Florida's Asian Swamp Eel
A group of scientists goes hunting for an aquatic interloper that's posing a serious new threat to south Florida's troubled ecosystem.
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.
I GREW UP ON THE EDGE OF THE EVERGLADES AND HAVE spent much of my career writing about them. I've been lucky to touch a Florida panther, examine crocodile nests, swim with manatees, and canoe past alligators.
A half-century ago, my dad and I liked to drive into the Everglades in his faded blue Nash, park in the weeds, and fish for largemouth black bass, catfish, and bluegills. True, we kept our eyes open for water moccasins and gators, but at least they belonged here.
When Leo Nico invites me on an eel hunt, I have mixed feelings that include both curiosity and revulsion. To my dismay, his hunting grounds turn out to be Snake Creek, a canal where my brother and I used to fish as teenagers. The waterway is within cheering distance of Pro Player Stadium, where the Florida Marlins and the Miami Dolphins play.
I watch Nico and a dozen researchers climb into a boat outfitted with an electroshock fishing unit. They use electrodes, hanging from poles like strands in a mop, to zap the water with 800 volts of electricity. When the dazed fish surface at the bow of the boat, twirling in unison, Nico scoops them up with a net.
On the bank, he dumps his catch into a variety of containers. He has stunned a handful of native largemouth black bass and bluegills, which he returns to the water alive. But much of his catch, creatures now reproducing in south Florida, originated in foreign lands.
Assistants scour the containers for eels. They don't have to look long. Round and muscular, the wriggling creatures are almost impossible to hold. They don't bite; they simply slither and squirm in their efforts to escape. "I just got slimed," cries a helper, hands dripping with the mucus that the eels excrete. "Don't drop the eels into the grass!" Nico shouts. "They'll slip right back into the canal."
A mustachioed lab technician dressed in a butcher's smock clips a small portion of each eel's tail and hands it to Tim Collins, a geneticist from Florida International University. Collins, who studies eel DNA, recently discovered that the Snake Creek eels originated from Chinese stock.
Warming to the task, the technician—after anesthetizing the eels—commences lopping off their heads and tossing them into a black plastic bag. Back in his Gainesville laboratory, he'll remove ear bones; rings in the bones can indicate an eel's age. The bodies are put in separate bags so the stomach contents can be studied to determine what the animals have eaten.
During the course of the day, the boat goes out once more and returns; fish are counted and identified. Somebody reaches into a bucket and withdraws—gasp, a human infant! No, just a discarded doll. "That's what's cool about south Florida," one scientist quips. "You never know what you'll come up with."
The dominant fish among all nonindigenous creatures in this catch is the Asian swamp eel. In one small section of canal—one canal among hundreds in south Florida—Nico's squad harvests 50 eels.
"We see the Everglades as a house of cards," says Bill Loftus, a USGS ecologist who has worked in the national park for two decades. "The house of cards might look stable, but we don't know what it'll take to make it fall apart. The eel could be it."
In their native lands, swamp eels don't overwhelm their environment. Everything is in balance; a variety of birds, animals, and reptiles are their predators. Natural parasites weaken them; diseases commonly kill them. But here in south Florida, apart from the occasional alligator, large fish or great blue heron, the eels have no enemies—at least none that scientists know about.
In a few months, Nico will bring his Gainesville team back to south Florida. They'll try to kill as many eels as possible in the canal nearest the park. Electrocution will be their weapon of choice, but the scientists are pessimistic that slaying even hundreds of eels a week will do much good. "Still, we've got to try," Nico says.
TOWARD DAY'S END, SOMEONE PULLS A YARD-LONG EEL from a bucket and asks if I'd like to get better acquainted.
I'm not squeamish. I've baited hooks, gutted fish, waded in thigh-deep mud, and plucked ticks from my own flesh. A swamp eel, after all, is like any living creature, just trying to survive.
But why here?
I stare at its slimy, dripping body, gaze into those beady, soulless eyes, and shake my head no.