A Study on the Piscifauna of the Idukki Reservoir and Catchment

dy on e sdfauna of the I u ldd eservoh· an atch ment Area P. GOPINATH and T. N. JAYAKRISHNAN Zoological Survey of India, Cochin- 682 011 From the area under report 17 species, 15 endemic and 2 exotic, of freshwater fish have been identified. Of these, 8 species are commonly found in the catches and are of fishery significance. The fact that small fish species which have no fishery importance also support life in other trophic levels of this ecosystem is well exemplified by the intera ction of the birds and mammals with these species. A scientific management and moni toring of the reservoir waters as well as the remaining segments of forests are recommend ed to salvage the wild life and vegetation from a possible rapid deterioration within years. Fish population is highly susceptible to spread over an area of 59.80km 2 and com the changes in the ecosystem and when these bines the course of the Cheruthoni and changes exceed beyond the tolerence level Periyar rivers. The catchment area of of the fish the population depletes. This the reservoir is 649.30km2 with gross storage in turn affects the floral and faunal elements capacity of 1996.3 Mm3 • The maximum at various trophic levels of the ecosystem. water level recorded was 734.3 m, when the In this context the present study is designed hillocks within the reservoir area would be to know the status of fish population in and submerged. The average depth of the reser around the ·reservoir waters. The signi voir varies from 50 to 80 m. During the ficance of this study is relevant, especially monsoon season the depth increases upto when one envisages that the changes caused 125 m or above around the dams. Since by a hyde! project on the piscifauna need the water of the Periyar River enters the not necessarily be deleterious. The present reservoir through Ayyappancoil, this zone study, first of its kind in the hyde! project area of Idukki, is an attempt to know could be considered as the upstream of the the diversity and abundance of the reservoir and is termed as the Periyar reach. various fish species in the reservoir waters The fish of the Periyar have access to the and catchment area. Besides, attempts reservoir only through this inlet. After the were made to analyse the interaction of fish construction of the dam the Cheruthoni River population with other faunal elements, aqua vanished into the reservoir waters. The tic as well as terrestrial in the ecosystem. traces of the old Cheruthoni River could be seen on the side of the spillway where Study area the water is released from the Cheruthoni Dam. The fish fauna of the reservoir should The studies were carried out in the Idukki therefore include the fish from both these Reservoir and the places surrounding it, rivers. At K.ulamavu the impounded water in Western Ghats at an altitude of about is diverted through a power tunnel, 2027 m 850 m above M.S.L., (Long. 76°59' E and long and 7 m in diameter into an under Lat. 9°51' N). The Idukki Hydel Project is a complex of three dams, namely, the Idukki ground power house at Moolamattom, which Double Arch Dam across the river Periyar, generates about 355 mw of power. After the Cheruthoni Concrete Gravity Dam the power is harnessed the tailrace water adjacent to the Idukki Dam and the biggest joints the Muvattupuzha river. This part masonry K.ulamavu Dam located about of the reservoir could be considered as the 30 km upstream of Idukki, on the left bank downstream of the reservoir and is termed of the reservoir (Fig. 1). The reservoir is as the K.ulamavu reach. FISHERY TECHNOLOGY PISCIFAUNA OF IDUKKI RESERVOIR 132 D Res~rvoir ® Landing centres Collecting centres Fig. 1. Idukki reservoir showing the sampling and collection centres Materials and Methods every month from September, 1982 to July, 1983 to collect fish samples to estimate the Quite a few inhabitants of the area around weight of each fish species in the landings. the reservoir are engaged in fishing in and The identification of the fish to the species around the reservoir waters, and the materials level has been confirmed by the ichthyologists for the present study are collected from these of the Zoological Survey of India, Calcutta. people, from Venganam, Pothumattom and The general classification of the fish adopted Manjakkuzy in· Kulamavu reach and Kochi in the present study is that of Jayaram (1981) dukki, Seethakkayam and Ayyappancoil in and Rosen & Patterson (1969) with slight Periyar reach (Fig. 1). The fishing gear modifications. With the aid of a 7 x 50 they use is known locally as 'Thandadivala' binoculars, attempts were made regularly to or 'Kettuvala', which has mesh sizes varying observe bird species used to prey on the fish from 26 mm to 180 mm with strings of population of the reservoir. thickness ranging from ~ mm to 2 mm, a crude gillnet, with no floats and weights. The catches obtained by this gear are sele Results and Discussion ctive, since the fishermen are concerned only about those fish which can readily be sold. The list of fish species (Table 1) includes Efforts have been made therefore to collect 17 species belonging to 6 orders, 8 families fishes from the reservoir, as well as from the and 14 genera. Among these, Cyprinus streams and puddles of Meenmutty, Kuda carpio, and Tilapia mossambicus are exotic murutty and Karimpan, using boxnet, species introduced into the reservoir by castnet and cloth pieces Kerala Inland Fisheries Department about 1975, and the rest are endemic. The catches are regularly being brought to the landing centres at Mayyanna, Nelli The quantitative analyses of the fish landed kappara etc. in Kulamavu reach and Vellapp from September, 1982 to July, 1983 at the ara, Vazhavara etc. in Periyar reach (Fig. I) landing centres are given in Fig. 2. During These landing centres were regularly< visited this period a total of 705.97 kg. of fish was Vol. 21, 1984 133 P. GOPINATH AND T. N. JAYAKRISHNAN Table 1. List of freshwater fish species <lJ collected and identified from the 300· (I) study area J::.~ -" -~--"- (/) Order CYPRINIFORMES 26 :J 0 Family CYPRINIDAE :0 E 0 Sub family Rasborinae (/) 220 (/) Genus Rasbora 0 1. R. daniconius 200 ~ ....,E Genus Barilius 0>190· 2. B. bendelisis .>< Sub family Cyprininae ,!; 16 .:::1 Genus Cyprinus .2' Q) 3. C. carpio* 31: 120 Genus Puntius 4. P. melanampyx 100 5. P. bovianicus 00 Genus Tor 6. T. khudree Genus Cirrhinus 7. C. cirrhosa Sub family Garrinae Genus Garra Species 8. G. lamta Fig. 2. Quantity of various speeies of fish. Family COBITIDAE landed during September '82 to Sub family N oemacheilinae July '83 Genus Noemacheilus 9. N. denisonii Table 2. List of birds regularly feed on the 10. N. scaturigina fish of the reservoir 11. N. rupicola Order SIL URIFORMES Common name Zoological name Family SILURIDAE Genus Ompok Dabchick Podiceps rujicollis 12. 0. bimaculatus Darter Anhinga rufa Family HETEROPNEUSTIDAE Little cormorant Phalacrocorax niger Genus Heteropneustes Cattle egret Bubulcus ibis 13. H. fossilis Little egret Egretta garzetta Order A THERINIFORMES Common sand piper Tringa hipoleucos Family CYPRINODONTIDAE Night heron Nycticorax nycticorax Genus Aplocheilus Pond heron Ardeola grayii 14. A. lineatus White-breasted Halcyon smyrtensis Order CHANNIFORMES kingfisher Family CHANNIDAE Small blue kingfisher Alcedo atthis Genus Channa Pied kingfisher Ceryle rudis 15. C. gachua Order PERCIFORMES Family CICHLIDAE analysed. In the landings, though 8 -spe Genus Tilapia cies are common, only 6 species are abun 16. T. mossambicus* dant; the two species, Ompok bimaculatus Order MASTACEMBELIFORMES and Heteropneustes fossilis, because they Family MASTACEMBELIDAE contribute only 2.01 kg and 0.26 kg, respe Genus M astacembelus ctively, are not included in the histogram. 17. M. guentheri Tor khudree is the most abundant, contri buting 267.67 kg. Channa gachua, which * exotic species weigh 7. 78 kg, is the least abundant in the landings. Cirrhinus cirrhosa weighed 32.53 FISHERY TECHNOLOGY PISCIFAUNA OF IDUKKI RESERVOIR 134 kg and Mastacembelus guentheri 10.22 kg. 649.30 km2 need not necessarily represent Cyprinous carpio and Tilapia mossambicus, all freshwater fish reported from Travancore with 197.69 kg and 187.79 kg are second (Pillay 1929; John 1936; Hora & Law 1941; and third in abundance. Raj 1941) which comprises a larger area. It is quite possible that certain species which Eleven bird species which mainly depend are well adapted to the habitat of flowing upon the fish population of the reservoir for waters might have failed to cope up with their food are listed in Table 2. Of these, 8 the new habitat and environment of the closed, species are water-birds and the rest are the static water of the reservoir. Owing to the main fish-eaters among the avifauna. changed condition of the lacustrine environ ment some of the fish may evolve into newer In the absence of previous studies from types (Tilak & Sharma 1982). The original this area before the dam was constructed it fauna of the reservoir may perish and later is not prudent to say that the piscifauna of a new generation of adaptive forms may the reservoir is depleted. But the present populate the waters at a later stage (Hora study gives a clear picture of the status of 1947). the piscifauna of the area at present. The 15 endemic species reported in this work The fish yield from the reservoir constitute only 19.7 3% of the 7 6 species of The presence or absence of animal life in freshwater fish reported by Hora & Law an ecosystem clearly reflects the quality and (1941) from the Travancore area.

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