Fish fauna in Bharathapuzha under severe threats, warn scientists

A view of Bharathapuzha (Image Credit: Wiki Media Commons/ Jjvellara)

Implement urgent conservation efforts or the rich and endemic fish wealth in the largest river in the Western Ghats of Kerala will remain only on papers, warns a new assessment on the threats to the fish diversity in the Bharathapuzha River, locally known as River Nila.

Through a survey on all the four major tributaries of the Bharathapuzha River system - Gayathripuzha, Chitturpuzha, Kalpathipuzha and Thoothapuzha – the study recorded 117 species of fishes in Nila with the highest species richness from the stretch between Parali to Purathur estuary. Among this, 33 are found only in Western Ghats and three are found only in Bharathapuzha River system. 

A group of researchers including A Bijukumar, Department of Aquatic Biology and Fisheries, University of Kerala, Siby Philip from Department of Zoology, Nirmalagiri College, Koothuparamba, Anvar Ali and Rajeev Raghavan from Conservation Research Group, St Albert’s College, Kochi and S Sushama from Department of Zoology, NSS College Ottapalam carried out the study which is published in the Journal of Threatened Taxa.

Top Ten Threats to River Nila

Despite the richness, the river system of River Nila is under threat from human interference, says the study which is published in the Journal of Threatened Taxa. “Several anthropogenic stressors including deforestation and loss of riparian cover, dams and other impoundments, pollution, sand mining, non-native species, climate change and destructive fishing practices are threatening the fish diversity of Bharathapuzha River system”, it says.

Threat #1: Sand mining

Most notorious, most widely known but most rampant, despite being regulated (encouraged ?) by the il-legal machinery. If we number the threat based on the calamity it brings, this one goes to top. The study marks the region between Pattambi and Thiunavaya as the superhot stretch of legal and illegal sand mining. Studies conducted by CESS in 1997 itself has shown that the rate of sand mining is way too above the rate of sand generation in Nila. For many fishes in Nila, Sand is the breeding substrate, and is the single crucial link that supports the aquatic food web. With the indiscriminate sand mining, it is just a matter of time for fishes like Glossogobius giuris and Sicyopterus griseus to vanish from Nila forever, warns the study.

Threat #2: Dams and impoundments

Known fact: Big dams are a major threat to the rich and endemic fish diversity of Nila, since they change the turbulence of the river causing high sedimentation and other problems. Lesser Known fact: Dozens of smaller check damk dams across Nila are also doing the same. Bigger dams are fixed in number so far – Nila has 11 irrigation dams. Impoundments are still proliferating, turning out to be a lesser noticed diversity killer in Nila. It has severely affected the movement of certain fish species and is believed to be a reason for the near absence of eels in the river system.

Threat #3: Pesticide pollution

When it comes to a River system like Nila, don’t think it is just the factories that are pushing chemicals to the water. River basin dependent extensive agriculture and plantations are also contributing their fair share to polluting this blood line of middle Kerala. Chemical fertilizers, pesticides, chemical nutrients, weedicides, you name it. The resulting eutrophication- the facilitation of aquatic plant growth which in turn decreases the available oxygen in the water, killing the aquatic fauna- is a major issue, especially from Chamravattom to Purakkad, says the study.

Threat #4: Urban sewage

Read Pattambi. According to the study, the town of Pattambi which falls under the Palakkad District of the state of Kerala is a major source of urban sewage which pollutes the river extensively, taking over the pollutant cocktail made by the agro-pollutants. “The urban sewage canals directly open into the river, through which the municipal waste is dumped. Such large scale pollution not only degrades the habitat but also causes endocrine disruptions and several other physiological imbalances in fish including breeding failure which could ultimately lead to their extirpation”, says the study.

Threat #5: Deforestation

According to the study, deforestation in its catchment areas like Mangalam, Nelliyampathy, Walayar, Malampuzha, Nellipuzha, Dhoni and Kalladikode is a major threat. The loss of natural native vegetation has triggered the invasion by exotic plants. Not only that the fishes loose a food resource, the high sedimentation rate due to deforestation is changing the natural composition of the river bed. It makes survival difficult for many endemic loaches in the river since they use the pebbles in the river bed for breeding.

Threat #6: Lime stone mining

Lime stone mining is rampant in certain areas of the catchment of the river, says the study. This is especially prominent in Malampuzha, part of the Kalpathipuzha tributary. The study claims that the lime stone mining in the catchment areas is leading to pollution and siltation in the stream. Apart from triggering an unnatural rise in the silicate content in the water, the dumping of mining debris also damages smaller streams in the system like Seemanthinipuzha.

Threat #7: Alien species

The study has spotted at least six non-native fish species in Nila. While three of them were non-native to Indian rivers, three were from the Gangetic plains. Though the Indian major carps were introduced as part of aquaculture, considered as a success, the study was able to spot them from lower reaches of the river, revealing that they have proliferated though the river beyond their actual reservoirs. Such proliferation of non-native species often wipes out native species in the fight for resources. Species foreign to India like the Nile Tilapia and Mozambique Tilapia were also spotted from Nila, showing that the alien invasion is possibly stifling the endemic fish fauna of the river. However, the surprise factor was that the study reportedly failed to fetch another notorious alien species – African catfish- which is a known diversity killer in Western Ghats Rivers.

Threat #8: Climate change

Studies conducted in 2010 and 2011 discovered that the temperature in the Bharathapuzha basin has been on the rise for a 36 year period from 1969 to 2005. Moreover, rainfall data shows that the Nila watershed gets less rainfall than the state average. Though the temperature rise is often cited as an impact of climate change phenomenon and the increasing anthropogenic pressure in the river banks of the Nila, its effect on the biodiversity of the river system is scarcely studied.

Threat #9: Aquarium fish trade

 Comes in many colours –state supported as well as clandestine. This greed trade is especially wiping away endemic and beautiful fishes like Miss Kerala (Sahyadri denisoni) and Mesonoemacheilus remadevii, the latter being found only in river system in Silent Valley which is part of the Bharathapuzha River System. As per a recent study, Miss Kerala has been found to be collected in massive amounts from Thoothappuzha tributary for pet trade.

Threat #10: Destructive fishing practices

Last, but not the least, as always. Poisoning, use of mesh nets and dynamiting – small effort, good catch. Though traditional fishermen abstain from practices like dynamiting, it is raising a major threat to the fish diversity in the tributaries where the traditional fishermen are lesser in number, warns the study.

Action Time: Conservation Points to save Nila

• Prioritizing integrated watershed programmes.
• No more new medium or big dams, cautious about new check dam proposals.
• Channelize district River Management Fund to Eco restoration of stretches of Nila.
• Regulation of sand mining has been proved to be futile. So finding an eco-friendly alternative to sand is the only option left. But that will be like legalizing marijuana- you have to first convince the cartels before you convince the government. (They will have to take it, since the sand is running out and the weed is on the rise).
• Beg people not to use pesticides or agro-chemicals near the river bed cultivations (otherwise also).
• Regulate large scale riverbed cultivation.
• Establishing Aquatic Biodiversity Management Zones (ABMZ) to conserve river stretches known to shelter endemic and rare fishes.
• Regulate the greed pet trade and destructive fishing practices, not to say dynamiting.
• Above all, let people know – ask them, request them, beg them, threaten them – You may go the extreme since water is the life blood of the green earth, as River Nila is for Kerala.