Previous Page Table of Contents Next Page


The south – eastern State of Tamil Nadu is an important geo – political, economic and cultural constituent of India. From the reservoir fisheries point of view, the State occupies a pre–eminent position, inasmuch as it has an ancient tradition of creating impountments for irrigation. Tamil Nadu is also in the forefront of research and development of reservoir fisheries in the country. Some of the pioneering research studies on limnology and fisheries of reservoirs were conducted in the State.

Situated in the rain shadow behind the Western Ghats, most part of the State is semi–arid and dry, drained mostly by the east–flowing seasonal, rain–fed streams. Northeast monsoon is more important to the State than the southwest, thus making Tamil Nadu unique among the Indian States. The districts of Chengalpattu MGR, South Arcot, Thanjavur, Madurai, Ramanathapuram and Tirunelveli Kattabomman receive rainfall mainly from the north–east monsoon, while North Arcot, Salem, Coimbatore and Tiruchirapally in the central region depend on both monsoons. North Arcot and Thanjavur districts receive rich rainfall of 102 to 114 cm per annum, while the range of annual rainfall in the rest of the State is 640 to 890 mm. Despite the limitations in water resources, the state has made great strides in agriculture. Tamil Nadu's rice yield of 2.5 t ha-1 is among the highest in India and its sugar cane yield of 100 t ha-1 is a world record.

People of Tamil Nadu learned to conserve water and store it for irrigation since time immemorial. The landscape of the State, especially in Madurai, North and South Arcot, Dindigul Anna, Tirunelveli Kattabomman and Pudukottai districts is dotted with thousands of small impoundments (locally called tanks) created to store the surface flow for irrigation. Ganapati (1956a), quoting Madeley (1914) reported as many as 141 minor irrigation tanks or reservoirs in the 363 km2 catchment of Red Hill reservoir. Madurai and Ramnad districts of Tamil Nadu have the maximum number of tanks and these areas are called the land of irrigation tanks (Pandian 1987). The Cauvery river was tamed in the first century A.D., when the Grand Anicut was built of stone and mud, covered with an outer facing of dressed granite, set in lime mortar. Upper and Lower Anicuts, the two barrages on the Cauvery downstream, were constructed by Sir Arthur Cotton in 1836 and the Mettur dam came into being in the 1930s. Even in the recent past, a large number of concrete masonary and earthen dams were built in the State, both before and after independence, resulting in the creation of 58 small and 11 medium and large reservoirs.

Fisheries Department of Tamil Nadu, with one of the best resource data bases in the country, has surveyed almost all the man– made lakes in the State, most of them being small irrigation reservoirs. Fifty-eight, out of sixty–nine reservoirs in the State fall under the category of small reservoirs (<1 000 ha). Even among them, the reservoirs less than 500 ha in size dominate. However, the small reservoirs form only 27% of the total water surface area. One reservoir in the category of 5 000-10 000 ha (Bhavanisagar) and one in the >10 000 category (Mettur) form 40% of the total water surface area. There are 9 reservoirs in the medium category (1 000 to 5 000 ha), covering an area of 19 577 ha (Table 2.1 ; Fig. 2.1).

Most of the earlier accounts on reservoir fisheries of the State seem to have overlooked the water bodies designated as tanks. In the southern States of Karnataka, Tamil Nadu and Andhra Pradesh, many small irrigation reservoirs in the country side, created by erecting small earthern dams to obstruct stream flow, are generally referred to as tanks. Many of them have a very small catchment, restricted to the immediate surroundings and the others receive water from small streams and rivulets. Tanks also include some community ponds of the villages and those attached to the temples. Nevertheless, vast majority of them are man–made impoundments created by obstructing surface flow, falling under the broad definition of reservoirs. Although some lakes of tectonic origin, meteorite craters, etc., must be masquerading among them, it is difficult, for the fisheries officials of the lower and middle rank, to tell the actual reservoirs from other lentic formations.

Table 2.1. Number and area of reservoirs in Tamil Nadu (by category)
CategoryNo. of unitsArea (ha)
At FRLAverage
Small reservoirs
<500 ha466 8583 594
500– 1 000 ha5815 6638 628
Total5815 6638 628
Medium reservoirs
1 000–5 000 ha   
Total919 5776 374
Large reservoirs
5 000–10 000 ha17 8763 208
>10 000 ha115 3469 324
Total223 22212 532
Grand total6958 46227 534

Small irrigation reservoirs (tanks) (Classification on the basis of level at FRL)

The Fisheries Department of Tamil Nadu has a village–wise inventory of all tanks in the State, and that is categorised into short seasonal and long seasonal (major irrigation) tanks. The short seasonal tanks having an average size less than 10 ha, retain water only for a period less than 9 months in an year, while the long seasonal ones have an average size of 34 ha and retain water for 9 to 12 months. In some of the districts, the major irrigation tanks have an average size of 156 to 222 ha. Total waterspread under tanks in 22 districts of the State is estimated at 740 182 ha, of which 439 904 ha are short seasonal, with the size of individual units less than 10 ha in most cases. These small tanks have been tagged with the ponds. There are 8 837 long seasonal (major irrigation) tanks, covering 300 278 ha, situated in 17 districts, which are de facto reservoirs and so treated in this work. Madurai, Tirunelveli Kattabomman, Pudukottai and South Arcot districts have maximum number of perennial tanks (Table 2.2), while the average size of tanks in Chengalpattu MGR, Salem and Pasumpon districts is higher.


Reservoirs of Tamil Nadu are scattered in 16 districts. The two large reservoirs (> 5 000 ha) viz., Stanley (Mettur Dam) and Bhavanisagar are situated in Salem and Periar districts respectively. Dharmapuri has the maximum number of reservoirs comprising 8 small and 2 medium reservoirs, with a total area of 3 600 ha; followed by Coimbatore, Dindigul Anna and Tirunelveli Kattabomman districts with 7 reservoirs each. South Arcot district with just 3 each of small and medium reservoirs has a waterspread of 9 933 ha (Table 2.3). While taking irrigation tanks also into consideration, Pasampon Thevar Thirumagan District has the maximum water area (48 734 ha), closely followed by Pudukottai and Madurai districts with 46 278 and 41 508 ha respectively. The State has 8 906 water bodies in total, spread over 358 740 ha at FRL (Table 2.4). Eleven medium and large reservoirs in 8 districts and 58 small reservoirs in 14 districts along with their annual fish production and major fisheries are listed in Tables 2.5 and 2.6 respectively.

Table 2.2. Distribution of major irrigation tanks in Tamil Nadu
DistrictNo.Area (ha)Average of a unit
1.Chengalpattu MGR45734 931222
2.N.Arcot Ambedkar96920 32821
3.T. Sambuvarayar   
4.Dharmpuri18113 96077
5.Soth Arcot84917 69521
6.Salem182 805156
7.Thiruchirapalli30310 06333
9.Coimbatore401 79245
10.Dindigul Anna88212 91515
11.Madurai1 83041 50823
12.Kamarajar31217 32855
13.T.Kattabomman1 17326 68323
14.V.O.Chidambarar1321 99015
15.Kanyakumari4732 9936
16.Pasumpon60348 73481
17.Pudukottai91146 27851
Total8 837300 278 

Table 2.3 Distribution of reservoirs in Tamil Nadu districts
DistrictNo. of reservoirsTotal area (ha)
SmallMedium and Large(L)At FRLAt. Av. Level
Chengalpattu MGR114 1631 931
North Arcot Ambedkar10678339
T. Sambuvarayar012 01056
Dharmpapuri012 01056
South Arcot823 6001 444
Salem01(L)15 3469 324
Periyar41(L)8 7863 766
Coimbatore703 1721 768
Dindigul Anna70829546
Madurai212 7361 768
Tirunelveli Kattabomman701 722883
V.O. Chidambarar10657328
Kanyakumari313 1841 649
Total581158 46227 534

Table 2.4. Number and area of reservoirs and perennial irrigation tanks in Tamil Nadu districts
DistrictsReservoirsIrrigation Tanks Total
No.Area(ha) (FRL)No.Area(ha)No.Area(ha)
Chengalpattu MGR24 16315734 93115939 094
North Arcot Ambedkar167896920 32897021 006
Dharmapuri103 60018113 96019117 560
South Arcot69 93384917 69585527 628
Salem115 346182 8051918 151
Thiruchirappally322730310 06330610 290
Periyar58 786427599061
Coimbatore73 172401 792474 964
Dindigul Anna782988212 91588913 744
Madurai32 7361 83041 5081 83344 244
Pudukottai--91146 27891146 278
Pasumpon--60348 73460348 734
Kamarajar593331217 32831718 261
Tirunelveli k.b.71 7221 17326 6831 18028 405
V.O.Chidambarar16571321 9901332 647
Kanyakumari43 1844732 9934776 177
T.Sambuvarayar12 010--12 010
Total6958 4628 837300 2788 906358 740

Table 2.5 Reservoirs in Tamil Nadu (> 1000 ha)
Name of ReservoirArea (ha)Fish f landingMajor fisheries
(at FRL)(Average)(t yr1)
Salem District    
1. Mettur15 3469 324115Rohu(19)%,Wallago attu(15%),catfishes (14%),Puntius spp.(14%),catla(10%)
Periyar District    
2. Bhavanisagar7 8763 208179L. calbasu (22%), L. bata (19%), M. aor (16%), Puntius dubius (10%)
South Arcot District    
3. Veeranam3 8853836Catla(31%), tilapia(44%), rohu (17%), silver carp(8%)
4. Perumaleri2 5901 295- 
5. Wellington1 5545009Catla(31%), common carp (8%), rohu (17%), tilapia(44%)
Chengalpattu MGR District    
6. Poondi3 2631 40215Tilpia (41%), common carp (9%), mrigal (9%), Puntius spp. (7%)
Madurai District    
7. Vaigai2 4191 55424 Catla (56%), mrigal (22%), silver carp (8%), tilapia (6%)
T. Sambuvarayar District    
8. Sathanur2 01056126Catla(51%), mrigal (27%), common carp (12%), tilapia (6%),
Kanyakumari District    
9. Pechiparai1 5157009Puntius spp. (45%), catla(19%), mrigal
Dharmapuri District    
10. Krishnagiri1 24876847Misc. (73%), tiapia (24%), catla (20%)
11. Vaniyar1 093613Misc. (48%), rohu (27%), catla (13%)

Compiled from: 1. Director of Fisheries, Tamil Nadu
2. Srivastava, et al., 1985
3. Anon, 1987

Table 2.6. Reservoirs in Tamil Nadu (<1000 ha)
Name of reservoirArea (ha)Fish landingsMajor fisheries
at FRLAv.t yr1
Chengalpattu MGR District Kolavai eri90052930-
N. Arcot Ambedkar District Goddar6783393Tilapia (57%), common carp (25%), catla (10%),rohu (6%)
Dharmapuri District Thumbalahalli1938911Tilapia (79%), catla (90%, silver carp (4%)
Kasarikulihalla105634Tilapia (73%), common carp (13%) mrigal (6%)
Sicclagiri Chinnar54278Misc. (58%), tilapia (28%), catla (5%), common carp (5%)
Pambar2436026Misc. (41%), tilapia (35%), c. carp (8%), rohu (7%)
Barur25612824Tilapia (90%), misc. (7%), catla (2%)
Nagavathy118715Tilapia (76%), Puntius spp. (9%), catla (6%)
Thoppaiyar1206015Tilapia (77%), catla (30%), rohu (5%), mrigal (4%)
Chinnar1701176Tilaia (26%), Puntius spp. (26%), common carp (13%)
Coimbatore District Pillur4002333-
Nirar (upper & lower)6835--
Nilgiris District Sandynulla3001565-
Ooty lake35164-
TR Bazar118--
Dindigul Anna District Kunthirayar--5Tilapia(50%),catla(16%), mrigal (9%)
Maruthanathi72428Tilapia(37%), common carp (24%), catla (23%, mrigal(9%)
Manoor10102Common carp (48%), catla (33%), silver carp(19%)
Parappalar114606Tilapia (37%), common carp (24%), catla (23%)
Kombai (Peria & Chinna)35197Tilapia (71%), catla (14%), common carp (4%), silver carp (4%)
Varathamanathi80397Tilapia (71%), catla (14%), common carp (4%), silver carp (4%)
South Arcot District Vidur7984796Tilapia (55%), common carp (9%), mrigal (9%), Puntius sp. (7%)
Gomukhi3602186Puntius sp. (35%), catla (41%), mrigal (11%)
Manimuktha74644712Catla (47%), common carp (17%), tilapia (6%),
Kamarajar District Vembakottai46716018Tilapia (22%), mrigal (17%), catla (13%), misc. (35%)
Periyar762617Tilapia (53%), mrigal (23%), catla (14%), silver carp (6%)
Kovilar742412Tilapia (48%), mrigal (24%), silver carp (11%), catla(10%)
Kullur Santhai31619048Tilapia (70%), mrigal (15%), catla (7%)
Anaikuttam--1Tilapia (40%), misc. (34%), mrigal (10%), common carp(9%)
Tirunelveli Kattabomman Dt. Karuppanathi50254Tilapia (91%), common carp (4%)
Ramanthi39204Tilapia (57%), common carp (22%), Puntius spp. (15%)
Gadana80482Puntius spp. (65%), common.carp (14%), tilapia (12%)
Manimuthar9404707Puntius spp. (56%), mrigal (16%), tilapia (15%), Labeo fimbriatus (6%)
Hope lake5803003-
Madurai District Manjalar19715428-
Sathiar120606Tilapia (48%), catla (30%), common carp (7%), rohu (6%)
Tiruchirapalli District Kannathudai50263Catla (56%), mrigal (22%), tilapia (6%), common carp (12%)
Ponnaniyar60164Catla (51%), mrigal (27%), tilapia (6%) common carp (12%)
Periyar DistrictUppar45340545-
Varattupallam89536Tilapia (56%), silver carp (17%), catla (17%)
Vattamalai (Karaiodai)307664-
Gunderipallem613415Silver carp (25%), tilapia (12%), catla (6%),
V. O. Chidambaranar District Kadama65732851Tilapia (85%), catfish (1%), misc. (13%)
kanyakumari District Chittar-129317512Puntius spp. (41%), catla (25%)
Chittar-2414248 tilapia(13%),silver carp (8%)
Perumchani9625269Puntius sp. (71%), tilapia (28%)


At least twenty reservoirs in Tamil Nadu have been studied and the literature on the subject is rich in descriptive limnology and production dynamics. No other State in the country has generated scientific information of this magnitude on the reservoir ecosystem. Ganapati (1940) through his epoch-making paper on Red Hills lake, a water supply reservoir near Madras, laid the foundation for reservoir limnology in India. The paper dealt with the plankton cycles in relation to the water quality and meteorological parameters. He followed up the studies with investigations on Stanley reservoir (Ganapati, 1955: Ganapati and Alikunhi, 1949, Errakuppam (Ganapati, 1956b). Hope lake (Ganapati 1956a), and irrigation tank near Madras, and Mukerti reservoir (Ganapati, 1957) in addition to his numerous papers on the pond ecosystem. Since 1960s, Sreenivasan, undertook a number of studies on a large number of reservoirs in Tamil Nadu. His studies on three lakes viz.m Stanley (Sreenivasan, 1966, 1969) Bhavanisagar (Sreenivasan, 1964a, Sreenivasan et al., 1964) and Amaravathy (Sreenivasan, 1965a) set the pace for other limnological studies for the rest of India. His contributions include some comparative studies on the reservoirs of South India (Sreenivasan, 1970a & b, 1976, and 1979). Sounder Raj et al., (1971) studied the limnology and productivity of Poodi reservoir.

The following account provides information on fish stocks and fisheries of 5 major reservoirs of Tamil Nadu.


Mettur dan, situated at 11°49'N, is often described as an engineer's delight. A straight gravity structure, 1 615 m long, rising 54 m above the Cauvery river bed, the dam is constructed across two hills of the EAstern Ghats. At the time of its construction, Mettur was the highest masonry dam in Asia and the larges in the world. The dam, constructed primarily to stabilise the irrigation in Thanjavur delta, caters to about one third of the irrigated area of Tamil Nadu, besides generating hydroelectric power of 240 MW. Commenced in 1925, the dam was completed in 1935. Stanley is the larges reservoir in Tamil Nadu.

Stanley reservoir was commissioned in 1939 and it continues to be the only reservoir in the State representing the >10 000 ha category. Situated at an elevation of 243 m above MSL in the Salem district, Stanley reservoir has a waterspread of 15 346 ha and capacity of 2 646 million m3 at FRL, the average area being 9 324 ha. It receives water from the Cauvery river basin of 42 217 km2. Morphometric indicators such as high shore development index (6.7) and a volume development index more than unity (1.4) point towards productive nature of the reservoir.

Information on Stanley reservoir comes mainly from Sreenivasan (1966, 1969, & 1976). The highest and lowest water temperatures recorded during 1962–63 being 32 °C (in May) and 24.2 °C in (January) respectively. Dissolved oxygen in the surface water layer in most of the months was above 4 mg 1-1 with the maximum supersaturated conditions at the surface, accompanied by a depletion of oxygen in the hypolimnion. The water was alkaline, the pH values ranging between 7.5 to 8.8. High values of methyl orange alkalinity (140 mg 1-1 to 278 mg 1-1) and specific conductivity (170–350 μmhos) indicated a fairly high ionic concentration, suggesting that the water body is reasonably productive. Total hardness as CaCO3 varied within a range of 86–128 mg 1-1 ranking the lake as a hard water one. Calcium has a negligible contribution (11–20 mg 1-1) to hardness.

Despite being a deep basin, the water column was not stratified thermally, in conformity with the situations reported from elsewhere in peninsular India. Even during the so called winter, air temperature in this part of the country does not drop below 15 °C keeping the water relatively warm. With the onset of summer, when the top layer warms up, there is no cool water below to offer any thermal resistance. Moreover, the release of cooler water from the bottom layer through the outlets of the dam remove any disparity in temperature between the top and bottom layers.

Figure 2.2

Figure 2.2 Stanley Reservoir (Mettur Dam), Tamil Nadu

There was distinct klinograde distribution of dissolved oxygen in the reservoir. Oxygen recorded from the tropholytic layer varied from nil to 6.8 mg 1-1 and the deficit of oxygen at the hpolimnion ranged from 0.64 mg 1-1 to 5.84 mg -1 during various seasons. Oxycline unaccompanied by a thermal stratification is a positive indication of the productive nature of the reservoir. On the one hand, the warm waters at the bottom hastened the bacterial decomposition of organic matter and on the other, the high dissoved oxygen levels in the trophogenic layer indicated high rate of photosynthesis. The low oxygen at the bottom indicated high oxygen demand for decomposing organic matter.

Oxygen depletion at the bottom was accompanied by a concomitant stratification of pH, CO2, total alkalinity and other related parameters. Inorganic soluble phosphate and nitrate were rarely recorded. Silicate ranged from nil to 19.9 mg 1-1. Unavailability of nutrients is a common feature of the South Indian reservoirs.

With Secchi disc visibility up to 1 m and a photosynthetic zone extending down to 5.0 m, the primary production rate was generally high within a range of 1.05 to 10.97 g O2 m-2 day-1. Sreenivasan (1976) estimated the photosynthetic efficiency of Stanley waters at 1.04%, based on the amount of solar radiation and the rate of carbon synthesis by primary producers. Only 0.0927% of the carbon fixed by primary producers was being harvested as fish.

Phytoplankton community of Stanley consisted predominantly of diatoms represented by the ubiquitous Nitzschia and Navicula, with occasional presence of blue greens like Merismopedia, and Oscillatoria. Microcystis, the common form in the warm water ponds and lakes of South India was conspicuous by its near absence in Stanley.

Net plankton was less important in the trophic chain of Stanley reservoir as they were outnumbered 10 to 1 by nannoplankton. This explains the rather unusual species spectrum of phytoplankton, despite the positive indicators of productive nature of the water body.

Fish and Fisheries

Indigenous ichthyofauna of the river comprised Acrossocheilus hexagonolepis Puntius carnaticus, P. dubius, Tor putitora, Labeo kontius, L. fimbriatus, Cirrhinus cirrhosa, C reba, Aorichthys aor, A. seenghala, Pangasius pangasius, Silonia silundia and Wallago attu (Chacko et al., 1955). The three downstream barrages on Cauvery viz., the Lower Anicut, the Great Anicut and the Upper Anicut restricted the upriver migration of the anadromous fish, Tenualosa ilisha and after the construction of Mettur dam, this fish was reported to disappear completely from upstream stretches of Cauvery. Sreenivasan (1976) reported the disappearance of Puntius spp., which used to form 28% of the landings in 1943–44. The indigenous carp C. cirrhosa showed an initial increase in catches, but later declined. Low water levels during July in the preceding two or three years were blamed for the spawning failure of C. cirrhosa. Labeo kontius, which was common and next only to C. cirrhosa oin the Cauvery, also disappeared from the reservoir.

Table 2.7 Fish production (t) trends in Stanley reservoir during 1960–61 to 1964–61 (Sreenivasan, 1966)
Catla catla15113816912639
C. mrigala2121354217
Other species427160.4

During 1960–61 to 1965, C. catla and C. cirrhosa dominated the fish landings. However, there was progressive decrease in the percentage of C. cirrhosa with a gradual increase in catfish populations (Table 2.7). The annual total fish landings from 1967–68 to 1976–77 ranged from 230 t to 555 t (Sreenivasan, 1976), the average production during this period being 344 t, equivalent to the yield of 22.76 kg ha-1 (based on reservoir area at FRL). From 1969–70 to 1972–73, catla was reduced to 10%.

Mrigal, introduced into the Stanley reservoir during 1950–51, appreared in catches during 1957–58 contributing up to 13.9% in 1966–67 and later on, it declined and reduced to insignificance. Rohu also showed some initial increase but later declined. Recruitment failure from the vicissitudes of water level fluctuations and predator pressure have been attributed by Sreenivasan (1966) for the erratic behaviour of the introduced carp species and the emergence of predatory catfishes as the most stable component of fishery in the reservoir. The latest report received from the State Fisheries Department in 1993 put the total catch at 115 t comprising Labeo rohita (19%), Wallago attu (15%), other catfishes (14%), Puntius spp. (14%) and Catla catla (10%).

Fishing gear

Mettur being one among the earliest dams to be commissioned in the State of Tamil Nadu, Stanley reservoir has been considered as a testing ground for evolving reservoir fishing practices in India. The use of gill nets, now used widely in reservoirs all over the country, was developed by the fishermen of Stanley by trial and error methods. They named the floating gill nets as Rangoon nets, after the migrant fishermen from Myanmar. This gear is the most suitable for reservoir conditions, inasmuch as most of them have rugged bottom with steep slopes. The fishermen have even evolved the best mesh size to suit each fishery. For instance, during 1964 to 1965, there were separate nets targetted against catla of 25 kg. mrigal of 16 kg.


Factory effiuents from the mettur Chemical and Industrial Corporation were reported to be discharged into the river course below the dam. During dry seasons, when the outflow surplus channels were closed, the effluents caused pollution in the deep pools of the river (Ganapati and Alikunhi, 1949). Bioaccumulation of mercury had been reported in many fishes (jayachandran and RAj, 1975; Table 2.8).

Table 2.8. Bioaccumulation of mercury in Stanley reservoir
Specieslength (mm)Wt (g)hg (mg kg-1)
Aorichthys aor3703500.250
Notopterus notopterus3402700.086
Cirrhinus cirrhosa3354500.047
Labeo calbasu4107200.090
Rhinomugil corsula3302750.085
Puntius sarana2552500.072
Labeo rohita43015700.027

2.4 BHAVANISAGAR (Fig. 2.3)

Chacko and Dinamani (1949) prepared a preliminary report on the fishery resources of the Bhavani river, three years before Bhavanisagar reservoir was formed. After the impoundment was completed in the year 1953. Dorairaj and pankajam (1956), and Menon and Chari (1959), provided the first insights into the limnology and fisheries of the reservoir. Pankajam (1956), Sreenivasan (1962 and 1964b) and Sreenivasan et al. (1964) studied plankton communities in the light of environmental changes due to impoundment. Franklin (1969) documented the phytoplankton species. Bhavanisagar is also mentioned in the comparative studies of Tamil Nadu reservoirs made by Sreenivasan (1970a and 1976). Biology of commercially important species of fish Puntius dubius (Ranganathan et al. 1962), Aorichthys aor (Ranganathan and Radha, 1966), Labeo calbasu (Natarajan, 1971a) and Channa marulius (Devaraj, 1973) was also studied. Bhavanisagar was covered under the All India Coordinated Research Project on Reservoir Fisheries, launched in 1971. The final report contains the results of investigations carried out in the reservoirs during 1971 to 1981 and a set of recommendations for the management of its fisheries (Natarajan et al., 1981).

Bhavanisagar dam is constructed on the river Bhavani at 11°30'N lat., below its confluence with the river Moyar in the Cauvery basin in the Periyar district (Fig. 2.3). The reservoir has a maximum waterspread of 7 876 ha at FRL which is 280.2 m above the MSL, and its net capacity is 908 million m3. the average reservoir area is 3 695 ha. During the driest years, the reservoir shrinks to 745 ha in summer (Natarajan, et al., 1981). Receiving water from catchment of 4 200 km2, the reservoir serves irrigation and flood control. The calculated mean depth of Bhavanisagar is 11.5 m, the maximum depth being 33 m. The shore development and volume development indices are 4.0 and 1.0 respectively.

Figure 2.3

Figure 2.3. Bhavanisagar reservoir, Tamil Nadu

Soil of Bhavanisagar reservoir bed is silty clay loam and mostly acidic in reaction. Judged by the presence of available nitrogen, available phosphorus and organic carbon, the soil was categorised by Gupta (1979) as conducive to aquatic productivity. During pre-monsoon months, the pH was found to increase towards neutrality. Water level fluctuations in Bhavanisagar are erratic. In the year 1961 and 1962, annual level fluctuations were of 15.2 and 7.9 m respectively. During 1971 to 1981, water level fluctuations varied from 5.46 m to 22.6 m yr-1, with the accompanied changes in area and capacity of the reservoir. Air temperature regime seems to have undergone a change during the last few years. The maximum air temperature recorded during 1957–62 was 38 °C, while the summer temperature during 1971 to 1981 was an average 40.5 °C. The highest temperature exceeded 45.0 °C during 1974–75 and 1975–76. However, the range of water temperature during 1956–61 and 1971–82 (23.7 °C to 30.2 °C) did not differ much.

Water temperature in Bhavanisagar is not depedent on the prevailing air temperature at the reservoir site. The inflowing water from Moyar and Bhavani rivers determines the water temperature of the reservoir (Sreenivasan, 1962). Absence of thermal stratification, oxygen depletion in the bottom water layer, and increase in total alkalinity, CO2 and specific conductivity towards the depth indicate the productive nature of the water body.

The reservoir has a rich plankton community dominated by Cyanophyceae (Microcystis, Oscillatoria and Anabaena), diatoms (Nitzschia, Melosira) and Chlorophyceae (Pediastrum, Mougeotia). During the early years (1956–61), Nitzschia and Melosira formed an important constituent of the phytoplankton community, along with Cyanophyceae (Sreenivasan, 1964b; Sreenivasan et al., 1964). During 1970's and 80s, however, the diatoms were not very important. Initially, Bhavanisagar had a very high phytoplankton species diversity (Sreenivasan et al, 1964; Franklin, 1969). By the 1970s blooms of Microcystis (occasionally Mougeotia) have become a common feature accompanied by substantial reduction in diversity (Abraham, 1980b). This fall in diversity and increase in dominance of lentic species, aprat from indicating organic enrichment, suggested a transient eutrophication stage through which the reservoir was passing. The rich benthic community of Bhavanisagar was represented by oligochaetes, Chironomus, Chaoborus and mayfly nymphs, with a population density of 483 organisms and 3.8 g m-2 respectively (Abraham, 1979).


Bhavanisagar reservoir receives effluents from the South India Viscose Factory at Sirumughai, 3 km downstream of Moolathurai, which is considered as the breeding ground for indigenous and introduced fish species. There is asharp fall in pH and dissolved oxygen at the discharge point with sharp increase in carbon dioxide and alkalinity. Free CO2 recorded at site is 27.6 mg 1-1, compared to 1.5 mg 1-1 upstream. However, further downstream in the lotic zone and the main reservoir sector, the water quality became normal (Natarajan et al., 1981). Fish mortality due to decrease in pH and oxygen depletion was reported occasionally (Sreenivasan, 1979b).

Ichthyofauna of the reservoir comprises 51 species belonging to 11 families (Natarajan et al., 1981). Among them, 18 species contribute to the commercial fisheries. Impoundment did not alter the fish faunistic spectrum to any appreaciable extent as most of the indigenous species (Chacko et al., 1955) except Tor tor continue to be caught in the reservoir.

Puntius spp., T. putitora, T. tor, Accrossocheilus hexagonolepis, Puntius dubius and Puntius carnaticus, along with Labeo kontius form the traditional fisheries of river Cauvery and the stretch above the reservoir are believed to be their breeding grounds (Wilson, 1920). One reassuring feature of the reservoir is the continued presence of these indigenous forms especially P. dubius, P. carnaticus, Labeo kontius, Cirrhinus cirrhosa and A. hexagonolepis. Their survival is attributed to the uninterrupted breeding activities at Moolathurai and Nellithurai, especially in the former when water is released from Pilloor. P. dubius which has a fecundity of 66 000, ascends the rivers Cauvery and Moyar during the north east monsoon for spawning and lays eggs in batches of 1 000 to 2 000 on the gravel bed (Ranganathan et al., 1962). It is due to the continued availability of breeding grounds that the indigenous fishes survive in the lake and therefore there is a need to conserve this biologically sensitive environment. Cirrhinus reba breeds during June–July at Moolathurai in Bhavani and Hogainakkal in the main river Cauvery (Rao and Gopinathan, 1972). Evidence for recruitment of Labeo fimbriatus, L. calbasu, L. kontius and P. carnaticus has also been obtained along with successful natural breeding of introduced carps such as catla, rohu and mrigal (Natarajan et al., 1981). Sharp variations in catch per unit of effort in respect of P. dubius indicated inconsistencies in annual recruitment (Natarajan et al., 1981). Water level fluctuations seem to be the major factor behind the fish catch fluctuations, rather than fishing pressure.

L. calbasu, which feeds mainly on bottom detritus, is reported to mature at a size of 400 mm. The fish spawns in Moolathural breeding grounds during south west monsoon (Natarajan, 1971a and b). The mean length in catch varies between 465 and 530 mm among the > 3 year group. Other southwest monsoon breeders are the Indo-Gangetic major carps Catla catla, Labeo rohita and Cirrhinus mrigala. The indigenous Puntius dorsalis breeds intermittently with at least three annual peaks in its spawning intensity (Natarajan et al., 1981). Commercial fish landings from the reservoir during 1964 to 1980 ranged from 85 t to 293 t at an average of 156.5 t. This is rather low, in view of the good primary production rate. Sreenivasan (1976) estimated that 0.0775% of the carbon synthesised and 0.000513% of the solar energy were converted into fish flesh in Bhavanisagar. Community metabolism is mainly through the detritus chain. In the absence of an adequate population of planktiphagous fish, most of the energy at plankton phase is added to detritus. Labeo calbasu (95%), Cirrhinus mrigala (87.5%), P. dubius (94.9%) and Catla catla (55%) had a predominantly detritus-based diet. L. calbasu, and C. cirrhosa are increasing in catches while P. dubius and C. catla show a decline (Table 2.9).


Conservation measures to be adopted in Bhavanisagar should be relevant to the feeding, breeding and other habits of the target fishes. P. dubius has a natural distribution in the upper reaches of Bhavani and Cauvery in the sub-mountainous Tamil Nadu. This fish feeds mainly on benthic chironomid larvae, oligochaetes, insects and nymphs at the depths of 2 to 10 m. It breeds once a year during October to December, and undertakes a distinct, short upstream spawning migration. The eggs are laid on gravel by the side of rapids and pools.

In Bhavanisagar, the breeding grounds of P. dubius are reported to be intact and the fish still thrives in the reservoir. In Stanley, the Hogainakkal fall is a natural barrier obstructing the upstream migration of P. dubius. Similarly in Amaravathy, the river stretch above the reservoir has Duvanam Falls where the ready to spawn breeders congregate in large numbers from December. Ranganathan et al. (1962) noted that the failure of migration caused atrophy of gonads and breeding failure. Stocking of fry above waterfalls is suggested by the above authors as a conservation measure. However, Sreenivasan (1976) felt that the natural cascades associated with Davanam Falls allowed upstream migration of this fish. Ranganathan et al., (1962) recommended stocking of P. dubius in reservoirs situated in the sub-montane areas, provided there was a suitable river stretch above and no barrier for upstream migration. Conservation measures should also include:

  1. total closure of fishing activities during the breeding season, and

  2. ban on gill nets < 6 cm in mesh size (stretched) so that fish of three years and less will not be caught.

Table 2.9. Percentage composition of fish landings in Bhavanisagar Reservoir
YearW. attuA. aorP. dubiusL. calbasuL. rohitaC. catlaL. bataC. mrigalaL. fimibriatusTotal catch (t)

From Sreenivasan 1976 and Natarajan 1981

2.5 AMARAVATHY (Fig. 2.4)

The river Amaravathy, a tributary of the Cauvery was dammed in 1958 at 10° 15'N, 5 km below the point, where the river debouches into the plains to create the Amaravathy reservoir. The reservoir water surface area is 850 ha at the full level of 358 m above MSL. Though small, Amaravathy is one of the most productive reservoirs in the State. The lake has a net capacity of 112.37 million m3 at FRL and the mean depth is 13.7 m. Volume development and the shore development indices are 1.2 and 2.3 respectively. The catchment area of the reservoir is 832 km2. The reservoir was described by Sreenivasan (1965a, 1965b, 1976 and 1979a, b, and c.).

Figure 2.4

Figure 2.4. Amaravathy reservoir, Tamil Nadu

Bottom soil of the reservoir is sandy loam with organic nitrogen @ 0.156%, organic carbon 0.397% and phosphate 0.362 g per 100 g. The catchment of Amaravathy is the thickly wooded, highly rain-fed Munnar hills of the Western Ghats. Geologically, the catchment comprises rocks of biotite granite gneiss and schistose gneiss. Hard, coarse, crystalline metamorphic rocks are highy resistant to weathering. The river originates at an altitude of 1 515 m and passes through forests. The inflowing water does not stratify in the reservoir. However, there is a distinct horizontal gradient in temperature between the water at the lentic zone (28°C) and the fluviatile sector (23.8°C), just 8 km distant from one another.

The reservoir has all the features of an oligotrophic lake such as low total hardness, virtual absence of nutrients like nitrate and phosphate and low electrical conductivity and total alkalinity. Morphometric indicators like shore development index and the deepness of water column also point towards oligotrophy. Yet, Amaravathy has the highest rate of primary productivity among the reservoir of Tamil Nadu. This shows the efficacy of tropical impoundments to turn eutrophic, taking advantage of the abundant sunlight and the warm unstratified water column (Table 2.10). The inflowing water is poor in nutrients and dissolved solids. The ionic build-up and nutrient loading are a local phenomenon happening through metabolic activities.

Table 2.10. Physico-chemical characteristics of water in Amaravathy reservoir
Specific conductivity (μmhos)38–6348
Total alkalinity (mg 1-1)7–8425.86
Total hardness (mg 1-1)18–5038
Chlorides (mg 1-1)0.4–10.7
Organic C (mg 1-1)12.5–21.618.2
Silicate (mg 1-1)1.4–38.5-
Phosphates (mg 1-1)0.0–0.01-
Gross primary productivity0.30–18.313.7
(O2 m-2 d-1)  

(Sreenivasan, 1965a; 1979c)

Methyl orange alkalinity of 7.0 mg 1-1 at the surface increases to 40 mg 1-1 below 8 m depth. The water turns acidic as the depth increases. At the top layer, apart from using up all the free CO2 for photosynthetic activities, CO2 is also derived from the bicarbonate, thus reducing its concentration, whereas in the non-photosynthetic zone, with the abundance of free CO2, bicarbonates are high. Amaravathy is a testimony to the fact that the conventional indicators of productivity in terms of morphometric and catchment parameters have limited validity in the warm tropical reservoirs, where the water body can develop intrinsic eutrophy. The high rate of metabolic activities due to conducive temperature hastens both photosynthetic production as well as the organic decomposition.

Amaravathy has one of the highest primary productivity rates, next only to Tirumoorthy. Carbon fixation rate, measured in terms of oxygen released, was estimated @ 11.320 cal m-2 yr1 × 10-6 at a photosynthetic efficiency of 1.442% from sunlight to carbon. An unusually high rate of oxygen release at the rate of 59.1 g m-2 day-1 has been reported from the reservoir by Sreenivasan (1965a). Plankton community of Amaravathy is dominated by Microcystis which blooms round the year.

Alterations in the plankton community due to the reservoir formation is believed to have contributed to radical changes in fish stocks. The indigenous fishes could not thrive on a Microcystis–dominated plankton. Almost all indigenous species of commercial value have disappeared. Puntius dubius, which ranked first till 1965– 66, forming 55% of the fish landings, dwindled to less than 2% from 1968–69 and disappeared later (Sreenivasan, 1976). P. carnaticus was another casualty. Today, the commercial fishery is entirely based on the transplanted fishes including some exotic species. Tilapia, Oreochromis mossambicus, which was stocked in the year 1957–58, gradually established a foothold any by mid-seventies, they formed more than 90% of the catch. The common carp, Cyprinus carpio has increased since 1975–76 (Table 2.11).

Table 2.11 Changes in percentage composition of fishes in the commercial catches of Amaravathy reservoir
YearTotal landing (t)Percentage composition
Oreochromis mossambicusCyprinus carpioLabeo fimbriatusCatla catlaRohu & mrigalPuntius dubiusPuntius carnaticus

(Modified from Sreenivasan, 1976)

Performance of tilapia in Amaravathy, over the years was phenomenal. Apart from adding 48 to 132 t to the production (average fish production 90 t yr-1), the individual fish grew to c.1.5 kg in 1968 (later reduced to 0.68 kg). This allayed the fears of stunted growth, a common complaint against this particular tilapia (Oreochromis mossambicus in pond environment. Tilapia also had the highest catch per unit of effort (CPUE) of 11 950 to 22 569 kg yr-1 (CPUE in Tamil Nadu reservoirs is calculated on the basis of units comprising 20 gill nets of 50 m length each, operated from a coracle as described by Ranganathan and Venkataswamy, 1967). Moreover, the fishery based on tilapia could effciently convert energy into fish flesh. The energy conversion rates from primary producer to fish and light energy to fish were 0.2081% and 0.003003% respectively, bot being very high and next only to Sathanur reservoir.

2.6 SATHANUR (Fig. 2.5)

Sathanur reservoir was created in 1957 on the River Ponniar at Sathanur Village in Tiruvannamalai Sambuvarayar district (12° 12'N). It covers 2 010 ha (Fig. 2.5) at the FRL of 222.2 m. The reservoir has a capacity of 228.91 million m3 at full level and a mean depth of 11.4 m. Shore and volume development indices are favourable for productivity. Sathanur is a hard water reservoir (total hardness range from 112–254 mg 1-1), with a matching high specific conductivity (320-800 umhos), and total alkalinity (145–616 mg 1-1). Values of all the three parameters mentioned above are some of the highest recorded in Tamil Nadu reservoirs. Nitrate nitrogen in water which is rarely found in Tamil Nadu waters is quite high (4.4–5.6 mg 1-1). There is no regular plankton bloom as in the organically rich reservoir. Amaravathy. Dissolved oxygen drops from 8.5 mg 1-1 to nil towards the bottom. However, the fall in pH is not steep, due to the buffering action and poor tropholytic activities (Sreenivasan, 1976). Alkalinity increases by 14.0 to 78.0 mg 1-1 from surface to bottom.

Both morphometric as well as metabolic indicators point to the productive nature of the reservoir There is a high rate of carbon fixation. The primary chemical energy fixed by producers is estimated at 8.1 × 106 cal m-2yr-1 at a photosynthetic efficiency of 1.047%. The fish, Wallago attu, Cirrhinus reba, Labeo kontius, L. fimbriatus, Notopterus notopterus and Mastacembelus armatus are indigenous species, while Catla catla, Cirrhinus mrigala, C. cirrhosa, L.calbasu, L. rohita and Cyprinus carpio (Bangkok strain) are introduced.

Drifting gill nets of mesh bar 5, 6 and 7.5 cm are employed for fishing. A fishing unit comprises 10 gill nets, each 50 m in length, a coracle (a saucer-shaped country craft made of split bamboo and hide) and two men. Annual fish landings recorded during 1964 to 1977 ranged from 48.1 t (in 1967–68) to 214.4 t (in 1976–77) with an annual average of 128.2 t. During this period, catla has established firmly in the reservoir. The indigenous L. fimbriatus, which was dominant (36%) during 1964– 65, represented only 3% of the total catch by 1976–77. W. attu, the main predator, is less in percentage, though steady in its occurrence (Table 2.12). Presently, catla along with other Indian major carps form more than 78% of the catch (1992–93).

It is encouraging to note that C. catla, the prime fish species of Sathanur, is represented in the catch by the 3 to 4 year class. The presence of W. attu has not affected the carp fishery. Prabhavati and Sreenivasan (1979) believe that small numbers of this predator are welcome as a means to check the weed fish populations. The decline in populations of L. fimbriatus and L. calbasu is attributed to their breeding failure. Until 1977, fish catches in Sathanur were steadily increasing every year, despite a steady increase in fishing effort (Sreenivasan, 1979a). The catch per unit effort (as described by Rangathan and Venkataswamy, 1967) still remained high at 7 318 to 14 295 kg yr -1, thus suggesting scope for further increase in effort.

Previous Page Top of Page Next Page