Curious case of disappearing fish

Fish species are rapidly disappearing from Himalayan rivers. Dams are not the reason. Human activity is.
Mahseer swim in the bracing waters of the Ganga in Uttarakhand. Mahseer swim in the bracing waters of the Ganga in Uttarakhand.

Jaman Ram, a resident of Bhikia Sain, a tehsil in Uttarakhand, remembers fishing with his father in the Ramganga. “We could catch 80-100 kilograms of fish a day. That is no longer possible,” he says. Shafiq of Haldwani shares an unsettling memory of the Ramganga. As a young man on a holiday, he was paddling in the river near Marchula when the rock he was standing on shifted. Thinking he was standing on a loose boulder, he stepped away from it only to see the “rock” glide away. It was a large “goonch”, a fish mighty enough to support a man on its back. “I haven't seen anything like that since,” says Shafiq regretfully.

Both Jaman Ram and Shafiq are confused by this decline in fish numbers in the Ramganga. While the dams and the resultant fragmentation of rivers are the single largest threat to fish species, especially in the mountain areas, the stretches of the Ramganga that Jaman and Shafiq refer to are free flowing still. Studies being conducted in places as far away as Germany, Brazil, and the United States of America may provide Jaman and Shafiq with the answers they need. The research has discovered that the changes in the land use and the resultant non-point source pollution may adversely impact riverine fish.

Understanding fish species

To understand why, we need to understand a little about the lives of fish in the Himalayan rivers. Arguably, the iconic fish in this region is the “mahseer”.  This is not a single species of fish, but a group of fish spread over two genera, mainly Tor and to a lesser extent, Neolissochilus. Besides these, it is the trout family that is appreciated by both anglers and the riparian communities.

The Pindar leaps over boulders in Uttarakhand.Speaking of the mahseer, one of India’s foremost experts on high altitude freshwater ecosystems, Dr Nautiyal of Hemwati Nandan Bahuguna Garhwal University says, "The (adult) mahseer lives in moderately cold waters of glacier-fed rivers, while in its larval and juvenile stages, it lives in relatively warmer waters of springfed streams. It has a terminal mouth (facing front) and is well adapted to feed on the bottom as well as in column. It is carnivorous in late larval and juvenile stages, while the fresh adults turn piscivorous during migration. As it grows in age, it becomes omnivorous. Thus, minor changes will not deter it.” It is the omnivorous nature of the mahseer group of fish, both in the manner of feeding (column as well as bottom) and the type of food (fish, plankton and algae) that makes it resilient to changes in the water.

Far more vulnerable are the snow trout (of genus Schizothorax). Dr Nautiyal explains, “The snow trout is a herbivore and inhabits ice cold to moderately cold waters. The mouth of the snow trout is ventral (facing river bottom) and can feed on river bottom only.” The snow trout are susceptible to changes in the stream flow, in temperature, in pollution levels and in the nature of the stream bed.

Feeding patterns

In addition to their own physical limitations, both mahseer and trout are dependent for life on the availability of food. Snow trout feed primarily on algae. A study of the feeding habits of Schizothorax revealed that 20 percent of its stomach contents was algae (mainly diatoms) with the rest of the matter being sand, mud, and detritus. This means that for the health of the fish species, it is crucial to maintain healthy populations of various diatoms and other algae in the river. The diversity of algae is especially important since, according to Dr Nautiyal, the fish exhibit food preferences and wouldn’t feed on whatever comes their way.

This fussiness is bad news for the fish since diatoms and benthic invertebrates (the animals that live on the river bed) are notoriously picky about the water they inhabit. It is this characteristic that has led to the popularity of benthic macroinvertebrates to assess the quality of the surface water.

How streams get polluted

There are several ways a river gets polluted. The most visible one is the point-source pollution. This is when the highly polluted matter enters a river through a single point of discharge such as a sewer outfall or waste from a factory. This receives the greatest amount of attention in river restoration programmes like the Ganga clean-up. But studies are now pointing out the deleterious impact of another cause of pollution--the changes in the landscape.
Land use changes can impact the riparian ecosystems simply by increasing the amount of effluents that enter the streams. Dr Nautiyal explains, "An ecosystem remains an ecosystem till its natural features are not modified by anthropogenic activities. Once it is modified, it tends to degrade; the degree of degradation depends on the extent of modification disturbances. Further, each ecosystem has a definite structure (flora and fauna in definite proportions which remain constant over a period of time) and each biotic component has a function or role in the ecosystem. A change in the land use decreases or increases the concentration of some ions (direct or through effluent). Some organisms are sensitive to these changes. They vanish,” he says.

He further observes,  “In recent years, the land use in Uttarakhand has changed from agriculture to residential or industrial which have resulted in increased discharge of civic and industrial effluents. In the Doon valley, the Song river which is a breeding ground and nursery for mahseer, is badly affected and only the lower stretch is suitable for breeding. But I have no data to support this observation.”

However, it is not just the direct influx of pollutants that harm a river. Anthropocentric activities in the vicinity of a river tend to degrade the ecosystem in any or all of the following ways:

Forests and their streams: The deforestation that results from increased human activity in a catchment results in significant changes in the hydrology of a stream. A study by Dr Kuemmerlen of the The Bhagirathi flows through pristine landscape at DharaliSenckenberg Research Institute proves that deforestation leads to higher peak flows and lower base flows. In the Himalayan context, this means lower water levels in the dry season (leading to higher water temperatures and possible loss of stream connectivity), and flooding in the monsoons (with increased sediment flow).

A separate study by Dr Kuemmerlen and his colleagues has determined that the negative effects of changes in land use (from forest to agriculture and tea) surpassed those of climate change by reducing richness and the range size of stream biota. The combined effect of climate change and land use changes shows a decrease in richness, range size and diversity of stream macroinvertebrates. This will impact predators higher up in the food chain, including the fish species.

Change in temperature: Anthropocentric land use changes also result in warmer streams. This is due to several factors. Maximum temperatures are closely related to the forest cover. A study by Dr Sponseller, Benfield and Valett of the Virginia Polytechnic Institute has observed that high mean and maximum temperature in the stream is the result of both solar radiation (which reaches the stream as a result of loss of streamside vegetation) and the surface runoff whose temperature is increased by the tarred and paved surfaces while on its way to the stream. This can have disastrous impact on thermally-sensitive invertebrates such as stoneflies, affecting larval growth.

Infrastructure and streams: Urbanisation also has an effect on stream health. A study by Dr Wang, Lyons and Kanehl of the Wisconsin Department of Natural Resources has concluded that the impact of ‘hardscaping’ or paving over the land is greater than any other intervention. If the connected impervious surfaces exceed 12 percent of the total area, then the stream quality is impacted to such an extent that it does not matter if this impervious surface is used for industrial purposes or relatively benign domestic use.
A matter of proportion

These are bad news for rivers. These studies point out that even if we manage to reduce the number of dams coming up in the Himalayas or prevent all industrial and municipal pollution from entering our rivers (both very tall orders), rivers are still doomed just by the presence of humans. Thankfully, this is not the end of the story.

Dr Sponseller, Dr  Benfield and Dr Valett would tell you that the impact of landuse changes in the catchment is not uniform. Some changes vary with their location relative to the stream. Their study says, “Stream water chemistry was generally related to features at the catchment scale. Conversely, stream temperature and substratum characteristics were strongly influenced by land-cover patterns at the riparian corridor and sub-corridor scales. Macroinvertebrate indices were most closely related to land-cover patterns evaluated at the 200-m sub-corridor scale, suggesting that local, stream-side development effectively alters assemblage structure.” This conclusion is supported by Wang, Lyons, and Kanehl who report that, “In a spatial analysis, connected imperviousness within a 50-m buffer along the stream had more influence on stream fish and base flow than did comparable amounts of imperviousness further away”. This means that while the chemical pollution in a stream (as well as its morphology) depends on what is happening in the entire catchment, the stream's biology is largely dependent on what is happening on the stream banks.

This is excellent news because it gives us three very focused strategies to protect our streams and fish.

  1. Maintain a riparian zone of at least 200 metres from the river banks. Forest cover in this belt will reduce temperatures and sedimentation, maintain adequate levels of plant detritus, and conserve both levels and diversity of benthic flora and fauna. In short, this will provide fish with all they need for a fighting chance to live.
  2. Ensure rational use and safe disposal of all chemicals (including agricultural fertilisers and domestic cleaning products) in the entire catchment to maintain low levels of toxins entering the streams.
  3. Minimise the connected impervious surface within the entire catchment by opting for sustainable urban design features such as porous pavings, rain swales and natural features.

The experts warn that these measures will not entirely negate anthropocentric impacts on river ecosystems but they will considerably reduce the extent and the intensity of these impacts.

Several government quarters have been constructed along the Ramganga at Bhikia SainJaman Ram has a tough fight ahead of him. Not only does the town of Bhikia Sain release sewage directly into the Ramganga, but it also forms a kilometre-long impervious strip parallel to the river. The floodplains of the Ramganga at Bhikia Sain have been traditionally used for farming. Of late, however, buildings are being constructed here. The culprits? The government of Uttarakhand. The state has constructed staff quarters on the floodplains and is now planning to construct a tourist guesthouse. These activities will destroy the important riparian buffer, and further reduce the already declining fish availability.

Why should we bother about conserving Himalayan fish and plankton? Two distinct viewpoints offer us good reasons. Atkinson, the author of the Himalayan Gazeteer writes, "Fish are universally eaten by the casteless classes...that are first to suffer in times of scarcity. It is not so necessary to protect the food sources of the rich and the powerful as those which might be made available for the poor labouring man and his family."

Dr Nautiyal offers us an equally cogent reason for conservation when he asks, "Should we protect a species only if there is a reason?”



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