Cauvery basin's iconic fish on the brink of extinction

The humpback Mahseer is a favourite of anglers and the introduction of non-native Mahseer has had a catastrophic effect on the numbers of endemic Mahseer

The legendary humpback Mahseer, one of the world's most iconic freshwater fish, is on the brink of extinction, researchers, including those from India, have warned.

Ever since the publication of H S Thomas's A Rod in India in 1873, this giant member of the carp family has been known to anglers around the globe as 'one of the largest and hardest fighting freshwater fish in the world'. With its distribution having always been limited to the Cauvery River basin, this fish is now believed to be so endangered it may be extinct in the wild within a generation, researchers said.

Adrian Pinder of Bournemouth University in the UK and Rajeev Raghavan of St Albert's College in Kochi have been studying the ecology, taxonomy and conservation status of 17 species of mahseer which populate rivers throughout south and southeast Asia from 2010.

Four of these species are already listed as 'Endangered' on the IUCN (International Union for Conservation of Nature) Red List.

The paper published in the international research journal Endangered Species Research demonstrates that the endemic humpbacked Mahseer is now on the brink of extinction having been replaced by non-native relatives (blue-finned Mahseer) which have been artificially bred and introduced to the river in the name of species conservation, researchers said.

The paper acknowledges that many pressures are placed upon fish of India's rivers, including pollution; poaching (using dynamite and poisons); sand and gravel extraction; low river flows due to abstraction; and India's continuing thirst for electricity, which has resulted in dozens of hydro-electric projects which restrict the ability of fish to migrate to their spawning grounds.

The research suggests that the introduction of non-native Mahseer has acted as the catalyst which has had a catastrophic effect on the numbers of endemic Mahseer remaining in the Cauvery river and its tributaries.

"In 2010 I made my first trip to the River Cauvery, where I realised the fish I was catching did not match the appearance of the iconic specimens I'd seen in historic photos," Pinder said. "Comparing photographs over the internet opened a can of worms and confirmed that very little was known about all of the Mahseer species found throughout south and south East Asia," said Pinder.

"As large monsoonal rivers are extremely difficult to survey, and angling was banned in all protected areas in India in 2012, I started to look for alternative data sources and discovered that the Galibore Fishing Camp (one of three former angling camps in the Karnataka jungle) had kept detailed angler catch records.

"This not only allowed us to analyse the temporal trends in population size over the previous 15 years but also form a detailed understanding of how the type and species of Mahseer had changed over time," Pinder added.