Historical misidentification, release into wrong areas as well as dam construction, all are imperilling this most iconic of Asia’s freshwater fauna
During the most recent broadcast of Mann Ki Baat by Prime Minister Narendra Modi, he detailed the discovery of a remarkable fish. “Meghalaya is home to a rare species,” he said. The blind mahseer is one of several Indian species of this most iconic of Asia’s freshwater fauna and, currently, the world’s largest subterranean fish.
My colleague, India’s leading fish taxonomist Rajeev Raghavan from the Kerala University of Fisheries and Ocean Science, was involved in assessing this fish and declared that it had many similarities with the golden mahseer, Tor putitora.
He cautions that “the genetic analysis is not complete and relying on morphology alone has resulted in several, historical mis-identifications.”
Daniel Harries of Heriot-Watt University, Scotland, the leader of the cave study and subsequent paper said: “We have a fish that is more than 10 times bulkier than other species of cave fish.”
The study of the ecology of wild mahseer is an area that lags behind other biological studies. “This throws up all sorts of questions such as what food source sustains them. We don’t have any clear answers for this yet; it is all very intriguing.”
This echoes PM Modi’s words: “The more you know, the more you realise the magnitude of what you do not know.”
Particularly in regions like India's North East, where there are several species of mahseer that are not described, or mis-identified, sometimes with devastating ramifications.
Gain one, lose two?
Even as we celebrate what is either a new species, or one well down the evolutionary route to speciation, we face losing others. Rampant and unbalanced development, along with unregulated releases of various native and non-native fish place pressure on vulnerable species including the International Union for Conservation of Nature (IUCN) red listed — ‘endangered’ — golden mahseer.
Recently, I was given access to a set of data starting in the mid-1980s, through to 2015, from a series of large-scale surveys of fish population and diversity.
These studies were carried out on the Gandaki River of Nepal by the Peace Corps programme, with Emporia State University professor David Edds, initially, and then David Gillette, associate professor at University of California, Asheville, with local field biologists in support.
This data paints an alarming picture for one species of mahseer, probably Tor tor; the fish from which the entire genus takes its name.
In common with many species, we have to rely upon the original painting by 18-year-old Bengali artist, Haludar, who provided the illustrations for British colonial naturalist Francis Hamilton's book on the Ganga river fishes, and the accompanying taxonomic description by Hamilton, for identification.
Since the publication of An Account of the Fishes of the Ganges, 200 years ago, there have been multiple errors of identification, compounded by repetition, to the point where only a comprehensive study in type localities can correct these discrepancies.
What we can say is that this fish is in catastrophic decline. This is just one study on one tributary of the Ganga basin, but anecdotal evidence says that numbers are falling in others.
Worse, in places where these fish are to be found, there appears to be no recruitment; populations are of large, old fish, with an apparent loss of spawning success.
This mirrors the decline of the largest mahseer of all, the hump-backed mahseer (Tor remadevii) of the Cauvery river. A poor spawning season was compounded by pressure from several decades of unregulated release of a different species of mahseer.
The mighty hump-backed mahseer never had a chance to re-establish itself and is now red listed as ‘critically endangered’, a status only one step away from extinction.
Luckily for the hump-backed mahseer, a team of scientists and field researchers from the Mahseer Trust, Bharathiar University in Coimbatore, Wildlife Association of South India and Coorg Wildlife Society managed to unpick the decades-old identification problems for this fish.
Once done, it was able to gain an IUCN Red Listing, opening up conservation possibilities. Tor tor, is currently listed ‘data deficient’ due to the identification issues, so no conservation plan can be prepared until the identity can be positively and correctly resolved.
For fish like Tor tor and the blind cave mahseer of Meghalaya, we must embrace the opportunity to discover more about them before it is too late.
“Send in your suggestions on lending more substance to this opportunity,” Modi told citizens at the end of his address. This is only part of the required agenda. Unfortunately, large scale, sometimes illegal activities are going on all around the Ganga and Brahmaputra basins where these fish live.
For a highly migratory fish like Tor tor, the massive dam construction project on the Sarda / Mahakali river at Pancheswar on the India-Nepal border, will surely spell the end of any hope that these fish may produce offspring.
Given that India is a net over-producer of electricity and that the Nepali side of this catchment has suffered four consecutive years of drought due to falling groundwater, this dam presents problems for fish and people alike.
In a country which, according to Modi, has a “boundless love for nature. All this is a part of our cultural heritage”, what biological cost is too high to pay for another intervention in a river’s natural process?
I mentioned earlier about mis-identification of fish in the North East. The Biodiversity Action Plan of Nagaland discusses stocking mahseer into the Tizu river, a tributary of the Irrawaddy that flows into Myanmar.
The native species there is called Tor yingjiangensis, another little-known mahseer and one easily confused with Tor putitora. Given that we have known for more than 150 years about the impacts of moving mahseer into places they should not be — Tor putitora taken to Bhimtal Lake in the Kumaon Hills in the 1850s wiped out the native ‘lesser mahseer’ Naziritor chelynoides — we cannot argue that such measures are taken in innocent ignorance.
We must follow Modi’s sage words: “our biodiversity is a unique treasure”, and set a new conservation agenda.
Steve Lockett is Education and Outreach Officer at the Mahseer Trust
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