NANFA-- swamp eel strikes again

Christopher Scharpf (
Thu, 02 Mar 2000 19:13:37 -0400

USGS Scientists Find New Population of Asian Swamp Eels in South Florida

A new population of non-native Asian swamp eels, a highly adaptable
predatory fish, has been found near the eastern border of Everglades
National Park in the area of Homestead, Fla. According to the USGS
biologists who discovered this new population in December, the eels
appear to represent a separate introduction from previously discovered
swamp eel populations in Georgia, north Miami, and Tampa because of
the widely separated ranges and apparent genetic differences between
the Homestead population and the north Miami and Georgia populations.

The eels have not been found within Everglades National Park, although
the latest discovery places the eels within a kilometer of the park
boundary, said Dr. John Curnutt, a biologist with the USGS Florida
Caribbean Science Center in Miami, who is coordinating the monitoring
studies of this new population.

"These fishes have the attributes necessary to successfully invade and
colonize the Everglades and other freshwater southeastern wetlands,
where they could adversely affect native fishes, amphibians and
invertebrates through predation," said Curnutt. "They have the
potential to disrupt food webs, eat native species, and compete with
native fish and wading birds for food. The interconnectedness of the
waterways and the eel's biology pose substantial risks of the species
becoming established in the Everglades."

Biologists have been monitoring the distribution of this new
population since its discovery in December and are studying the
effects on native species of the swamp eels discovered last year in

Of particular concern to scientists and resource managers is that
these highly adaptable eels have the ability to thrive in a wide
variety of natural habitats and in adverse conditions. In addition to
marsh and swamp habitats, Curnutt said the fish survives quite well in
ponds, canals, roadside ditches and rice fields - "just about any
freshwater habitat with a few inches of water."

Another trait that could help these fish successful colonize
southeastern waterways is that swamp eels are air breathers, enabling
them to survive long dry spells. In fact, said Curnutt, their use of
air is so efficient that the eels can readily migrate short distances
across land from one water body to another. In addition, the eels can
live easily in even a few inches of water, especially in warm water.

Swamp eels, which reach lengths of three feet or more, are predators,
feeding on animals such as worms, insects, shrimp, crayfish and other
fishes and frogs. Yet, said Curnutt, the eels are also able to survive
weeks - and possibly months - without food. The eels are highly
secretive, with most of their activities occurring at night. In the
day, the fishes hide in thick aquatic vegetation or in small burrows
and crevices along the water's edge. In many populations, all young
are hatched as females, and then, after spending part of their life as
females, some eels transform into large males.

At first, said Curnutt, biologists believed that the Homestead
population represented a range expansion by animals from the
population known to exist around the Miami-Dade/Broward County line,
but recently completed genetic tests at Florida International
University indicate that the Homestead population differs genetically
from eels in northern Miami-Dade. The newly discovered Homestead
population is genetically closer to animals from populations
originating in southeast Asia, whereas the populations found
previously in the Miami and the Tampa areas are nearly identical to
samples from more northern parts of China.

To determine the abundance and more precise distribution of this
population, USGS biologists are collaborating with partners in the
Florida Fish and Wildlife Conservation Commission, National Park
Service, Florida International University, South Florida Water
Management District, and the U.S. Fish and Wildlife Service to perform
rapid monitoring. This program, funded by the Department of the
Interior's South Florida Restoration program, is now under way, said
Curnutt, and the results will help to determine resource managers'
options for trying to contain or eradicate the eel before it can enter
the national park.

Swamp eels belong to the family Synbranchidae, a group of fishes found
in fresh and brackish waters in Central and South America, Africa, and
from India east to Australia. These fish are not true eels, in part
because they do not migrate to the ocean to spawn. The species
introduced to Florida is native to tropical, subtropical and somewhat
temperate climates in Eastern Asia. In Asia, the eel is a popular food
fish. In North America, the species is sometimes kept as an aquarium

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