11. HIMACHAL PRADESH

Himachal Pradesh is a small State of 55 673 km², away in the the Himalayas. It is drained by a number of rivers, the most important among them being Chanab. Ravi, Beas, Sutlej and Yamuna. All the rivers are snow-fed and hence perennial. Topographically, the State has considerable potential for hydel power generation.

11.1 RESERVOIRS OF HIMACHAL PRADESH

The two major projects situated in the State, viz., Bhakra Nangal (Gobindsagar reservoir) and Beas (Pong reservoir) are primarily meant for hydel power generation, apart from serving other needs such as irrigation and flood control. Pandoh, with an area of about 200 ha, is a small impoundment created across the river Beas in the Kullu valley and Chamera is a small reservoir (100 ha) across the river Ravi in Chamba district (Fig. 11.1). The four reservoirs in the State. have a total waterspread of 41 696 ha (Table 11.1).

11.2 GOBINDSAGAR

Gobindsagar is an important reservoir for more than one reason. The Bhakra-Nangal project was launched at the dawn of independence, signifying the beginning of an era of large developmental projects in India and the project was considered as an icon of the young nation's pride, aptly described by Jawaharlal Nehru as one of the temples of modern India. Secondly, the reservoir, by virtue of its location at a high latitude, transcending the limits of the tropics and cold water influx from the Beas system, simulates some sub-temprature environment that interests the limnologists. Thirdly, it provides a unique opportunity for the fishery biologists to study the behaviour of the exotic silver carp in an Indian reservoir. Gobindsagar has attracted the attention of a number of scientists including limnologists, fishery biologists, gear technologists and general fishery managers. The reservoir was studied by All India Coordinated Project on Reservoir Fisheries from 1971 to 1985.

Figure 11.1. Distribution of reservoirs in Himachal Pradesh

The reservoir

Gobindsagar reservoir, one of the largest man-made lakes of India, was created by a 255 m high, straight gravity dam at Bhakra (31° 25'N and 76° 25'E) on the river Sutlej. Construction of Bhakra Nangal dam was initiated in 1947 and the reservoir was formed in 1963. The river Sutlej, originating from Mansarovar lake on the Tibetan plateau at an elevation of 4572 m, flows in a southwest direction, cutting 915 m deep through the plateau and later entering India after traversing a distance of 320 km in Tibet. River Spiti, the largest tributary of the Sutlej, joins it near Pooh. Important tributaries (Khuds), such as Lunkharkhud, Sirkhud, Gambharkhud and Alikhud enter the reservoir directly. Downstream of the reservoir, the Sutlej joins the river Beas at Harike and enters Pakistan. Located in the Bilaspur and Una districts, Gobindsagar reservoir covers 16867 ha at the FRL of 514 m above MSL and 5063 ha at the minimum water level. The reservoir has been designed to hold 9621 million m³ of water, when full, and 2431 million m³ at DSL. However, due to silt accumulation, the capacity has declined to 7118 and 1973 million m³ respectively (Table 11.2).

The Sutlej river receives cool, snow-melt water from the upper catchment during the spring and summer months and from monsoon precipitation during July-September in its lower catchment. A number of seasonal rivers, viz., Gambroula, Gamloha, Sir, and Lunkhar join the reservoir. The total catchment area of the reservoir is 56980 km². The annual runoff is estimated at 16775 million m³, brought in from the drainage area receiving a precipitation of 100 to 150 cm per year, apart from the snowmelt. Commissioning of the Beas Sutlej Link (BSL) scheme in 1978 added a new dimension to the hydrographic cycle of the water body. Under the BSL scheme, Beas water is diverted to Gobindsagar for augmenting the power generation and irrigation capacity of the reservoir. The Beas water joins the lotic sector at flow rates ranging from 57 to 212 m³ sec^-1 during diferent seasons, contributing 4477 million m³ annually. Blending of the cool Beas water and the warmer Sutlej water in the reservoir leads to some unique pattern in the thermal and oxygen regime and other processes which influence the life and production cycle of organisms.

The reservoir provides warm, mixed and cool lacustrine conditions for its biota. It has 3 distinct zones, viz., Lunkharkhad zone, lentic zone and lotic zone, covering 26.0, 42.0 and 32.0% of the area respectively. At Dehar, the edge of the lotic zone, the water from Beas enters Sutlej. The Lunkharkhad joins the reservoir near the dam (Fig. 11.2).

Gobindsagar is a 96.56 km long, 6 km wide reservoir with an irregular shoreline, as indicated by the high shoreline development index of 12.86. The maximum and mean depths of the reservoir are 163.07 m and 55 m respectively, making it one of the deepest man-made lakes in the world. A volume development index of 1.01 indicates a concave bed level. Discharge through the outflowing channels varies from 1.21 million ha m in the year 1974–75 to 2.35 million ha m during 1978–79, causing a level fluctuations of 67.96 m. The two power plants at the base of the Bhakra dam and the Ganguwal and Kotla power houses on the Nangal hydel channel downstream, have a total installed capacity of 1204 MW of power. The irrigation canals originating from Gobindsagar support a command area of >4 million ha of agricultural land making it one of the largest multi-purpose river valley projects in the world.

Figure 11.2. Gobindsagar reservoir, Himachal Pradesh

Physico-chemical limnology

Sarkar et al. (1977) and Anon (1989b) describe the soil and water quality of Gobindsagar reservoir. The soil flooded by the reservoir is alkaline (pH 8.2 to 8.8) and silty, with less than 40% clay content in all sectors (24.2 to 36.6%). It is poor in nutrients. The available nitrogen ranges from 13.0 to 20.5 mg 100 g^-1 and phosphorus 0.47 to 0.53 mg 100 g^-1. The organic carbon in the reservoir varies from 1.03 to 3.1%, calcium carbonate from 4.2 to 16.1% (Table 11.3). The soil differs considerably in the different zones. In the intermediate sector, the percentage of silt is high, with equal proportions of sand and clay, while in lotic and lentic sectors the clay portion is high. Chemical features also show seasonal differences. The flooded soil seems to have very little impact on the quality of water as the latter mainly derives nutrients from the catchment area.

Water quality

Water temperature at Slapper (confluence point of Beas water) used to range from 17.0 to 27.0 °C before commissioning of BSL in 1978. But after the Beas water started entering the reservoir, the range has come down to 9.0 to 11.0 °C in 1983–84, 10.5 to 17.5°C in 1984–85, 9.0 to 18.0 °C in 1986–87 and 15.0 to 16.5 °C in 1987–88 with a concomittant rise in dissolved oxygen level which increased from 8.0 to 12.48 mg l^-1. The incoming cold water remains as a distinct layer at the bottom, further strengthening the thermal stratification. pH of water varies within a range of 7.3 to 8.4, suggesting a strong buffering capacity. The water is generally clear during post- monsoon (winter) months and the transparency is reduced from March to April due to turbidity caused by run-off from snowmelt and monsoons. The Secchi disc visibility depth varies between 135 and 690 cm.

Total alkalinity and specific conductivity are within the productive ranges of 50 to 88 mg 1^-1 and 169 to 331 μmhos repectively. Values of phosphate (0.05 to 0.08 mg 1^-1) and calcium (22.0 to 24.6 mg 1^-1) are high. The limnological characteristics of different zones are given in Table 11.4. The lotic sector is characterised by low temperature, high oxygen, and ion-rich water, more akin to a temperate regime, compared to Lunkharkhad, a warm, lentic bay of tropical nature with high carbon dioxide, CO₃ and HCO₃, moderately high values of phosphate, specific conductivity, and high silicate content. These also show that the cool Beas water exerts its influence up to Bilaspur in lotic zone. The features distinguishing Beas water are low temperature, low specific conductivity, low bicarbonate, phosphate, silicate and organic carbon, but high dissolved oxygen content.

Thermal stratification

Thermocline, observed in Gobindsagar is sharper and longer in duration, compared to the reservoirs in the lower latitude. In the lotic sector and Lunkharkhad, thermal stratification is observed until September or October. The difference in temperature between the surface and bottom layers is 5 to 8 °C in the lotic sector and 6.5 to 9.5 °C in Lunkharkhad. A fall in values of dissolved oxygen and pH is generally associated with thermocline. CO₂, although generally absent at the top layer, is present at the bottom layer, which, in fact, triggers the release of H⁺ ions and hence the fall in pH. All these suggest tropholytic activities at the bottom. The breakdown of thermal and chemical stratification during the monsoon turbulence releases nutrients to the euphotic zone, where it leads to a higher primary production. The limno-chemical indicators strongly point towards productive nature of water despite a poor soil quality, the nutrient and salts being received from the inflowing waters and the biodegradation processes within the lake.

Primary productivity and plankton

Gobindsagar being located at the highest latitude among the reservoirs studied in India, receives the least amount of incident solar radiation (172× 10⁴ cal m^-2 yr^-1). The rate of energy fixation by primary producers is, however, higher, obtaining better energy conversion (0.68°) rate than in the reservoirs closer to the equator (0.20% to 0.49%). The gross primary production observed during seven years has an average range of 316.86 to 1 088 mg C m^-3 day^-1. The net production for the same period is 186.6 to 670.28 mg C m^-3 day^-1.

The annual average plankton biomass which ranges from 2.1 to 16 ml m^-2, increases from September onwards, reaching the maximum in December and February. There are two pulses of plankton in a year with spring and autumn blooms. The ratio between zooplankton and phytoplankton, as estimated by various workers, is 1:6.5. Zooplankton dominates only in September and October, while in other months the phytoplankton is dominant. Lentic sector is the most productive sector of the reservoir with planktonic biomass ranging from 0.-75 to 6.32 ml m^-3 (1975–83). Ceratium is the dominant planktonic alga, the abundance of which varies in different zones.

Benthic invertebrates

The benthic macrofauna of the reservoir is not very rich both in qualitative and quantitative terms, the density varying from 345 individuals m^-2 in the lotic to 677 in the Lunkharkhad sector. Oligochaetes (58.8%), culicids (22.4%), chironomids (12.6%) and molluscs (3.0%) form the benthic community. Benthos shows a bimodal pattern of fluctuation with two peaks, one in winter (January) and the other in summer (May). The overall abundance of benthos is high in the intermediate sector, whereas moderate in the lotic and poor in the lentic sectors due to their gravelly and rocky beds.

Fish fauna and fisheries

Ichthyofauna of the reservoir comprises 51 species belonging to 9 families, including the brown trout Salmo truta snow trouts, Schizothorax spp., and several species of hillstream fishes (Anon., 1989b). The species spectrum of the reservoir is distinct due to the sub-temperate climate and the zoogeographic affiliations with the Himalayan region. Prior to the construction of the dam, the cold water of the upper reaches of the river Sutlej used to sustain 30 species of fish, of which Tor putitora, Labeo dero, L. dyocheilus, Schizothorax sp. and Aorichthys seenghala were the dominant ones. A decline in the number of species has been reported by Dua (1993) on account of the changed ecological conditions, especially the silt deposition at the bottom. Apart from the minnows, coldwater species such as L. dero, Schizothorax plagiostomus and T. putitora have also been reported to have been affected. Presently, besides the two exotic species viz., Hypophthalmichthys molitrix and Cyprinus carpio var. specularis, Catla, T. putitora, L. rohita, L. dero, L. calbasu, L. bata, L. dyocheilus, Cirrhinus mrigala, Wallago attu and A. seenghala constitute the commercial fisheries in order of their abundance. Common predatory catfishes of the tropical region such as Wallago attu, Aorichthys aor, Bagarius bagarius and Silondia spp. are absent. Channa spp. and A. seenghala are two predators known in Gobindsagar.

In 1961–62, Catla catla, Labeo rohita and Cirrhinus mrigala were stocked, followed by a regular stocking of Cyprinus carpio. Until 1974, the gid (L.dero), mahseer and common carp were the major components of catch and later, catla and rohu became dominant. Breeding of Indian major carps in the reservoir has been reported by Kaushal and Rao (1990). Silty, muddy and grassy areas at the upper Lunkharkhad are the spawning grounds of Catla catla and Labeo rohita. The emergence of silver carp in 1979 marked the beginning of a radical change in the catch structure. Having struck a favourable note vis-a-vis breeding and feeding in the reservoir, the fish has established the fish has established an overriding dominance over all other species.

Fish yield

The current (1992–93) fish production from Gobindsagar is 964 t, which is 96.4 kg ha^-1, based on an average reservoir area of 10 000 ha, one of the highest yields from a large reservoir in India. The increase in fish yield of Gobindsagar over the last two decades has been remarkable. From a modest 160 t in 1970-71, the production rose steadily to 700 t in 1977–78. It remained above 700 t for the next four years with a peak of 754 t in 1978–79. After remaining steady (377 to 653 t) during 1981–82 to 1986–87, the yield started increasing rapidly every year, reaching an all time high of 964 t in 1992–93 (Fig. 11.3).

Figure 11.3 Fish prodcution trends (t) in Gobindsagar 1971-72 to 1992-93

A six-fold rise in fish production has taken place during the 20 years in the wake of steeper increase in the fishing units. Number of licensed units in the reservoir registered a ten-fold increase from 100 in 1970–71 to 963 in 1992–93. A perusal of data presented in Table 11.5 clearly indicates that the catch per unit did not show wide variations, despite a noticeable hike in both fish yield and number of fishing units.

Major fisheries

Among the four Indian major carps, L. rohita has undergone a marked decline since 1979 due to inadequate recruitment and wanton killing of brooders in their breeding season during the period 1977 to 1982. The minor carps are represented mainly by L. dero, L. dyocheilus, L. bata. C. reba and P. sarana and the hillstream species. The share of these fishes in the catch started declining after 1982, reaching an all time low of 1.2% in 1989–90 (Table 11.6). During 1990–91 to 92– 93 they ranged from 3.5 to 4.5%.

The major carnivorous fish of the reservoir are mahseer (T. putitora) and A. seenghala. Their contribution has declined over the last two decades from 18.6 to 5%. A. seenghala, over the last 19 years, fluctuated between 0.4 and 4.0% of the total catch. The low percentage of the catfish has helped in fast build-up of Indian major carp during the initial years and silver carp in the post-1978 period. T. putitora, the prized game fish, constituted a major fisheries in the river Beas before the reservoir was filled. Although its percentage contribution has dropped from 16.7 to 5.8% (1974 to 1987), the actual production in terms of landings has not appreciably changed, when compared to the catch from the initial years of impoundment.

Exotic carps:

Silver carp, grass carp and common carp represent the exotic component in the fish landings. In recent years, the exotic carps, by virtue of their prolific breeding, have virtually dominated the whole reservoir. Their contribution to the total catch increased from 14.2% in 1974–75 to 87.4% in 1989. Despite a downward trend noticed in the subsequent years, the exotic carps especially the silver carp, are still dominating (Fig. 11.4).

Mirror carp (Cyprinus carpio var. specularis) constitutes an important fishery of Gobindsagar. The fish is well-entrenched in the lake as indicated by its percentage composition in the total landings, which ranged from 13.8 to 32.8 during the period 1974–87. Regular stocking has been carried out by the Department since 1965. This species attains an average size of 0.8, 1.4, 2.2 and 3.1 kg in its first, second, third and fourth year respectively. The dearth of aquatic plants in the reservoir prevents spawning of the mirror carp, as it has no suitable substrata to which to attach its eggs. Specimens of grass carp have rarely been encountered in the reservoir during the last 19 years. Kaushal and Rao (1982) observed a few large specimens of 542 to 1 225 mm (2 to 20 kg), including an oozing female among the commercial fish landings at Lathiani. The non-establishment of grass carp in the reservoir is attributable to the virtual absence of aquatic weeds.

On the basis of experimental gill netting, George et at.(1977) found a strong seasonality and zonal variations in fish landings. The catch per 100 m^-2 of gill net was 6.34 kg in upper reaches of Lunkharkhad, as opposed to 2.37 kg in the lower reaches. The values in respect of the main river course and Sir arm were 0.758 and 2.758 respectively. While Labeo diplostoma was well represented in catch throughout the year with its peak in December, most of the Indian major carps were caught during the monsoon months.

Figure 11.4. Changes in fish catch composition (t) in Gobindsagar

Biology of fishes

Feeding habits and reproductive biology of some of the fishes from the reservoir are known. Kaushal et al. (1980a) reported that the silver carp in Gobindsagar lived mainly on a phytoplankton diet comprising green algae, diatoms, dinoflagellates and blue-green algae in the order of importance. T. putitora subsists mainly on a fish diet, supplemented by zooplankton (Kaushal et al., 1980b). Bhatnagar (1964) studied the spawning periodicity of some of the commercially important fishes of Gobindsagar. T. putitora spawns intermittantly throughout the greater part of the year. Cyprinus carpio, and A. seenghala spawn once a year with a prolonged spawning duration. Labeo dero, L. bata, Mystus bleekeri, Crossochellus lattus latius and Garra gotyla also spawn once, but with a short spawning season. The snow trout, Schizothorax plagiostomus, Clupisoma montana and Mastacembelus armatus are reported to have two periods of spawning in a year.

Silver carps in Gobindsagar

The silver carp, Hypophthalmichthys molitrix got an accidental entry in Gobindsagar in 1971, when 47 specimens in the size range of 290 to 530 mm (0.5 to 2.5 kg) were washed out into the reservoir from the nearby Deoli fish farm. Although stray individuals (2.5 to 10 kg) and a few juveniles were reported in the landings in 1974, a significant appearance of the species in the fishery was noticed only since October 1977, when a number of juveniles below 300 mm (< 400 g) appeared in the commercial landings. During 1977 – 78, 10 t of silver carp, were captured, which accounted for 1.4% of the total landings. In the subsequent years, the fish contributed up to 72% to the total catch. Its population increase had also aided in an unprecedented rise in the fish yield from the reservoir.

In view of the wide feeding spectrum and high fecundity (average of 167 000) of the silver carp, the species appears to have ecological advantage over the other species. The fish has extended through all zones of reservoir with stable winter and spring fisheries, whereas the fishing grounds of Indian major carps are location-specific. While 90% of the catla catch is harvested during the monsoon season, silver carp supports a steady fishery throughout the year, thereby apparently making it more lucrative from economic angle. However, the role of silver carp in the fisheries development of Indian reservoirs in general and the Gobindsagar in particular is a subject of animated controversy.

Major disadvantages of the fish are its poor shelf life and low market preference. Although the low price fetched by the fish is compensated to some extent by the higher production obtained by the fishermen, there is a widespread discontent among them against the change in catch structure over the years. Ecologists fear that the exotic carp, by virtue of its common food niche threatens the indigenous catla. Despite its gaining entry in a number of Indian reservoirs located at varying geoclimatic regions of the upper peninsula, Deccan plateau and the southern tip of the sub-continent, silver carp is not naturalised in any of them. Only in the cold water regime of Gobindsagar, where the fish was exposed to an environment akin to its original habitat, it commenced successful breeding and proliferation. Thus, the fear of silver carp obliterating the indigenous catla populations in warm water reservoirs seems to be unfounded.

Fisheries management

Stocking:

The exotic mirror carp, Cyprinus carpio var. specularis, introduced into Indian waters in 1939, entered the region in 1955 when it was cultured in a tank at Nahan. Because it thrived in cold waters and at high altitude, this species was preferred and introduced into the newly created Gobindsagar reservoir in 1962. Stocking of the mirror carp became regular after the fish farm at Deoli was built in 1964. Till 1979, on an average, 0.55 million fingerlings (size 50 to 80 mm) were stocked annually. In fact, mirror carp was the only fish stocked regularly, as the seed of Indian major carps was still hard to produce. Further, it was scarce and costly.

Based on a general consensus among the leading biologists that none of the local fish would be able to offer viable commercial fishery, it was recommended that the reservoir should be stocked with Indian and exotic carps. Taking this into consideration, during 1967–71, the State Fisheries Department stocked 3 500 gravid spawners and 0.5 million of fingerlings of Indian major carps ranging in size from 100 to 150 mm. By 1979. major carps had established themselves in the reservoir and started breeding.

Stocking the reservoir with spawners and seed of Indian major carps as early as 1960s was a positive management decision that led to the establishment of a lucrative fisheries. As per various estimates, the reservoir is to be stocked annually with 2.0 million fingerlings, but the average stocking rate was only 0.3 million fingerlings per year which was 16% of the required number. The stocked seed was of small size, ie. 20 to 30 mm against the recommended 125 to 150 mm. No study was undertaken on the survival of the stocked seed, but in all probability it was very low.

Fishing:

Before the reservoir was created in 1959, fishing activities in the river were limited to angling and cast nets targetted against mahseers, L. dero and Schizothorax spp. Even after the impoundment, there were no organised fishing activities or management till the 1960s, when new fish species were introduced into the lake. Fishing operations began with 16 nets in 1964–65 which yielded 29 t of fishes. By 1974–75, the fishing was extended to all zones by deploying 230 nets with the fish production going up to 250 t. Later on, management measures, including increase in fishing units and mesh sizes and sustained stocking, led to a remarkable yield of 96.4 kg ha^-1.

The subsistence fishery that existed in the rivers and streams before impoundment was of inconsequential nature. With the formation of the reservoir the lucrative fishery started attracting a large number of fishermen and the evacuees who lost their property due to submergence. At present the rehabilitated families settled near the reservoir account for about 20% of the active fishermen population.

The fishermen in Gobindsagar are full-time licencees and members of cooperative societies who own their boats. On an average, 40% of the fishemen have some education, their monthly income ranging from Rs. 800 to 3 000. Each fisherman has, on an average, 3 to 4 gill nets of 100 to 140 mm mesh size, which last for 1–2 years. The common craft is the wooden boat measuring 5m x 1m x 0.5m, costing approximately Rs. 2 000. Till 1974-75, the Fisheries Department issued licences at the rate of Rs. 10 per gill net and fishermen were free to dispose their catches without any restriction. Later, a new fishing policy was introduced, under which the fishermen were organised into cooperative societies and an apex body was entrusted with the responsibility of selling fish outside the state. A federation of local societies was made responsible for marketing of fish within the state.

Presently, there are 11 Fishermen Cooperative Societies functioning in the reservoir with a total membership of 1 479 active fishermen. Different areas of the reservoir have been earmarked for these societies for fishing and fish marketing activities.

Marketing

The catch is brought to landing centres where the representatives of the Fisheries Federation receive the fish and keep daily records on the category and species of fishes in the presence of a Fisheries Officer. The Federation hands over the catch to the contractor appointed through general tenders at the beginning of the year. The contractor makes weekly payment to the Federation, besides keeping a fixed deposit of Rs. 500 000 to 600 000 with the Federation. The Federation makes the payment once in 15 days to the Societies after deduction of a royalty of 15% for the Department and a commission 5% of its own. The fishermen get their remuneration from the Societies after the deduction of a nominal commission, which is fixed by the General Body.

Rates for various categories of fish have been fixed on a year to year basis since 1988–89 (Table 11.7).

11.3 PONG RESERVOIR (Fig. 11.5)

Pong reservoir on the river Beas, commissioned in 1974, is primarily meant for power generation, irrigation and flood control. It has a catchment area of 12 561 km² and a surface area of 24 529 ha at FRL and 14 312 ha at DSL. Originating in the southern face of Rohtang Pass at an elevation of 4 062 m above MSL, the river Beas has a steep gradient in its headwater zone with a fall of 24.0 m km^-1. On its way, the river receives a number of tributaries, the principal ones being the Manalsu, the Parbati and the Sainj on the left bank and the Uhi on the right. Further downstream, the river takes a sharp turn towards the west and cascading down, receives the whole drainage of southern slopes of Dhauladhar chain of mountains. The Beas and its principal tributaries being snowmelt or glacier fed, are perennial, but the flow rate in the river fluctuates widely during the course of the year. The discharge is at its minimum during mid-February while floods occur from July to September. The inflow rate increases with the influx of snowmelt water and continues till July-August due to the monsoon runoff. The reservoir discharge is the highest during July and lowest in February (Table 11.8).

Figure 11.5. Pong reservoir, Himachal Pradesh

The reservoir bottom soil during the pre- and post monsoon months is alkaline. The soil is deficient in nitrogen (14.4 to 17.2 mg 100 g^-1) and phosphorus (0.27 to 0.34 mg 100 g^-1), with a low organic carbon due to intensive siltation (Table 11.9). The soil exhibits considerable variations in different zones in respect of its physical and chemical characteristics. Nevertheless, the reservoir soil seems to have a limited role in determining the quality of water as the latter mainly derives from the nutrients from the catchment area.

Excepting the rainy season (April to August), the water of Pong reservoir remains generally clear. While the surface water temperature of the main reservoir varies between 22.2 and 25.1 °C, the incoming river water has a temperature range of 6 to 26 °C. Table 11.10 shows average values of selected physico-chemical parameters recorded at four different stations of Pong reservoir for the year 1987-88.

The reservoir is rich in organic nutrients and planktonic and periphytic assemblages. The plankton community of the reservoir is very rich qualitatively and quantitatively. Plankton density of 1 053 to 18 661 individuals 1^-1 is matched by a high rate of photosynthetic activities by the phytoplankton. Mean gross primary production is estimated at 507.77 mg Cm^-3day^-1 with high net-gross production ratio of 0.55. Diatoms represented by 16 taxa constitute the largest component of plankton (69.75%), followed by green algae (22.22%) blue-green algae (3.72%) and dinoflagellates (0.7%). Chlorophyceae, with 18 genera exhibit the maximum diversity. The average standing crop of benthic macrofauna varies from 496 to 513 individuals m^-2. Oligochaetes, dipterans, ephemeropterans and the molluscs represent the major benthic organisms in the reservoir.

Pong is a shallow reservoir with a lower organic production than Gobindsagar and the fish catch was originally dominated by carnivores. On account of systematic stocking over a number of years with seed of mirror carp and Indian major carps, the catch structure of the reservoir was completely altered and carps eventually accounted for 61.6% of the total landings (1987–88). The fish yield of the reservoir also increased significantly from 6.5 kg ha^-1 during 1976–77 to 53.1 kg ha^-1 during 1987-88. Catfishes and carps accounted for 70.1 and 29.9% of the total production of the reservoir during 1982–83 against 27.8 and 67.6% during 1989–90 respectively.

Commercial fishing was initiated in the reservoir soon after the impoundment and the important species in order of abundance were Labeo rohita, Aorichthys seenghala, Labeo calbasu, Tor putitora, Cirrhina mrigala, Wallago attu, Cyprinus carpio, Labeo dero, Catla catla and Channa sp. The total catch during the first year of fishing operation was 98.1 t which increased progressively, attaining a peak of 797.4 t during 1987-88. During 1977-78 to 1986-87, the landings fluctuated within a narrow range of 443 to 596 t. In the year 1988, due to heavy rains and floods, the water level of the reservoir reached an alarming level of 442 m and forced the dam authorities to open the flood gates. This caused heavy loss of fish from the reservoir, obviously affecting the catches in the following years which plummeted to 475.8 t during 1988–89 to increase marginally to 489.2 t during 1989–90. The quantum of fishing effort, however, continued to rise in spite of the falling yield. The maximum yield of 53.1 kg ha^-l was obtained in 1987–88. On an average, the yield was 32.2 kg ha^-1 (range 6.5 to 53.1 kg ha^-1) during the l ast 14 years (Table 11.11).

Catch of L. rohita increased progressively from 0.4 to 42.5% from 1982–83 to 1987–88. Catla catla failed to get a foothold in the reservoir despite the stocking effort. Its contribution to the total catch remained only 0.04 to 1.6%. The percentage composition of C. mrigala increased from 5.3 to 9.7 from 1982–83 to 1987–88. Cyprinus carpio specularis, the only exotic carp of the reservoir, sustains a low population, despite heavy stocking, its percentage fluctuating between 2.6 and 5.9. The major carnivores of the reservoir are Tor putitora, A. seenghala, W. attu and Channa spp. (Table 11.12).

Initially, the fish fauna of the reservoir consisted mainly of catfishes, minor carps and few coarse fishes mainly residual and acclimatised from the river. Stocking of 130 000 fingerlings of mirror carp was done during June 1974, followed by 149 000 seed of Indian major carps in 1976–77. It has been estimated that 30 million fish seed comprising L. rohita, C. catla, C. mrigala and C. carpio have so far been stocked in the reservoir in the ratio of 2:2:1:1. The overall stocking deficit is estimated at 53.4 to 80% in case of mirror carp and 83.9% for Indian major carps. However, overstocking of mirror carp had beeen reported during 1988–89 and 1989-90 to the tune of 18.8% and 329.1% respectively. Fisheries development in Pong reservoir has helped in rehabilitation of the families displaced due to inundation. The Government's initiative to stock the reservoir with the Indian major carps has gone a long way in establishing the population of L. rohita which contributes as much as 42.5% to the fisheries.

11.4 PANDOH RESERVOIR

Pandoh reservoir, located at 31° 50'N, at an altitude of 987 m above MSL has a waterspread of 200 ha. It is a part of the Beas-Sutlej Link Project, diverting the Beas water into the Sutlej basin. In the process, the water flows down from a height of 320 m and hydel power is generated at the Dehar power station. The earth-cum-rock fill dam was constructed in 1977. The reservoir has a gross capacity of 4.1 million m³. The morphometric, hydrographic and hydrological characteristics of the reservoir are detailed in Table 11.13.

Kaushal et al. (MS.) provide a limnological profile of Pandoh reservoir. Thermal stratification between 13 and 14 m has been reported, the temperature dropping from 16.5 to 10.5 °C from surface to 19 m. The dissolved oxygen, following a similar trend, declines from 9.56 mg 1^-1 at the surface to 7.84 mg 1^-1 at 19 m. Although total alkalinity and specific conductivity increase towards the bottom, no such difference in pH is reported. The low temperature regimen and nutrient status of the reservoir point towards oligotrophic tendencies. This is strengthened by the poor plankton count of 100 organisms 1^-1 and primary production rate (484 mg C m^-3 day^-1. The main component of phytoplankton is Bacillariophyceae represented by Rhizosolenia, Diatoma, Cocconeis, Frustulia, Mastogloia, Amphora, Tabellaria, Navicula, and Stauroneis. The benthic community is represented by Branchlura. Limnodrilus, Tubifex, Nais and Chironomus.

(After Kaushal et al., MS.)

Common carp was stocked in 1978, but discontinued afterwards. There is no organised fishing in the reservoir, except occasional sport and recreational fishermen. Salmo trutto fario, Schizothorax richardsonii Labeo dero, L. dyocheilus, Tor putitora and some hillstream fish are present in the reservoir.

11.5 RESERVOIR FISHERIES IN HIMACHAL PRADESH

The reservoirs in Himachal Pradesh serve primarily as flood control and irrigation systems and next as hydro-power generating units. Fish stocking and production in the reservoirs were initiated with the aim of rehabilitating the displaced families and ensuring gainful employment to people affected by the inundation. However, the State has made great strides in reservoir fisheries development. During 1992-93, the production from Pong and Gobindsagar reservoirs was 448 (30 kg ha^-1.) and 964 tonnes (96.4 kg ha^-1) respectively based on the average reservoir area. Compared to the national average, the two reservoirs in Himachal Pradesh are well-managed and the yield of Gobindsagar is one of the highest from a large reservoir in the country. The amendment of the State Fisheries Act 1976, the enforcement of mesh size regulations, the organization of fishermen in a cooperative, establishment of the Fisheries Federation, settling of fishermen during the initial stage from outside the State, establishment of fishermen welfare schemes, etc., are measures which have assisted in the optimal development of the reservoir fisheries and provided vocation to the oustees of the reservoirs.