Scientists Fear Leaping Carp to Invade US Great Lakes
By Andrew Stern
CHICAGO — Fish that leap into passing boats may be a fisherman’s fantasy, but scientists fear that hyperactive Asian carp will reach the U.S. Great Lakes, devour the base of the food chain and spoil drinking water for 40 million people.
In less than a decade since escaping southern U.S. fish farms, the hardy and voracious carp have come to dominate sections of the Mississippi River and its tributaries.
“It is a crisis,” said Phil Moy of the University of Wisconsin and the government-affiliated water protection group Sea Grant. “We’ve seen some pretty significant adverse invaders in the Great Lakes. Right now, it’s the carp, but what’s around the corner?”
The leaping fish are silver carp that jump haphazardly when alarmed by passing boats and have injured boaters, some of whom have taken up garbage can lids as shields.
The only barriers between dense populations of silver and bighead carp — two closely related Asian carp species — and the world’s largest collective body of fresh water are a few miles (kms) of waterway and a little-tested underwater electrical field spanning a canal near Chicago.
The idea of adding a few more varieties of fish to the Great Lakes — which have been abused by polluters, overfished, invaded by scores of unwanted species and repopulated with nonnative fish to eat invaders and please anglers — would not appear catastrophic in light of the range of global environmental crises.
But scientists believe the carp, which escaped lagoons in Arkansas during late 1990s flooding, could set off an ecological collapse in the lakes, ruining the primarily recreational $5 billion fishery and posing a threat to water quality for millions of people.
“With invasive pest species, we can’t turn back the clock, the lakes will be altered for good,” said Cameron Davis of the group Alliance for the Great Lakes. “Not only do invasive species unravel the food web they also fool public perception: The lakes look cleaner because the food has been stripped out.”
Carp that can grow to 100 pounds (45 kg) filter huge amounts of water, consuming 40 percent of their body weight per day in microscopic plant and animal life that form the foundation of the aquatic food chain. The loss of this food relied on by crayfish and smaller fish such as alewifes, sculpins and perch would in turn eliminate the prey for popular game fish such as salmon, trout and bass.
Lake water would become less cloudy, allowing sunlight to penetrate to greater depths and enhancing algae growth, some of which emit toxins that can cause itchiness, illness and even death. Varieties of toxic blue-green algae already hold an ecological advantage because they are avoided by the zebra mussel, another prolific Great Lakes invader that filters out plankton.
Lake Saint Clair, which connects Lakes Erie and Huron, is sometimes choked with algae that tangles up boat props and swimmers, and algae blooms have fouled Green Bay off Lake Michigan.
A few weeks each summer, bacteria that consume rotting algae lend a swampy taste to treated lake water. Rare bacteria outbreaks have fouled the lakes and made people sick, though advanced treatment systems have proven largely effective.
The dire consequences from the carp’s arrival may serve another purpose: publicizing the global issue of invasive species that cost hundreds of billions of dollars to fight.
Public outrage that followed the Cuyahoga River catching fire in Cleveland in 1969 spurred passage of the U.S. Clean Water Act.
Many ecologists have concluded the Great Lakes and Mississippi River watersheds need to be separated permanently.
The temporary electric barrier — a $9 million replacement is under construction — guards a man-made channel that at the turn of the last century was dug to link the lakes and the Mississippi and to reverse the flow of the Chicago River, sending Chicago’s sewage inland instead of out into the lake where it fouled the city’s water supply.
“The electric barrier is crude but it’s the best thing we have now,” said ecologist David Lodge of Notre Dame University. “The irony is the barrier was first proposed to keep round gobies (another fish invader in the Great Lakes) from colonizing the Mississippi River watershed, but by the time the barrier was built they had already passed it. Now the motivation is to keep the carp from coming from the other direction.”
Because many harmful invaders, though not the carp, arrived in ballast water dumped in Great Lakes ports by ocean vessels, one audacious proposal is to bar ocean vessels from the lakes.
But such a drastic approach has drawn howls of protest from shipping interests, who instead are pursuing a foolproof method of killing the creatures that hitchhike in ballast water.
International cargo, which is mostly imported steel and exported grain, carried by ocean-going vessels represents one-quarter of the 200 million tonnes shipped on the Great Lakes yearly, but as much as two-thirds of its value.
A new species arrives in the lakes about every nine months. A few are introduced by fisherman dumping bait or aquarium owners setting animals loose. Illinois enacted a ban on transporting live carp out of fear of a Buddhist tradition that calls for setting one fish free for each one eaten.
Lake watchers had a scare in 2004 when a Chicago fisherman caught a Northern snakehead, but no other examples have turned up of the voracious fish that can wriggle across land.