The Asian invasion
By Paul Breschuk
Features Editor
March 31, 2010
 While the phrase “Asian import” has troubled the sleep of North American automakers, it carries an even greater fear for members of the fishing industry.
Asian carp, a tenacious freshwater fish species, has been multiplying at an alarming rate since its recent introduction to North American waters. According to the 2010 Asian Carp Control Strategy Framework report, the invading fish were originally imported to the southern U.S. states where they were put to use in wastewater treatment facilities to keep retention ponds clean. There, they were expected to stay in isolated locations, cut off from outside waterways and ecosystems. The floods of the early 1990s, however, allowed the Asian carps to be carried into the Mississippi River basin in an uncontrolled overland flow of water.
Since their introduction into North American waters, the carps quickly spanned north to populate the entire length of the Mississippi. Currently, they are perilously close to entering Lake Michigan, approximately 50 kilometers from entrances near Chicago.
While an electric barrier has been set up by the United States Army Corps of Engineers, which has held the fish at bay with a segment of electrically charged water, it can only be seen as an imperfect, temporary measure. Many threats still remain, including fishers misidentifying baby Asian carps and thus transporting them for use as bait in the Great Lakes. The event of a flood could also aid in the carp’s northern migration, lifting them out of previously isolated bodies of water and placing them on course for Lake Michigan.
“I would say to the Canadians, look at what is happened down here in the U.S.,” said Jerry Rasmussen, U.S. Fish and Wildlife Service biologist. “We have them. You do not want them. You need to do everything you can to assist in keeping them out of the Great Lakes.”
Voracious feeders, eating up to 40 per cent of their body weight per day, Asian carps are swiftly replacing native fish species by monopolizing local food supplies. With such domination, it seems inevitable that these fish will someday invade the waters of the Detroit River, spreading across the Great Lakes and into the St. Lawrence Seaway. The effects of such a migration would be catastrophic.
In the Mississippi River, where Asian carps are most prolific, native fish populations have been reduced to almost unfishable levels. In some areas, Asian carps have come to represent over 90 per cent of the total fish biomass. This takeover comes as a dire warning for Canada’s ecosystem, with the carps poised to spill into the preferred colder waters of the Great Lakes.
Members of the Cyprinidae family of fish, Asian carps come in three main varieties: Bighead carp, Black carp, and Silver carp. All three can reproduce both earlier and in more plentiful numbers than native fish. They also have much more aggressive feeding habits as well as larger appetites.
By filtering plankton through its gills, Bighead carp can consume vast amounts of food. This feeding technique also makes them difficult to catch by typical fishing practices. Growing over five feet in length, sometimes weighing more than 100 pounds, these fish can easily dominate native fish such as the paddlefish, gizzard shad, perch, and buffalo fish.
The even larger Black carp has been known to grow over seven feet long, tipping the scales at over 150 pounds. An eater of mollusks and snails, adult Black carp can consume up to five pounds of muscles per day. The recent invasion of Zebra muscles into the Great Lakes will only add to the ease of this carp’s northern proliferation. And while a reduction in Zebra muscles may seem beneficial, the endangered lesser species of muscles will surely perish, causing further unbalance in the ecosystem.
Silver carp, known as flying fish, offer a unique detriment to their newly discovered North American waters. They have the distinctive behavioral trait of leaping above water at the sound of passing boat engines. Scientists describe it as a fear response to the disruptive noise which makes these fish jump at and into offending watercrafts.
“They jump eight to ten feet in the air,” said Rasmussen. “It could kill you. We have not had that yet but we have had some very serious injuries: broken noses, cuts, bruises… broken fingers, broken arms. It is creating chaos with people being injured by flying fish.”
The mere thought of a confrontation between a speeding water skier and a 40-pound flying carp is enough to make one cringe.
Many videos of this jumping phenomenon have been recorded, capturing scenes ranging from comedy to horror. As if taken from a cheesy drive-in movie script, Silver carp have been known to seemingly attack boaters with their missile-like behavior. Ultimately, the silver hailstorm of carp has made aquatic transportation undesirable and leisure activities unthinkable.
So, what can be done to solve this carp calamity? Since human controls on the environment often result in bad situations, is there any chance that nature can fight back on its own?
Not likely.
“Adult Asian carp have few predators,” explained Dr. Glenn Thomas of Louisiana’s Department of Wildlife and Fisheries. “Juveniles are probably on the menu for any number of species but they grow through the preyed-upon size ranges really fast, and the adults are very fecund.”
Perhaps it is up to humans, then, to take up the role of hungry exterminator. While native carp have been plagued with a bad reputation as being dirty bottom feeders, the Asian carp may be a cleaner, tastier alternative.
“Bighead and Silver carps feed high in the water column, away from sediments and low in the food chain, resulting in low levels of pollutant concentration,” said Dr. Thomas. “They are excellent on the table, but are very bony.”
There are, however, special techniques of deboning Asian carp. And it can only be assumed that more and more recipes will appear for these ever-plentiful fish. Thus, after a small shift in dietary preferences, North Americans could perhaps solve this problem by doing what they do best: overeating.
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