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As bullfrogs spread, Venezuela jumps to a variety of solutions

MERIDA STATE, Venezuela -- People here have traditionally hunted armadillos and large rodents. Recently, they have set their sights on a new target -- bullfrogs.

 

Thousands of frogs have invaded streams, puddles, and cattle ponds in this bucolic hill country near the northern tip of the Andes mountains. The creatures gaze happily out of ponds, startle schoolchildren by plopping into roadside gullies, and fill the once-quiet evenings with loud croaking.

The frogs have made the biggest splash with environmental officials.

"This frog eats anything which fits in its mouth," said Yolanda Herrera, head of the bullfrog-eradication effort for Merida's Environment Ministry. "It is going to finish off our [biodiversity]."

The North American bullfrog (Rana catesbeiana), native to the East Coast of the United States, is several times larger than native yellow frogs. Full-grown adults can grow to 8 inches long and weigh as much as 3 pounds. The invaders are wiping out native amphibians, officials say.

In ponds inhabited by the bullfrogs, "there's nothing else" alive, said National Assembly Deputy Julio Garcia, who visited frog territory recently. "These frogs have an incredible reproductive capacity."

Since they were first reported here in October 2001, the frogs have colonized about 30 ponds and small lakes. In the warm climate and with few predators, they are spreading steadily, doubling their territory over the past year.

The frogs may seem like a minor nuisance for a nation afflicted by such environmental problems as deforestation and widespread water pollution, not to mention a political controversy over the rule of President Hugo Chavez.

But Venezuelan officials worry that they will unleash a large-scale environmental calamity if they reach Lake Maracaibo, South America's largest lake, 40 miles north, which is connected by three streams to bullfrog territory and which abuts fragile wetlands.

Merida isn't alone in its struggle. The bullfrogs have also spread to areas in Europe, elsewhere in South America, and parts of the western United States.

Amelia Diaz, biology professor at the University of the Andes in Merida, made the first official report of the frog's presence in October 2001. She says the species is "an extremely adaptable animal with great tolerance for adverse environmental conditions. It can live off of anything."

Diaz said humans had transported bullfrogs worldwide with hopes of breeding them for sale and by accidentally capturing tadpoles while collecting ornamental fish.

Venezuelan officials have gone to great lengths to wipe out the frogs: dropping explosives into frog-infested ponds, zapping the water with electric shocks, pouring in calcium bicarbonate and chlorine, shooting frogs with rifles, netting larvae and eggs, and even draining ponds. But a few always survive to repopulate and spread. A single female can lay more than 10,000 eggs at a time, biologists say.

The latest strategy for dealing with the frogs is a Ministry of the Environment's bounty offer. Posters around Merida State promise 1,000 bolivars, or about 50 cents, per dead female frog, half that for a male, and about 15 cents a kilogram for tadpoles.

The rewards are welcomed in a region where ranch hands earn about $2.50 a day. So far, officials have paid $1,640 in bounties for more than 4,700 frogs and 10 kilograms of tadpoles.

Some say the bounty program has a downside. Andres Chacon, who is helping coordinate a bullfrog-eradication program with the Environment Ministry and a local university, said he worries that the bounty will worsen the problem by encouraging locals to breed new frogs and then sell them to authorities.

"When you put a price on them, rather than eradicating the frogs, the people have an incentive to preserve them," he warned.

Others are concerned that residents will develop a taste for frog legs and want to protect them. Officials said they suspect somebody may have imported the frogs and planned to raise and sell the legs for food.

Most locals point to Pablo Celis, a wealthy landowner in whose pond the frogs were first reported. Celis denies the allegation, saying he discovered bullfrogs in his cow pond when he bought his ranch 15 years ago.

Frog eradicators are guardedly optimistic about the prospects for halting the spread of the bullfrogs. But local residents have doubts. "How can they eliminate them?" asked ranch hand Victor Fonseca. "Kill one, and a hundred more are born."

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