International Journal of Ecology and Environmental Sciences

Riverine fisheries are of particular importance in the tropical regions as they provide food and nutrition to millions of people and support their livelihood. However, ever-increasing, multiple demands on water for irrigated agriculture, domestic and industrial supplies and hydropower generation have greatly impacted upon the river flows and riverine habitats and consequently the fisheries and riverine-fish-dependent communities. Other anthropogenic activities such as deforestation, mining, urbanisation and various flood control measures have further degraded the river ecosystems. Yet, little attention is paid to the fisheries and issues of conser-vation and sustainability of riverine ecosystems which contribute significantly to the food security and economy of the people.

Three major Himalayan rivers - Indus, Ganga and Brahmaputra - are of greatest importance the Indian subcontinent as their drainage basins lie in China, India, Pakistan, Nepal, Bhutan and Bangladesh, cover nearly two-thirds of the subcontinent and are among the most densely populated regions of the world. Of these, Ganga and Brahmaputra, drain 26.2% and 5.9% respectively, of the total Indian territory, and join (together with another river, Meghna) in their lower reaches within Bangladesh before forming the world's largest delta and supporting the single largest patch of mangroves, the Sundarbans. The Ganga and Brahmaputra basins are sometimes treated as sub-basins of the combined Ganga-Brahmaputra-Meghna (GBM) basin. We review here the state of two major Himalayan rivers of India, Rivers Ganga and Brahmaputra, with reference to their fisheries, summarise various threats to them and discuss strategies for their sustainable management in the context of current policies, laws and institutional arrangements.

Physiographically, the Ganga river is divisible into Upland reaches (from sources at 4100 m altitude to Rishikesh at 360 m; gradient 1:67; and equivalent range of its northern tributaries), Upper plains (from Rishikesh to Allahabad (58 m altitude; gradient 1:4100), Middle plains (from Allahabad to Farakka (19 m altitude; gradient 1:13000) and Lower plains (the delta in India and Bangladesh, which includes the Sundarbans and an extensive floodplain). River Ganga in the upper stretch has a vast catchment formed by River Yamuna and its tributaries joining it from the south, and the many tributaries originating in the Central Himalaya. River Brahmaputra has more than one-third of its catchment within India where it receives a large number of tributaries on its both banks. The upper reaches flow through mountain ranges and narrow valleys but later the river forms extensive floodplains.

The Ganga and Brahmaputra basins experience a monsoonal climate that exhibits extremes of spatial and temporal variability in temperature (sub-freezing to nearly 50 ºC) and precipitation (10 cm in westernmost parts to >500 cm in the east). About 80% of rainfall occurs during the monsoon months (June to September) and this is reflected in the discharge of the two rivers and their tributaries that increases up to 100 times its dry season values. The two rivers are also unique in carrying huge sediment loads that are among the highest in the world.

Both Ganga and Brahmaputra are rich in their fisheries (265 species in Ganga and 167 species in Brahmaputra that include both freshwater and estuarine species). River reaches vary greatly in the proportion of species they contain; the Alaknanda has the lowest number of species (41). The upper stretches of the two rivers (up to Haridwar in river Ganga and Pasighat in river Brahmaputra) support Mahseers, carps, snow trouts and catfishes. Commercial fisheries in both the rivers assume importance in the middle and lower stretches. Over the years, drastic decline in fish catch from the rivers has adversely impacted the livelihoods of landless fishers; they simply fish poverty every time they go to river to catch fish. This situation has been caused also by factors other than the fishery in these river systems.

Although the flows of River Ganga and its tributary Yamuna had been diverted soon after their descent on to the plains more than a century ago, intensive river regulation has occurred in the post-Independent India. Numerous dams and barrages have been constructed over all tributaries, and their large stretches have been channelised by embankments. Numerous hydel projects have come up throughout the mountain stretches and many more are in different stages of development. Thus, both longitudinal and lateral connectivity of the rivers has been greatly lost and the migration of the fishes to their breeding and feeding sites has been obstructed. These changes have resulted in significant decline of fisheries, particularly the the cold water fishes (snow trout and mahseers) in the upper stretches and Indian major carps (IMC) in the plains. Among the more prominent and well known effects has been that of the Farakka barrage on river Ganga shortly before it enters Bangladesh. While the Indian shad, Tenualosa ilisha has declined almost completely upstream of the Farakka barrage, the fisheries downstream have increased several fold.

Increased deforestation in the upper catchment basins of rivers is also having an adverse effect on water quality through increased siltation and alteration of river regimes with increased runoff during the rains and reduced flow during dryer periods. Besides extensive alteration of flow regimes and the loss of floodplain habitats, the rivers have been severely impacted by excessive discharge of untreated or only partly treated domestic sewage and industrial effluents all along their course. Climate change is projected to stress the fisheries further with the melting of glaciers, rise in water temperature, alteration of flow regimes, extreme events like flood and drought, and change in water demands for other uses.

Conservation and sustainable management of fisheries must be based on natural recruitment by protecting the micro- and macro-habitats of different fishes for their breeding, spawning, feeding and refuge. Maintenance of environmental flows is urgently required in the affected reaches. Further, management for sustainable fishery in the Ganga-Brahmaputra river system requires effective networking of the multiple stakeholders through appropriate institutional arrangements for development, implementation, policy and planning of management of fish stock, production, marketing and distribution. There is a strong need to involve all basin states of India to evolve policies on water and biological resources of the rivers. Cooperation between India and Nepal in the management of the migratory stock of Mahseer and between India and Bangladesh in the management of Hilsa is also needed. It is hoped that the recently constituted Ganga River Basin Authority in India will address some of these issues to achieve the objective of sustainable fisheries in future.