EXOTIC FISH A CONCERN FOR STATE'S NATIVE FISH, SPORTFISH MANAGEMENT

Aug. 23 2004

Two bighead carp recently caught by an angler at Cherry Creek Reservoir have raised a red flag for state aquatic biologists, who are concerned the discovery could have serious, long-term implications for state fisheries and recreation.

“This is the first time we have seen this unwanted species in any of our sportfishing waters in Colorado,” said Pete Walker, senior fish pathologist for the Colorado Division of Wildlife. "I'm sure whoever released them did not understand the potential impacts, but it's a terrible thing, and it's very much against the law to let fish like this loose in state waters."

Walker identified the fish as bighead, a species of Asian carp that eat large quantities of zooplankton. He and other aquatic experts worry that, in sufficient numbers, bighead carp could negatively impact sportfishing at impoundments around the state. Aquatic biologists said zooplankton is the primary food source for young fish and adult gizzard shad, the most important forage species for eastern Colorado reservoirs. Fishery managers use shad as food for larger, more desirable sportfish such as walleye.

Another serious and more immediate threat to humans is the bighead carp’s reaction to motor boats. The fish, which can grow more than 4 feet in length and weigh 100 pounds, tend to swim through surface waters. When startled, they can jump up to six feet in the air, sometimes right onto boat decks.

“They actually have caused serious harm to people—broken arms and legs,” said Tina Proctor, aquatic nuisance species coordinator for the U.S. Fish and Wildlife Service. “We obviously are very concerned for the safety of people as well as the effects they can have on the native species.”

State and federal biologists are concerned that bighead carp might have spread downstream to the South Platte River, where river flow could provide the habitat they need to successfully reproduce. Large adult females can produce as many as 900,000 eggs per year, according to research data.

Available evidence indicates that fish farmers imported bighead carp to the southern United States in the early 1970s. Two other species, grass and silver carps, also were imported into the country. In the early 1980s the fish began to appear in public waters, the likely result of escape from fish farms and aquaculture facilities. Bighead carp have now been recorded in or along the borders of at least 18 states. More recently, another Asian species, the mollusk-eating black carp, was imported into the U.S. Southeast.

Federal wildlife officials are concluding a three-year research project to study the effects of bighead carp on native species in Colorado, Montana, Wyoming, Utah, the Dakotas, Nebraska and Kansas. Results are due to be released this fall, the U.S. Fish and Wildlife Service's Proctor said.

Proctor said there are many things people can do to prevent the spread of bighead carp and other invasive species, including:

-- Learn to identify bighead and other large carp species;
-- dispose of unwanted live-bait fish in the trash, and not in the water, because bait fish could contain unknown species;
-- never move live fish from one body of water to another;
-- drain lake or river water from a boat’s live well and bilge before leaving a body of water;
-- and inspect and remove aquatic plants from boat water and trailer.

The bighead carp is characterized by its terminal mouth, located toward the front of the head; a pronounced under-bite; small trout-type scales; low- and forward-set eyes; and other distinguishing features.

The Bighead and Silver Carp Watchcard, a pocket-size card containing identification and prevention information, is available from the Colorado Division of Wildlife via e-mail at robin.knox@state.co.us or from the USFWS via e-mail at bettina_proctor@fws.gov.

In addition to the bighead carp, two other exotic fish species have been identified this month by Colorado wildlife biologists. A pacu, a vegetarian relative of a piranha, and an arawana, a large top-level predator species, were caught by anglers in the southeast Denver metropolitan area. Both of these species are often kept as pets in tropical aquariums, and owners sometimes release them when they get too large for tanks.

Colorado's Walker said people illegally release a number of exotic fish species into Colorado waters each year, which could result in far-reaching, long-term impacts on the state's $650 million-per-year sportfishing industry.

“People think all the aquarium species are tropical and unable to stand the cold weather in Colorado, but that is often not the case," he said.

Releasing fish and other aquatic wildlife into Colorado ponds, streams and lakes is illegal without proper licenses and permits. State wildlife officials ask anglers who catch exotic species to report them in person (with fish in hand), or via phone or e-mail. Information can be sent to the Colorado Division of Wildlife, Aquatic Wildlife Section, 6060 Broadway, Denver, CO 80216; by phone at 303-291-7362, or via e-mail to robin.knox@state.co.us.

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