Fish in Cauvery face the risk of extinction

A combination of factors, including extreme weather events stemming from climate change, habitat fragmentation and unregulated fishing, has placed many of the endemic fish species in the river Cauvery, which flows through Karnataka, Kerala, Puducherry and Tamil Nadu, at the risk of extinction, researchers say.

The fish at risk include the various mahseer species found in the river, including the giant hump-backed mahseer (Tor remadevii), which can grow up to 1.5 metres in length and weigh 55 kilograms. It is considered one of the 20 mega fish of the world.

Other fish species such as the red-tipped halfbeak, the slender stone loach, the mrigal, the Wayanad mahseer, the Korhi barb, the Nilgiri barb, the Nilgiri mystus, the Bhavani barb, the Cauvery barb, and the Nemacheilus pulchellus (which is so rare it doesn’t have a common name) are at risk of extinction as well.

“The Cauvery is subject to an intense range of anthropogenic impacts which act either independently or in combination to threaten the existence of fish populations and all aquatic flora and fauna,” Adrian Pinder, a fisheries scientist at Bournemouth University in England and director of research at the UK-based Mahseer Trust said in an emailed response to queries from HT .

“These include pollution, habitat destruction and blocked migration pathways, overfishing using illegal methods such as dynamite and poison, and alien species which are generally stocked intentionally by the fisheries departments.”

For example, the hump-backed mahseer was once found throughout the Cauvery, but today its distribution and population have declined by more than 90%, according to Pinder. The species was recently assessed as being critically endangered by the International Union for Conservation of Nature (IUCN).

Pinder added: “This fish is considered an umbrella species. If it is present, then we know that the water quality habitat and migratory pathways are good. Today we are aware of only two small spawning populations, both sited within tributaries of the main river Cauvery.”

Unlike large mammals or marine life, there are no dedicated protected areas for India’s freshwater fish species. In the Western Ghats, some 50 % of endemic fish species are threatened with extinction although the region is considered one of only two biodiversity hotspots in India, researchers say.

“Fish are not even considered as wildlife and protection is only restricted to the existing wildlife sanctuaries and national parks,” said Rajeev Raghavan, South Asia coordinator for the IUCN’s freshwater fish specialist group and an assistant professor at the Kerala University for Fisheries and Ocean studies (KUFOS).

Unlike the habitat of large mammals, the habitat of a fish species can spread across both protected and so-called ‘non-protected’ areas of the river and its tributaries.

Raghavan added: “Most endemic fish in the Cauvery is found in its upper reaches – places like Coorg, in the Cauvery’s tributaries such as the river Moyar, Bhavani and Kabini. The area from Shivasamudram to Hogenekkal also harbours populations of endemic and threatened species. The fish are mostly microhabitat specialists, restricted to specific areas of the river.”

Scientists say awareness creation among local communities and officials is essential to stave off the spectre of extinction of the Cauvery fish species.

“Improving awareness among local communities and frontline forest staff on ground enforcement to stop illegal and destructive fishing is required. Also, we need to demarcate ‘no-take zones’, close fisheries during the spawning seasons and begin to consider fish species in the management and environmental impact assessment plans associated with developmental projects,” Raghavan said,