The species is restricted to a few stretches of rivers in Karnataka and Tamil Nadu
Known to be among the “largest and hardest fighting freshwater fish in the world”, the majestic hump-backed mahseer (Tor remadevii), once a prize catch for anglers, is on the verge of extinction.
In fact, the Moyar, flowing through the Mudumalai and Sathyamangalam Tiger Reserves, is one of the last strongholds for Tor remadevii, known as the “tiger of the Cauvery river”.
Once seen in rivers across the Cauvery basin, the mahseer, also known as the orange-finned mahseer, is now restricted to a few protected stretches of rivers in Karnataka and Tamil Nadu. The International Union for the Conservation of Nature (IUCN) has listed it as being “critically endangered”.
Recent surveys done by the Wildlife Association of South India (WASI) indicate that the population of the species in the Moyar is likely to be genetically pure owing to its isolation. “The chances of hybridisation of Tor remadevii is higher in the main Cauvery river where different species of the mahseer could interbreed,” said Naren Sreenivasan, a conservation biologist of WASI, which has been working on protecting the species for the last half-a-century.
Mr. Sreenivasan estimates that Tor remadevii is functionally extinct along 90% of its home range.
The hump-backed mahseer need to swim upstream during rains to spawn along rocky riverbeds. The construction of dams along many parts of their habitat could have played a part in their decline, conservationists said.
While dams and reservoirs could have contributed to their decline elsewhere in the Cauvery basin, the isolation of the Moyar population, caused ironically by the Bhavani Sagar Dam on the one side and the Moyar falls on the other, could have helped to keep the other introduced fish species from competing with the mahseer. “The Moyar, between Thengumarahada, Mangalapatty and the power station, is one of the last pristine habitats for the mahseer. The absence of invasive and introduced fish species here could be another reason for its being a stronghold for the species,” WASI honorary secretary Sandeep Menon said.
Threats in the Moyar
Threats to the mahseer need to be minimised along the Moyar, according to conservationists. “It is clear that non-protected areas cannot support mahseer populations,” said Mr. Sreenivasan. Conservation efforts should include sensitisation of local residents to the need for selective fishing, talking them into releasing the captured mahseer back in the river.
The Tamil Nadu Forest Department is working with the WASI to study the hump-backed mahseer population to aid in their conservation.
“The Tamil Nadu and Karnataka Forest Departments have been incredibly supportive in conservation efforts. The next step would be to get them to include the species in their conservation plans and ensure intervention strategies, based on research, to bolster the existing populations,” Mr. Menon said.
As the species faces extinction, more direct intervention strategies, including captive breeding, may need to be formulated, conservation biologist A.J.T. Johnsingh said. “We need to look into whether there could be a breeding programme for this species in Thengumarahada village…,” he said.