Saving a lifeline and a majestic fish

Every winter, the skies of Nepal welcome migratory birds, embarking on epic journeys from Siberian realms covering thousands of kilometers. Their graceful flights wow many hearts and minds. On a parallel realm, beneath the shimmering surface of the river, a similar marvel unfolds with the onset of monsoon (rainy season)—the migration of majestic Mahseer. Migration, a vital journey taken by animals regularly for a particular reason, usually at a particular time of the year, is an essential adaptation strategy for survival. Unlike bird migration, fish migration is intricately tied to the availability of free-flowing waters. This crucial journey is being jeopardized by a rapid development of hydropower projects and river modifications. These engineering feats, while harnessing energy and water resources, are disrupting the natural flow of the river, obstructing the Mahseer’s migration cycle and driving them toward extinction.

As the monsoon rains recede, a mesmerizing natural event unfolds in the rivers of Nepal. Freshwater fish embark on epic journeys, traversing hundreds of kilometers to reach their spawning grounds. This epic phenomenon is a critical part of many fish species’ life cycles, including the iconic Mahseer. Fish migration is the periodic seasonal movement between breeding and foraging grounds. This is an important cycle of life for most migratory fish species meant to prevent the extinction of species.

Mahseer, often referred to as ‘the tiger of the river’ (first used by conservationist Jim Corbett), symbolize Himalayan rivers. Mahi means ‘fish’ and sher, meaning ‘tiger’, and the word reflects their cultural, economic and recreational significance. These are apex species, which indicate the overall health of the ecosystem, just like apex terrestrial species such as tigers. They are important food fish and a delicacy for many indigenous communities. They are important game fish among anglers, for their strength, stamina and splendor. Mahseer undertakes awe-inspiring journeys, navigating rapids in search of critical spawning habitats. Golden Mahseer are listed as endangered on the IUCN Red List of Threatened Species.

Nepal rivers flow through varied ecological realms, hosting many indigenous, rare and endangered fish species. Unfortunately, the migration behavior of these species remains understudied and misunderstood. This knowledge gap has contributed to overlooking the impact of hydropower and irrigation projects. Recent reports from the Asian Development Bank (ADB) reveal that dam locations are selected without considering the cumulative impact on fish migration routes.

Most of Nepal’s river systems are already obstructed by dams, restricting seasonal fish migration to the upper reaches for spawning and feeding and returning. The consequences extend beyond the blockage of migratory paths, affecting water discharge downstream, breeding grounds, limnological parameters, nutrient flows and the overall ecological balance.

It is widely observed that the barrier effect is responsible for a sharp decline in fish populations in rivers with dams. Case studies from the Kaligandaki have revealed that populations of migratory species like Goonch, Raj Baam and Sahar have declined after the construction of the Kaligandaki A project (144MW). Similar is the case in other rivers. Government policies waiving environmental impact assessments (EIA) for projects up to 50 MW capacity have exacerbated the issue, impacting fish species without accountability.

The implementation of mitigation measures such as fish passages, environmental flow, restriction on fishing and sand mining from rivers is crucial for the conservation of fish species. Unfortunately, their effectiveness has been compromised by poor implementation and lack of monitoring. The correct choice of fish passage design is a critical factor, and needs to be tested for known fish species by fishery specialists. Engineers and environmental experts must find the best modifications that facilitate migration. Overlooking the migratory pathways is a mistake which is hampering the economy and ecological balance of aquatic systems.

Saving a lifeline

The Karnali river stands as a testament to the untamed beauty of Nepal's waterways. As the last free-flowing river in the nation, it holds a unique ecological heritage, providing sanctuary for a diverse range of species, including the revered Mahseer. The river supports habitat for 50 migratory species, including the Golden Mahseer and 24 species currently on the IUCN Red List for conservation.

Access to quality spawning habitats is vital for survival and productivity of fish populations. The uninterrupted natural course of the Karnali river provides pathways for migratory fish like Mahseer to spawn and thrive. However, the rapid development of hydropower projects and river modifications has cast a shadow over this pristine watercourse, threatening the very existence of its iconic inhabitants. If such happens, Mahseer and other migratory fish face insurmountable obstacles, jeopardizing their populations and causing a ripple effect of ecological disruption.

The Karnali, as the last free-flowing artery in Nepal, is not only a sanctuary for fish; it is the lifeblood of communities lining its banks. The annual migrations of fish hold profound cultural, historical and economic significance. They fuel local economies through activities such as angling, ecotourism and fisheries. Moreover, the presence of healthy fish populations sustains countless individuals, who rely on the river for their livelihoods.

Despite their ecological and economic importance, the Mahseer populations have witnessed dramatic declines. Overexploitation, habitat fragmentation and loss, and pollution pose significant threats. Destructive fishing practices and unregulated sand and boulder mining have further deteriorated the potential breeding grounds of the Mahseer.

Hydroelectric dams, touted as symbols of progress, inadvertently disrupt the natural flow of rivers, obstructing migratory routes. Reduced migration means limited access to crucial breeding grounds, leading to a decline in genetic diversity and overall Mahseer population. With each passing year, their numbers dwindle, pushing this iconic species closer to the brink of extinction.

The Mahseer are migratory species and rely on free-flowing rivers. Free-flowing rivers are the lifeblood of migratory fish species. The unobstructed waterways provide the essential pathways that allow fish to reach their spawning grounds, contributing to the sustainability and resilience of their populations. However, the rapid pace of hydropower development has threatened their survival.

The cost of decreased Mahseer and other migratory fish populations is not just ecological, it creates a domino effect of ecological disruptions, affecting the health of ecosystems, local communities, and cultural traditions of various indigenous riverine communities. 

Their annual migrations have become interwoven with local traditions, providing livelihoods, and enhancing the cultural fabric to the communities.  Mahseer are an important game species, thus communities can also make earnings through ecotourism and angling. Additionally, healthy fish populations contribute to the livelihoods of countless individuals dependent on the rivers. Their loss could lead to food security issues among fishing communities. Beyond their intrinsic value, conservation of Mahseer yields a multitude of ecosystem services, from balancing the aquatic food chain to supporting healthy aquatic and terrestrial environments. Once lost, restoring and conserving such obstructed habitats will be a costly process.

In conclusion, the preservation of natural river flows is not just an environmental endeavor; it is a pledge to safeguard the legacy of Nepal’s rivers for generations to come. Collaborative efforts between engineers and conservationists, along with prioritizing research, are essential for ensuring that future generations witness the grandeur of the Mahseer in Nepal’s rivers.