Climate crisis threatens survival of ‘Tigers of the River’

The ‘Tiger of the River’. pic: Julie Claussen

                       Tiger of the River will be only in photos down the line


The mighty Golden Mahseer, or Tor putitora also known as the tiger of the river, is of great reverence both spiritually and environmentally in Bhutan. For its survival like any other species, the whole majestic golden-scaled fish is battling against climate change and global warming.

Marine life is threatened by climate destabilisation and other anthropogenic factors making the mighty endangered freshwater river fish a vicious victim of climate change and human behaviours.

Karma Wangchuk, Deputy Chief Livestock Production Officer, specialising in fishery biology from the National Research and Development Centre for Riverine and Lake Fisheries (NRDCRLF) said that before 2015, no empirical data existed on the status of Golden Mahseer in Bhutan, except for the fact that they are a migratory species while they were found aggregated at certain points in our river system. 

However, almost nothing was known about mahseer biology, movement patterns, reproductive biology, critical habitats, and population status.

The current knowledge on Golden Mahseer from the wild has been greatly enriched by the information documented from the telemetry research conducted from 2015–2019 in the Manas River basin.

Biologists are using radio telemetry to track the mahseer in the wild to learn about their migration pattern, genetics and spawning.

The joint field research project using radio telemetry techniques on Golden Mahseer and Chocolate Mahseer conducted by Departments of Livestock and of Forest and Park Services (DoFPS) under Ministry of Agriculture and Forests (MoAF), World Wildlife Fund Bhutan (WWF), and the Fisheries Conservation Foundation (FCF), USA, found that the river basin has a thriving population of Golden Mahseer, that mostly remain in Bhutan and do not migrate into India.

It was also found that both mahseers have a consistent pattern of seasonal movements with upstream migration during the spring (starting in February) and downstream migration during the autumn season (October onwards) to overwinter in the lowest 8-10 km of the Manas River, with only a few moving into India.

David Philipp, Chair of FCF in Illinois, USA said Bhutan is the only country in the world where populations of masher can be found in a pristine environment.

Golden Mahseer and Climate Change

Fish biologists David Philipp and Julie Claussen, Head of Operations at FCF, states that climate change may have long-term effects on the species. They said all indications show the situation can be grim for the species in the future.

They said that the predicted increases in water temperature and a rise in water levels could change the pattern of the spawning migration of Golden Mahseer. 

The greatest threat to the fish population, according to Julie, could be caused by unpredictable and powerful monsoon seasons and creating extreme weather conditions in the future.

The two fish biologists also stated that if there is less rain keeping the river from flooding in a timely manner, that too would keep the fish from spawning, which would definitely be problematic.

Singye Tshering, Program Director for NRDCRLF said Golden Mahseer might be found to migrate further upstream and to higher altitudes as a result of the rising water temperature.

He said a change in climate pattern can also cause erratic and irregular rainfall, which can cause flash floods from glacial lake outbursts and landslides, which will ultimately cause a high mortality rate for aquatic species and the Golden Mahseer as well.

Similarly, David Philipp said that the flood caused by Cyclone Aila in 2009 is said to have drastically reduced the number of fishes and aquatic life across the country. 

According to Julie and David, the mahseer’s current spawning season lasts from June to September, but if glaciers melt and disappear in the future, the fish’s spawning season would likely be shortened.

Karma Wangchuk added that a few studies from India suggest that climate change may have already impacted the Golden Mahseer by reducing the spawning period. Those scientists compared the reproductive timing between 1981 and 2018 and those data indicated there has been a two-month reduction in spawning period.

That two-month reduction in reproductive span suggests the potential influence of climate change on the timing of reproduction in Golden Mahseer and similar problems may arise in Bhutan as well, but for now, there is no data, said Karma.

David said melting of glaciers is also going to change the hydrology of the rivers in Bhutan. “Their habitat needs during the spawning season could become tricky.”

He explained that in the future, if there is less snow cover and glaciers, it could result in shorter melting times, which could reduce the duration of the monsoon season and reduce the frequency of flooding of streams, tributaries, and the main rivers across the nation. A fish species annual recruitment (the successful reproduction of a year class) will decline as river flooding declines.

In 2019, a survey conducted by the DoFPS, as part of the Strategic Program for Climate Resilience preparatory project, found that 35 percent (2,317) of the 6,555 water sources surveyed were drying up, while two percent (147) were reported as ‘completely dried’. 

Further, over the last 10 years, almost 25 percent of Bhutan’s springs have either dried up or are experiencing diminishing discharge. 

If tributaries dry up or volume decreases, there will be a decrease in oxygen during the hot summer months, and the fish in that stream may not be able to survive in those hostile environments according to David. 

Climate change, according to David, will undoubtedly increase the mahseer’s susceptibility to human errors such as introducing non-native fish that will compete in the ecosystem and destroy or alter the ecosystem’s entire equilibrium.

“The introduction of foreign species into the ecosystem would put additional selection pressure on native species already present, such as Golden Mahseer, and make their survival more difficult”, David said.

The radio telemetry project of 2015-2019 revealed that of the two mahseer species in Bhutan, the Chocolate Mahseer was way more numerous compared to Goldens.

David and Julie hypothesize that the quantity of Chocolate Mahseer may be attributable to its position one rung lower in the food chain than the Golden, that the species may exhibit distinct spawning habits, and that their capacity for survival in nursery areas may also differ.

Anecdotal evidence from elderly residents of the country’s primary river basins describes how they used to see large numbers of Golden Mahseer in the river, but that this sight is now a thing of the past. The elders and others are perplexed as to why such an iconic species has declined.

Other anthropogenic factors impacting Golden Mahseer

Out of the 12 identified threats to Golden Mahseer conservation in the country, the ‘Golden Mahseer Conservation Action Plan for Bhutan 2022-2032’- identified illegal fishing, hydropower dams, and weak protection of spawning areas as the top three threats in the country.

Likewise, David and Julie also mentioned that there have been signs of a decline in the quantity of Golden Mahseer, with 50% of the tagged mahseer from the 2015-2019 study having been taken out of the ecosystem due to illegal fishing during the five study years.

Illegal fishing is one the dominant short-term threat, says David and Julie and they have mentioned that while travelling along the various river basins in Bhutan, they have witnessed illegal evidence of fishing like gillnets, fishing lines and hooks, traps and others.

Tshering Dorji, a senior forest ranger at Royal Manas National Park says, “It is very difficult to apprehend the offenders as they are always ahead of us. Due to the improved communication network of the offenders, they are very well aware of the rangers’ movement in the field.”

He adds that due to the geographical terrain of the country’s river system, it is very difficult to monitor the Golden Mahseer using traditional patrolling methods.

Julie and David have also mentioned that a dam built across a migratory fish’s migration route, that dam won’t allow the fishes to get to their normal spawning area, and becoming locked in a high thermal environment can be lethal to them. 

The fish ladders in the dams in Bhutan and across Asia are typically built for Atlantic Salmon, which jump up rapids. Because mahseer doesn’t jump, they are not of much help.

Hydropower dams are known to impact aquatic biodiversity in general, and particularly the migratory species, as it forms a physical barrier to their movement. “We know the fish are migrating to spawn, so when they cannot move upstream, they cannot reproduce, so the future population is disturbed,” said Karma Wangchuk.

Short term threats like road construction, sand mining, gravel crushing and pollution also put pressure on the species, said Julie and David.

Way forward, measures and mitigation

In order to better understand Golden Mahseer in Bhutan, the scientists hope to start a similar project of radio telemetry carried out in 2015-2019 in other parts of the river basins of Bhutan. 

“It would monitor spawning activities, the health of spawning, individuals and spawning-grounds, and track the migration pattern of adult Golden Mahseer. Whole tributary sampling of Golden Mahseer would also be carried out”, said Julie.

As a long-term strategy, David suggested that the government create community-based conservation programs and use recreational fishing to significantly reduce illegal fishing while at the same time aid in attracting tourists and generating revenue for the nation.

Community-based conservation initiatives have been launched by DoFPS, one of which is developing high-end Mahseer Recreational Fishing Program, being piloted by DoFPS, WWF-Bhutan, and FCF, USA.

Tshering Dorji, the forest ranger at Manas stated that although they do provide the necessary awareness to the fishing community along the river, for the mahseer species to thrive, the government or relevant agencies should allocate additional funds for educating the nearby villages about the significance of this species before it is too late. 

“Other-wise the Tiger of the River will be only in photos down the line,” Tshering said.

The Golden Mahseer is currently under Schedule list II of completely protected species of animals under the Forests and Nature Conservation Bill of Bhutan 2021. 

So, it cannot be harvested at any cost, and there are hefty penalties for doing so. Further, DoFPS is actively patrolling and monitoring the mahseer waters.

Additionally, the DoFPS has taken a proactive role in delineating the river systems in Bhutan into trout water and mahseer water using the elevation limit for mahseers to be 1000 metres above sea level. Furthermore, DoFPS has developed species-based regulations for these two water bodies.

It is also learnt that Hydro-power projects also allocate aquatic funds to preserve the water animals.

Karma Wangchuk said, “We have yet to learn and understand the impact of climate change and other anthropogenic activities on the Golden Mahseer population of Bhutan. We have just scratched the tip of the iceberg with our recent studies.”

He added focus should be on expanding studies into other river systems and focusing on critical habitat use in spawning tributaries, habitat use, and reproductive biology. A long-term monitoring program for Golden Mahseer as well as other aquatic biodiversity should be put in place to ensure sustainability and effective conservation of these species.

Julie said that the more intact the eco systems are, the more resilient will be the environment in this era of climatic change.

According to International Union for Conservation of Nature (IUCN), the Golden Mahseer is listed as endangered on the IUCN Red List of threatened species. 

David, however, said that even though it is possible that there has been a decrease in the number of Golden Mahseer compared to five decades or so, he reiterated that Bhutan still has the highest and healthiest Golden Mahseer populations around the world and in the Himalayan region.

David emphasised that spiritual and environmental conservation policy have contributed to the preservation of this endangered species in Bhutan.

He said, “People really need to realize that a live mahseer in the river is worth much more than a dead mahseer on the plate.”

Know the Golden Mahseer

The Ser Nya is what the Bhutanese refer to as the Golden Mahseer, and it is one of the eight lucky signs that symbolize good fortune. The fish thrives in parts of Bhutan, Afghanistan, Pakistan, India, Nepal, Myanmar, and Bangladesh. 

With thick golden scales, the Golden Mahseer has protrusible and large powerful jaws. Mahseer belongs to the bottom feed species as their lips adapted at the bottom for taking its feed and they grow fleshy.

Karma Wangchuk said that Golden Mahseer acts as an apex predator at the top of the aquatic food chain (feed on other smaller fishes and aquatic species) at least in Bhutan, and it shapes the ecosystem below them. Without a predator, the regulating forces change, and the entire food chain becomes altered, making the Golden Mahseer an extremely important target for conservation.

At the elevations of 100-1000 metres, the species can be found in all of Bhutan’s major river basins as well as the lesser Aie Chhu and Nyera Ama Chhu River basins.

Comparing it to other fish species in the country, the species has the most strength, and it can reach a maximum size of over four feet long and weigh 40–50 kilograms.

Of the 16 mahseer species found in South East Asia, the Golden Mahseer is the largest. There are two mahseer species found in Bhutan: The Golden and the Chocolate Mahseer, Neolissochilus hexagonolepis.

The story is funded by BMF’s project titled “Strengthening the capacity of Bhutanese Media for Climate Change Reporting,” supported by Canada Fund for Local Initiatives.