New research shows that India’s ambitious Interlinking of Rivers (ILR) programme can spread invasive, alien fish to waterbodies that are home to endangered fish species, posing ecological, economic, and livelihood threats. ILR envisages 30 connections amongst some of the major Himalayan and peninsular rivers through a countrywide network of canals, reservoirs and channels, to manage water shortages and floods.
The threatened environments listed by the new study published in The Environmental Monitoring and Assessment include the biodiversity hotspots of the Western Ghats, northeast India and the Sundarbans delta.
“India’s proposed river linking projects … may cause homogenization that may threaten our native and endemic freshwater biota,” noted M. Nobinraja of S. M. Sehgal Foundation Centre for Biodiversity and Conservation, Ashoka Trust for Research in Ecology and the Environment (ATREE), Bengaluru and colleagues, in their new study.
“Predominantly introduced for food, pet trade and biocontrol, these species wreak havoc in the invaded areas,” Nobinraja told Mongabay India.
Threat to biodiversity
Invasive species affect biodiversity and ecosystems by increasing competition for food and taking up space which, coupled with changing biotic environments, habitat degradation and pollution, often negatively affects native species populations. In the case of invasive fish, which may display aggressive territorial behaviour, it can cause a decline in the number of native fish, which in turn, affects fishing livelihoods. Globally, habitat destruction, increasing aquaculture and the introduction of ornamental species are altering freshwater ecosystems.
Researchers and co-authors of the study, Nobinraja, N. A. Aravind and G. Ravikanth used species occurrence records with select environmental variables and deployed species distribution models to identify, map and assess trends in biological invasion.
“Our study looked at how these alien species are invading newer areas and how they might spread in the future in rivers and lakes. We explored the plans to link rivers in India and found they might make matters worse,” said Ravikanth, Senior Fellow, ATREE.
About a third (31%) of the total area in India provides suitable habitat for invasive alien fish, the study found. The major river basins of Pennar, Kaveri, Godavari, Krishna and Mahanadi that spread across central and southern India were found to be highly vulnerable to invasion.
Aliens have landed!
The authors modeled the current distribution of 12 alien fish identified by the Centre for Biodiversity Policy and Law (CEBPOL) and the National Biodiversity Authority (NBA) of India. They are Cyprinus carpio (common carp), Clarias gariepinus (African catfish), Gambusia afnis (western mosquitofish), Gambusia holbrooki (eastern mosquitofish), Hypophthalmichthys nobilis (bighead carp), Oreochromis mossambicus (Mozambique tilapia), Oreochromis niloticus (Nile tilapia), Poecilia reticulata (guppy) and four species of Pterygoplichthys (sailfin catfish) – pardalis, multiradiatus, disjunctivus and anisitsi.
Gambusia, native to the USA and Poecilia from South America are widely used in mosquito control. Pterygoplichthys are popular ornamental fish. The rest are from different East European, African and Asian countries and are grown in aquaculture farms in India. Gambusia has shown the highest area of occupancy in the study. It covers over ten times more area than Pterygoplichthys. However, Pterygoplichthys has the highest potential for range expansion in a changing climate. Range expansion denotes how a species spreads in new geographical areas.
Hypophthalmichthys nobilis, native to China, has a suitable habitat in the Narmada, Mahi, Mahanadi, Kaladan, Irrawaddy, Godavari, Ganges, and Damodar river basins, the study showed. Nobinraja and colleagues warn that the Manas-Sankosh-Tista-Ganga link leading to the Sundarbans delta of Ganga and Brahmaputra could make one of India’s most important biodiversity hotspots that support the livelihoods of thousands of fishers vulnerable to biological invasion.
Spreading through links
The Subarnarekha-Mahanadi link that connects with southern India can expose threatened and endemic species to alien species. Krishna and Kaveri (Cauvery) basins are also crucial areas for endemic and threatened fish species according to the study.
The Kaveri-Vaigai link, Pamba-Achankovil-Vaippar link and the Netravati-Hemavati link that connects the west-flowing rivers with the Kaveri and the link between the Bedti and Varda can make the endemic and endangered species vulnerable to invasion, the study added.
The ATREE team also looked at future biological invasion patterns under different climate scenarios projected till 2100. In the minimum greenhouse gas emission scenario (denoted as Representative Concentration Pathways or RCP 2.6), the Gambusia and Poecilia reticulata species might further spread towards southwestern and northeastern India, projects the study. There would be a 2% reduction in niche suitability for invasive alien fish under this scenario. However, the study found a 91% increase for all the 12 species, under the maximum greenhouse gas emission scenarios (RCP 8.5).
“Interbasin water transfers such as river interlinking are recognised as major pathways for the expansion of aquatic invasive species,” P. R. Jayachandran, a coastal-marine ecologist who has studied the invasive species in the Kerala backwaters, told Mongabay India. “These efforts can have aggressive and detrimental effects on waterways as they tolerate a wide range of environmental conditions, compete with native species for resources, reproduce rapidly and prey on native species, leading to a loss of biodiversity and disruption of food webs.” Invasive alien fish can also impact human and animal health, Jayachandran added.