Release: May 18, 1999
Contact: Jim Williams 352-378-8181 jim_williams_at_usgs.gov
Catherine Haecker 703-648-4283 catherine_haecker_at_usgs.gov
INVASIVE FISHES POSE INCREASING THREAT TO U.S. WATERS AND NATIVE FISHES
Skyrocketing numbers of invasive non-native fishes in the nation's waters
are increasingly threatening aquatic systems, according to three USGS
biologists writing in a book recently published by the American Fisheries
The book, Nonindigenous Fishes Introduced into Inland Waters of the United
States, provides a wealth of current information on the status and impacts
of non-native fish in America's waterways.
For example, the authors write, non-native fish species are causing
declines in the abundance and genetic integrity of native fish species --
including highly valued game and fisheries species -- and are probably an
important factor in the extinctions of many of our native fish species.
The spread of non-native plants and animals has become a serious problem
both in the United States and worldwide. A number of resources are being
mobilized to address this issue, particularly following the recent signing
of a presidential executive order on invasive species.
Non-native, or nonindigenous, species, are those which have established
populations outside their native range. Many non-native fish in the United
States were introduced by deliberate stocking, others have spread through
releases of live bait or unwanted aquarium pets, or arrived in ballast
water discharged from ships.
The new book provides detailed information on more than 500 non-native fish
species, including methods of introduction, ecological and economic
impacts, range maps and identification aids. "It represents the state of
our current knowledge of nonindigenous fishes, and fills a large void by
consolidating previously scattered information," says co-author Dr. Leo
Nico, a biologist with the USGS Florida Caribbean Science Center in
Over the past 50 years the number of introductions of non-native fishes has
increased dramatically as a result of the rapid expansion of travel and
international shipping, as well as the increased interest in the aquarium
fishes. About 40 percent of U.S. non-native fish species come from foreign
countries; the rest are species that have spread into new environments
outside of their native U.S. geographic range. "Many of
these transplants are just as bad or worse than those from foreign
countries," says Pam Fuller, another co-author of the book and a USGS
scientist in Florida.
Scientists believe that non-native species were a factor in 24 of the 30
known cases of a native fish species becoming extinct. USGS Chief Biologist
Dr. Denny Fenn says that the effects of invasive fishes on endangered
species and aquatic biodiversity will likely increase in the next 25 years.
"They can and do impact entire ecosystems," Fenn says.
Examples of systems affected by exotic fish species, including:
* The Great Lakes, where populations of the introduced ruffe and round goby
are exploding and where introduced sea lampreys, which parasitize other
fishes, have been implicated in the collapse of the lake trout fishery.
Ruffe and round goby were introduced to the Great Lakes via ship ballast
water, and the sea lamprey entered through the Welland Canal.
* The Desert Southwest, where a number of small endangered fish species
such as sunfishes, catfishes, and bullheads, are being wiped out by stocked
largemouth bass and other species.
* South Florida, where populations of Asian swamp eel were discovered in
1998 in several locations, including just outside the Everglades. These
fish, which are sold in the aquarium trade and which may have escaped or
been released into the state's waters by aquarists, are voracious predators
that could threaten a number of native species.
While many state agencies still stock nonindigenous species for sport
fishing, Fuller says there is a price to pay for introducing any fish into
waters where they did not evolve. Non-native fish often prey on native
species, or compete with them for food and spawning sites.
Another danger invasive species pose is the loss of biological diversity
through cross-breeding, or hybridization, between exotic and native
species. This has become a particular problem for some western trout
species in areas where rainbow trout have been introduced. "We are losing
the genetic integrity of many of the western cutthroat subspecies," says
co-author Dr. Jim Williams, also a biologist with the USGS Florida
Caribbean Science Center. "Many populations are being wiped out, and once
lost, they can't be replaced."
Fuller says she hopes the publication will help educate people about the
magnitude of the problem. "I think a lot of people will be astonished at
the extent to which fish have been moved around," she says. Fuller notes
that many familiar species that people often assume are native -- such as
the brown trout -- were actually introduced to this country in the 19th
The authors also hope to educate anglers and aquarium hobbyists about the
consequences of releasing live fish into natural waterways. "These fish
sometimes carry diseases and parasites that can affect the native species,"
says Fuller. "I've had fishermen tell me they never gave a thought to
dumping their unused bait minnows at the end of the day. They didn't
realize it could be a problem."
The book is published by the American Fisheries Society, a professional
organization composed of fisheries scientists and managers dedicated to the
conservation and sustainability of fisheries and aquatic ecosystems. The
Society's Acting Executive Director, Dr. Robert Kendell, says the
organization seeks to publish the latest research in fisheries and aquatic
sciences. The book is available from AFS by calling 412/741-5700.
More information on problems associated with non-native fish can be
obtained from the USGS Nonindigenous Aquatic Species web site:
http://nas.er.usgs.gov. Users can perform queries to see which species have
been introduced into their state and to get species-specific information.
As the nation's largest water, earth and biological science and civilian
mapping agency, the USGS works in cooperation with more than 2000
organizations across the country to provide reliable, impartial, scientific
information to resource managers, planners, and other customers. This
information is gathered in every state by USGS scientists to minimize the
loss of life and property from natural disasters, to contribute to the
conservation and the sound economic and physical development of the
nation's natural resources, and to enhance the quality of life by
monitoring water, biological, energy, and mineral resources.
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