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Alien invasion poses threat to biodiversity cover

Alien invasion poses threat to biodiversity cover
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First Published: Mon, Jun 21 2010. 07 51 PM IST
Updated: Tue, Jun 22 2010. 09 44 AM IST
New Delhi: This fish eats birds. It can breathe out of water. And sometimes, is even known to walk on land.
The African Mangur, as its name suggests, isn’t native to India. It took Anoop K.R. a year to rid his beloved Keoladeo National Park of this ravenous invasive fish. The bulging bellies of the fish made him suspect that they were eating birds; a few dissections confirmed his worst fears.
“Now we have managed to clear 92-95% of the fish. But it is a continuous process,” says Anoop, director at one of India’s best known bird parks.
The recent drying up of the Sultanpur Lake in Gurgaon’s bird sanctuary of the same name, which killed most fish living in the lake, including the African Mangur, may have provoked a sharp response from some environmentalists, but experts and forest department officials maintain that this is a natural cycle—and in this case, one that could actually help the park rid itself, albeit temporarily, of an invasive species.
Click here to view a slideshow on how alien species are threatening local eco systems
“In India, what we don’t understand is that there are various kinds of wetlands. Monsoonal wetlands need a dry shock in summer. While not all wetlands need to dry up, Sultanpur Park has tubers, weeds, all of which need dry shock—and it blooms again post-monsoon,” said K.S. Gopi Sundar, research associate with the International Crane Foundation, who works in the area of wetland ecology.
Sundar adds that this is also the time when, for instance, heron chicks leave the nest but are yet to become experts at hunting fish. “The shallow waters at this time make fish more accessible to the chicks,” explained Sundar. A report in the Hindustan Times said the Sultanpur Lake has all but dried up with hundreds of surviving fish teeming in the remaining patches of water.
And even should all these fish die, you won’t find too many people shedding a tear for them.
It still isn’t clear how the African Mangur entered India. Scientists and experts say it was brought in illegally for aquaculture from Bangladesh some 15 years ago. A 2006 paper in the Journal of Ecophysiology and Occupational Health says the Mangur, a kind of catfish, entered some reservoirs and rivers such as Ganga, Yamuna, Sutlej and Godavari.
This invasive species poses a serious problem to Bharatpur’s Keoladeo Ghana National Park because of its ability to crowd out local fish species. That reduces the food base for water birds; and some of the African Mangur grow large enough to prey on birds themselves. Scientists say when invasive species are introduced, it disturbs and distorts the ecological balance.
“The introduction of African catfish has brought about significant loss to indigenous fish biodiversity. In Bangladesh it has been reported to deplete 56 fish species,” the 2006 paper adds. One of the reasons this fish has been used in aquaculture, Anoop says, is its ability to grow rapidly. “It can grow up to 2 kgs in a few months. (And) unfortunately, it already exists in most wetlands by now.”
The African Mangur can adapt very easily and can shift its diet depending on availability of food. Worse, it has the ability to survive a dry spell. Like most fresh-water fish, the Mangur does this by laying eggs in river-beds; the eggs survive dry spells and hatch with the first rains.
The Keoladeo wetlands also dry up summer. The monsoon refills the park before the arrival of migratory birds from the north in September-October.
“This shows the fascinating evolution of the species for systems like this, which are supposed to dry up seasonally. In Africa, they can even wriggle from wetland to wetland on their fins,” says Sundar.
The African catfish was banned by the ministry of agriculture in 1997. It ordered immediate steps to destroy the existing stocks of exotic Mangur that was introduced in the country without official sanction. The order was challenged in the Kerala High Court, but the challenge was dismissed after consultations with the Central Institute of Fisheries Education. The court order said the decision to introduce any exotic species into the system cannot be taken in isolation based on factors such as high yielding capacity or market value alone, and that other factors especially its impact on the native species and on the ecosystem had to be paid due attention. The National Committee on Exotic Species has already declared the African Mangur a “dangerous invasive”.
Protected areas across the country are fighting battles, sometimes losing ones, with invasive species, which have been introduced either by design or accident. The African catfish, and plants such as water hyacinth, lantana, parthenium are all invasive alien species. They were introduced with apparent ease, but biologists across the country are now struggling to find ways to cleanse ecosystems of these alien pests.
Innovative ideas and a balanced approach helped Anoop clear Keoladeo of another intruder, Prosopis juliflora, locally known as vilayati babul (foreign babul). The species were introduced in 1950s to combat desertification. A hardy plant, which grows in arid conditions, seeds were aerially scattered using helicopters in the dry belt of Rajasthan, which is probably how some landed in Bharatpur. Like the catfish, this plant does not allow anything else to grow and kills everything under it.
The Keoladeo park’s management, however, focused on one of the plant’s positives, its firewood value for the neighbouring villages. “Firewood demand is high here. And this (plant) provides fuel-wood. There is a good part. Every year we remove it and give it to eco-development societies, which fulfil firewood demand for 15-16 villages with 300-400 families each,” said Anoop, who pays labourers to clear forests of this plant using funds from the Mahatma Gandhi National Rural Employment Guarantee Scheme.
But not all alien invaders are harmful. The Mexican beetle, has been used to remove another alien species, parthenium (a weed), which entered India through contaminated wheat imports. The bicoloured beetle has a fetish for the weed, which almost all of India is fighting.
While there is no real threat of the beetle going native, there is always a risk with invasive species, says Sundar.
“It’s kind of like Russian roulette. We don’t know what will happen,” he said.
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First Published: Mon, Jun 21 2010. 07 51 PM IST