Kaveri Kumar | November, 2002

The pace of industrialisation and urban life threatens the ecology of the Ganga and her fish.

	A steady increase in industrial pollution relates to a steep decrease in fishermens' catch at the Ganga

Attention is often focussed on Ganga degradation caused by industrial pollution and effluents but not much thought appears to have been paid to factors like water abstraction for irrigation and storage and river training. These problems cannot be shrugged aside. Fishing is a vital industry that is also important for the nutritional needs of India's ever expanding population.

The Ganga river system, including tributaries like Yamuna and Ramganga, is the original abode of prized major carp like catla, mrigal, rohu and calbasu, while also sustaining catfish, mahaseers and hilsa. Ganga is also the source of riverine spawn, which meet about 30 per cent of the carp seed requirements.

However, disturbing trends in the riverine environment and the fish population have long been apparent. Apart from steady decline of the fish yield, there is an alarming downswing in the number of major carp in favour of catfish and carp minnows. The output of the major carp spawn has also declined.

Impact of water abstraction
The Farakka barrage illustrates what a dam can do to the riverine environment and fish population. It also brings into sharp focus the conflict of interest in multiple usage of riverine resources. Before the construction of the barrage in 1975, the tongue of the estuary extended 290 km into the river, which is now pushed 20 km downstream.

The Hilsa catch has declined to as much as 96% due to the Farakka barrage

"A sharp decline in salinity is due to extra discharge of fresh water, leading to conspicuous qualitative changes in the plankton community. The catch of andromous hilsa, bountiful till 1972 at all centres above the Farkka barrage, has declined by 96 per cent due to the obstruction to its migration. In the upper reaches, mahaseers are already threatened by extinction," says Dr. B. C. Jha, principal scientist at the Central Inland Capture Fisheries Research Institute.

He says, "low velocity due to abstraction steps physiologically upset fish communities adapted for the rapids and may give place to those adapted to lesser velocities akin to pool zones. The impact of Ganga water abstraction is seen mostly in the case of breeding and recruitment of major carps. Man-made changes in the river flow regimen have far-reaching effects, because many varieties of fish depend on annual flooding for food and spawning."

"Spawning grounds are situated in the flood plains that are inundated during the monsoons. Breeding and recruitment are seriously hampered when the water level in the river does not reach the spawning ground due to inadequate discharge rates," he says.

Flood levels, too, have a close relationship with spawn availability because ox - bow lakes, deep pools and other lentic bodies act as sanctuaries for the brooders and get connected to the mainstream during the monsoon. Velocity of stream is also an important factor for fertilisation of fish eggs, oxygen supply and survival of the spawn. In monitoring fish yields in the country for about five decades, the Fisheries Institute has found a noticeable decline in the total fish output of the Ganga and an undesirable change in the species spectrum.

Impact of river training
The common methods of river training are construction of guide banks, spurs and river revetments. These decrease the roughness or friction along the riverbanks, upsetting the energy expenditure balance. It is often found that disequilibrium created by embankments tends to readjust at a point where the stream channelisation ends and destruction of banks and bed resumes with renewed vigour. One of the direct impacts is the increase in river velocity, which upsets the life habits of riverine organisms. Most stream fish exhibit a strong territorial orientation and territory is often recognised in terms of velocity and current. The need of the hour is to ensure that economic expediency does not mar ecological and social interests. Loss of precious genetic resources of river Ganga would be an ecological disaster - an irrevocable loss of nature's endowments.

Kaveri Kumar is a Kolkatta-based journalist