Warming waters spell trouble for Gangetic species (Indian Express 25 July 2010)

As global warming takes its toll, the fish biodiversity in the Ganges is not left untouched. The effect of the change in climatic conditions on the Gangetic fish surfaced significantly in a recent study undertaken by the National Bureau of Fish Genetic Research (NBFGR), Lucknow. The study was aimed at evaluating and mapping the fish biodiversity of the Ganga.
A first of its kind project for documenting the species and estimated fish population in the Ganga, the study was done over three years between April 2007 and March 2010 throughout the length of the river. The results of the project reflect the shift in the bio-geographical distribution of the fish in the river bed. “Fish, being cold blooded animals, have to change their habits with the change in temperature. We found many interesting changes in the distribution of fish. For example, we found that the eel, which is generally a warm water fish, had found a habitat in the cold water zone of the Ganga between Haridwar and Tehri Garhwal in Uttarakhand,” said UK Sarkar of NBFGR. The research was led by WS Lakra, Director of NBFGR, and six other scientists including Sarkar, Ajay Pandey, AK Pathak and AK Pandian of NBFGR were involved. “Similarly, the Common Carp, which is an exotic variety, and the native Tank Goby, both of which are known to be warm water fish, were found thriving in cold water zones,” added Sarkar.
The 1,000-km length of the river has been divided by scientists into the upper zone, which is the cold water zone, from Gangotri till Haridwar, the middle or the northern plane zone, from Haridwar to Ballia, and the lower zone, from Patna to Hooghly in Kolkata where it meets the Bay of Bengal.
“Mahseer, or the Tor species, a cold water fish, is now amongst the endangered species of the area, with a population of less than one per cent of the total fish population in the area. The ray finned fish of the Himalayas, called the Snow Trout, is also endangered,” Sarkar said.
“Strangely, not only are the warm water fish shifting to cold water, one species of catfish, Glyptothorax brevipinnis, commonly called Nau, usually found in the upper zone of the river, was found in the warm water zone in the river Ken in Madhya Pradesh, which is a tributary of the Yamuna,” Sarkar said. “Also, marine water species like the Panna microdon croaker were found thriving in the Ganga in Patna, Munger and Rajmahal in Bihar.”
The study also noted that a number of species matured much earlier than their usual cycle. Amongst the fish with altered biological cycles were Nandus and Tengara from Allahabad, fresh water murrel of Kanpur, and Pirohia or Aspidoparia and Vachwa or Vacha in the Patna region. Scientists fear that early maturity might lead to loss of progeny of these fish.
Another warning bell is the replacement of indigenous species of fish in the Ganga by exotic species. The reason, say experts, is the lack of a quarantine law which allows the entry of foreign species in the river bed the consequences of which can be grave. Talking to The Sunday Express on phone, RK Sinha, an ichthyologist at Patna University, with whose help the project was completed, said, “In 1993-94, when I surveyed the river in Patna, there were hardly any exotic species. Today, more than 15 per cent of the total fish catch is of the exotic variety. Also in 1993, the total species in the Ganges at Patna was 106 ; today it is only 99. About 15 species out of the earlier 106 have disappeared completely, replaced by seven or eight new species.” Similar conditions prevail in Allahabad where 50 per cent of the catch was found to be of exotic variety, said Sinha. “Species of major Indian carp like Rohu, Catla and Mrigal, are only 8 per cent of the total fish population now and are fast being replaced by exotic varieties like the Silver Carp, the Common Carp and the Grass Carp, which together form 60 per cent of the fish catch today. Thai Mangur and Tilapia are other major species which are fast outnumbering any other species as they do not allow others to survive in the water,” he said.
The study traced a total of 143 species in the Ganga. Of this, 10 are exotic species and at least 29 are threatened. The most common fish in the Ganga belong to the Cyprinids family, including the carps, constituting more than 50 per cent of the fish population. Catfish were the next most common fish with more than 15 per cent of the population. “For the first time, we reported Southern Sailfin Catfish in Indian waters in Patna during the study. This variety is common in aquariums but is not healthy for fresh water habitation as it threatens indigenous species,” Sinha said. In the northern plains, the Devil Catfish or Gonch, Butterfish, Chital and Catla are on the brink of being classified as endangered while the Gangetic Shark have become extinct, said Sarkar.