4. KARNATAKA

Karnataka, the eighth largest State in India, is situated on the western edge of the Deccan plateau. The climate and physiography of the region make the State one of the most important in the country with regard to water resources. Karnataka has been harnessing these resources to the fullest extent over the years, creating a chain of storage reservoirs all over the State. The four physiographical regions of the State are the coastal region, the Malnad, the northern plains and the southern plains. The coastal region is a 240 km wide strip of land between the Arabian Sea and the Western Ghats, covered mainly with the alluvium deposited by the short, turbulent, west-flowing rivers, receiving an annual rainfall of 250 cm. Malnad is the undulating land lying east of Western Ghats at an average elevation of 150 m, with many tall peaks (average elevation of peaks, 900 m). With a wet, hot climate and a rainfall of 250 cm yr¹, the region has thick forest cover. The northern and southern plains are a part of the Deccan plateau, with the characteristic dry, semi-arid climate and scanty rainfall of 50 to 75 cm year^-1.

Karnataka has two types of drainages, viz., the east-flowing large rivers Krishna and Cauvery with their tributaries (Fig.4.1) and the short, west-flowing rivers. The Western Ghats, which remain as a wedge between the two major watersheds, feed both the east-flowing and west-flowing rivers with an impressive amount of water. The surface flow, in many rivers and their tributaries, has been interrupted for irrigation and power generation and in the process, a large number of storage reservoirs have come up all over Karnataka. Today Karnataka occupies a prominent position in the reservoir map of the country.

The main river Krishna flowing to Andhra Pradesh carries an annual discharge of 37 000 million m³. The river has five main tributaries in the State, of which Tungabhadra and Bhima are the largest. Most of the tributaries and their subtributaries have been dammed. The Cauvery, which originates in the State flows into Tamil Nadu, and being an upper riparian State, Karnataka taps a substantial quantity of the river water. The main river is dammed at Krishnarajasagar and all the tributaries upstream and below Krishnarajasagar are also obstructed to create reservoirs. While all the east-flowing drainages are harnessed mainly for irrigation, the west flowing streams are impounded to tap their hydro-electric power potential(Table 4.1).

4.1 RESERVOIR FISHERIES RESOURCES

Karnataka, like Tamil Nadu has a traditional irrigation system of impounding surface flow by creating small earthen dams across streams, creeks and rivulets. Locally called tanks, these small irrigation reservoirs can be seen in all the districts of the State, except Kodagu. Based on the available data, there are 4 605 large irrigation tanks in the State covering an area of 213 404 ha, with an average area of 50 ha, as opposed to 19 673 small tanks, with an average area < 7 ha (Anon., 1989). Large tanks have been considered at par with small irrigation reservoirs for the purpose of this study, whereas the small tanks are reckoned as ponds and excluded.

The 74 reservoirs in Karnataka cover an area of 223 887 ha, nearly four times that of Tamil Nadu. Among them, 46 belong to the category of small reservoirs, vix., < 1 000 ha with a waterspread of 15 253 ha. After taking into account the irrigation tanks, the total surface water area of small reservoirs goes up to 228 657 ha. The 16 medium reservoirs have an area of 29 078 ha and the large reservoirs (> 5 000 ha), over 179 556 ha. Among the small reservoirs, those less than 500 ha outnumber the rest (Fig. 4.2). Thus, Karnataka has 437 292 ha of water area under different categories of man-made impoundments.

Figure 4.1. Major river systems of Karnataka

Figure 4.2 Distribution of reservoirs and tanks in Karnataka

Large reservoirs constitute 80% of the total area, followed by the medium (13%) and small (7%) ones. However, when the 4 605 minor irrigation reservoirs, designated as tanks are included in the small category, their share goes up to 51% (Table 4.2).

The largest reservoir Linganamakki is situated in Shimoga, a district having maximum number of reservoirs in the State. Bellary, Belgaum, Mandya, Bijapur, Uttar Kannada, Chitradurga, Hassan and Mysore also have large reservoirs (Table 4.3). Small reservoirs are mostly irrigation impoundments, distributed in all the districts, the richest being Kolar, with 625 tanks and 2 reservoirs. Shimoga (662 units; 13 762 ha) and Bellary (193 and 46 022 ha) are also rich in man-made lakes (Table 4.4). The list of reservoirs in Karnataka is given in Table 4.5.

Karnataka's total water area under man-made impoundments covering an area of 437 291 ha is undoubtedly one of the largest in the country, holding tremendous potential for fisheries development. Yet, very little scientific studies have been made on the reservoirs of the State. Of the seventy-four reservoirs, only the Tungabhadra has been studied on a long-term basis. The Central Inland Fisheries Research Institute (CIFRI) has investigated the lake from 1958 to 1966, covering a wide range of limnological parameters. Some information is also available on half a dozen other reservoirs in the State. The tanks have been studied, in detail, by the CIFRI in the 1960s. The information available on limnology and fisheries of reservoirs and tanks of Karnataka is summarised below.

(Figures within paranthesis denote number of units)

4.2 TUNGABHADRA RESERVOIR (Fig. 4.3)

Tungabhadra reservoir was subjected to scientific study by the Central Inland Fisheries Research Institute from 1963 to 1965. Most of the information available on the reservoir stems from David et al. (1969a), Govind (1963 and 1969), Krishnamoorthy (1966) and Subba Rao and Govind (1964). A recent survey conducted by the CICFRI revealed the latest trends in limnology and fish productivity of Tungabhadra reservoir (Ramakrishniah, 1994).

Tungabhadra is the largest tributary of the river Krishna, contributing an annual discharge of 14 700 million m³ at its confluence point to the main river. The reservoir was created by erecting a dam at Mallapuram, 5 km away from Hospet in the Bellary District. At the full level of 497.7 m above MSL, the reservoir extends over 37 814 ha; the lowest and average areas being 9 194 ha and 23 504 ha respectively. It has an extensive catchment of 28 168 km², chiefly fed by the southwest monsoon. The annual rainfall in the upper catchment of the river is 104 cm. Minor rivers that feed Tungabhadra are dammed at many places creating small to medium sized reservoirs such as Vanivilas Sagar and Anjanapur, and several large tanks such as Shantisagar and Madag. Orogenic and minerogenic materials, derived from both the main catchment and the submerged area influence the silt and nutrient content of the reservoir. Silt deposition within the reservoir is high, which has reduced the capacity of the lake by 13.5% in its first decade of existence. The reservoir receives rich humic and other organic and inorganic nutrients from the dense forests of the upper catchment and the cultivated areas around the tail end of the reservoir. Black cotton soils of Shimoga and Dharwar districts also bring in soil washings.

The climate at the reservoir site is mainly dry (humidity 80.7% to 93.7%); the average monthly maximum and minimum air temperatures ranging from 31.0 to 39.5°C and 13.8°C to 22.3°C respectively. The basin soil is rich in calcium (200 to 300 mg 100 g^-1) and magnesium (50 to 100 mg 100 g^-1). The high available nitrogen in soil (25.8 to 27.8 mg 100 g^-1) indicates intense biological activity at the soil phase. Phosphorus level is, however, very low.

Although many individual parameters of soil and water quality, coupled with the favourable thermal and solar regimes, portray a productive ecosystem, certain hydrographic, morphometric and meteorological features retard the growth and smooth succession of the standing crop of plankton, benthos and macrophytes. The water remains warm (23.1 to 29.5°C) and rich in dissolved salts, throughout the year as evidenced by high values of total alkalinity and specific conductivity in the range of 30 to 100 mg 1^-1 and 240 to 359 μmhos respectively. The nutrient status of the impoundment is also moderately high, with level of nitrate at 0.2 to 0.5 mg 1^-1, phosphate traces to 0.03 mg 1^-1 and silicate 9 to 16 mg 1^-1. Dissolved oxygen in the range of 4.8 to 11.5 mg 1^-1 (80 to 90% saturation) suggests that the oxidation of organic matter is taking place easily at a reasonable rate. But the plankton community is not stable enough to utilize the nutrients. In the absence of a clear demarcation between the trophogenic and tropholitic zones, a steady decline of oxygen towards the bottom is not reported. Similarly, there is no vertical gradient in respect of pH, total alkalinity and carbon dioxide.

The sharp level fluctuations and abrupt drawdown of water have a destabilising effect on phytoplankton community, which fail to sustain themselves and thus utilize the congenial environment for primary productivity. Another retardant is the wind action. Apart from the monsoon turbidity, the wind-induced turbulence between May and September is caused by heavy particles and colloidal silt suspensoids, which severely restrict light penetration. Frequent water level fluctuations affect the substrata of benthic an periphytic communities. It is only for a brief period between October and December that the reservoir is stable and water clear and undisturbed. The rate of primary production in the reservoir is reported to be low (Banerjee and Ray, 1979). Carbon production at various centres, at various depths, ranges within 16.2 mg C m^-3 hr^-1 to 189.3 mg C m^-3 hr^-1. This is equivalent to annual gross production of 26.75 g C m^-3 yr^-1. The total annual production of carbon is estimated at 57 000 t.

Figure 4.3. Tungabhadra reservoir, Karnataka

Govind (1963) demarcates three seasons, based on the plankton abundance, viz. the productive period (December to April, 85 to 233 units 1^-1), retardation period (May to July, 14 to 27 units 1^-1) and the recovery period (August to November, 49 to 74 individuals 1^-1). Chlorophyceae and Cyanophyceae form the major components of phytoplankton, contributing 24.4% and 18.6% to the total plankton respectively. There is a rich spectrum of planktonic organisms in the reservoir. Blue-green and the green algae are represented by six genera each, while there are three genera of diatoms. Ceratium sp. is the lone member of Dinophyceae. Eighteen genera of zooplankton are recorded (Govind, 1969).

Benthic invertebrates are subjected to the vagaries of water level fluctuations, affecting their effective colonisation of the organically rich bottom (Krishnamoorthy, 1966). The admixture zone, where the riverine flow is neutralised by the backwash of reservoir, provides ideal habitat for molluscs and burrowing aquatic insects. The density of benthic organisms in the reservoir ranges from 147 to 421 unit 1^-1. Insects (52%), molluscs (31%) and oligochaetes (16%) form the major constituents by number. Plankton and benthos communities did not change appreciably during the last few decades (Ramakrishniah, 1994).

Ichthyofauna of the reservoir comprises 81 species belonging to 8 orders and 14 families (David et al., 1969a). Cyprinids with 37 species show maximum species diversity.

Fisheries

The fish catch of Tungabhadra reservoir during the mid-1960s was dominated by predatory catfishes, an undesirable component of fisheries by any standards. The plankton, benthos and detritus resources were not directly utilized by any of the major commercial species. More than 75% of the total catch comprised Aorichthys seenghala, Wallago attu, Silonia childreni and Pseudeutropius taakree, all living on a long-food chain. This is clearly the result of management failure to induct fast-growing, short food chain fishes into the system, during the early years of the reservoir.

Tungabhadra reservoir, when it was impounded, had a population of Puntius kolus, which contributed up to a third of its total catch. Other species of Puntius (P. dubius, P. sarana and P. pulchellus), Tor tor, Labeo fimbriatus, L. calbasu, L. porcellus, L. potail and L. pangusia formed the other indigenous forms (Krishnamoorthy, 1979). Most of the native species found the changed environment after impoundment hard to cope with and started declining, the main reasons being destruction of breeding grounds, absence of fluviatile environment, and the changed trophic structure. Their share in the total fish catch has declined drastically from 74.89% in 1958 to 28.91% in 1965 (Table 4.6). Unlike the case of reservoirs in Tamil Nadu, no serious attempts were made in Tungabhadra to introduce Indo-Gangetic major carps to fill the vacant niches created by the receding population of Puntius and Labeo species. As a result, the carp minnows and minor weed fishes took advantage of the new spurt in plankton and benthic communities and these fishes, in turn, provided good forage to predatory catfishes.

After Krishnamoorthy, 1979

Singit et al., (1987)

Tungabhadra reservoir seems to have come out of a long trophic depression as evidenced by the increase in catch from 15 to 156 t during 1950s and '60s to 2 068 to 4 200 t during 1980s. This increase in fish production is accompanied by matching increase of fishing effort, especially in the form of shore seines (Table 4.7). According to a latest survey, the fish production during 1993 was estimated at 1 500 to 1 600 t i.e., 40 to 42 kg ha^-1. The higher production notwithstanding, the most disconcerting fact remains that 88 to 92% of the yield emanates from the destructive gear, alivi (a small-meshed giant shore seine which removes small fishes of all categories in large numbers) and 90% of the catch comprises trash fishes, which are sun-dried and sold. Only 10 to 12% of the catch, either from gill nets or from alivi is sold fresh. Moreover, the size of the economic catfishes and carps has gradually reduced and mostly 0+ and 1+ juveniles are harvested (Singit et al., 1987). Breeding of Puntius kolus, P. sarana, P. dobsonii and Labeo fimbriatus, has been reported by Bhatnagar (1963, 1979) who spotted their spent females and spawn. However, the spawning did not seem to have contributed to recruitment, as evidenced by the progressive decline in populations of these fishes. In reservoirs, it is often observed that even after successful spawning, the spawn drifts down to the main reservoir and perish due to unfavourable deep and lentic conditions. Occupying the apex of a grazing food chain, the commercial fishes of Tungabhadra poorly convert energy from the primary producer level to the fish flesh. Banerjee and Ray (1979) estimated the production potential of the reservoir at 33 333 t, on the basis of a conversion rate of 0.40% from primary carbon to fish. The actual fish yield during the period of study was considered as 0.8% of the actual yield potential. However, the higher fish yield reported during 1980s is 9.2% of the estimated potential.

Ills of the reservoirs are many. Firstly, the sharp decline in water levels reduces the fishing season and leads to over-exploitation (Singit et. al., 1987). Secondly, inadequate stocking results in vacant niches which encourage forage species and thirdly, destructive fishing practices like alivi and other small-meshed gear offset the advantages of any possible autostocking and artificial recruitment.

Stocking

Stocking, done so far, remains inadequate and ineffective. During 1958–59, 300 000 Gangetic carps, procured from Calcutta, (obviously undersized) were released into the reservoir. This practice was continued till 1963–64, when the farm facilities became available at the dam site. Later, the seed produced in the farm (40 to 60 mm in size) was stocked. However, these stocking attempts were grossly inadequate to make any dent on the undesirable fishery spectrum. Annual stocking figures ranged from 49 000 to 410 000 during a period of 17 years from 1963–64, at a per ha stocking rate of 1 to 11 fish ha^-1. Survival of the stocked fishes was very poor, as most of the stocking was done in wrong places (David et al., 1969a). The spots selected for stocking did not have the essential pre-requidities to provide food and shelter to the growing fish seed. The stocked fishes were left to fend for themselves against all odds. The pervasive presence of predatory catfishes frustrated all efforts to build up a stock of desirable carps by stocking. Significantly, Mystus punctatus, the largest growing species of the genus commonly grows to a size of 25 to 35 kg in the reservoir and largest specimen recorded weighed an incredible 120 kg.

However, after the introduction of pen rearing in 1983, the annual stocking rate has been raised significantly touching more than 100 fingerlings per hectare in recent years. The stocking material consisted of rohu and mrigal of size 30–70 mm. In 1991 about 2.6 lakhs of catla (12 fingerlings ha^-1) have been stocked (Ramakrishniah, 1994). However, the impact of increased stocking of major carps to the catch has not been studied. As per the officials of Board fisheries the stocked carps of size 250 to 300 mm are exploited in large numbers during April–June when water levels go down. The size of catla in the catch during 1994 ranged 720 to 810 mm (7.0–9.0 kg). Stray specimens of over 900 mm (14 kg) are also observed. In contrast, L. rohita records three distinct groups viz., 300–350 mm, 500–575 mm and >800 mm. The 500–575 mm group forms the major segment of the catch.

The occurrence of major carps in considerable quantity reflects the success of stocking of these species. Catla is reported to have been stocked only during 1991 and the present catches could be traced to this stock. The size group 720–810 mm (7–9 kg) could be 2+ age indicating good growth of the species. This points towards the potential role of stocking catla in yield optimisation from the reservoir. The present fishery of L. rohita reflects the stocks introduced during different years. Though 500-575 mm group (2–3 kg) is dominant, specimens weighing 9 to 12 kg occur sporadically indicating the impressive size the fish attains in the reservoir (Ramakrishniah, 1994).

Craft and Gear

Coracle, the saucer-shaped country craft, made of split bamboo and covered with hide, is the most commonly used fishing craft. A normal unit has a diameter of 1.5 to 2 m. Fifty to sixty coracles are in operation in the reservoir at a given time; more than 70% of the licensed fishermen own one. Apart from the coracle, improvised rafts, made of empty cans, barrels and logs, are also in vogue, usually fabricated by fishermen themselves.

Surface gill nets (Rangoon nets), bottom set gill nets (udu valai), large shore seine (alivi), small shore drag net (kunti valai), cast nets, and hook and line are the commonly used fishing tackle. The gill nets, used throughout the year, catch all kinds of fish ranging from large catfishes to large and medium carps, depending on the mesh size. Small-sized gill nets (bedisi valai) bring in a host of small fishes which are normally processed by drying.

Alivi nets of Tungabhadra

The giant shore seine, alivi of Tungabhadra is characteristic to Tungabhadra and extremely rare in other reservoirs. This controversial fishing gear merits a separate discussion. Singit (1987) gives a graphic description of this net. Since the creation of reservoir in 1953, the fishermen of Tungabhadra have been using konti valai, Rangoon nets and other gill nets of various dimensions. Made of cotton, the above nets had a short life and the fish catch was too little for the fishermen to make both ends meet. As most of them were migrant fishermen from Andhra Pradesh, they brought in the alivi from their native place where it was known as pedda alivi. This experiment was not only a success, it gave them a windfall. Gradually, many fishermen took to alivi and soon most of them were operating more shore seines than gill nets. By 1970, there were 50 alivis in the reservoir.

The most disturbing feature of the gear is its capacity to remove indiscriminately fish of all hues in large numbers. Fishery scientists and conservationists have always viewed the net with concern. All attempts to ban the net have failed due to the passionate appeals made by the fishermen community and the lack of any enforcement machinery at the disposal of authorities. After considering all aspects of the subject, the Tungabhadra Board allowed alivi with a stipulation to release juveniles of desirable species back to the reservoir. This did not work and the net was finally banned by the Board in 1975. The ban, however, was ineffective as the alivis were continued to be operated in a clandestine manner in the night, especially in the inaccessible areas of the reservoir. The ban was later withdrawn due to pressure from the fishermen community.

Today, licensed alivis are in operation contributing 88 to 92% of the total fish catch from the reservoir. Alivi brings in juveniles of economic carps, Labeo calbasu, L. fimbriatus, Puntius kolus and P. pulchellus (9%), important economic catfishes (11.5%), Mastacembelus armatus, Channa spp. and Notopterus notopterus (4.5%). Bulk of the catch (75%) comprises uneconomic weed and catfishes, viz. Chela atpar, Oxygaster clupeoides, O. phulo, Barilius bendelensis, B. barila, B. barna, Danio aequipinnatus, Esomus dandricus, Rasbora daniconius, Amblypharyngedon mola, Puntius ticto, P. ambassis, P. sophore, Cirrhinus spp., Garra spp., Osteobrama vigorsii, Mystus cavasius, Pseudeutropius taakree, Ambassis ranga, A. nama and Glossogobius giuris. All the above species are invariably sun-dried.

Alivi nets are operated on a cooperative basis with sixteen to eighteen people involved in operation. Four to six hauls are made in a day, each lasting 2 to 2.5 hours. Well-to-do fishermen pool their resources and fabricate the net which normally costs c. Rs. 30 000. The dry fish merchants often lend money for the venture. Alivi provides livelihood to at least 1 500 people who are involved in fishing and other ancilliary activities. Another 500 live on the dry fish trade. Other forms of fishing being grossly unremunerative, fishermen take to alivi on economic compulsions. This aspect needs consideration while banning the shore seining. Despite its drawbacks, alivi keeps the populations of predatory and weed fishes in check and, if operated with care, it can become an instrument to manoeuvre the fish stock. However, this cannot be achieved without the whole-hearted cooperation of the fishermen community. An awareness campaign is necessary to educate the fishermen about the need to conserve the fishes and increase fish production.

Pen culture

Rearing fry to fingerlings in the pen enclosures erected on the periphery of the reservoirs is an ideal way of raising stocking material. That the pen culture of fingerlings will cut down the production cost and obviate the necessity of cost-intensive nursery farms has long been known. Yet, Tungabhadra is the only reservoir in the country to try this as a management option. This practice has been followed in the reservoir for the last 11 years in a row. During 1992–93, pens were erected in Ladakanabhavi, 25 km from the dam site. There were 21 pens, covering a total enclosed area of 3.30 ha. The pen site was situated at 496 m above MSL and the erection job was completed during July, when the site was still exposed. Later, as the water level increased, the pen got inundated.

The pen area was pre-treated with organic manure to ensure a rich growth of plankton after the filling. A total of 15.0 million spawn were stocked in the pens which comprised 6.75 million Labeo rohita and 8.25 million Cirrhinus mrigala.. After three months of rearing, 2.41 million fingerlings were collected and stocked in the reservoir. This included 1.085 million rohu and 1.325 million mrigal, worth Rs.495 875. The present rate of survival (15 to 16%) and the size at harvest (40 to 70 mm) are rather low. Efforts are on to improve the survival rate and the growth of fingerlings. The break-up of cost involved during the pen culture operation of 1993 is as follows: recurring cost - Rs.30 100, non-recurring cost - of Rs.16 180 and the cost of spawn- Rs. 253 650. Thus, the net profit was estimated at Rs. 165 945 for the whole operation. This is a commendable performance by the Tungabhadra board worth emulation in other reservoirs of the country.

4.3 MARKONAHALLI

Markonahalli is an old irrigation reservoir, created on the river Shimsha in the year 1939 to irrigate 6 070 ha of land in Tumkur district. The dam comprises a 139 m masonry structure and a pair of earth dams on either side extending to 1 470 m. The reservoir has a catchment area of 4 103 km² and a capacity of 68 million m³ at the FRL of 731.57 m above the MSL. The catchment is, however, intercepted at several places to create at least 647 irrigation tanks, depriving the reservoir of its water and nutrient source. The reservoir area at FRL is 1 336 ha and at lowest storage level, it is reduced to 128 ha.

Morphometric features of the reservoir are very favourable to productivity. This includes a large catchment for the size of the reservoir and the rich allochthonous nutrient inputs derived from the catchment. A low mean depth, fairly good storage ratio (2.5), high temperature regime and the age of the reservoir are favourably disposed for organic productivity (Table 4.8).

High levels of methyl orange alkalinity and specific conductivity indicate ideal conditions for high photosynthetic rate. However, the phosphate and nitrate in water are low.

(CICFRI Barrackpore)

Rate of carbon fixation by phytoplankton is moderately high (gross primary productivity 125 mg C m^-3 hr^-1), although the standing crop of net plankton is rather modest. The total count of plankton ranges from 7 to 35 units l_-1. Ceratium hirudinella, Nitzschia, Navicula and Pinnularia are the common phytoplanktonic forms generally encountered in the reservoir. Thirty-one genera of phytoplankton, belonging to Cyanophyceae, Chlorophyceae, Bacillariophyceae and Dinophyceae are recorded from the reservoir, though Ceratium hirudinella alone is present in appreciable quantity throughout the year. Zooplankton is rich in diversity as well as abundance. Probably, they live mainly on nannoplankton. The high rate of photosynthesis in the absence of rich phytoplankton suggests the possibility of nannoplankton playing the main role in carbon synthesis.

Benthic invertebrates of the reservoir comprise mayfly nymphs, damselfly nymphs, dragonfly nymphs and a rich molluscan population mainly represented by Viviparus bengalensis, C. peninsularis, Lamellidens marginalis.. The common forms encountered in samples are L. marginalis, L. corianus, V. bengalensis, Melania striatella tuberculata, Melania (Blotia) scabra, Bithynia stenothyroides, Lymnaea luteola, L. acuminata, Chironomus spp. Tubifex spp. and Ephemerella spp. The thick colonisation of the bottom by the benthic macro-invertebrates indicates an organically rich bottom. The rich macrophyte community of the reservoir comprises Hydrilla verticillata, Vallisneria appendicularis and Potamogeton spp., among which Vallisneria appendicularis is the most dominant (4.4 kg m^-2).

Fisheries

Twenty-seven species of fishes have been recorded from the reservoir, among which 13 contribute to the commercial catch. Puntius has the maximum species diversity with five species. Even after 55 years of its existence, the reservoir sustains populations of indigenous fish species such as Puntius sarana, P. dorsalis, Cirrhinus reba, and Labeo calbasu, along with the transplanted carps. The fishery management should address the problems in enhancing the productivity of endemic fishes and the stocking should be limited to the extent of filling the vacant niches.

The stocking done so far, is arbitrary. In 1990, 91 000 fingerlings of rohu and catla were stocked in the reservoir (124 ha^-1). As a direct impact of this stocking, coupled with the increased in fishing effort, the yield has increased to 63 kg ha^-1 in 1992–93 from the earlier level of 5.5 kg ha^-1. The catch of 46 t comprised catla (36.86%), rohu (23.74%), mrigal (1.6%), common carp (2.27%) Wallago attu (2.44%) miscellaneous fishes such as featherbacks, murrels etc. (32.7%) (Table 4.9).

Catch per unit effort was uniformly good, varying from 3.34 to 8.88 kg unit^-1 (of gill net) from April 1992 to March 1993. Performance of introduced carps in the reservoir is good. Catla catla appears in the catch at a mean length of 378 mm (15 months old) in the range of 290 to 670 mm, the modes being at 390 mm 490 mm and 590 mm. Labeo rohita appears at a mean length of 272 mm in April (16 months) and at the end of 2 years attains a mean length of 474 mm. The length range of rohu in catches is 200 to 800 mm, with modes at 390, 490 and 590 mm.

(Figures"(CICFRI Barrackpore)

During 1991–92, 600 000 fingerlings of catla (74%) and rohu (26%) have been stocked, which is equivalent to 922 fingerlings ha^-1. This was followed by putting in 450 000 more fingerlings of catla and rohu during 1992–93. Stocking during the last two years has a heavy bias in favour of catla and rohu at the cost of detritivorous species and therefore mrigal and Cyprinus carpio need stocking support.

The reservoir does not offer scope for the breeding of Indo-Gangetic major carps as the inflow from the southwest monsoon is negligible. Therefore, these species are to be managed on the basis of an annual stocking and harvesting schedule. Despite favourable conditions for its breeding, Cyprinus carpio failed to establish itself in the reservoir, probably due to predator pressure from Gambusia (predates on the larval stages), Wallago attu and Channa marulius.

Macrophytes remain as an unshared niche in the ecosystem which needs to be filled by stocking herbivorous species of fishes. The peninsular carp, Puntius pulchellus, an endemic species which can utilise the macrophytes, is an ideal candidate for stocking in the reservoir. The Central Inland Capture Fisheries Research Institute has suggested the following management measures for control of predator population and fish yield optimisation:

1. Introducing long line fishing, targeted against Channa marulius and Wallago attu,

2. extensive drag netting operations under Departmental supervision to remove weed fishes like Gambusia, using fine-meshed (3 mm bar) drag nets; fingerlings of the desirable species, collected in the nets, must be returned to the reservoir,

3. imposing restrictions on the use of small-meshed gill nets (<50 mm bar), encouraging fishermen to increase the mesh size to catch larger fishes, increase the total number of units only after careful monitoring of the catch per unit effort, and

4. initiation of programmes to train and educate the fishermen about the norms of conservation and sustainable use of resources.

4.4 HEMAVATHY (Fig. 4.4)

Hemavathy is an irrigation reservoir created in 1981, on the river Hemavathy at Gorur, Hassan district. The reservoir with an area of about 8 000 ha is situated at 12° 4' N and 76°3'E at an elevation of 840 m above MSL. The river Hemavathy originates from the Western Ghats at Bellalarayanadurga in Chikmagalur district and joins the river Cauvery at Akkihebbal in Mandya district. River Yagachi and Aigoor Halla are the two main tributaries of the Hemavathy (Table 4.10).

(After Devaraj et al., 1987

Devaraj et al. (1987) made a comprehensive study on the reservoir, the salient findings of which are presented in the following account.

The climate at the reservoir site is mainly dry and the mean air temperature ranges from 13.5 to 20.0 ° C (minimum) to 25.5 to 34.0 °C (maximum). Monthly rainfall varies from 1.33 to 122.60 mm. The reservoir is exposed to intense sunlight, skies being cloudless from October to May.

Figure 4.4. Hemavathy reservoir, Karnataka

The reservoir starts filling by late June or early July, due to early rains in the Hassan district. The water level reaches its peak of 37.19 m by the end of August or early September. During September and October or sometimes even in November, it becomes somewhat stable. From the month of November, the level declines steadily.

Soil and water quality

Basin soil is acidic (pH : 6.3 to 6.9) and generally coarse and sandy in texture. A mixture of silt, sand and clay, is however, found in the intermediate zone of the reservoir. The mean water temperature (25.85 °C) and transparency are high in the lentic zone, compared to the middle and riverine zones. Difference in temperature between the surface and bottom layers of water is not very significant. The level of dissolved oxygen at the surface is fairly high, with mean values for differenrt sectors ranging within 5.78 and 6.37 mg l^-1, and there is no oxygen deficit at the bottom. Incoming floodwaters chiefly determine the clarity of water. The Secchi disc transparency varies between 23.5 and 228 cm, the riverine zone being more turbid, compared to the rest of the reservoir. Hemavathy can be designated as a soft water reservoir, based on the total alkalinity values which vary within a range of 23 and 49 mg 1^-1. The values are reported to be increasing progressively over the years, suggesting a possible improvement in terms of alkalinity in future. The pH is within the range of 7.05 to 8.00 (Table 4.11). There is decline in pH at the surface during summer months, leading to a weak vertical stratification.

After Devaraj et al., 1987

Average values of free carbon dioxide in water are below 3.0 mg l^-1 and its concentration increases slightly towards the bottom. The young reservoir is rather poor in dissolved nutrients, the phosphate values mostly being in traces. On a few occasions, sudden rise in the phosphate level is reported, with values going up to 0.28 mg l^-1. Silicate is recorded at the rate of 0.51 to 6.72 mg l^-1, with an average of 1.59 mg l^-1.

Biotic communities

Plankton: The density and composition of the plankton do not reflect any eutrophic tendencies. The modest plankton community (68 to 112 organisms l^-1) comprises phytoplankton to the extent of 48.85%. Characteristic feature of the phytoplankton is the domination of Chlorophyceae, followed by Cyanophyceae and diatoms (Table 4.12). Enrichment of the plankton community is influenced by the nutrients brought in by the rain washings (Devaraj et. al., 1987). Maximum plankton is during the post-monsoon period, extending from late August to February and a significant increase in phytoplankton is noticeable during April to August.

Littoral and bottom biota: Nutrient status of the soil is high, compared to the water and this is amply reflected in a rich community of littoral organisms comprising crustaceans, insects, molluscs, small fishes, tadpoles and oligochaetes, at a density ranging from 64 to 966 organisms m^-2. Insects, the major component of this community, are represented by chironomid larvae, waterbugs and the nymphs of dragonfly and damselfly. Viviparus and Gyraulus are the common genera of gastropods found among the littoral community, while the bivalves encountered are Corbicula and Unio. Insects, molluscs and worms constitute the benthic invertebrate community in that order of abundance, their density varying between 2 042 and 4 174 organisms m^-2. The riverine zone has a highpoper ulation density of benthic organisms than the rest of the reservoir.

Macrovegetation: The aquatic macrophytes of the reservoir comprise mainly submerged and rooted vegetation belonging to seven species viz., Ceratophyllum demersum, Chara spp., Cyperus corymbosus, Hydrilla verticillata, Nymphaea odorata, Potamogeton nodosus and Utricularia vulgaris.

Ichthyofauna and fisheries

Fish fauna of Hemavathy comprising 43 species includes a number of native fishes deserving attention from conservation point of view. This includes 11 species of Puntiusand 3 species of Labeo and two species of Ompok. All the known predactors i.e.Wallago atto, four species of Channa,2 species of Aorichthys and 1 species of Mystus are present, apart from Mastacembelus armatus and the air breathing fish, Heteropneustes fossilis. Total estimated fish catch for 1984–85 is 115 t, which is equivalent to 12.5 kg ha^-1, calculated on the basis of area at FRL. The catch and yield increased to 146 t and 14.8 kg ha^-1 during 1985–86. A disturbing feature of the catch structure is the disproportionately high numbers of catfishes and minnows. Eels, catfishes and murrels together constituted nearly 22% of the total catch during 1984–85 with another 43% contribution from minnows and other low value species. Thus, the share of Indian and exotic economic carps in the fish landing was only 35% (Table 4.13). The situation was more or less the same during the succeeding year, although a slight increase in the share of carps was noticed.

* Minnows, mainly Salmostoma phulo

**Small fishes, mainly G. giuris

Fishing in Hemavathy is yet to be organised. Barring a few migrants from the neighbouring State of Andhra Pradesh, most of the fishermen are the local farmers and farm labourers who changed their profession in favour of fishing. There are 5 main fishing camps in the reservoir namely, Kerodi, Beejaghatta, Haluvala, Beekanahally and Shettihally, each with 35 to 50 fishermen families. However, only 25 to 30 families among them have fisheries as a full time vocation. Average catch per individual fishermen on a normal day is 3 to 6 kg, which fetches them Rs. 10 to Rs. 15, though during the peak fishing season the daily earnings can go up to Rs. 60.

Gill net, with mesh range of 2.5 to 25 cm, is the most popular gear in the reservoir, which are operated from coracles. Cast nets and traps are also used. The catch is sold to middlemen who cart the fish everyday by road to market. The womenfolk in the fishermen families often hawk fish in local markets and residential areas. A substantial part of the catch is sun-dried.

Fishery management

A study of the feeding habits of fish in the reservoir indicates that none of the the main fish food biotic communities are fully utilised by the major economic fishes (Table 4.14). Although Catla catla feeds on copepods, given the negligible population of this fish in the reservoir, the niche can still be considered as underutilized. Presently, the carp minnows and other uneconomic species feed directly on plankton and littoral/bottom biota, and ultimately provide forage for predators. The energy loss involved in this rather long food chain is the main retardant to fish productivity. Interestingly, the detritivores, which are better converters of energy than the predators, are poorly represented in the catch. A qualitative change in the species spectrum, could be achieved through careful management.

Very little has been done to develop the fisheries of Hemavathy on scientific lines. The reservoir harbours a kaleidoscopic spectrum of the riverine fish fauna which need attention from conservation point of view. The reservoir is in its formative stage and unless effective measures are taken to induct some high value species that utilise the plankton and detritus, the present minnow-predator combination will get entrenched. Both peninsular and Gangetic species should be considered for stocking in the reservoir, after prior assessment of their potential impact on other fish.

4.5 VANIVILAS SAGAR

Vanivilas Sagar is situated on the river Vedavati in Chitradurga district, about 104 km northeast of the Babudan Hills, the source of the river. It is one of the oldest reservoirs in the State. Created in 1901, the impoundment has a water area of 8 640 ha at the full reservoir level of 621 m above MSL. The catchment area of the river is rich in iron ores, limestone and sodium salt deposits (Ray, 1969). The river, at its origin, receives rich rainfall to the tune of 375 cm a year. However, the precipitation in the local catchment is just 60 cm per year, as the reservoir is situated in the semi-arid plains.

The upper catchment of the river being dammed by numerous tanks for local irrigation, which leaves the inflow into the reservoir rather erratic. Low water renewal rate has an undesirable influence on the biotic communities. A substantial part of the reservoir is shallow and the annual level fluctuation of 0.2 to 0.6 m makes the environment ideal for rapid colonisation by aquatic macrophytes. Rich growth of Hydrilla, Potamogeton, Aponogeton and Vallisneria covers one third of the total reservoir bed, down to 2.4 m (Ray, 1969). In this way the reservoir is rapidly changing itself into a wetland, an ecosystem akin to the floodplain lakes of Ganga and Brahmaputra, where the cut-off meanders become full of submerged vegetation. Excessive vegetation is undesirable from the fisheries point of view. The weeds remove nutrients rapidly from the system and utilise the solar radiation, leaving very little of the two inputs for the photosynthetic activities of plankton. Thus, the energy is diverted through a weed-detritus chain. The constant decay of vegetation at the bottom fouls the bottom bed, making anaerobic and toxic conditions. Moreover, they hasten the process of conversion of the reservoir to swamp and eventually dry land.

The reservoir water is uniformly warm throughout the year (22.3 to 26.3 °C) and no thermal stratification develops. With minimum disturbances from the level fluctuations, and due to the presence of submerged plants, which arrest and settle the suspended load brought in by the inflowing river, the water is clear most of the time. Although the pH (8.4 – 8.5), total alkalinity (194–228 mg l^-1) and hardness (108–128 mg l^-1) are high, the macrophytes take advantage of such environment, leaving little room for the plankton community to flourish. Consequently, the phytoplankton productivity is a negligible 0.39 to 3.25 mg C m^-3 day^-1.

The bottom, having been colonised by the macrophytes, does not offer much substrate for benthic invertebrates. Gastropods and bivalves are abundant among the plants, forming an important food of fish. The ubiquitous presence of macrophytes and their constant photosynthetic activities enrich the dissolved oxygen content of water (6.56 to 9.8 mg 1^-1). There is no decline of oxygen towards the bottom, indicating a slow pace of organic decomposition at the bottom. Lack of organic acids at the bottom is confirmed by the high pH of soil (8.0 to 8.5). This alkaline nature is characterised by high soil calcium (200 to 300 mg 100 g^-1). Phosphate is low both in the water and soil phase. No published account is available on the fish and fisheries of the reservoir.

4.6 SUPA RESERVOIR (Fig. 4.5)

Supa reservoir is one of the three impoundments of the Kalinadi hydro-electric project, the other two being Bommanahalli (1 836 ha) and Tattihalla (2 700 ha). The project is aimed at tapping the hydel potential of the west-flowing river, Kalinadi at the confluence of its three tributaries viz., Pandri, Naginalla and Kaneri (diverted). Supa is one of 10 dams to be constructed on Kalinadi to tap its full hydel power potential of 1 298 MW. The reservoir has a total area of 12 900 ha and a catchment of 1 067 km², draining mainly the Western Ghats. The 161 km long Kalinadi has its catchment rich in iron and manganese ores, limestones, quartz, bauxite and silica, and the mean annual rainfall is 274 cm, largely from the southwest monsoon.

Despite draining a mineral-rich, heavily wooded catchment area, the reservoir remains oligotrophic. Birasal et al. (1991) points out the poor ionic composition of the lotic region of the reservoir. The total dissolved solids increase substantially from the lotic to the lentic zone, as refelected by the specific conductivity (68.8 and 99.2 μmhos respectively). It is reported that during the initial phase of the impoundment, decomposition of submerged vegetation contributed to the ionic build-up. The decomposing vegetation also increased the acidity of water.

Vertical profiles of oxygen and other chemical parameters are not available. Being a hydel reservoir with a substantial part of its water locked up in a deep basin, the bottom accumulation of H₂S is natural. Heavy accumulation of the offending gas is reported in the lentic sector of the reservoir (0.24 to 0.68 mg 1^-1) and in the outflowing water (0.68 to 1.82 mg 1^-1). Massive fish kills are reported from the reservoir and the dead fishes usually pass through the turbines. While metalic ions are present (Fe³⁺ 1.08 1^-1; Mn²⁺, 1.35 mg 1^-1) in the water phase, nitrate is in low concentration (0.08 mg 1^-1). Phosphate is high (0.2 mg 1^-1), in comparison with many other South Indian reservoirs. On account of the high concentration of iron and manganese, the water of Supa is not potable. The available information on physico-chemical parameters is inadequate to draw conclusions about the productivity of the reservoir. Birasal et al. (1989) reported the presence of 25 species of zooplankton in the reservoir, i.e.., rotifers (7), copepods (9) and cladocerans (9), but gave no information on their quantitatives abundance. The reservoir is oligotrophic, but this has to be further verified through biological parameters.

There is no organised fisheries in the reservoir. The Karnataka Power Corporation (KPC), which owns the reservoir, has plans to develop the fisheries of Supa and three other reservoirs in the Uttar Kannada district. In 1990, 265 000 fry/fingerlings of Catla calta. Labeo rohita, and Cirrhinus mrigala, were stocked, along with a few silver carp, Hypophthalmichthys molitrix (Rahman, 1993). During 1992–93, 724 000 seed of Indo-Gangetic carps, and milkfish Chanos chanoswere stocked. The KPC intends to stock 1.07 million fish seed during 1993–94. They have also plans to establish mahseers for attracting tourists, to stock the non-predatory catfish Pangasius pangasius, peninsular herbivorous carp Puntius pulchellus, and the giant freshwater prawn Macrobranchium rosenbergii.

Figure 4.5. Supa reservoir, Karnataka

4.7 KABINI RESERVOIR

Kabini reservoir is situated on the river Kabini, a major tributary of the Cauvery at Sargur in Mysore district. The 2 732 m long dam was constructed in 1974 for the twin purpose of irrigation and hydel power generation. At full reservoir level, the lake has a waterspread of 6 020 ha and storage capacity of 553 million m³. No ecological studies have so far been made on the reservoir. Neither have any records been maintained about the fish production, as the fishermen themselves dispose off the catch to the merchants. The following information on Kabini reservoir is gathered from Murthy et al. (1986) and Srivastava et al. (1985)

There are eleven important fish landing centres around the reservoir. Fishermen of Antharasanthe, K.G. Hundi, Ponapura and Gundathalu centres use gill nets while sosalu bale, a small drag net, is used by fishermen of Hosur, Nerale, Ramenhally, Hosamala, Jogihally, Bidarhally and Thoramante. Rod and hook, and long lines are also used for fishing. The licence for the former is issued to those who fish for pleasure. The catch being negligible, they often consume the catch themselves. Long lines often comprise 50 hooks, licence for which is owned by part-time fishermen who catch fish as an extra source of income.

(After Murthy et al., 1986; Srivastava et al.,1985)

The fish production from Kabini reservoir is decreasing over the last four years (Table 4.15), total fish catch plummeting from 450 t to 75 t (74 kg ha^-1 to 20 kg ha^-1). Cirrhinus reba which used to contribute 70% of the catch in 1980–81 has declined to 20% with a similar fall in the percentage of carps and other fishes. Tilapia has improved its position from 8% to 60%, while the predatory catfishes maintained its position of 8 to 10%. The reservoir has been stocked regularly with the fish seed of Indian and exotic carps (Table 4.16).

The stocking in the reservoir has become effective only after 1979. All the earlier efforts in this direction were nullified due to the complete draining of the reservoir in 1976 and 1978. Over the years, nearly 2.3 million Indian major carps (mainly Labeo rohita and Cirrhinus mrigala), and 2.9 million common carp were released. In 1980–81, mrigal contributed 90% of the seed stocked and during 1981–82 there were only 100 specimens of catla in the seed. The species-mix of stocking material has always been arbitrary. The stocked fish neither appeared in the catch nor was there any improvement in the yield. On the contrary, there was a steady decline and the indigenous C. reba is fast giving way to tilapia which competes with the desirable carps for food. Major factors contributing to the negative trends have been identified as :

(Murthy et al., 1986)

1. Ad-hoc and arbitrary approach towards stocking: species selection and stocking density are governed more by expediency than any ecological considerations.

2. Lack of conservation measures: No closed seasons are observed to protect the brooders; no attempts have been made towards mesh size control and effective monitoring of fishing effort.

3. Draining of the reservoir: Sometimes the reservoir is totally drained for repair of the dam, causing destruction of the brood stock and stocked fingerlings.

4. Social problems: Lack of credit for the migratory fishermen and lack of social support for the fishermen are the disncentives for fisheries development.

Srivastava et al. (1985) pointed out the need to remove the bottlenecks in the transport of fish from fishing sites to the assembly centres. It is also recognized that cooperative societies need to play a more meaningful role in market intervention and smooth flow of credit to the fishermen.

4.8 KRISHNARAJASAGAR (Fig. 4.6)

Krishnarajasagar, a multi-purpose reservoir on the main river Cauvery below the confluence of the tributaries, Hemavati and Lakshmanathirtha was constructed during 1911 to 1932. The dam is a brainchild of the celebrated Indian engineer and visionary, Mokshakundam Visweswaraya. The reservoir was created originally for irrigating 50 585 ha of semi-arid land of Mandy district and to generate hydro-electric power at the Shivasamudram Power Station. Now, as the water requirement for power generation is being met from the Kabini river, Krishnarajasagar water is utilised for irrigation, water supply to Mysore city and for meeting the demands for the industries nearby.

At the full level of 752.23 m above MSL, the reservoir has an area of 13 200 ha (average 8 156 ha). The catchment area of 10 619 km² comprises rocky hills, wooded forests and agricultural land, bringing in different types of water. The reservoir has a relatively deep basin (mean depth 30.17 m) and a long and irregular shoreline (shoreline development index : 7.25)

A characteristic feature of the lake is its rapid level fluctuation, the water level dropping by 15 m from the FRL every year during May–June. Apart from influencing the physio-chemical quality of water and soil, this has a direct effect on the fishery, by allowing intensive fishing activity during the low level phase. The mainstream Cauvery and its tributaries, Hemavathy and Lakshmanathirtha are the main source of inflow and all the catchment areas are fed by the southwest monsoon.

Water quality and plankton of the Krishnarajasagar have much in common with the low productive Western Ghat reservoirs of Kerala. Water is mostly clear, primarly because of the pick-up tanks in the upper catchment that act as silt arresters. The pH value rises during summer when water stagnates, with very little inflow from the river. Bicarbonate alkalinity ranges from 36 to 140 mg 1^-1 and CO₂ is usually present. Low values of phosphate and nitrate are recorded during the flood season.

The water is thermally stratified and a weak oxycline (oxygen deficit of 1.3 mg 1^-1) develops, but it is unaccompanied by any increase in bicarbonates towards depth. Since CO₂ is present in dissolved form at the top layer all the time, there is no extraction of the gas from the bicarbonates for photosynthetic purpose. Thus, there is no decline in bicarbonate at the top all the and the top layer does not derive CO₂ from bicarbonates, resulting in the absence of any stratification. At the same time, not much carbonate is left at the bottom in the presence of CO₂. This is confirmed by the lesser increase in H⁺ and thereby no appreciable decrease in pH values (deficit 0.3) towards the bottom.

Water quality parameters point towards a very slow rate of organic production which is further confirmed by the subdued rate of carbon fixation by phytoplankton (gross production nil to 63 mg C m^-3 hr^-1) and a lower plankton density (13 to 121 units 1^-1). There is a conspicuous absence of phytoplankton blooms. Benthic and littoral biota, on the other hand, is rich and varied, playing a vital role in the trophic events of the reservoirs. The shallow, irregular margin of the reservoir provides a conducive environment and suitable substratum for the benthic invertebrates.

A variety of insects, their nymphs and larvae form 50% of the benthic invertebrates, which give mean density of 1 342 organisms m^-2. A number of gastropods and bivalves, mainly Bithynia stenothyroides, Viviparus bengalensis, Melania striatella, M. scabra, Lymnaea acuminata, Lamellidens marginalis, and Corbicula peninsularis, insects such as Caenis, Notonecta, Ranatra, Diplonychus, Corixa, Cybister and the nymphs of dragonfly and damselfly, and oligochaetes are the common members of the benthic littoral community. Food and feeding habits of 7 species of fish (Labeo calbasu, L. rohita, Cyprinus carpio, Cirrhinus reba, Ompok bimaculatus, Glossogobius giuris and Oreochromis mossambicus) wer studied and all of them except C. reba have the bottom detritus and bentic invertebrates as the main or a major component of diet (Table 4.17).

Figure 4.6. Krishnarajasagar reservoir, Karnataka

CICFRI Barrackpore

Thirty-three fishes belonging to 11 families are recorded from the reservoir. These include the mahseer, Tor tor and the chocolate mahseer Acrossocheilus hexagonolepis. The indigenous Puntius has the maximum diversity (6 species), followed by Labeo (5 species). Predators belong to catfishes of Bagridae and Siluridae and the murrels, Channa spp. Significantly, the minnows and weed fishes thriving on plankton are not many. The carp minnows are mainly Rasbora daniconius, Puntius ticto, P. sophore and Chanda ranga. Plankton-feeding minnows being fewer, the predatory catfishes and murrels do not exceed 12% of the total catch.

A perusal of fish production trends for 25 years from 1956–57 (Srivastava et al., 1985) reveals that the total catch was erratic (45.83 to 189.0 t) at an average of 96.2 t. This is equivalent to a yield rate of 7.28 kg ha^-1 (at full area). Between 1980–81 and 1987–88 the yield has been gradually increasing (Table 4.18).

Fish catch in Krishnarajasagar is related to the water level, the catch being the highest in the months of low water levels (Fig. 4.7). During 1987–88, common carp, contributing 36% to the catch, was the single largest component of the fisheries, the indigenous economic carps (Labeo spp. and Puntius spp.) representing only 21% and the transplanted Indo-Gangetic carps a negligible 1%. The predator catfishes and murrels contributed nearly 12% and the forage fish share was 30%.

Figure 4.7. Fish landings in relation to water level in krishnarajasagar reservoir

There has been a qualitative change in the fish species composition over the years. The resident carps of the Cauvery such as Puntius dubius and P. carnaticus were reported to be the dominant species in the late 1950s contributing 39% and 25% of the catch respectively. Obviously, these native species have suffered a setback due to the changed conditions, especially in the fish food biotic communities. As at present, most of the energy transfer is channelled through the detritus/benthic chains, it is not surprising that the common carp gets an edge over others. This fish is a prolific breeder and a competitor to Cirrhinus sp. for food. Failure of Indian major carps to appear in the fishery is due to the poor plankton community, inadequate stocking and competition with common carp (in case of C. mrigala).

Stocking

Stocking has been arbitrary both in quantitative and qualitative terms. The total number of fish seed stocked during 1956–57 to 1980–81 varied from 2000 in the year 1964–65 to 888 000 in 1980–81. The selection of species was equally erratic. A large number of common carp was stocked during certain years, obviously because of their easy availability, and not based on any scientific reasoning. For instance, in the year 1978–79, 100 000 Indian major carps were stocked along with 352 000 common carp. Considering that the fish breeds readily in the reservoir, there is no necessity for the continued stocking of common carp. Moreover, the fish, especially if it is very big in size, has a low consumer preference, compared to Cirrhinus mrigala and the indigenous competitors like the other Cirrhinus species. Bulk of the gill nets used in the reservoir are surface gill nets and they do not effectively catch the common carp. Stocking, done so far, has little impact on the fisheries.

Fishing activities

There are 25 fishing villages around the reservoir and a local fishermen population of 2000. Fishing activities continue round the year without any closed season or fishing holidays.

The main fishing gear employed are gill nets, drag nets, cast nets, and lines. Locally fabricated coracle is the main craft used in the reservoir. Coracles of Krishnarajasagar are prepared with HDPP (high density polypropylene), and coal tar as an external covering, in place of the normal hide. This improvised coracle is cheaper and more durable. About 90% of the fishermen use gill nets, licence for which is issued by the local fisheries authorities without any limit, on payment of fee. Each fisherman normally uses 7 pieces of gill nets. There are different rates for different kinds of gear; the charge varying fromRs. 1 to Rs. 129. Total number of licences has gone up from 646 to 1150 during the 25 years from 1956–57 to 1980–81, with a corresponding increase in the revenue from Rs. 4333 to Rs. 18075.

Long lines, hook and lines, traps and a few giant shore seines (alivi) are also in operation.

Production problems

Krishnarajasagar reservoir produces much less fish than its potential. The main problem is an undesirable species spectrum, where neither the indigenous carps nor the Gangetic carps could carve out a niche for themselves. The stocking done, so far, being totally ineffective, a scientific stocking policy needs to be evolved, based on ecosystem considerations, with a complementary conservation effort aimed at the indigenous ichthyofauna. The absence of restrictions on fishing during the breeding season and use of small meshed nets result in destruction of broodstock and juveniles with far-reaching ecological consequences. This situation, coupled with, the predator pressure from catfishes and murrels is the main factor responsible for the inadequate population of desirable carps.

4.9 OTHER RESERVOIRS

Nalligudda

The 112 ha Nalligudda reservoir (listed as tank in Karnataka Fisheries Department records) is situated in the Bangalore Urban district, 40 km away from the city. Though free from pollution, it shows strong eutrophic tendencies. Water quality parameters indicate a rapid photosynthetic activity at the surface with high dissolved oxygen rate and a matching decomposition process at the bottom, as evidenced by heavy accumulation of CO₂ and oxygen consumption. Nalligudda is rich in nitrate and phosphate. There is a rich standing crop of plankton characterised by blooms of Microcystis sp. This high natural productivity could be used beneficially for aquaculture.

Byramangala

Byramangala reservoir is created on the river Vrishabhavati, 38 km away from the city of Bangalore. The 437 ha man-made lake has been receiving a steady inflow of treated sewage from the city and wastes from many industrial establishments for the last two decades. The water is slightly alkaline (pH 7.5) with high concentartion of CO₂ that ranges from 11 to 20 mg l-^-1. Total Kjeldhal nitrogen (27 mg l^-1) and ammonia (16.0 mg l^-1) show heavy nitrogen loading due to pollution. A very low dissolved oxygen (1.0 mg l^-1) and high levels of chlorides (164 mg l^-1), BOD (7.0 mg l^-1) and COD (58 mg l^-1) indicate the eutrophic nature of the water body.

The heavy organic load results in luxuriant growth of water hyacinth, Eichhornia crassipes, which chokes the reservoir almost completely. Fish mortality has become a recurring feature in the reservoir. The problem is more acute during the initial incursion of rain washings and during the summer peak. Raghavan et al. (1977), reported a case of a very heavy mortality in May 1977, when more than 1500 kg of fish were killed. The dead fish comprised Catla catla, Labeo rohita, Cyprinus carpio, Puntius dorsalis, P. ticto, Mystus cavasius, M. vittatus and Ompok bimaculatus. Among them, catla was in the size range of 1.25 to 9.75 kg and rohu 1.25 to 1.75 kg. During the fish kill, the water was acidic, with no dissolved oxygen and the CO₂ level was 292 mg l^-1. No hydrogen sulphide, or any other poisonous substances were reported. The high carbon dioxide and gill coating by suspensoids and the absence of dissolved oxygen were the chief reasons attributed to the fish kill. Significant accumulation of heavy metals such as zinc, chromium and copper in the soil and water phase and their uptake by water hyacinth has been reported in Byramangala reservoir (Joshi, 1990).

4.10 STATUS OF RESERVOIR FISHERIES IN KARNATAKA

Of the 74 reservoirs in the State, 10 have at least some ecological data. A proper scientific study covering all the major environmental parameters, the biotic communities and the production processes has been conducted only in Tungabhadra, Krishnarajasagar, Markonahalli and Hemavathy. Data available on the others are too insufficient to evaluate the ecodynamics of the system. Moreover, almost all the reservoirs subjected to the scientific study belonged to the large category, leaving the medium and small ones, which together constitute 84% of the total number. In the absence of a reliable scientific database on the essential ecological attributes, it is not yet possible to make any generalisations, based only on their morphometry, location, or the nature of drainage.

Deep reservoirs created in the uplands of Malnad tend to be oligotrophic and organically less productive. Supa and Krishnarajasagar are very deep and the benefits from the rich nutrient input from the heavily wooded catchment is almost nullified as the allochthonous nutrients get locked up in the deep water. Nevertheless, the conducive temperature regime and the ionic build-up over the years due to ageing have started showing their impact on the production process. After a long depression, the aquaticc productivity in Krishnarajasagar has started improving. However, the management measures have not been adequate to take advantage of this increasing productivity.

Supa reservoir, after the initial trophic burst, has just entered a phase of trophic depression and may take a few years to regain its initial level of production. Tungabhadra is a typical Deccan Plateau reservoir, having all the ingredients for a productive water body such as warm, well-illuminated and ion-rich water. However, the fish production in the earlier years has been very low due to the undesirable species-mix. Having failed to induct the fast-growing carps at an early stage, a forage fish-predator chain has been established at the cost of fish yield. Due to accumulation of nutrients over the years, the productivity is on the rise and effective management can enhance the production substantially. Careful manoeuvering of gill nets, shore-seines and long lines can check the growth of predators and carp minnows. At the same time production of the desirable carps can be enhanced through stocking and proper conservation measures.

A third category of reservoirs represents the small impoundments of the plains which are shallow and highly productive. Nalligudda has a rich natural build-up of nutrients which makes it very ideal for culture-based fisheries. Experience elsewhere in the country indicates enormous scope for enhancing yield from such water bodies. A large number of them are situated in the northern plains, where the temperature is high and by virtue of their small size, light penetrates up to the bottom. As most of them do not offer scope for autostocking, annual stocking and harvesting has to be adopted. Markonahalli in Tumkur district is a testimony to the effectiveness of this stock and harvest system.

The reservoirs of Karnataka are the sanctuaries of a rich ichthyofauna, especially the species of Puntius and Cirrhinus. Some of them grow better than the transplanted fishes. Despite being riverine species, they have adapted themselves well to the reservoir conditions. The main factors that can lead to their decline are the breeding failure and predator pressure. Small reservoirs leaving little room for autostocking and conservation, focus should be on the large and medium reservoirs in our efforts for conserving fish biodiversity.

4.11 TANKS OF KARNATAKA

Small irrigation impoundments listed as tanks (Please see the chapter on resources) constitute an important inland fisheries resource of the State. David (1974) made a comprehensive survey of such water bodies in Karnataka, covering a number of morpho-edaphic limno-chemical and biotic parameters. The status of these water bodies is given in the foregoing account.

The soil and water qualities of tanks in Karnataka depend, to a large extend, on their location. Therefore, David et al. (op. cited) classified them as:

1. Coastal and Malnad tanks.

2. Transitional zone tanks of Shimoga, Chickmagalur and stretches of Hassan, Mandya and Mysore.

3. The black soil zone tanks of Bidar, Gulbarga and Bijapur.

4. Red soil tanks of Bellary, Tumkur, Kolar, Bangalore, parts of Mysore, Mandya, fringes of Hassan, Chitradurga and Dharwar.

Coastal and Malnad tanks:

The lateritic soils of Malnad and coastal plains contain only traces of lime, magnesium and potash and are poor in silica and finer fractions of soil like clay and silt. They are acidic and low in nutrients except in the densely forested areas, where laterites are covered by forest litter, and very rich in organic matter and nitrogen. Soil quality plays a vital role in determining the soluble salts, nutrients and hydrogen-ion concentration of water. Disintegration of surface humid matter release elements like calcium, magnesium and other salts. Exchangeable salts in the presence of humic matter are more readily released, which help the growth of aquatic plants. Water of Malnad tanks, as a whole, has pH, alkalinity hardness and specific conductivity in the ranges of 6.8 to 8.4 , 16 to 118, 21 to 158 mg l^-1 and 213 to 42 umhos respectively. Majority of them is full of aquatic vegetation. Apart from the marginal vegetation comprising mainly Pseudoraphis and Scirpus, all the 25 species of floating, submerged and emergent vegetation recorded from the tanks of Karnataka are found in this region. Floating weeds are restricted to Pistia and Lymnanthemum in most of the districts, but Lemna is more common in Dharwar. Hydrilla, Chara and Ceratophyllum constitute the submerged vegetation. Most tanks in Malnad are swampy with various rooted vegetation including Typha, Scirpus and Nelumbium. The vegetation offers good substrate for a number of associated fauna, mainly tubificids, oligochaetes, Stylaria and Chaetogaster spp. But the typical forms associated with disintegrating vegetation, such as trichopteran and neuropteran insects, are conspicuous by their absence.

The main channel of energy transformation taking place through the macrophytic chain-plankton community has a subordinate role in the trophic structure and functions. Of the plankton count of 567 l^-1, phytoplankton constitutes 409 units. Among the blue-greens, Phormidium and Rivularia are common in the North Canara and Shimoga areas, whereas Microcystis, Anabaena, Chathrocystis, Osillatoria and Cydindrosperium are found in Chackmagalur and Hassan districts. Diatoms, as a group, are not well-represented in the tank ecosystems of Malnad and coastal belt. Desmids are abundant and include the genera Cosmarium, Selenastrum, Xanthidium, Microasterias, Closterium, Euastrum, Desmidium and Gonatozygon. A rich variety of Chlorophyceae is reported, the common forms being Spirogyra, Mougeotia Pediastrum simplex, P. duplex, Zygnema, Oedogonium, Crycigenia, Tribonema, Chaetophora and Microspora.

Transitional zone tanks :

These tanks are situated in the transitional zones between the Malnad (hills) and plateau, characterised by high soil and water fertility. Soil vary mostly from laterite to red and water quality parameters such as pH (8.7), alkalinity (223 mg l^-1) hardness (150 mg l^-1) and specific conductivity (737 umhos) are higher than in the Malnad and coastal tanks. The improved ionic build-up is due to indirect fertilization from disintegrating organic debris and humus from the forests, fertilizer leachings from the coffee plantations of Chickmagalur and the fields in the surrounding Hassan. Mandya and Mysore districts.

In most of the tanks, aquatic plants, though present, are not choking the water body. Emergent weeds are confined to the margins. The composition of littoral and bottom biota is the same as that of Malnad-coastal tanks. Macrophytes being relatively sparse, the plankton count reaches to 1708 units l^-1 (phytoplankton 1616 units). This region has the maximum concentration of Cyanophyceae and Bacillariophyceae. Blooms of Microcystis aeruginosa are very common in tanks especially in Chickmagalur, Hassan and Mysore districts.

Black soil zone :

Tanks of the black soil zone are characterised by either black or mixed, black and red soil. Black soil is derived from rocks containing soda lime felspars, produced under impeded drainage conditions. The soil has a rich clay content, a high proportion of alumina, lime, magnesia, and potash. Humus content is 1 to 10% and the soil is very fertile and high in base status and base exchange capacity. The area being warmer, the rate of decomposition of organic matter is high and water quality, in general, is quite conducive for organic productivity (pH 7.8–9.0, alkalinity 108 to 263 mg l^-1, hardness 52 to 97 mg l^-1, and specific conductivity 297 to 1197 μmhos).

Aquatic plants are mostly submerged and emergent (Hydrilla, Chara and Nitella) or filamentous rather than spatulate type. They do not pose any major impediment for fishing as the swampy condition prevails only in very few tanks in the area. With the vegetation cover considerably reduced, the associated fauna is less in variety and density, compared to the two preceding zones. Invertebrates, are mostly chironomids and tubificids. Culicidae are also found (mostly in Chitradurga district). Plankton population is more or less similar to that of transitional zone with a preponderance of Cyanophyceae, with Anabaena, Microcystis and Phormidium manifesting into blooms in many tanks.

Some characteristic features of the tanks in the black soil region are their high productivity, good soil and water quality. They are very conducive for fish production.

Red Soil zone:

Tanks in the red soil zone are characterised by the red loam or tropical red earth which are derived mainly from granites and gneisses with low water holding capacity. These soils are usually neutral, but tend to become acidic. Poor in nitrogen, phosphates and humus, manuring is required to make them productive. However, potash and iron oxide are present. Compared to the other zones, water portrays a poorer quality in terms of total alkalinity (61–125 mg 1^-1), hardness (58 to 88 mg 1^-1) and specific conductivity (185 to 474 μmhos). The low concentrations of phosphorus and calcium in the slightly acidic water is considered unfavourable for plankton.

Most tanks are seasonal and the littoral vegetation renews itself every year, after a period of quiescence in summer. Weed–choking, though rare, is reported when influx of sewage into the system promotes a luxuriant growth of Eichhornia. The plankton density is 847 individual 1^-1 and the phytoplankton count of 734 unit 1^-1 is more comparable with the black soil zone.

In general, where tanks are full of aquatic plants, they are deficient in plankton, as rooted weeds utilise all nutrients, depriving plankton of its share. In the absence of many herbivores in the tank ecosystem, the weeds are not directly utilised by fish. Even the Microcystis blooms are not utilized by fish. Both macrophytes and Microcystis contribute towards detritus and indirectly form food of detritivores. As most of the tank fish, such as Cyprinus carpio, Cirrhinus, Labeo, and Puntius, live mainly on detritus, energy channelled though plankton and macrophytes is utilised at the detritus phase. Invertebrates associated with the plants, especially the molluscs, are an important link in the food chain. Pangasius pangasius, the non-predatory catfish and the herbivorous peninsular carp, Puntius pulchellus are very important fish in the tak the tank ecosystem by virtue of their short food chains.

Fish fauna of tanks

Ichthyofauna of a tank reflects the faunistic composition of the river system to which it belongs and the transplanted Indo-Gangetic carps (Table 4.19). More than 70 species of fish have been recorded from various tanks in the State, out of which 20 are considered to be economically important. They include the large fishes viz., Catla catla, Cirrhinus mrigala, Cyprinus carpio, Labeo rohita, L. calbasu, L. fimbriatus, Puntius kolus, P. carnaticus, Tor spp; and Wallago attu and the medium sized fishes such as Notopterus, Puntius sarana, Ompok spp., Clarias batrachus, Channa spp. Mastacembelus spp., Labeo ariza, L. boggut, C. reba and C. fulungee. The majority (60–70%) of the catch, however, is represented by minor uneconomic species such as P. dorsalis Amblypharyngodon spp. The growth of some important fish species in tanks of Karnataka is given in Table 4.20.

Fisheries management

Fishing rights, including exploitation, stocking and disposal by leasing or licencing of inland waters (rivers, reservoirs and tanks), as a rule, are vested with the Department of Fisheries. In some areas, the Revenue Department has either the exclusive right or a conditional one with a stipulation to pay earnings from fisheries to the Fisheries Department. In Coorg, Department of Fisheries pays 50% of the total catch from tanks to the local village panchayat (local self government). Minor tanks are managed by the village panchayats. Generally, licenses are issued by the Fisheries Department, according to the fishing gear.

A variety of fishing gear is employed for fishing. Gill nets, both surface and bottom set, are the most common. The fishing tackle is used mainly in large water bodies. Drag nets, cast nets and an improvised triangular scoop net are the other favourite fishing implements. A variety of traps are employed for catching prawn, air breathing catfishes and murrels, while rod and line are sometimes employed to hook Wallago attu, Ompok spp. and Mastacembelus spp. Poisoning, shooting and use of dynamite, though reported, are not very common.

According to David et al. (1974), the fish yield of perennial tanks was 148 kg ha^-1 and that of seasonal tanks 10 kg ha^-1. Total fish production from tanks in 1974 was estimated at 30 000 t.

After David et al., 1974

(After David et al., 1974)