Eugene Datta | February, 2002

Why fish harvests along the Ganga have plummeted.

A variety of reasons has led to a drastic drop of fish catch in the mid-stretch of the Ganga.

Increased sedimention has wreaked havoc with fish stocks.

The annual average fish catch, which was about 205 tons during the 50's and 60's plunged to a mere 59 tons by the late 90s.

The fall is even more ominous for carp as a pollution-sensitive species. Catchments plummeted from 91.35 tons in the 1950s to only 4.9 tons in the late 90s. A similar decline is detected in the lower-middle stretches of the river, both quantitatively and qualitatively.

The ultimate causes of this devastation have been pieced together by scientists at the Central Inland Capture Fisheries Research Institute (CIFRI). They point the finger at increased sedimentation in the river, along with pollution and river "taming" measures like dams.

The Gangetic catchment experiences a torrential monsoon that annually discharges an average 85,000 cubic meters of water per second following the long dry season. This precipitation carries erosion-prone topsoil to the Ganga, thanks to deforestation, and thus adds to overall sediment load every monsoon.

"High levels of sediments prevent sunlight from penetrating into the depths, where it normally would have nourished plankton," says Dr. V.V. Sugunan, director of CIFRI. Plankton forms a vital link in the food chain. Researchers have observed a significant reduction of plankton in the Ganga over the past three decades.

The devastating decline of the Ganga fish industry has meant heavy job losses.

This has led to the "desertification" of the riverbed. Increased sand on the riverbed has seen a corresponding decline in the water-soil interface-spelling doom for the benthic carp species. They live on the riverbed, and also form a vital link in the food chain. Excessive sedimentation also raises the riverbed level, leading to greater turbulence during monsoons.

In addition: researchers at the National Academy of Agricultural Sciences have observed that biologically and economically desirable species have, over the years, given way to low-value species.





Fatal abstraction
Fish, and indeed the entire ecology of the Ganga, are also affected by water "abstraction," defined as the removal of freshwater from the river. A total of 1.4 million cubic meters of water are abstracted for irrigation, power generation, storage, mining and a variety of other purposes. Water abstraction also affects siltation- the decrease in flow rate accelerates the deposition of particles on the riverbed. Siltation deprives fish of the type of depth, flow and other conditions suitable for their breeding and survival.

Major points of abstraction include The Upper Ganga Canal at Haridwar, the Lower Ganga Canal at Narora, the pumped canals of Dalmau, Bhoupali, Zamanie and the Farakka Barrage.

Abstraction not only reduces or eliminates flooding in the marshes and estuaries, depriving fishes of suitable habitat conditions. It also adversely affects water temperature, transport of organic material and sediment, and other factors.

The velocity of a stream's flow is crucial for fertilisation of eggs, oxygen supply and survival of the spawn. Most fish have strong territorial orientation, which is contingent on stream velocity and current. Flow regimen also tends to affect fish harvesting. This cycle of breeding and recruitment is seriously hindered when water discharge is inadequate.

The oxbow lakes, deep pools and other water bodies associated with the river all function as sanctuaries for brooders, connected to the main stream during the monsoon season. Insufficient water discharge prevents these bodies from being connected to the river, making it impossible for brooders to perform breeding runs. Inadequate flow during the post-breeding season leaves the fry and the fingerlings trapped in pools along the river course. What is worse, fishermen find it hard to resist the temptation to catch these in large numbers, hampering the process of recruitment.

Trained to kill
The flow of the Ganga is also affected by river "training" measures for controlling floods, such as guide banks, spurs and river revetments. "But you can't solve any problem by training a river," says Dr. Sugunan. "You merely shift it from one place to another."

These measures decrease the roughness of friction along the riverbanks and upset the energy expenditure balance, exposing unprotected parts of the banks to added velocity from the flow. "That's why we have such extensive floods these days," says the CIFRI director.

Structures built to train a river, such as dams and embankments, physically obstruct the movement of fish, affecting all kinds of fish migration. Impounding water in barrages compounds the problem, because it reduces freshwater flows. The state of Uttar Pradesh in northern India causes maximum Ganga impoundment, amounting to 17.2 billion cubic meters.

Hilsa fish are an instructive example of the anadromous variety affected by man-made obstructions in their migratory pathway. "There was a time, before the Farakka Barrage was built, when the yearly catch of hilsa used to be about 20 tons," Dr. Sugunan says. "That figure had plummeted to almost zero immediately following the construction of the barrage." Although hilsa are once again found north of the barrage, the output (2.47 tons in Allahabad. and 0.38 tons in Bhagalpur) is nowhere near pre-Farakka years.

Staggering pollution
Pollution, too, is cause for serious concern. Industrial, municipal and agricultural effluents constitute the chief sources of pollution in the Ganga. According to official estimates, the total quantity of freshwater used in the basin is 142.6 billion cubic meters, of which 20 per cent is finally discharged as wastewater. Interestingly, the wastewater generated from irrigation is a staggering 26.8 billion cubic meters as opposed to the 1.528 billion cubic meters coming from industrial, domestic and other uses.

While the mountainous stretch of the river above Rishikesh is free of industrial pollution, the stretch across the upper plains is moderately polluted. This is due to effluents generated by the pharmaceutical and heavy electrical factories in Rishikesh; the tanneries, textile and jute mills of Kanpur, and fertiliser plants in Allahabad. Industrial pollution is negligible in the non-tidal deltaic area. Along the lower estuary, however, between Nabadwip and the bar mouth, there has been rapid industrial growth in recent years. The deltaic tidal stretch receives approximately 430 mld of industrial effluents from 96 factories producing paper, yeast, viscose rayon, cotton, paints and varnishes, rubber, vegetable oil and soap, fertilisers, antibiotics and a whole variety of other commodities.

Quite apart from sub-lethal chronic effects on the environment, industrial effluents also cause direct fish kills. Oil-laden wastes at Barauni affect major and minor carp populations, causing their periodic mortality. Industrial waste washings, as well, kill fishes in the Gomti, a significant tributary. Distillery wastes have proved toxic for the Puntius Sophore and Mystus Vittatus species, while cycle rim factory wastes kill off Catla and Labeo Rohita fish.

But pesticides are by far the worst culprit. Organo-chlorine pesticides are lipophilic, highly toxic and non-biodegradable. Like heavy metals, they assume alarming proportions by being biologically magnified and accumulated in fish, posing serious threats to human health. Most of the commonly used pesticides (DDT, BHC, endosulfun, ethyl parathion, etc.) are toxic for micro-organisms as well as fish.

"An overall habitat degradation" is how scientists at CIFRI wrap up the situation. But what are the chances of improvement?

Not much, unfortunately. River cleaning plans such as the Ganga Action Plan have been failures: Water is viewed as a product that is best exploited when diverted into a water-scarce region.

Fish and the fishing industry in the Ganga basin have thus become the victims of a strategy that ignores the ultimate economic damage caused by Ganga defilement.

Eugene Datta is a Calcutta-based journalist.