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Florida's Asian Swamp Eel

Wayne Willison

Photo: Wayne Willison

The Everglades are the wild heart of Florida, home to cypress swamps, mangrove mazes, and wet prairies that stretch to the horizon. They supply south Florida urbanites and farmers with water, and are the lifeblood for countless plants and animals: indigo snakes, swallow-tailed kites, alligators, and North America's rarest large mammal, the Florida panther.

But the Everglades also shelter such interlopers as catfish from Africa that can crawl out of the water and creep through the grass after dark, and poisonous marine toads from the tropics that hop onto residents' back porches and gobble food from dogs' dishes. There are parrots from Honduras, iguanas from Central America, and armadillos from the American Southwest.

Now there's something worse.

It's called the Asian swamp eel, and it has few natural enemies in North America. Recently discovered in the canals that border the 1.5 million—acre Everglades National Park, these amphibious creatures could destroy the delicate ecological balance of south Florida's wetlands.

The olive-brown swamp eel, Monopterus albus, has a voracious appetite. It's particularly fond of minnows, tadpoles, and insects—the food supply for native fish, reptiles, amphibians, and birds.

Swamp eels are good at sex. In south Florida's mild climate, they mate year-round. A female may lay hundreds of eggs at a time. Like a few other aquatic species, the eels can start out as females and turn into males, ensuring the survival of the breed. They protect their young more aggressively than do native fish and have been known to eat the offspring of indigenous species.

Nocturnal predators, they can grow as long as three feet and are practically indestructible, which is the reason U.S. Geological Survey biologist Leo Nico can be found standing on a canal bank in North Miami with his team of scientists. "We don't want to be alarmist," says Nico, "but we're very worried about this animal."

Leo Nico is studying ways to eradicate the swamp eels, which reproduce at a rate that renders most control methods ineffective. Poisoning the water doesn't work; they poke their two-holed snouts out of the water and breathe fresh air. Explosives don't kill them; the shock waves can't rupture the eels' large air bladders. Draining ponds and lakes isn't practical. Even if it were, the eels would slither away after dark—across dry land—and find a new, wet haunt. "We're looking for a chink in their armor," Nico says, but he isn't optimistic. Thousands of Asian swamp eels are believed to live in the United States.

NOBODY KNOWS HOW THE SWAMP EELS GOT HERE, BUT experts can guess. As the headquarters for the nation's tropical fish trade, Florida is already home to more than a dozen alien critters that either escaped their cages or tanks or were set free. Among them are the ugly, brown South American armored catfish that are sold to suck algae off aquarium glass, but end up being flushed down toilets and into Florida waterways, where they grow to two feet in length.

Swamp eels, considered a delicacy in parts of Asia, are occasionally available live in Miami markets. Scientists suspect that the animals may have been deliberately released in canals to breed. They are suited to the environment, and it's also thought that they can tolerate extremes of temperature. "That means they could spread throughout the United States," Nico surmises. So far, a small population of swamp eels has been found in a pond north of Atlanta. Nico discovered another pack of eels living in a ditch near a tropical fish farm outside Tampa. The most recent population was spotted in a canal less than a mile from Everglades National Park.

The park, of course, represents just a small portion of the Everglades system, which actually begins with a chain of lakes near Orlando. The system then meanders south along the Kissimmee River, through Lake Okeechobee and the Shark River Slough, before flowing into the park.

The heart of the Everglades, known as the river of grass, remains largely untouched. Some 50 miles long and 30 miles wide, it can be a couple of feet deep during the rainy season or bone-dry in winter. No eels have been found in the river of grass. If they should arrive, however, they'll be in swamp-eel nirvana, where the food supply is abundant and the grass provides a perfect place to reproduce and hide. They could even survive droughts by burrowing into the mud.

As an experiment, Nico once kept a live eel away from water and food for a month. "It did just fine," he says.

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