Degrading quality of natural water bodies and rivers, coupled with climate change, could set the stage for alien (invasive) species to multiply and alter aquatic flora and fauna in biodiversity hotspots, warned scientists, documenting alien fishes in the Western Ghats.
In a paper, scientists at the University of Kerala reiterated concern over the expansion of alien, or non-native species in biodiversity hotspots triggered by extreme climate events, such as the flood-driven release of alien species from illegal aquaculture in Kerala.
“In India, there are no specific policies to address the issue of invasive alien species (IAS), though it is part of several existing biodiversity legislation and regulations,” explained Smrithy Raj, lead author of the paper and a PhD student working on alien species at the university.
The researchers call for monitoring tools such as environmental DNA to keep tabs on these hardy non-native species in Indian waters. Gaps remain in the countrywide assessment of impacts of IAS on the economy, biodiversity and food security. There is a need to better understand the factors that trigger alien species to become invasive, experts said.
Invasive alien species are species that are introduced, accidentally or intentionally, outside of their natural geographic range and that become problematic, states the International Union of Conservation of Nature. For a species to become invasive, it must successfully out-compete native organisms for food and habitat, spread through its new environment, increase its population and harm ecosystems in its introduced range, states the Convention on Biological Diversity (CBD).
High magnitude floods in August 2018 and 2019 resulted in the escape of at least ten alien fish species that were recorded for the first time in the water bodies and rivers snaking through the Western Ghats, following the floods.
The future management of IAS should consider and integrate climate change as a major factor, adds Bijukumar, another co-author of the study, sharing that “we need to come up with strong policies on importing dangerous (large-growing carnivorous) fishes such as arapaima and alligator gar into the country.”
Bijukumar, professor and head of the university’s Department of Aquatic Biology and Fisheries adds that many existing farming and rearing systems have very little biosecurity related infrastructure to prevent the escape of captive fish into adjoining natural ecosystems during floods and ECEs. The issuance of specific guidelines by state fisheries departments and other environment and biodiversity agencies is needed.
Most of the alien species that enter India are principally for ornamental trade. West Bengal is the largest ornamental fish producer in India, followed by Tamil Nadu; the trend is catching up in Kerala, fanned by a swelling rank of aquarists, many of who are not aware of the potential pitfalls of dumping exotics in water bodies, after they exceed the length of their tanks.
Identify invasive species
A list of IAS compiled by the Centre for Biodiversity Policy and Law (CEBPOL), National Biodiversity Authority (NBA) and updated in 2018 identifies 169 species as invasive. The Zoological Survey of India under India’s environment ministry has listed 157 animal species, including 99 marine species as invasive and 19 species of freshwater fishes.
S. Sandilyan, fellow at CEBPOL, who led the IAS list compilation, suggested a mapping exercise of aquaculture farms in flood-prone areas so that aqua-culturists can be advised to prohibit the culture or stocking of alien varieties in the flood/monsoon season, as a stop-gap measure.
Researchers note that many local community members, residing near beels (flood-plain wetlands) in Assam, grow the carnivorous African catfish (Clarias gariepinus) in their backyard drain or nalas, feeding them with household sewage and that it has a “great chance” to escape to the nearby beels during the flood or heavy rain. The Indian government banned the breeding of the species in 2000 but the practice still thrives in many parts of the country.
In Manipur, the recent reports of the emergence of Amazon sailfin catfish in water bodies have concerned experts. Ichthyologist Rameshori Yumnam based at the Manipur University also attested to the accidental release of exotic fishes from aquaculture farms to rivers, during floods.
For the fisherfolk community, based in the East Kolkata Wetlands, considered as the world’s largest wastewater fed aquaculture system, where city sewage feeds traditional practices of aquaculture and agriculture, the suckermouth catfish is of particular concern.
“We first came to know about the suckermouth catfish in the wetlands around 20 years ago. Since then, they have expanded exponentially. They have a spiny exterior that injures the native fishes that we cultivate in our ponds and they modify the pond ecosystem, so that other organisms cannot survive properly,” 53-year-old fisher Shyamal Mondal told Mongabay-India.
Sneaking their way through sewage feeder canals, the fish embraced the shelter and breeding refugia provided by water hyacinth, another invasive aquatic species that was introduced to India by the British in the 1890s.
Mondal and his fellow farmers have been trying to innovate to control their populations but nothing seems to work. They are usually averse to consuming the fish; setting up bamboo fences and netting to stop their spread hasn’t borne fruits – the hardy fishes disrupt the barriers with their spiny bodies.
More exotic than native
It is also important to understand when to declare a species as invasive. “All aliens (species) are not invasive species, but all invasives are aliens. Most aliens are in a lag phase in India (adjusting to their environment); we have to examine what kind of environmental factors trigger them to be invasive.
Given the multifaceted nature of the problem, Sandilyan feels a shift in tone is inevitable, i.e., a new law or regulation on IAS management is crucial; but that would entail attention to a few focal points and having an implementing/monitoring agency is necessary. “One is strictly regulating ornamental species trade, both online and conventional. We have to educate pet owners to be more responsible. If you want to introduce a species in India, we have to develop indigenous risk management tools/kits. We have to stop the introduction of alien aquaculture species and also plants,” he added.
India’s share in the global ornamental fish trade (export) is less than one percent. The majority of fish breeders in India breed exotic fishes and very few breed indigenous fishes. Over 300 exotic species are believed to be integral to India’s ornamental fish trade. (TWF)