Science·In Depth

The battle to stop the Asian carp invasion

Hulking invasive fish with voracious appetites pose a growing threat to native species in the Great Lakes despite U.S. and Canadian efforts to keep them out of these waters.

U.S. announces new measures to keep invader from entering Great Lakes

Minnesota fisheries supervisor Brad Parsons, holds a 12 kg bighead carp, at the state's Department of Natural Resources headquarters in St. Paul, Minn. on April 20, 2011. The 86 cm carp, caught two days earlier in the St. Croix River near Prescott, Wis., is among several invasive Asian carp species that could cause serious damage to the Great Lakes region's aquatic ecosystems. (Richard Marshall/The St. Paul Pioneer Press/Associated Press)

The Obama administration has announced additional measures to combat the Asian carp. This hulking invasive fish with voracious appetites continues to pose a growing threat to native species in the Great Lakes, despite U.S. and Canadian efforts to keep them out of these waters.

U.S. officials said the new measures, which will cost $50 million, include stepped-up trapping and netting in rivers that could provide access to the lakes, as well as initial field tests of chemicals that could lure carp to where they could be captured.

Authorities on both sides of the U.S.-Canada border have been worried about several kinds of Asian carp that have been making their way up the Mississippi River system to the Great Lakes for several decades.

Asian carp were first introduced to the southern U.S. in 1970 to control the growth of algae in Arkansas aquaculture ponds and escaped into the Mississippi River during flooding in the early 1990s. The descendants of those carp now account for more than 90 per cent of the weight of all fish in some parts of the upper Mississippi.

The biggest threats to the Great Lakes are bighead carp, which can reach a mass of 27 kilograms — the weight of an average eight-year-old child — and silver carp, which can grow to almost double that size.

Both fish vacuum up huge amounts of plankton, the tiny organisms that form the foundation of the Great Lakes food chain, and threaten to starve native species, like lake trout and walleye, that feed on the plankton as small fry.

Electric barriers

Three underwater electric barriers have been installed in the Chicago Sanitary and Ship Canal, the man-made waterway connecting Lake Michigan and the Mississippi River Basin, in an effort to prevent Asian carp from entering the lake. Each consists of equipment that creates an electric field of pulsing current in the water that makes it uncomfortable for fish to swim through. Because there is no physical barrier, ship traffic is unaffected.

The first barrier, built in April 2002 at a cost of $4 million, is formed of steel cables attached to the bottom of the canal. It was originally built as a demonstration project by the U.S. Army Corps of Engineers.

The second barrier, installed about 300 metres downstream starting in 2004, was intended to be more permanent and is made up of two sets of electrical arrays that can generate a more powerful pulsed electric field over a larger area. So far, $8.5 million has been spent on this barrier, and more funding is needed to complete the second set of arrays.

The third barrier, located between the first two, was activated in April 2011.

They also have two other qualities that could help them out-compete native fish: they grow quickly and are prolific breeders.

Bottom feeder

Signs of bighead and silver carp have been detected in waters beyond the electric barriers that have been installed in the waterway connecting Lake Michigan and the Mississippi River Basin to try and keep them out of the Great Lakes (see sidebar).

"When we have an invader that's operating at the bottom of the food chain, it poses quite a serious threat," said John Cooper, spokesman for the Ontario Ministry of Natural Resources.

The carp became enough of a threat that in 2005, Ontario made it illegal to posses live invasive species, including bighead, silver, grass and black carp.

On March 2, 2011, an Ontario court handed down the province's biggest fine yet for violating that law. It fined a Markham, Ont., owner of a fish-importing business $50,000 for possessing almost 2,000 kilograms of live bighead and grass carp. It was the man's second conviction. Authorities seized the fish on the Canada-U.S. border in Windsor, Ont., in November 2010.

Several months before that, in June 2010, a bighead carp nearly a metre long was caught by commercial fishermen in Lake Calumet in Illinois, about 10 kilometres downstream from Lake Michigan and beyond the electric barrier system meant to bar the fish from the Great Lakes. Tests suggested the six-year-old fish had lived most of its life in waters in the Great Lakes region.

Bighead carp have also been found in Lake Erie. According to the Asian carp regional co-ordinating committee in the U.S., which includes federal authorities as well as state and local agencies in Illinois and Chicago, a total of five were collected between 1995 and 2003, although DNA tests suggested the fish had not grown up in the lake but had been released there as adults.

In January 2012 the U.S. Geological Survey released a study reporting that Lake Erie and its largest tributaries are suitable habitats for the establishment of breeding populations of Asian carp.

Emergency response needed

In October 2010, Canadian Fisheries officials announced a joint 18-month study with the U.S. and $415,000 in funding to assess the risks the carp pose and to identify the waterways they use.

The International Joint Commission, which manages the rivers and lakes along the U.S.-Canada border, recommended in its March 2011 report that the two countries establish a bilateral organizational structure to deal with the threat posed by carp and other invasive aquatic species. Such a structure, it said, should be modelled on the incident command system used to manage major emergencies such as disease outbreaks, natural disasters and hazardous material spills.

In order for such a system to work, the discovery of Asian carp in the Great Lakes would have to be treated as an urgent environmental threat that could affect the biosecurity of U.S. and Canada, the commission said, and an emergency response to it involving several agencies would have to be mounted. Such a response would need the support of not only governments but also the public, including anglers, commercial fishers, hunters, naturalists and recreational boaters.

Authorities argue that, left unchecked, Asian carp threaten to disrupt not just native fish stocks but also the commercial fishing industry in the Great Lakes region.

This bighead carp was caught on June 22 in Lake Calumet, beyond the electric barriers intended to keep carp away from the Great Lakes. (Canadian Press)

The Great Lakes Fishery Commission, a U.S.-Canadian partnership that manages fish stocks and fights invasive species in the countries' shared waters, estimates recreational, commercial and tribal fishing throughout the Great Lakes is worth $7 billion a year.

"Our concern … is we have a commercial fishery that's probably worth about $200 million a year to the Ontario economy, and then we have sport fishing that's worth upwards of $600 million," said Cooper

Hugh MacIsaac, a University of Windsor biologist who studies invasive species, said officials are particularly worried given the extensive spread of Asian carp that occurred in the Mississippi River following the introduction of the fish in the 1990s and how completely it has pushed out other species there.

180 invasive species

According to the Ontario government, about 180 foreign species have already invaded the Great Lakes, including zebra mussels, round gobies and sea lampreys. Most have come in through the St. Lawrence Seaway via the ballast water of transatlantic ships and were discovered in the Great Lakes too late to curb their spread. Some later failed to breed and flourish. Others, such as the sea lamprey, a blood-sucking parasitic fish, have had a devastating effect on local species.

A taste for carp?

Bighead and silver carp often end up on dinner plates in other countries, and until recently, tens of thousands of kilograms were sold each year in Canadian fish markets.

Three bighead carp that have been caught in Lake Erie in recent years are believed to have been released by people who bought them at food stores, said John Cooper, spokesman for the Ontario Ministry of Natural Resources. East Asian Buddhists sometimes release live fish as part of their religious practice.

Two Toronto-area supermarkets that were selling Asian carp were fined thousands of dollars each in 2010 for violating Ontario's ban on possessing invasive species.

Cooper said he doesn't think there will be a big market for Asian carp in Canada, even if the species overruns and replaces popular native sport fish.

"I just think many of us here in North America, given the choice of carp or walleye or yellow perch, salmon or trout, would prefer to catch and eat those species."

What sets the Asian carp apart from many of the other invasive species, and what has spurred dedicated, costly efforts against them, is that the fish's invasion of the Great Lakes can potentially be halted.

"We know where they are, and where the most likely point of entry will be," Cooper said. "That's what's focusing a lot of attention on what we can do to stop it."

In February 2010, the Obama administration released a $78-million carp control plan that included the third electric barrier between the Mississippi River system and Lake Michigan, along with plans to catch and poison the fish.

Michigan and neighbouring states have gone to the U.S. Supreme Court multiple times, requesting orders to close Chicago-area shipping locks — the gateway to the Great Lakes — to keep the fish from getting through. Their efforts have been supported by the Ontario government. However, the court has turned them all down.

Shortly after the carp was caught in Lake Calumet, two Illinois senators introduced a federal bill pushing for costly infrastructure to hold the carp back. If passed by Congress and approved by U.S. President Barack Obama, the bill would force the U.S. Army Corps of Engineers to find a way to physically separate the waters of the Mississippi and the Great Lakes. 

On Jan. 31, 2012 The Great Lakes Commission, which represents states and cities in the Great Lakes region, issued a study that argues separating the Great Lakes from the Mississippi River basin is the best way to keep the Asian carp out of the region. The report explained how to permanently separate Lake Michigan from the Chicago Waterway System and the  basin.

The U.S. Army Corps of Engineers is already conducting its own study of how to keep Asian carp from invading Lake Michigan but it doesn't plan to release its findings until late 2015.

Beyond the electric barrier

Of course, it is possible the efforts come too late. When the bighead was found in Lake Calumet, it wasn't clear whether the fish was an isolated case or a sign of a large invasion. But researchers led by biologist David Lodge at the University of Notre Dame in Indiana had been detecting silver and bighead carp DNA in the waters of that area since the fall of 2009.

About 180 foreign species have already invaded the Great Lakes, including the round goby and zebra mussels pictured here. (Ontario Ministry of Natural Resources)

That data, along with the Calumet catch, suggest there is likely more than one bighead and more than one silver carp above the electric barrier, said Christopher Jerde, a research assistant professor who works with Lodge.

"It really isn't good news," he said. But he added it's possible the population is small enough the fish will have trouble finding each other to spawn.

Jerde thinks the fish could swim around the electric barriers during a flood.

Following the chemical tests that showed the Lake Calumet carp had lived in Great Lakes waters for years, the Illinois Department of Natural Resources suggested the fish may have been released by humans.

Kinds of carp

There are five species of Asian carp listed by Ontario as "invasive." Two — silver and bighead — are now threatening to invade the Great Lakes. Black carp are still confined to aquaculture and research facilities in the U.S.

Grass carp have escaped into the wild in Alberta and have been caught a few times in the Great Lakes, but those are believed to be isolated incidents. The fifth species, common carp, was introduced in the 1880s and is now widespread in Ontario waterways. It, too, can cause damage to Ontario ecosystems, said Ministry of Natural Resources spokesman John Cooper.

"They root around the vegetation and roots of aquatic plants in shallow areas and certainly have altered wetlands in Ontario," he said, "but they've been here now for over 100 years, so most people consider them part of the environment."

MacIsaac said officials are keeping an eye out for more Asian carp and plan to poison sections of the Chicago Sanitary and Ship Canal if they find any. But this isn't the ideal solution.

"At the end of the day, you cannot rely on this forever," he said.

He believes a physical barrier, like the one the senators are seeking with their bill, is necessary if people are serious about keeping bighead and silver carp out the Great Lakes. He proposes treating the water in locks between Lake Michigan and the Mississippi with heat or a chemical each time a ship comes through.

However, that could delay the ship's journey by a few hours.

Even if silver and bighead do ultimately establish breeding populations in the Great Lakes, MacIsaac said, it's not certain they would do as well there as they have in the Mississippi.

"But you don't want to find out."

The introduction of an invasive species is essentially an "uncontrolled experiment," he said, and no one can really predict how it will affect the ecosystem.

"Once they come in, all you can do is sit back and watch."


Emily Chung

Science, climate, environment reporter

Emily Chung covers science, the environment and climate for CBC News. She has previously worked as a digital journalist for CBC Ottawa and as an occasional producer at CBC's Quirks & Quarks. She has a PhD in chemistry from the University of British Columbia. In 2019, she was part of the team that won a Digital Publishing Award for best newsletter for "What on Earth." You can email story ideas to