This paper briefly describes the current status of ecology, fisheries and biodiversity of the River Ganges. Apart from being the original abode of the most prized Indian major carps, viz., Catla catla, Labeo rohita, Cirrhinus mrigala and Labeo calbasu, the river sustains fisheries of large catfish, mahseers, hilsa and other miscellaneous fishes. Over the years the fish catch per kilometre stretch in the river has declined significantly and species composition has changed more in favor of non major carp and miscellaneous species. It has also been observed that some exotic fishes have gained a foothold in the ecosystem at favorable stretches, where flows have drastically reduced as a result of abstraction of water from the main river. Changing hydrology, apart from deteriorating environmental conditions, has been to a large extent responsible for change in the fishery scenario in the river. This change has also affected the income levels of riparian fishers. Review of the data generated, over the years, also indicated deteriorating water quality at the stressed sites. The contamination of river water, sediments and fish with heavy metal and pesticide residues is also a factor of concern. With continued stress on the river system an environmental restoration plan was launched by the Indian authorities; its impacts over the years on ecosystem health is also discussed.
The River Ganga (Ganges) is the most important river system in India. It originates from the Gangotri glacier at Gomukh, at an altitude of about 6000 m in the Garhwal Himalaya. The river receives water from the Alakapuri glacier also. After flowing through the Sivalik hills it enters the plains at Haridwar. Then it flows southwards, passing through the plains of Uttar Pradesh, Bihar and West Bengal. To the north of the Ganges, the important tributaries are Ramganga, Gomti, Ghagra, Gandak, Kosi and the Mahananda. Beyond the Mahananda the river enters to its own delta, formed by its distributaries, and then merges into the combined delta of the Ganges, Brahmaputra and Meghna rivers before draining into the Bay of Bengal. The tributaries to the south of the Ganga are the Yamuna and the Son. Ganges is about 2525 km long, covering a basin area of 861,404 km2. The river system drains about one fourth of the Indian subcontinent. The river system covers cool upland streams and warm water stretches, including deltaic habitats. The freshwater flow in the river system is mostly from its tributaries and therefore, the water availability greatly varies from 59 billion m3 at Allahabad, before the confluence with river Yamuna, to 459 billion m3 at Farakka in the lower stretch (Joshi et al., 2009). The source of water is the melting of snow in the Himalayas and monsoon rains. The river supports abundant biological wealth, characterized by its rich fisheries and faunal diversity. Apart from being the original abode of the most prized carp species of the subcontinent, viz., Catla catla, Labeo rohita, Cirrhinus mrigala and Labeo calbasu, the river sustains fisheries of large catfishes, mahseers, hilsa and several other fish species. Ganges is also the major source of riverine spawn, which meets 30% of the carp spawn requirements of the fish culture sector in India. Over the years there has been a measurable shift in the hydrology and water quality of the river. The fish catch from the river has declined significantly and species composition changed more in favor of non major carp and miscellaneous species. Exotic fishes have invaded some stretches of the river. Hence the status of the ecology and fisheries of the river Ganges has been a serious concern. This communication gives an overview of the current status of the environment and fishery of the river and discusses major issues.
The information on sediment and water quality of the river is mostly based on the report of the exploratory surveys conducted by the Central Inland Fisheries Research Institute (CIFRI) during 1995–1996 of 43 centers of the river from its origin to sea (Sinha et al., 1998). The map of the River Ganges, from its origin to its merger in Bay of Bengal is given in Figure 1. The riverbed from Tehri to Patna (upper and middle stretch) is sandy; the proportion of sand 79 to 100%, clay being 0 to 12%. However, the proportion of sand decreased to 34–79% in the lower stretch (Sultanpur to Katwa) with corresponding increase in clay and silt load. The stretch between Tehri and Patna suffered severely from textural deformities and sand drifting through a number of tributaries (Ramganga, Yamuna, Gomti, Ghagra, Son, Gandak, and other rivers). This heavily blankets the river bed. The runoff from denuded catchments is also responsible for deformities of the river bed. Naturally, blanketing prevents the soils from contributing to aquatic productivity. Downstream of Patna, the tributaries of Ganges are much more seasonal and here pass through a predominantly clayey bed. As such, a sudden transformation in sediment texture is observed as the river flows through the lower stretch.
The water in the entire stretch of the river has strong buffering capacity and showed little fluctuation in pH (7.7–8.1), while dissolved oxygen (mg l−1) exhibited variation among different stretches (7.0–11.2 in the upper stretch, 3.6–11.9 in the middle stretch, 4.8–9.0 in the lower stretch and 4.3–8.9 in the estuarine stretch). The alkalinity, specific conductivity, dissolved solids, calcium, magnesium and hardness however, showed considerable variation. These parameters exhibited minimum values in the upper stretch (101 mg l−1, 245 μS cm−1, 124 mg l−1, 14.6 mg l−1, 5.6 mg l−1 and 98.2 mg l−1, respectively) and showed a sudden rise in the middle stretch between Kanpur and Patna (179 mg l−1, 521 μS cm−1, 262 mg l−1, 38.7 mg l−1, 16.8 mg l−1 and 173 mg l−1, respectively). In the lower stretch, their values decreased again (126 mg l−1, 178 μS cm−1, 89 mg l−1, 16.6 mg l−1, 11.2 mg l−1 and 110 mg l−1, respectively). In the gradient stretch the values of alkalinity, conductance, dissolved solids, calcium, magnesium and hardness sharply increased (128 mg l−1, 759 μS cm−1, 379 mg l−1, 52.3 mg l−1, 38.0 mg l−1 and 282 mg l−1, respectively) and reached highest levels in the marine zone (119 mg l−1, 14118 μS cm−1, 7054 mg l−1, 266 mg l−1, 413 mg l−1 and 782 mg l−1, respectively). Dissolved oxygen being an important parameter for river health, ranged from 5.0–10.5 mg l−1 in the Kanpur stretch of the river during the 1960s, while its values reduced to 3.8–8.6 mg l−1 during the 1980s and the values improved to 5.0–9.0 during the 1990s, indicating improvement over what had been seen in the early 1980s. In general, dissolved oxygen values have regained the healthy conditions that prevailed during the early 1960s (Vass et al., 2008). This was possibly due to different restoration initiatives taken by the Government of India through the Ganga Action Plan (NRCD, 2009).
Wide variability in plankton density, composition and seasonal variations along the river has been recorded. The Ganga basin has a typical monsoon climate with warm and dry summer from March to May, monsoon season from June to October and winter from November to February. In the upper stretch, between Tehri and Kanauj, the average total plankton density ranged from 58 to 1578 number per litre (l−1), 95 to 1050 l−1 and 60 to 1435 l−1 during summer, monsoon and winter months, respectively. The bulk of it was contributed by phytoplankton while zooplankton formed only 16.6%. Bacillariophyceae being 83.4% was the main representative of phytoplankton. Zooplankton formed 7.9 to 34.8% of the total plankton in the stretch between Haridwar and Kanauj. Rotifers and protozoa were recorded in the Anupsahar and Farukhabad stretches. The overall plankton density in the middle stretch varied from 24 to 782 l−1, 146 to 3649 l−1 and 14 to 8049 l−1,respectively, during summer, monsoon and winter seasons respectively. The maximum density was found in the Kanpur stretch (8049 u l−1) during winter. About 18 taxa of phytoplankton and 11 taxa of zooplankton were recorded in the stretch between Kanpur and Allahabad (Sinha et al., 1998). In the lower stretch, between Sultanpur and Farakka, the plankton density ranged between 34 and 1204 l−1. Of this, phytoplankton formed 70.9 to 89.2% and the rest was zooplankton. The total plankton production of the freshwater zone of Hooghly estuary varied from 26 to 935 l−1. In the marine zone of the estuary, the bulk of plankton was Bacillariophyceae (70–95%). Other phytoplankton groups observed were Chlorophyceae and Cyanophyceae. A lower density of plankton in middle and lower freshwater stretches of the river was reported in the mid 1990s compared to the levels reported in early 1960s (Sinha et al., 1998), but the composition showed little change. The occurrence of pollution indicator species like Ankistrodesmus sp., Coelastrum sp., Pediastrum sp., Scenedesmus sp., Actinastrum sp., Cymbella sp., Cyclotella sp., Fragillaria sp., Anabaena sp., Lyngbya sp., Merismopedia sp. and Spirulina sp. in low density in lotic waters of Ganges during 1990s indicated reasonably good water quality (Sinha et al., 1998).
Macro-benthic population increased gradually from Tehri to Haridwar (189 to 628 m−2). Insects were the only component in the entire stretch. Chironomids were reported at Rishikesh. At Anupsahar, the benthic population was 644 m−2, 2108 m−2, and 811 m−2 during summer, monsoon and winter respectively, with annelids (Tubifex) forming 55.8 to 62.9%, insect larvae (Chironomids) forming 32.0 to 40.3% and nymphs forming 3.9 to 5.1%. The occurrence of gastropods was observed in the stretch between Anupsahar and Kanauj, although they contributed very little to the total benthic population. The insect population had a decreasing trend from the upper to middle stretch of the river. Bivalves formed the bulk of the benthic population in the middle stretch, represented by Lamellidens marginalis and L. corrisnus. Among gastropods Melania striatella, M. plotia, Bellamia bengalensis were the main forms. Insect population was represented by Tricoptera sp., Chironomus sp. and stone fly nymph. In the freshwater zone of Hooghly the dominant forms were gastropods, followed by polychaetes, oligochaetes, decapods and bivalves. The density of macro-benthos in the marine zone of the estuary varied between 74 and 1472 m−2, mostly with a dominance of gastropods. In general, the macro-benthic population of the river system is low since the river bed is either sand dominated or pure sand.
Fish and fisheries
The fish fauna of Himalayan and Indo-Gangetic plains was described by Menon (1974). The commonly available fishes in the river are Indian major carps, snow trouts, catfishes, mahseers and lesser barils. However, the mainstay of fisheries in this region is the species belonging to the family Cyprinidae and Siluridae. Sinha et al. (1998) reported the presence of 140 fish species in the river. The fishes in the river above Farakka comprise freshwater forms, while the lower part is dominated by estuarine species. Important fin fish species from the point of view of fisheries and their distribution in the river are given in Table 1. Along with the fin fishes, prawns like Macrobrachium rosenbergii, M. lamarrei, M. choprai, M. malcolmsonii, Parapenaeopsis sculptilis, P. stylifera, Metapenaeus brevicornis, M. monoceros, Penaeus mondon, P. indicus, P. semisulcatus, Expalaemon stylifera, E. tenuipes and Leptocarpus fluminicola are also available in different stretches of the river.
Catch trends and production
The fish catch from the river Ganges is declining (Vass et al., 2008). The estimated average catch per kilometer of the river at Allahabad, recorded by CIFRI, shows that in the 1950s the catch was 1344 kg km−1, declining to 362 kg km−1 during the 2000s (Table 2). The estimated yearly catch per kilometer stretch of the river at Allahabad during 1955 to 2004 is depicted in Figure 2, substantiating a gradual decline in catches. There has also been noticeable shift in species composition in catches (Figure 3). The catch of major carps declined drastically; hilsa disappeared from the catch and exotic fishes (tilapia and common carp) have started appearing in the 2000s. Hilsa, Tenualosa ilisha, formed a major fishery in Ganga until the 1960s (De, 2001). The Farakka barrage, commissioned during 1971 at Farakka obstructed the migration of hilsa, collapsing the fishery in the river above the barrage. The mean landing of hilsa along Allahabad, Baxur and Bhagalpur stretches, upstream of Farakka declined to negligible levels (Figure 4), a glaring example of impact of river modifications. The fishery now thrives only downstream of the barrage. The estimated production potential of Ganges, in its lower reaches, has been estimated at 198 kg ha−1y−1, whereas the actual fish yield has been 30 kg ha−1y−1. Thus, only 15.2% of the potential has been available as fish (Sinha, 1999).
Market share of riverine catch
Data on market arrivals of fishes from the River Ganges and its tributaries and also from other water bodies were collected and analyzed. Out of the total fish landings, 29.8% formed the fishes from riverine sources and 70.2% from other water bodies (CIFRI, 1996). About 97% of the carps caught were from other water bodies reducing the riverine contribution to 3%. In the case of catfishes, the river contributed to over 80%.
Fishers and their status
Until the mid 1970s, the fishery had been open access in nature, but due to declining catch, the local fishers started prohibiting fishers from other areas and the fishery gradually turned into common property in nature. The fishing period extended year round with a lean period during monsoon months. The remuneration for catch as net returns was INR 29869 per family for an average catch of 1431.7 kg in the Kanpur to Farakka stretch of the river; the sale price is INR 24 per kg (Sinha and Katiha, 2001). The age distribution of the fisher community showed a higher proportion of minors (55%) compared to adults (45%).
More than 29 cities, 70 towns and thousands of villages are situated along the banks of the Ganges. They discharge a portion of their generated sewage, over 1.3 billion liters per day, directly into the river. Another 260 million liters of industrial wastes are added to this by hundreds of factories situated along the river banks. City sewage constitutes 80% by volume of the total waste dumped into the Ganges. The majority of the pollution of Ganges is organic waste, sewage, solid waste and human and animal remains. The industrial pollutants also contaminate the Ganges. The major polluting industries are the leather industries, especially near Kanpur, which use large amounts of chromium and other toxic chemical waste and much of it finds its way into the Ganges. From the plains to the sea, pharmaceutical companies, electronics plants, textile and paper industries, tanneries, fertilizer manufacturers and oil refineries discharge effluent into the river. This hazardous waste includes hydrochloric acid, heavy metals, bleaches, dyes and pesticide residues from riparian agriculture.
Studies indicated that the residues of organochlorine pesticides, including HCH, DDT, Endosulfan and their metabolites are the commonly occurring pesticides in water of the Ganges and its estuary (Samanta, 2007). Moderate levels of HCH compounds (189–2597 ng l−1) were reported by Kumari and Sinha (2001). Moderate levels of DDT and its analogues (0–4000 ng l−1) were recorded by Ray (1992) and Halder et al. (1989). Ray (1992) also reported moderate levels of Endosulfan compounds (0–2890 ng l−1). Comparison of the data with the United States Environmental Protection Agency (US EPA) permissible limits for aquatic organisms or their consumers clearly indicates that the river water is contaminated with the residues of organochlorine pesticides (Samanta, 2007). Significant accumulation of DDT (60–3700 μg kg−1) was reported in the body of fishes from the river by Senthilkumar et al. (1999). Kumari et al. (2001) reported that the levels of some pesticide viz. HCH and DDT were 55–1207 μg kg−1 and 14–1666 μg kg−1, respectively. Levels of Aldrin and Endosulfan were relatively low (0–225 and 0–175 μg kg−1, respectively). In the estuary zone, the reported levels were relatively low (HCH compounds 0.1–9.0 and DDT 1.4–460.0 μg kg−1) (Joshi, 1986; Samanta, 2006). Thus, it may be concluded that the pesticide levels in fishes sometimes exceed the limits in the case of HCH and Endosulfan (Kumari et al., 2001). However, in the majority of cases, the observed residues of DDT in fish samples were more than that of HCH or Endosulfan; the permissible limit, however is not exceeded. Probably the dilution effect in the estuary zone is protecting the fishes from accumulating these persistent compounds.
Heavy metal contamination
The uppermost stretch of the river is relatively free from pollution. The middle stretch, receiving different kinds of effluents, was heavily polluted with heavy metals (Cd 0-28, Cr 2-119, Cu 0-170, Zn 1-311 μg l−1). Although a significant stretch of the estuarine zone is densely industrialized and regularly receives effluents, the mixing and dilution with marine water is maintaining the metal levels in water lower than that of the middle stretch (Cd 0-70, Cr 0-60, Cu 0-90, Zn 10-248 μg l−1) as reported by Vass et al. (2008). In the majority of cases the reported levels were much higher than the US EPA permissible limits for aquatic organisms. All the effluents were found contaminated with heavy metals and sometimes had unusually high levels as observed by Ghosh et al. (1983), Prasad et al. (1989) and Joshi (1991). The metal concentration in sediments indicated that the upper stretch is not affected. In the middle stretch (from Rishikesh to Ramghat); highest content of the metals was recorded at Ghaziabad, receiving industrial discharges (Cd 1.2, Cr 51.0, Cu 45.0, Pb 16.0, Zn 259 μg g−1 as reported by Israili, 1991). Although the Kanpur stretch of the river is reported to be heavily polluted (NRCD, 2009), these are not reflected in the metal content in sediment. As a whole the river is found moderately polluted with respect to the permissible limits for heavy metals in sediments (Vass et al., 2008). Joshi (1991) studied heavy metal content in fish along the Rishikesh to Kolkata stretch of the river. The levels of Cr, Cu, Pb and Zn was found high in the fish samples from the middle stretch, while Hg was high in the estuarine samples. Kaviraj (1989) reported relatively high content of Zn (135.6 μg g−1) in Penaeus indicus. Mastacembelus pancalus accumulated 108.2 μg g−1 of Zn. As per the United States Food and Drug Administration (US FDA) limit for human consumption, Pb and Cr cross the limits in some occasions.
Environmental restoration (The Ganga Action Plan)
In December 1984, the Department of Environment, Government of India, prepared an action plan for immediate reduction of pollution load of the Ganges to bathing standard (DO not <5 mg l−1; BOD not >3 mg l−1, coliforms not >10,000 per 100 ml). The Government of India approved the Ganga Action Plan (GAP) in April 1985 as a 100% centrally sponsored scheme. The GAP aimed to tackle sewage at 2794 million litres per day (mld); 882 mld under the GAP-I and 1912 mld under the GAP-II. The National River Conservation Directorate records indicated the total sewage generation in towns along river Ganges and its tributaries at 5044 mld (of which a portion reaches the river). Delhi alone accounted for 2270 mld. The GAP-II was to tackle only 20 mld in Delhi and the Delhi Government was to handle the rest (2250 mld) separately from augmentation of its own available installed capacity. To achieve the objective of pollution abatement, the GAP took up core and non-core schemes. The core sector schemes consisted of interception and diversion schemes and STPs (Sewage Treatment Plants), designed to tackle point pollution, i.e. pollution that is from measurable sources such as drains, sewage pumping stations and sewage systems. Non-core schemes comprised low cost sanitation schemes, river front development schemes, electric and improved wood crematoria and tackled non-point, non-measurable pollution, such as dumping of solid waste and open defecation, dumping of un-burnt/half-burnt dead bodies, etc. Opinions differed regarding the water quality of the Ganges after implementation of the GAP. The water quality data of National River Conservation Directorate (NRCD), Ministry of Environment, Government of India, showed that the Ganges had deteriorated over the period 1993–1999. During 1999 the BOD levels exceeded the permissible limit in 10 out of the 27 stations. The coliform levels exceeded the limit in 17 out of 60 stations sampled during 1999. The studies of the zonal office of Central Pollution Control Board during 2006 indicated that the water quality in the Haridwar to Allahabad stretch was class-B of Designated Best Use criteria, which implies that water quality conforms for uses like bathing, swimming and water contact sport. However, in summer season, the river stretch did not conform to the water quality of class-B, exceeding the BOD limit. The high BOD (5.0 ppm) at Sangam in Allahabad and Dashashwamedh ghat (Varanasi) rendered the water unfit for bathing in winter season. During 2002–2006, the BOD in the Ganges showed a decreasing trend. The conclusions of GAP however are: after launching in 1985, it may not have completely achieved its objectives, but the river is protected from further deterioration.
Riverine eco-systems in India are considered to be among the most threatened of all aquatic resources (Singh and Singh, 2007). In the recent past, riverine eco-systems in India have been altered to meet the growing demand for power generation, irrigation and also due to anthropogenic activities. The fish stocks of the rivers are over exploited and continue to be exploited from these resource. There has been decline in fish landing from Ganges, which is significantly attributed to the increased rate of water abstraction from almost all tributaries of the river system (Vass et al., 2008). The total length of canal networks in Ganges basin is over 15000 km. As a result of the continued increase in water abstraction, the volume of water available in this river system has declined. Based on the daily water-level data of the Central Water Commission, the mean water level of river Ganges at Allahabad during July to September (the period of maximum water availability) had declined by about 4 m between 1970 and 2008.
A gradual decline in fish catch, both quantitative and qualitative is clearly evident in the freshwater zone of the river above Farakka barrage (Figures 2– 4). Environmental aberrations in the form of high rate of sedimentation (586 million tons annually, UNEP, 2001), increased water abstraction and river course modifications, coupled with excessive fishing, appear to be the main factors for this situation. High rates of sedimentation, due to deforestation in catchments, have caused ‘desertification’ of the river bed in major part of the freshwater zone (from Haridwar to Patna), blanketing the soil-water interface and, thus, causing loss of productivity of the ecosystem. In view of this, it can be said that the present available productivity of the river water in this stretch is the result of nutrients being drained from allochthonous sources. Sedimentation and water abstraction has drastically decreased the flows, which has resulted in habitat loss for several biotic communities inhabiting the system (Vass et al., 2008). The spawning of several fishes has also been affected due to non-inundation of original breeding grounds. River course modifications have affected migratory species (hilsa, for example). The sharp decline in the hilsa fishery above the Farakka barrage, immediately after its commissioning, is a glaring example of river-course modification affecting the fishery of a migratory species (Sinha et al., 1996). Apart from other factors, the fish production in rivers depends on the degree of recruitment. Studies conducted by Natarajan (1989) and also by CIFRI (1994–2004) indicated that, on an average, the major carp spawn availability index in Ganges declined from 1.490 million fisher−1 day−1 during the 1960s to 0.014 million fisher−1day−1 during 1994–2004. The failure of recruitment of major carps in the river system was because of failure in their natural breeding. Majority of the fishes in the Ganges River system breed during the monsoon months. But decrease in precipitation over the years in the catchments and obstruction of flows due to river valley projects and barrages resulted in impaired flows. As a consequence the required hydrological regime and turbidity of the water, essential for effective breeding of major carps, is not available now (Das, 2007).
A shift in distribution of some of the fish species in Ganges has been recorded. A number of fish species which were predominantly available only in the lower and middle Ganges in 1950s as reported by Menon (1954) are now being recorded from the upper cold-water stretch up to Tehri (Vass et al., 2009). Among them Xenentodon cancila is available between Tehri and Rishikesh and Glossogobius giuris is available in the Haridwar stretch (Vass et al., 2009). This may be due to rise in temperature in the upper Himalayan stretches of the Ganges making it conducive for the warm water fishes of the lower stretch to establish. The cool upper stretch with the earlier minimum temperature conditions of 13°C were not suitable for these fishes, but with the increase of the minimum temperature in this stretch to 14.5°C, it has become conducive to the warm water fishes. The minimum water temperature has increased by 1.5°C during the span of 1975 to 2005 (Vass et al., 2009).
The River Ganges has greatly influenced human habitations along its littoral zone, supporting the livelihoods of many people, but suffered from unregulated fishing, environment degradation, water abstraction and encroachment. The increased fishing pressure due to higher demand for fish, followed by indiscriminate fishing methods increased the fishing effort leading to over exploitation, which gradually led to a drop in the catch per unit effort. With the decreasing natural stocks the fishers had to increase fishing effort for whatever species or size of fish were available to support their livelihoods. Interventions like regulations/wise use or increased awareness may not yield desired results to reverse the trend as fishers’ livelihoods are affected. Without alternate livelihoods, any form of management plans will only be pressing on peoples’ existence, which a civilized society cannot afford to allow. Although the ecology, fish species composition and landing trends are studied in Ganges, there is also acute paucity of sound empirical information on the fish population, exploitation levels and sustainable yields from the river to implement effective resource management plans.
There has been change in the environment and overall ecology of the River Ganges in the recent past resulting in shift in fish species composition, decline in fish catch and productivity. The environmental flows have been impaired, impacting habitats and ecology, particularly breeding and recruitment of fishes. Effects of water pollution and toxicant contamination are now evident on fish stocks as well. Eco-restoration plans have been put in place, which arrested further deterioration of environment; however, the impact of restoration efforts on the fishery are not evident.