

Coastal connections

These are the connections available for diadromous and estuarine fishes to move from one basin to another, during monsoon season, when large amount of freshwater enters the sea from the estuary. Fishes that can withstand the reduced salinity of the sea possibly migrate to the nearest basin and recolonise.

Falls as barriers to fish migration

Within a river basin, presence of falls greatly hinders the upstream and downstream movement of fishes. Most of the west-flowing rivers in the Western Ghats originate at the hilltop and after covering certain distance, they leap down over a great depth, forming natural falls. A study carried out by Bhat (2003) in four west flowing rivers of the Western Ghats of Karnataka found that upper reaches of the falls between the rivers were more similar to each other than comparing upper and lower reaches on the same river.

THREATS TO FRESHWATER BIODIVERSITY WITH SPECIAL REFERENCE TO WESTERN GHATS REGION

The Western Ghats region, like other parts of the tropics, is undergoing rapid transformation. The deforestation rate is high and forests are being transformed into agriculture and monoculture plantations. Hydroelectric projects, mining, and extraction of forest products are also altering the landscape (Bawa and Menon, 1997). Major human induced ecological changes in the Western Ghats begin with the arrival of agriculture and pastoralism. A climatic change towards the middle of fourth millennium BP, which induced widespread human migrations within the Indian sub-continent, is correlated to decline of forests and mangroves in Western Ghats. The ecosystems in the Western Ghats do bear the imprints of human actions through history (Chandran, 1997).

Habitat fragmentation

Fragmentation, the loss and isolation of natural habitats, is one of the greatest threats to regional and global biodiversity. Habitat fragmentation takes place when the continuity is broken. This may be mainly through the construction of dams across the rivers, conversion of wetlands into other forms of land uses, destruction of riparian vegetation, etc. Eight kinds of species have been identified that are likely to be especially vulnerable to the effects of fragmentation: rare species, species with large home ranges, species with limited powers of dispersal, species with low reproductive potential, species with short life cycles, species dependent on resources that are unpredictable in time or space, species of habitat interiors, and species exploited or persecuted by people. Due to the terrain of the Western Ghats, the rivers are extensively harvested for hydroelectric power through the construction of dams resulting in the fragmentation of the rivers. Anadromous fishes begin their life in freshwater, move to the marine environment to grow and mature, and then return to freshwater to reproduce. In Western Ghats decline in the population of Anguilla bengalensis has been attributed to fragmented rivers.

Land use change in the catchment

The cumulative geographical, hydrological, and ecological impacts of deforestation, timber harvesting, destruction of riparian vegetation, agricultural development, urbanization, land drainage, and flood protection on rivers have been documented worldwide. Deforestation of the catchment area usually results in soil erosion and nutrient input into the rivers. Destruction of riparian vegetation damages the coarse stream substrate where several fishes find their shelter. High suspended sediment concentrations in rivers and sediment deposition on the riverbed can affect the health, habitat and particularly damage the gills. It has been estimated that about 25.6 % of the forest cover in Western Ghats is lost over a span of 22 years.

The Western Ghats region is prone to large-scale mining activities. These activities contribute huge quantities of silt into the aquatic systems. The rapid transformation of habitats in the form of silt deposition may result in the total changes in the species composition of the particular habitat.

Flow regulation

Flow regulation is mainly due to the construction of dams across the rivers. It can be estimated that more than 60 % of the worlds is and many rivers have reduced to cascades of manmade lakes. This clearly reveals the magnitude of flow regulations all over the world. The flow regulation removes the lotic habitats and give rise to lentic habitats. Also, the homogenization of the habitats and within which it forms the temperature gradients.

Interlinking of river basins

The concept of interlinking of river basins is gaining importance in recent years. Several such schemes in India and abroad have already being commissioned. However the serious repercussions in terms of water balance, water quality, the spread of pests and diseases, alterations to natural biotic distribution patterns and the disruption of significant ecological processes. In Indian context, the Western Ghats are characterised by high levels of fish endemism and the Himalayan region in terms of high diversity. Interlinking of the rivers of India may disrupt the distribution patterns of the fishes. Some fishes may find new optimal habitats and flourish prolifically on the expense of other native fishes. Possibly the native fishes may be rare and endemic fishes needing immediate conservation measures. Thus in the process several species may become extinct and several may flourish. The concept of interlinking of the rivers of India is in the process of implementation. In this connection the above-discussed possibilities may be quite relevant to be considered.

Over harvesting destructive fishing methods

Fishes are regarded as the rich sources of protein. Throughout the world, fishing has offered employment to thousands of families. Subsistence fishing in streams, rivers and tanks has been a source of living for weaker section of the society. All these aspects have resulted in commercialization of fishery. The annual commercial catch from the fisheries of the world is approaching 100 million t. Such a tremendous rate of extraction from the aquatic ecosystem has adversely affected the fish base of the world. Human uses of freshwater resources have threatened the sustainability of these resources. Increase in the fishing population and the demand for fish has intensified the fishing activities. Fishermen are using the destructive methods of fishing to get higher yields. Illegal usage of small meshed fishing gears that damage the juveniles, is still in use. Fishing using chemical and herbal poisons like copper sulphate, bleaching powder, tree extracts damage the entire fish population of the aquatic body. Dynamiting is another destructive method by which fishermen easily collect huge quantity of fishes. Use of dragnets which sweep away the entire fish resource of a particular area including juveniles can be disastrous to both target and non-target fishes of the area.

Introduction of alien species

A number of species get introduced into the waters, most of which are to the reservoir areas of dams with a view to increase the net fish yield of the reservoir. Of these introduced fishes, many have naturalised in the streams, ponds and tanks of the region. Species like Oreochromis mossambica, Gambusia offinis, Poecilia reticulata, etc. are exotic species, which are originally from Africa and South America and introduced extensively in India. Species like Labeo rohita, Catla catla, Cirhinus mrigala have been introduced recently in to the reservoirs. Importantly Cyprinus carpio has been widely introduced into the reservoirs of Western Ghats. This kind of haphazard introduction not only jeopardized the reservoirs but also threatened the freshwater biodiversity.

Chemical and thermal pollution

Changes in water quality due to discharge of effluents from various industrial, domestic and agricultural sources have deteriorated water quality. The toxic elements in pollutants may be total, killing all the fish species present, or selective, destroying a few sensitive species or so altering the environment that some species are favoured and others not.

Diseases

Several incidences of outbreak of the diseases such as EUS (Epizootic Ulcerative syndrome) have been witnessed in freshwater habitats of Western Ghats. These have affected the sensitive native fishes of the region. For instance, in the last decade, large-scale mortality of freshwater fish took place due to EUS in most parts of the Western Ghats and the country as well.

Conservation practices of freshwater fishes in Western Ghats region

Roughly 318 species of fish, which have been identified, are undoubtedly the relics of the several hundreds of species that have ever existed in this region. The reason behind existence of these modern survivors may be presence of some of the excellent basins in good condition within the region and traditional conservation practices in terms of protected sites, temple ponds, etc. The traditional practices involve declaring a stretch of river or a pond as sacred and giving the fullest protection to the fishes dwelling in them. However, to conserve the existing fish resources of the region, several other management strategies need to be designed and implemented.

Properly maintained scientific data on the fish fauna of the water body, participatory approaches in conservation, educating the fishing communities, managing the terrestrial ecosystem in healthy condition, stopping the introduction of exotic species, and careful extraction, in situ and ex situ conservation practices for the critically endangered species, etc. can be listed. However, the basic requisite is the change of view about the Western Ghats from a region of production to a region of conservation.

References and Books

*Checklist of freshwater fishes of Western Ghats (Compiled from various published sources)
Note : CR - Critically Endangered, EN - Endangered, VU - Vulnerable, LR - Lower Risk, DD - Data Deficient.

Endemic Species of Western Ghats

Non-endemic Species of Western Ghats

Introduced Species