Seeing the River for the Fish

Scientists and local communities are working to save an iconic but little-known species of fish in India—but first, they have to find it.

On a tropical morning in March 2016, wildlife researcher Dencin Rons Thampy sat motionless on a large rock among the Kuruvadweep Islands, which cluster in the middle of the River Kabini, in the Indian state of Kerala. Surrounded by the islands’ softly rustling evergreen trees, along with patches of eucalyptus and teak that dot the forests upstream like giant heads of broccoli, this interface between land and river is rich with life. On previous visits to the region, Thampy, who focuses his research on freshwater habitats, had recorded 136 species of fish, 62 adult crocodiles, five packs of small, clawed otters, and countless waterbirds. The islands also serve as an important elephant and tiger corridor that connects to the Wayanad Wildlife Sanctuary.

Today, he had come to survey the population of crocodiles, but he spotted something unexpected. Frolicking in the shallow waters were two of the biggest fish he had ever seen. “They were massive, as big as a human,” he says. And they were beautiful. Each fish had a prominent hump on its back and scales that gleamed silver and gold. Before he could take a photo, or even a step forward, the fish disappeared, melting into the turbid water.

Intrigued, he asked about the creatures among the Mullu kuruma, the prosperous tribal people that inhabit these islands in a settlement of about a thousand. Some of the elders knew the species well. About 50 years ago, they told him, the fish were abundant. They called them velimeen, the common name for the hump-backed mahseer, or orange-finned mahseer.

Although Thampy had spent hundreds of days surveying the Kabini, he had never spotted the fish before. As he would learn, the hump-backed mahseer had undergone a steep and startling decline throughout its range. Thampy and others couldn’t help wondering what had happened to this magnificent fish. The answers to that question would ultimately shed light on factors that were harming the river system itself, including a misguided effort to boost the numbers of related species. As the complexity of the problem became clearer, scientists and conservationists soon realized that efforts to revive the hump-backed mahseer population would have to be as intricate and multifaceted as the threats that cut it down in the first place, and they would have to begin soon.

Flowing through the jungle-clad mountains of northeastern Kerala, the Kabini is one of several major tributaries of the Kaveri River. The Kaveri originates deep in Brahmagiri Hills, a mountain range in the Western Ghats of India, and threads its way through a wild 88,000-square-kilometer (34,000-square-mile) basin. Among the longest rivers in the country, it is the lifeblood of the southern states of Karnataka, Kerala, and Tamil Nadu, as well as the Union territory of Puducherry, a region administered directly by the federal government. It is also one of India’s seven holy rivers. An estimated 300 Hindu temples line the river’s banks, built by the Chola Dynasty, Tamil rulers of Southern India for more than 1,500 years starting around 300 BCE.

But reverence and historical significance have not protected the river, nor its tributaries. To researchers like Thampy, the rising stresses have been all too apparent. Raw sewage and plastic waste from towns and settlements along the banks of the Kabini have found their way into the water, and wetlands have been cleared for banana and areca nut cultivation. Tea and banana plantations across Wayanad use strong chemical pesticides and fertilizers, which leach into the river during monsoons. Sand quarries and illegal and unsustainable development of hotels and other properties have consumed river banks and eaten into slopes, marshes, and floodplains, causing widespread soil erosion and siltation. “This rising influx of sediment and pollution has impacted many native fish species,” Thampy says.

Adrian Pinder knew none of this when he visited the River Kaveri for the first time in 2010. A fisheries scientist who directs an environmental consultancy at Bournemouth University in England, Pinder had admired the hump-backed mahseer since he was a child, when he first saw a picture of one on the cover of a fishing magazine. He had longed to see one in person ever since. Finally, the avid angler had found his way to the Galibore Nature Camp on the Kaveri to realize his dream of catching the giant fish. But the fish he and other anglers hooked there looked nothing like the one that had lured him. He wondered what had become of the hump-backed mahseer.

Galibore Nature Camp, along with other angling camps along the Kaveri, such as those at Bheemeshwari and Doddamakali, followed the practice of catch-and-release fishing. The conservation-friendly technique was first introduced in the area by the Wildlife Association of South India (WASI), a non-governmental organization that has worked toward river protection and conserving the mahseer for the last 50 years. When anglers caught a fish, they lifted it from the river long enough to get a photo, water streaming off of its scales, before setting it free again. All were marked in a meticulous set of records, January through March each year, going back to the 1970s, with anglers’ names, dates, and times of their catch, as well as each fish’s weight and color. “G” referred to the golden-hued hump-backed mahseer; “S” was for the silvery blue-finned mahseer. The only records that went into the book during Pinder’s first visit were marked with an “S”.

Flummoxed by his experience, in 2012, Pinder asked to see the camp’s records from the previous two decades. Blue-finned mahseer, he saw, had once been much rarer in the river. Twenty years prior, there had been no record of it. In 1998, there were four to every hump-backed mahseer that anglers caught. But by 2012, there were 218 blue-finned mahseer to every hump-backed mahseer. Plotting 15 years of camp fishing data, Pinder pinpointed the hump-backed mahseer crash around 2004 and 2005. “At that point,” he said, “there were no small fish and all you caught was an aging population heading toward extinction.”

At the time, researchers weren’t sure if the hump-backed mahseer had been formally described and given a Western scientific name. But genetic testing in 2018 revealed that it was, in fact, Tor remadevii, which scientists had first described in 2007 in the Pambar river, another Kaveri tributary in Kerala. It was one of just eight species of freshwater carp that remained of India’s 15.

Once they had confirmed its identity, Pinder and other scientists raced to determine how endangered the hump-backed mahseer might be. Rajeev Raghavan, assistant professor at the Kerala Institute of Fisheries and Ocean Studies and the South Asia coordinator for International Union for Conservation of Nature (IUCN), began working with Pinder to examine a growing body of data about the fish’s current and historical distribution, the threats it faced, and how many might be left. Their findings were startling: The population had shrunk rapidly, with a 90 percent decline over just 15 years. Based on this and other information, in 2018, the IUCN declared the hump-backed mahseer Critically Endangered.

It was a significant move. An IUCN listing is important to conservation efforts in India, researchers say, because its urgency gives the species more attention. Many of the country’s wildlife conservation efforts and associated funding have so far aimed at larger, more charismatic species such as the Bengal tiger (Panthera tigris tigris). Lesser-known species that may need just as much protection are often left out. Worse for the hump-backed mahseer, existing wildlife protection laws don’t apply to fish, because Indian law treats them as a natural resource to be stocked, a means of food, and not as wildlife to be protected.

It was clear to scientists that habitat loss was a major cause of the hump-backed mahseer’s decline. There was dramatic expansion in dam building along critical tributaries in the 1970s, and this caused a ripple effect. As more dams were built, development increased, which required the construction of even more dams, according to Steve Lockett, Executive Director of the Mahseer Trust, a UK-based charity established in 2016 to support mahseer conservation. “Forests were cleared, water diverted for agriculture (coffee in the upper rivers and sugar in the lower areas), plus a growing population and industry add[ed] to the pollution burden,” he says.

But there were other, more unusual challenges—one of these the result of efforts to mitigate some of those harms and promote biodiversity. Since 1915, TATA Power has generated and distributed electricity from thermal power plants and hydropower dams for commercial and industrial use across much of India. The company is run by one of the country’s largest business conglomerates, and is based in the western Indian city of Mumbai. For the past 50 years, it has worked with state fishery departments around the country to restock rivers that have seen their fish populations decline. For the company, it’s a well-intended conservation effort, an earnest initiative toward sustainability. However, researchers claim that it has been introducing species of mahseer into rivers where they are not native. “They have bred at least three different species of mahseer, and at least two have been stocked outside their native rivers,” says Lockett.

The blue-finned mahseer is endemic to the Krishna River Basin, flowing through the states of Maharashtra, Karnataka, and Andhra Pradesh. The species was never a part of the Kaveri, and was introduced during TATA’s conservation efforts, says J. A. Johnson, a scientist in the Department of Habitat Ecology at the Wildlife Institute of India. TATA Power set up a hatchery in the town of Lonavala, which, according to an internal company report, has a capacity to hatch 400,000 – 500,000 fingerlings annually for distribution across India, including into the Kaveri basin. Scientists estimate that TATA has stocked rivers across India with more than 11 million hatchlings over the past 50 years, and worry that many of these wound up in the wrong river systems. (Neither TATA Power nor the manager of the hatchery in Lonavala responded to requests for comment.)

The blue-finned mahseer has proved remarkably resilient in the Kaveri River system. “They’ve established a population and have out-competed the native population of hump-backed mahseer, all in a short time,” Pinder says. It may be a numbers game as much as anything: When non-native fish are released by the thousands in places where native populations are small and struggling, they simply overwhelm the native species, Raghavan says. The blue-finned “compete with the native fish for food and shelter, they are faster, they breed more prolifically. [For] fish like the hump-backed mahseer, there’s no chance of surviving or competing.”

While the abundance of the blue-finned mahseer could be a cause for concern for the hump-backed mahseer, some experts feel the problem may be more complicated. “We have recorded 17 non-native species of fish in the Kaveri river system,” says Naren Sreenivasan, an ecologist at WASI. Non-native, invasive fish can be more problematic for an indigenous species when a water system is already polluted, because their body condition, feeding, and behavior are already compromised. “More ecological and molecular studies are needed to fully understand the decline of the hump-backed mahseer before we can draw conclusions,” Sreenivasan says.

Dwindling water reserves are adding to the pressure of habitat loss and chemical pollution that hump-backed mahseers have had to contend with. Southern Indian states have fought bitterly for 150 years over their increasing water needs from the Kaveri, and the poor monsoon seasons in 2004 and 2005 left many rivers in the region almost completely dry. That drought may have been largely responsible for the dramatic crash in hump-backed mahseer populations that Pinder found in the angling data, Lockett says.

But ironically, while dams have reduced the water available for hump-backed mahseer downstream, they have helped to protect the species, too. According to Pinder, the only place where hump-backed mahseer are found today is in two or three tiny pockets of the Kaveri River system, which are isolated from the main river by dams that prevent the entry of the blue-finned mahseer.

“We’re still documenting the sheer biodiversity—and have barely scratched the surface of the ecology. And we don’t know how much we’ve lost.”

— Neethi Mahesh, Foundation for Rivers and Ecosystems

Given the challenges, conserving what’s left of hump-backed mahseer populations, and ultimately restoring them, will require a multi-disciplinary approach. Large charismatic species like tigers thrive when their habitat is healthy, researchers say, and that applies to the hump-backed mahseer as well. For example, Thampy’s field research in the upper Kabini shows that aquatic diversity is greater in riparian habitats dense with native trees and shrubs along riverbanks, and that the hump-backed mahseer still holds on in such locations.

An ecologist at the Foundation for Rivers and Ecosystems, Neethi Mahesh has made similar observations at the source of the River Kaveri in Kodagu, where she’s based, a district in Karnataka with dense forests interspersed by coffee estates. Using blue-finned mahseer as an analog, since hump-backed mahseer were too difficult to find, in 2015 Mahesh used radio transmitters to track about 40 fish. Though they eventually lost track of their study subjects, she and her colleagues found that the fish depended heavily on trees in the riparian zone. The trees provide shade, which regulates water temperature, and drop fruit and insects into the water that the omnivorous fish rely on for food. “Our riparian habitats are very unexplored, even though they form a crucial part of river ecosystems,” she says. “We’re still documenting the sheer biodiversity—and have barely scratched the surface of the ecology. And we don’t know how much we’ve lost.”

What’s clear, however, Lockett says, is that “steps to conserve the hump-backed mahseer should include rehabilitation of riparian cover—a source of groundwater recharge and water store for rivers—and lifting habitat pressures, which will also be the best steps back to whole river health.”

Mahesh is already doing that work, albeit on a small scale. With the help of a conservation grant in 2019 from the Habitats Trust, she surveyed the riparian zone in the Dubare Reserve Forest, and, relying on the expertise of the local indigenous Jenu Kuruba community, identified 12 native trees to help guide restoration efforts. So far, Mahesh and her team have planted about 10,000 saplings from nine of these species in the riparian zone along the Kaveri.

The project now has support from the Kodagu Forest Department, which will fund more planting and help with monitoring and restoration efforts of the riparian cover. “It’s a long-term collaborative approach that will span 10 to 15 years,” says Mahesh. And since many of these lands are private estates, Mahesh and the Kodagu Forest Department are holding meetings with landowners to ensure that everyone is aware of the need for restoration efforts and approves how they’re being implemented.

In addition to helping protect the hump-backed mahseer and other freshwater fish, the project will afford local communities some protection from floods and extreme weather events, Mahesh says.

Learning much more about the species itself will also be critical to protecting it, says Johnson, who has spent years surveying fish in rivers across the country. The hump-backed mahseer’s life history, habitat requirements, and current population size are still uncertain. “Any conservation program requires information on viable populations,” he says. “In general, mahseer thrive in clean water and they need a deep water flow. Many species spawn after the monsoon, because they need a shallow habitat to deposit their eggs. [But] we don’t have any idea how the hump-backed mahseer behaves,” he says. In June, Johnson surveyed the Moyar River, a smaller tributary of the Kaveri that flows along the fringes of a protected forest reserve called the Bandipur Tiger Reserve and National Park. Johnson had seen many hump-backed mahseer there while surveying the river as a PhD student in the late ‘90s. He hoped to see how many remained.

Working with the Karnataka Forest Department, he performed a systematic sampling of fish in the Moyar River for three days before the monsoons began in June. “We found some encouraging results,” he says. “The river has a good population of adult mahseers.” They were able to catch three adult fish after setting up ten casting nets on the first day. “We would like to repeat the exercise after the monsoons,” he says.

Considering how the hump-backed mahseer is found only inside these protected areas that are governed by forest and fishery officials, conservation programs can only be successful with the help of authorities, says Sreenivasan. WASI is working with 500 recreational anglers and Indigenous fishers, as well as government forest and fishery officials across the Kaveri basin to conceptualize a plan to save the hump-backed mahseer. The Karnataka Forest and Fisheries departments intend to build a repository this year where live hump-backed mahseer specimens can be studied in semi-captive conditions. In order to catch these specimens, they will tap into WASI’s network of anglers. Though angling has been banned in protected areas in India since 2012 in accordance with wildlife laws that do not allow trapping and baiting in reserves, it’s allowed outside their boundaries. WASI uses their recreational angling program to generate money for locals and to support educational efforts to prevent local fishers from indulging in harmful practices such as indiscriminate trapping and dynamite fishing in the rivers, and helping them develop alternative livelihoods and reasons to protect the fish.

To track the fish in the wild, other researchers are tapping the Indigenous knowledge of local communities, such as the Mullu kuruma. Thampy has recruited eight “trackers” from Kuruvadweep Islands and from nearby Wayanad, a rural district in Kerala state, to tell him whenever they encounter hump-backed mahseer. Tracking the fish down is critical to studying its habits in the wild. “Without [the trackers], it would have been difficult for me to identify the exact locations where the hump-backed mahseer are found,” says Thampy. He hopes the information will help him study the fish in more detail and possibly identify local spawning grounds. A detailed study of spawning needs could greatly boost conservation efforts, he says. “The Mullu kurumas have helped us in studying some of the important ecological aspects of the species.”

Thampy has also trained the trackers to collect DNA samples from fish caught by local fishers, to see if any hump-backed mahseer are among them. The trackers work to educate local communities about the importance of preserving the mahseer, something that would have been difficult for outside researchers to do, says Thampy.

In 2017, the Mahseer Trust engaged with TATA Power and state officials, in a bid to help them understand the serious threats faced by the hump-backed mahseer. The stocking program was halted following initial talks, Lockett says, and they were invited to future meetings to discuss the issue and resolve their concerns. But the employees who initially worked with the researchers have since left, Lockett says, and the talks must start over again.

“We tell [children] that this is one of the rarest fish in southern India…. We ask them what they can do to help.”

— Rajeev Raghavan, Kerala Institute of Fisheries and Ocean Studies

Still, other outreach efforts are ongoing. Scientists regularly speak with local communities and school children living near mahseer habitat to better educate them about the species and the importance of protecting it. Pinder has even published a children’s book about the mysterious, underwater world the mahseer encounters and the many threats to its wellbeing.

“We try to tell [children] that this is one of the rarest fish in southern India,” says Raghavan. “One of the world’s largest freshwater fish, it needs to be protected, because with this sort of population decline, it won’t survive the next 20 years. We ask them what they can do to help.”

Many locals already recognize the importance of this work. One member of the Mullu kuruma, a 47-year-old named Handreen, who works with Thampy as a tracker, remembers seeing the fish as a child. “Shoals of huge velimeen used to live in the river then,” says Handreen, who goes by one name. “We consider them river gods. Unlike other fish, they are hard to spot and powerful enough to pull a man into the river once they are caught on a line and a hook.”

Saving the fish would mean protecting the river and preserving the forests where he was born and raised, he says. “Finding this unique fish in the wild shouldn’t be just a story we can tell our kids.”

Header video credit: BlackBoxGuild / Shutterstock; P.V.R.M. / Shutterstock; Image Bank Film / Getty Images

Kamala Thiagarajan

Lauren Owens Lambert

Kamala Thiagarajan is a freelance journalist based in Madurai, South India where she reports on environmental issues, global health, and science. Her work has been published in The New York Times, NPRBBC, The Guardian, Hakai Magazine, Ensia, Al Jazeera, South China Morning Post, and many others. You can see more of Thiagarajan’s work on her website.





Dhritiman Mukherjee

Dhritiman Mukherjee

Dhritiman Mukherjee is a renowned nature photographer based in India. He has received numerous national and international photography awards, including the 2014 RBS Earth Hero Award and the 2013 Carl Zeiss Conservation award. Mukherjee’s photos have been published in National Geographic, The New York Times, The Guardian, BBC, and Lonely Planet, to name a few. He typically spends 300 days a year in the field, capturing photos in a wide range of habitats, from deserts and rainforests to mountaintops and rivers. Mukherjee recently published a book titled Magical Biodiversity of India.

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