Biodiversity Status of Fishes Inhabiting Rivers of Kerala (S. India) With Special Reference to Endemism, Threats and Conservation Measures

Kurup B.M., Radhakrishnan K.V. & Manojkumar T.G.

School of Industrial Fisheries, Cochin University of Science & Technology, Cochin 682 016, India
E-mail: madhukurup@hotmail.com

ABSTRACT

The identification of 175 freshwater fishes from 41 west flowing and 3 east flowing river systems of Kerala were confirmed. These can be grouped under 106 ornamental and 67 food fishes. The biodiversity status of these fishes was assessed according to IUCN criteria. The results showed that populations of the majority of fish species showed drastic reduction over the past five decades. Thirty-three fish species were found to be endemic to the rivers of Kerala. The distributions of the species were found to vary within and between the river systems and some of the species exhibited a high degree of habitat specificity. The diversity and abundance of the species generally showed an inverse relationship with altitude. The serious threats faced by the freshwater fishes of Kerala are mostly in the form of human interventions and habitat alterations and conservation plans for the protection and preservation of the unique and rare fish biodiversity of Kerala are also highlighted.

INTRODUCTION

Kerala is a land of rivers which harbour a rich and diversified fish fauna characterized by many rare and endemic fish species. The Western ghats are recognised as one of the 21 biodiversity hotspots of the world. A data base on fish biodiversity is essential as a decision making tool for conservation and management of fish germplasm, declaration of part of the rivers as aquatic sanctuaries, protection and preservation of endangered species and mitigation of anthropogenic activities so as to fulfil India’s obligations under conventions on biological diversity with special reference to Articles 6 and 8 of UNEP (1992). Notable studies on the freshwater fish fauna of Kerala are those of Day (1865, 1878, 1889); Pillai (1929); John (1936); Hora and Law (1941); Silas (1951a, 1951b); Remadevi and Indra (1986); Pethiyagoda and Kottelat (1994); Kurup (1994); Kurup and Ranjeet (2002); Easa and Shaji (1995); Menon and Jacob (1996); Manimekalan and Das (1998); Ajithkumar et al (1999); Raju et al. (1999a and b) and Biju, Thomas and Ajithkumar (1999). In the present paper an attempt is made to prepare a consolidated list of freshwater fishes of Kerala and to assess their biodiversity status as per IUCN criteria. Their patterns of distribution have been delineated giving special emphasis to endemism and various anthropogenic threats which aggravate the degree of their endangerment. This communication also deals with various management plans relevant to the conservation of freshwater fish biodiversity of Kerala.

MATERIALS AND METHODS

Data on qualitative and quantitative abundance of fish species inhabiting various rivers were gathered during extensive surveys and sampling carried out as part of various externally aided research projects such as the ongoing NAT-ICAR project on Fish germplasm inventory evaluation and genebanking of freshwater fishes of Kerala, the ICAR sponsored population characteristics, bionomics and culture of Labeo dussumieri (1987-1990), the Kingdom of Netherlands financed project entitled exploited fishery resources of Vembanad lake (1988-1990). Experimen-tal fishing was conducted from not less than 10 sites on each river. Habitat diversity was given foremost importance during selection of locations within the river system. The sites for habitat inventory were selected based on channel pattern, channel confinement, gradient and streambed and bank materials. All the physical habitat variables in the selected reaches were studied (Anon. 2000). The position of the selected zones was determined using hand held GPS, altitude was estimated using electronic altimeter, conductivity and TDS using Lynx microprocessor based conductivity meter. Dissolved oxygen levels at each survey location were measured using Eutech cyberscan DO100 dissolved oxygen meter. Light intensity on the surface water and flow velocity was measured using Lux meter and water current meter, respectively. Total alkalinity and hardness were estimated based on Clesceri, Greenberg and Trussell (1989). The specimens were collected using various types of fishing methods such as cast nets (16 mm, 18 mm, 22 mm), gill nets (32 mm, 38 mm, 64 mm, 78 mm, 110 mm), drag nets (4 mm, 15 x 3 mtrs), scoop nets and other local contrivances. Collections were made from all selected locations during 8:00- 18:00 h and 20:00-06:00 h. Visual observations were also carried out if the water was clear with a view to assess the distribution of the fish and abundance. Special care was taken to maintain uniformity in fish catch per unit effort (CPUE) (effort in hours) so as to compare the populations at selected locations of a river system. Density of fish populations at each location was estimated as abundance index

where AI = Abundance index, n(k) = number of individuals of the species k caught at the study site and N = Number of individuals of all fish species caught at that site, FU = Fishing unit as described by Arun (1997). The Shannon-Weaver diversity index (H= Â n₁/n Ln n/n

Where H = Diversity index, n₁ = number of individuals in species of a population or community, n = number of individuals in sample from a population for each river systems were calculated using the software Primer 5. Apart from this, the catches of the freshwater fishes from the landing centres and markets adjacent to the respective rivers were also inspected and specimens were collected for detailed examination. Samples were preserved in 8 percent formalin and kept for identification. Fishes were identified following Day (1878); Talwar and Jhingran (1991); Jayaram (1981, 1999); Kishori Lal Tekrival and Arunava Rao (1999). About 125 research papers on the freshwater fish fauna of Kerala available during the period 1965- 2000 were also consulted towards compiling the past data of abundance and availability for assessing biodiversity status. The status of each species, whether threatened or endemic, was assigned based on IUCN categorization (NBFGR 1998).

RESULTS

BIODIVERSITY STATUS OF THE FRESHWATER FISHES DELINEATED

One hundred and seventy five fish species under 13 orders, 29 families and 65 genera were collected and identified from the rivers and streams of Kerala. The name of the species, together with their commercial importance, status as per IUCN criteria and the river sources from where their occurrence has been recorded are shown in Table 1. This includes 25 new species recorded and described in the recent past. Of the 175 species, 4 species are exotic and alien. Among the species listed under threatened category, 18 were critically endangered while 38 species are endangered, whereas 28 species are vulnerable. There are 48 species under the non-threatened category, among which 21 are nearly threatened with low risk whereas 34 species belonged to low risk of least concern. (Figure 1). Among the 18 critically endangered species, 7 are confined to only a single locality while 5 species are found in 2 locations in the same river (Table 2). Among the endangered species, 5 are confined to a single location while 6 are from 2 locations of the same river system. The distributions of 15 species are found to be restricted to 2 rivers, while 12 species are recorded from 3 rivers (Table 3). Species such as Lepidopygopsis typys, Silurus wynaadensis, Gonoproktopterus micropogon periyarensis, Osteochilichthys longidorsalis, Horaglanis krishnai and Labeo potail are critically endangered and among them, Silurus wynaadensis, Osteochilichthys longidorsalis, Horaglanis krishnai and Labeo potail have shown a population reduction of 99 percent over the past two decades. The distributions of these fishes are restricted to one or two locations. Silurus wynaadensis, Labeo potail and Osteochilichthys longidorsalis are reported from the upstream locations of Kabbini and Chalakkudy rivers respectively where as Horaglanis krishnai is known to be only recorded from the subterranean wells of Kottayam district. While delineating the distribution pattern of freshwater fishes, it could be seen that more than 90 percent of the fishes so far reported from Kerala were encountered from the 5 major rivers. (Kabbini, Kallada, Bharathapuzha, Periyar and Chalakkudy).

Table 1: List of freshwater fish species reported from the Kerala part of Western Ghats

*Important CR-Critically endangered
**Highly important EN-Endangered
***Very highly important VU-Vulnerable
LRnt-Low risk nearly threatened
LRlc-Low risk least concern
DD-Data deficient
Intr - Introduced

Table 2: Critically endangered fresh water fishes of Kerala and the regions where they are found

Table 3: Endangered fresh water fishes of Kerala and the regions where they are found

ENDEMIC FRESHWATER FISH DIVERSITY OF KERALA

Of the 175 fish species reported, 33 species were found to be confined to the water bodies of Kerala (Table 4, Figure 1). This group includes species such as Puntius denisonii, Nemacheilus keralensis, Oseobrama bakeri, Chela laubuca, Gonoproktopterus micropogon periyarensis, Silurus wynaadensis Neolissochilus wynaadensis, Puntius ophicephalus, Garra surendranathinii, Garra menoni. The distribution of these species varies both within a river system and also between river systems and many of these fishes have a highly restricted distribution. While assessing the biodiversity status of these fishes, it appeared that 9 species are critically endangered while 10 are endangered. Lepidopygopsis typus, Labeo potail and Gonoproktopterus micropogon periyaresis are critically endangered and species such as Puntius denisonii, Osteobrama bakeri, Chela fasciata, are endangered according to the IUCN crieria. Currently many of the endemic, high value ornamental fishes are exploited for commercial purposes from the wild, thus aggravating their degree of endangerment. However, the quantities of these fishes exploited for trade purposes are not available. The rehabilitation of populations of endemic fishes through standardisation of captive breeding techniques and massive seed ranching are necessary for restoration and replenishment of their stock.

Figure 1. Biodiversity status of the freshwater fishes of Kerala based on IUCN

Table 4: List of Endemic freshwater ornamental fishes of Kerala and their biodiversity status and regional distribution

ORNAMENTAL, CULTIVABLE AND FOOD FISHES OF KERALA

Of 175 species identified from the diverse river systems of Kerala, 106 are ornamental while 67 species are food fishes (Figure 2). Among the 106 ornamental species, 10 species including Puntius denisonii (Red line torpedo fish), Puntius arulius (Arulibarb), Puntius conchonius (Rosy barb), Puntius filamentosus (Tiger barb), Puntius ticto ticto (Ticto barb), Puntius vittatus (Koolie barb), Puntius fascialtus (Melon barb), Parambassis thomassi (Glass fish), Hrabagrus brachysoma and Horabagrus nigricollaris (Yellow cat fishes) have already secured positions in the national and international markets as ornamental fishes. The rest of the species have tremendous potential for development as candidates for the international ornamental fish market. Captive breeding and seed production technology of most of these fishes are not yet standardised and this forms the major bottleneck for their introduction in domestic and international trade. Puntius carnaticus and Gonoproktopterus thomassi have already been identified as potential candidate species suitable for aquaculture and can be developed as substitutes for Grass and Chinese carps in composite farming. 67 species of potential food fishes were recorded from the Kerala part of the Western Ghats, including species like Mastacembeles armatus, Gonoproktopterus curmuca, Gonoproktepterus micropogon periyarensis, Channa marulius, Channa striatus, Mystus guliio, Mystus cavasius, Anguilla bengalensis and Puntius sarana subnasutus.

Figure 2. Percentage of ornamental relative to food fish species reported from Kerala

FISH DIVERSITY AND ALTITUDE

Examination of fish biodiversity at various altitudes from 6 rivers of Kerala showed that species diversity was inversely related to altitude (Table 5). In the Bharathapuzha river system between altitudes of 0- 774 m the Shannon-Weaver diversity index varied from 0-2.9 and the diversity indices showed maximum value between altitudes of 0-65 m while it was lowest at altitudes ranging from 580-645 m. The presence of quite large numbers of waterfalls in this region might have contributed to the biodiversity decline of this reach. In the Chalakudy River system the diversity index ranged between 1.76- 3.8 between altitudes of 0- 1032 m. The highest diversity was found between 0-65 m while it was lowest at reaches between 516-580 m. In the Pamba River system the Shannon Weaver diversity index ranged between 0.67-2.64 between altitudes of 0-161 m. The diversity was highest at altitudes between 0-65 m while it was lowest from 903-968 m. In the Periyar River system between altitudes of 0-839 m the diversity ranged between 1.55-3.056. Highest fish diversity was observed in the lower stretch (0-65 m), while the diversity was poor at 194-452 m due to the commissioning of some mega hydroelectric projects. In the Kallada River system the diversity was highest in the stretch between 258-323 m altitude. Interestingly, in lower stretches with an altitude of 0- 65 m the diversity was poor due to habitat alteration on account of various human interventions. The fish diversity in the entire river system was in the range between 0.99-2.25. In the Kabbini river system the study was confined only in the upstream habitats having an altitude of 710-968 m and the diversity index in this stretch ranged between 1.24-3.57. The remaining parts of the river system pass through Karnataka state. At Kabbini the highest fish diversity was observed at an altitude ranging between 710-774 m, while it was lowest at altitudes ranging from 903-968 m. The results of this study revealed that fish diversity was highest in the lower stretches of the Chalakudy River system (0-65 m) while it was lowest in the upstream reaches of the Bharathapuzha River system at an altitude between 581-600 m (Table 5). Among the six river systems studied, the Chalakudy and Kabbini River systems showed the highest diversity index ranging between 1.76-3.8 and 1.24-3.37 respectively. In contrast, in the upstream reaches of the Periyar River system, between 774-968 m biodiversity showed an unusually increasing trend. This is due to the dominance of some critically endangered endemic species such as Lepidopygopsis typus, Gonoproktopterus micropogon periyarensis and Crossocheilus periyarensis which show high degrees of habitat selectivity and can sustain themselves only in the microhabitats prevailing in these areas. Abundance of L. typus showed a positive correlation with amount of bedrock substrate, chute type microhabitat, overhanging boulders, overhanging vegetation, total shade and stream cover. Optimum habitat of G. micropogon periyarensis was found as midchannel pools with comparatively good depth, overhanging vegetation, slope and excellent shade while that of C. periyarensis is lateral pools and scour-out pools with enough woody debris, overhanging vegetation and tree cover. According to Freeman, Bowen and Crance (1997), animals preferably occupy areas that best support survival, growth or reproduction. It may, therefore, be inferred that altitude has a clear-cut influence on the type of habitat prevailing in different reaches of the river systems. Survey and sampling conducted at six major river systems of Kerala also discloses that out of the 7 types of channel reaches, regime reaches showed the highest species diversity followed by pool-riffle and cascade. The contribution of regime reaches decreases with increasing altitude; meanwhile cascade and pool-riffle reaches are invariably high in the upstream habitats. Though beyond an altitude of 645 m, the contribution of these habitats shows a decrease and the river reaches are mostly represented by bedrock and step-pool type of habitats, the species diversity in these habitats are relatively minimal, with the presence of a few species characterised by very peculiar morphological adaptations which can only survive in these regions.

Table 5: Shannon-Weaver diversity index at different altitudes in six major river systems of Kerala

HABITATS OF CRITICALLY ENDANGERED SPECIES

Microhabitat details of 7 critically endangered and endemic species are shown in Table 6. In the Kabbini River system the habitat of Silurus wynaadensis species is characterized by an average sinuosity of 1.21 while the entrenchment ratio, w/d ratio and the slope are 0.09, 5.3 and 0.09 respectively. The dominant substrate is sand and the stream comes under the A1 type in Rosgen’s classification (Anon. 2000). The microhabitat of Neolissochilus wynaadensis is also located in the same river, where the average sinuosity, entrenchment ratio, w/d ratio and slope range between 1.2-1.6, 0.09-1.2, 3.2-5.3 and 0.06-0.09 respectively. Substrate is dominated by sand and the stream comes under the A5 type in Rosgen’s classification. The Periyar River system requires special conservation measures due to the presence of five endemic and critically endangered species in its upstream region. Lepidopygopsis typus, Nemacheilus menoni, Garra periyarensis and Gonoproktopterus micropogon periyarensis were found in microhabitats characterised by a sinuosity ranging between 1-1.4 while the entrenchment ratio, w/d ratio and slope are in the range of 1- 1.1, 0.87-28 and 0.1-0.15 respectively. The substratum is dominated by bedrock. The streams fall into both A1a+ and F1b classes. The sinuosity, entrenchment ratio, w/d ratio and slope are in the range of 1-1.3, 1- 1.09, 1.14-28 and 0.1-0.15 respectively in the microhabitat of Crossocheilus periyarensis. The substrate is dominated by bedrock and the species found only in A1a+ type streams.

BIODIVERSITY THREATS TO THE FRESHWATER FISHES OF KERALA

The available information on the freshwater fishes of Kerala is mostly on systematics, distribution and abundance (Pillai, 1929; John 1936; Chacko 1948; Menon 1951, 1993; Kurup 1994; Easa and Shaji 1995; Zacharias, Bharadwaj and Jacob 1996; Ajith Kumar et al 1999; Raju Thomas et al 1999; Biju et al 2000; Kurup 2001; Kurup and Ranjeet 2002). The present database is compared against past data to determine the degree to which the fishes have become depleted over the last 50 years. Anthropogenic activities are the main cause for the alarming decline of fish populations in most of the rivers of Kerala. Unsustainable and unethical fishing by using fish poisons, dynamiting and a wide array of prohibited fishing methods are rampant in the uplands and lowlands of most rivers. Habitat destruction of natural spawning and breeding grounds of the fishes through sand extraction and construction of physical obstructions across rivers has contributed to the population decline and the endangerment of the freshwater fishes. Many of the species reported as endangered are now found only in areas protected under Forest and Wildlife jurisdiction, which clearly indicates the reasons for their endangerment.

Table 6: Major physical habitat variables at the area of occurrence of some critically endangered species

The various types of destructive fishing activities practiced along the river systems of Kerala are summarized below.

Use of small meshed fishing gears

The use of small meshed fishing gears is prevalent in downstream sections of most of the rivers including the Achenkoil, Kallada and Pamba. Such practices, which are adopted for short-term profit, kill the fry and fingerlings of the fishes thus ultimately leading to regular growth over fishing and consequent reductions in populations.

Fishing using chemical and herbal poisons

Diverse types of fish poisons both of plant chemical origin are widely used in upstream, middle and downstream parts of most rivers.

Use of chemicals as poisons

Copper sulphate and bleaching powder are widely used in areas of rivers where water velocity is low. Fishes become inactivated or intoxicated and fishes including fingerlings are easily caught.

Use of insecticides as poisons

Insecticides and pesticides are used as a fish catching method, specifically for fishes that are either nocturnal or dwelling in small caves or crevices.

Seeds, bark and leaves of plants as poisons

Leaves, stems and seeds of different types of plants are used as poisons in shallow or low velocity waters. The seeds of palm, Othalathumkaya, Vakkanakkaya are regularly used for fishing.

Dynamiting

Dynamiting is a major method for catching food fishes but is less commonly used to catch ornamental varieties since it kills fishes instantaneously.

Electro-fishing

Electro-fishing is increasing in popularity in the down streams of the rivers like the Achenkoil and Pamba. It is mainly targeted at larger fishes; however, smaller, ornamental fishes are also killed by this method.

Destruction and modification of habitats

Destruction of fish habitat is another major cause of the decline in the ornamental fish population. Dams, bunds and levees act as barriers for free migrations of fish in the rivers. Deforestation accelerated the decline of fish populations due to excessive siltation and soil erosion.

Introduction of exotic species

The introduction of exotic and alien species to the natural waters of Kerala has resulted in competition for food and space and ultimately in the decline of indigenous species. In Periyar Lake, which is well known as one of the biodiversity hotspots of Kerala, exotic species such as Cyprinus carpio have already established breeding populations and contribute more than 70 percent of the exploited stock. A high percentage of diet overlap exists between native fish species like Tor khudree, Gonoproktopterus curmuca, Lepidopygopsis typus and exotic species like Tilapia (Oreochromis mossambicus) and Common carp (Cyprinus carpio) (Table 7). Percentage contribution of exotics in the landing showed clear cut preponderance over indigenous fish species by weight (Figure 3). Tilapia has established its populations in almost all rivers of Kerala. The exotic high yielding African catfish (Clarias gariepinus) is another potential danger to the indigenous species. Alien species such as Catla (Catla catla), Rohu (Laboe rohita) and Mrigal (Cyrrhinus mrigala) have been cultured in most of the reservoirs and ponds of Kerala and consequently a gradual reduction of the endemic populations in these water bodies.

Water quality

Agriculture in the catchment area has aggravated water pollution by the application of pesticides and insecticides as well as having brought about a reduction in the available space for the free movement of the fishes. Over 200 medium and large-scale industries and 2 000 small-scale industries discharge effluents containing heavy metals such as mercury, zink and cadmium above the permitted level. There are regular mass mortalities of fish in the major rivers. The ammonia content of effluents discharged into these rivers was reported to be 432-560 ppm. Pollutants such as acids, alkalis, fluorides and radioactive materials were detected in the effluent waters of the industries at the Cochin area as a result of which the Eloor-Varappuzh areas of the Cochin backwaters are being transformed into a barren contaminated zone. According to the data compiled by the KWBSP, 10 types of pesticides with a

Table 7: Diet overlap of fish species in Periyar Lake, (Underlined figures indicates high overlap)

Figure 3. Percentage catch composition by weight of fish species from April 2002 to January 2003 total quantity of 490 tons are used in Kuttanad, the rice bowl of Kerala and samples of sediments and clams collected from the lower Kuttanad region had high concentrations of organic pesticides (Nair 200).

Over fishing

Over fishing of potential ornamental species without assessing their population size could lead to their extinction in the near future. Unfortunately, with the targeting of half a dozen fishes for the domestic and international trade, the stock size of these fishes has declined drastically and, as a result, most of them are now endangered. In addition, the spreading of fish diseases, especially in the downstream reaches of the rivers has resulted in mass mortalities of fishes such as barbs. Ever since from the outbreak of EUS in 1991, its recurrence had been invariably reported during the past 12 years from different water bodies of Kerala, thus acting as another major biodiversity threat to the inland fishes of Kerala.

MANAGEMENT MEASURES RELEVANT FOR CONSERVATION OF THE FRESHWATER FISHES OF KERALA

Management measures aimed at conserving freshwater fish biodiversity should be inserted into the fishery policies of the Govt. of Kerala. In addition the information given can be utilized by central and state government agencies, such as the Western Ghat Development Authority, Kerala Fisheries Management Society, local NGOs etc. who are deeply involved in implementing various measures for the protection of the fish biodiversity of the state.

Further measures should include:

The data base on population size and geographical distribution of endangered and endemic species should be strengthened by undertaking extensive micro geographical surveys. The knowledge of area of distribution and information on the micro geographical characteristics of the habitats of these ecologically sensitive fishes will be inputs for establishment of aquatic reserves for the conservation of the species.

Information regarding migration, breeding behaviour and spawning grounds of threatened fishes should be generated through extensive surveys and analysis. Such a database is essential for both ex situ and in situ conservation of the species.

Techniques should be developed for the captive breeding and broodstock development of fishes of potential economic importance. These should be standardised and the commercial scale exploitation of the species only be encouraged after standardising these techniques. Such information should be extended to the small and large-scale aquarists for the enhancement of ornamental fish exports.

Broodstock maintenance centres and hatcheries should be established exclusively for indigenous endangered and critically endangered fishes for their in situ conservation and aqua ranching as a substitute for their natural recruitment.

Investigation on the invasive nature of exotic species in the natural habitats should be carried out with a view to establish how many of them could achieve natural breeding populations and also to what extent their feeding spectrum habits overlap with that of the indigenous fishes. The functioning of the committee constituted under Govt. of India to quarantine and control the exotic species introduction to the country should be made more effective. The introduction of exotic and alien species of fishes in open waters for the purpose of resource augmentation, as is currently practiced in many of the freshwater dams of Kerala, should be discouraged and before any exotic species are introduction, its potential threat to local species should be studied and the introduction shall be subjected to the establishment of non threatening nature of the species.

CONCLUSION

The present study shows that the rivers and streams of Kerala have exceptional fish biodiversity with a high degree of endemism due to the presence of many rare and localised forms. These areas are conspicuous among the biodiversity hot spots of the world and therefore call for protection and preservation as bio reserves. Long-term management plans are needed to conserve and preserve this treasury of fish germplasm. Measures should include standardisation of captive breeding and seed production technology of endangered and critically endangered fishes and their massive ranching in the rivers. Efforts should be made to regulate various human interventions that are being imposed in the freshwater habitats of the fishes and strict regulations should be imposed on the introduction of exotic and alien fish species in the natural waters. The present study also revealed that the physical habitat variables play a leading role in the distribution of fishes in streams and the habitat alteration brought about in various rivers contribute significantly to the endangerment of freshwaters in the rivers of Kerala.

ACKNOWLEDGEMENTS

The authors thank the Director, School of Industrial Fisheries, Cochin University of Science & Technology for providing the necessary facilities. The financial assistance from ICAR-NAT project on Germplasm inventory, evaluation and gene banking of freshwater fishes is gratefully acknowledged.

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