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.

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.

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.

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."

Google map of area where Asian carp may enter the Great Lakes
View Asian carp invasion in a larger map