Can Asian carp invasion be averted?

In December 2009, an environmental emergency brigade of 450 Americans and Canadians descended on Romeoville, Ill., armed with nets, boats, and thousands of gallons of poison. The urgent, 20-agency response was brought on by recent environmental DNA (eDNA) tests indicating that Asian carp were closer to invading Lake Michigan than previously thought. The tests detect traces of Asian carp DNA in water samples within a 48-hour period.

One of the 450 who dropped everything and headed to Romeoville was Phil Moy, a fisheries and aquatic invasive species specialist with the University of Wisconsin Sea Grant Institute. Fifteen years ago, Moy served as the first manager of a project to erect an electric barrier in the Chicago Sanitary and Ship Canal to repel foreign fish.

Chicago dug this canal more than a hundred years ago to manage wastewater, and its construction joined two major ecosystems that until then had remained isolated. Over the last several decades, Asian carp that escaped from Southern aquaculture and wastewater facilities have been moving up the Mississippi to the Illinois River, and the canal connecting it to Lake Michigan is an ideal pathway for the fish to advance into the Great Lakes.

In December, scheduled maintenance required temporarily shutting down part of the barrier. Because eDNA tests showed Asian carp advancing, a 5.7-mile section of the canal was treated with rotenone, a fish poison, to ensure that no carp would breach the barrier during the maintenance.

Moy was on hand-and often on a boat-during the seven-day effort that required coordinating all of the state and federal agencies involved using the Incident Command System, a procedure similar to that used to coordinate efforts to fight large wildfires in the West.

Moy has remained active on the electric barrier project as co-chair of its advisory panel. However, he admits that the barrier is only a temporary solution. Ultimately, he said, the only sure way to keep Asian carp and other invasive species out of the Great Lakes is to permanently sever the link between the Mississippi River and Great Lakes basins.

“I really think that’s the direction we have to go,” Moy said.

What Would Carp Need?

The four species of Asian carp-bighead, silver, black, and grass-pose a significant threat to the Great Lakes commercial and sport fisheries, collectively valued at more than $7 billion annually.

The filter-feeding fish can grow to be more than 100 pounds, and they are capable of daily gobbling up 20 percent of their weight in plankton, the tiny organisms that provide the foundation of the Great Lakes fishery food chain.

In addition, motor boat engine noise startles silver carp, causing them to shoot up in the air as high as 10 feet. Airborne silver carp have injured several boaters on the Mississippi and Illinois rivers-where Asian carp, imported from Taiwan in the 1970s to consume the waste in aquaculture and wastewater systems, have elbowed out native fish to become the dominant species in many areas.

Although there’s no question the carp pose a threat to Great Lakes fish and boaters, Moy said a successful Asian carp invasion is by no means a sure thing. “It takes some specific habitat for them to do really well,” he said.

Scientists estimate that the carp need access to a river with a deep, free-flowing main channel in order to successfully reproduce. If their eggs settle to the river bottom before hatching, the embryos will suffocate and die.

“One hundred kilometers-about 63 miles-is roughly the distance needed to provide enough current to keep the fish’s fertilized eggs suspended in water while they incubate,” Moy said. Out of thousands of tributaries that feed the Great Lakes, only 22 on the U.S. side (four in Wisconsin) meet this criterion. Adding another criterion-the availability of quiet, fertile backwater areas where the newly hatched fish larvae can eat and mature-reduces the list even more.

However, before they can reproduce, the fish would need to find each other within more than 94,000 square miles of the Great Lakes. While a few bighead carp have been captured in Lake Erie, probably due to someone releasing them there, they have yet to multiply into any significant numbers.

Indeed, Moy said it’s all about numbers now, and that’s why the electric barrier is still important.

“We have to keep the numbers as low as humanly possible,” he said. “Even if there are a few Asian carp upstream of the electrical barrier, there is absolutely no assurance that they’ll be able to establish a population.”

However, Moy said that the electrical barrier is not a permanent solution, because it depends on the fish reacting predictably to a technology that could potentially fail. In addition, it doesn’t do anything to protect the Mississippi River basin from small, floating invasive species coming from the Great Lakes, such as quagga mussel larvae.

“We really need to establish a two-way separation in order to really protect both basins,” he said.

Restoring the Natural Separation?

Accomplishing this would be challenging, but possible, Moy said, and shutting down the canal locks would only be one step.

The Des Plaines River runs parallel to the Sanitary and Ship Canal, and flooding in 2008 sent water from the Des Plaines overland into the canal upstream of the barrier. The Army Corps is now investigating how best to address this “leaky” spot.

Other potential leaks around the Great Lakes would likely need to be addressed, too. A mere two miles of marshy, flat terrain separates the Mississippi and Great Lakes basins at Portage, Wis., where a canal was dug in 1851 to connect the Wisconsin and Fox rivers. Asian carp have now advanced as far north as Lake Pepin in the Mississippi River, well upstream of its confluence with the Wisconsin River.

Moy and other biologists worry that Asian carp could drastically change the Great Lakes food chain, just as a string of other aquatic invasive species have caused sweeping changes over the last century.

In the 1800s, blood-sucking sea lamprey invaded the lakes through locks and shipping canals connecting the Great Lakes to the Atlantic Ocean. The lamprey’s introduction caused a major collapse of lake trout, whitefish, and chub populations during the 1940s and 1950s. The absence of large predator fish like lake trout caused an explosion in the population of small, silvery alewives, which were introduced to Lake Erie in the 1930s and soon spread throughout the Great Lakes. Then, to fill the gap left by lake trout, fisheries agencies introduced coho and Chinook salmon to control alewife numbers and provide an exciting sport fishing experience.

Canada and the United States spend approximately $18 million a year to control sea lamprey numbers using a toxin that specifically targets the lamprey. Moy said a similar effort might have to be launched for Asian carp if they successfully invade the Great Lakes, although a carp-specific toxin has not yet been developed.

Kathleen Schmitt Kline is a science writer at the University of Wisconsin Sea Grant Institute, which supports research, education, and outreach dedicated to the stewardship and sustainable use of the nation’s Great Lakes and ocean resources. Visit seagrant.wisc.edu for more on Asian carp, including video of the fish.

Asian Carp Facts

The common term “Asian carp” includes four types of carp native to Asia that have been introduced in the United States over the last three decades: bighead, silver, black, and grass.

Size: Commonly 24-30 inches and 3-10 pounds, but capable of growing to more than 50 pounds.

Preferred habitat: Large warm-water rivers and impoundments.

Threat: Asian carp are tremendous filter feeders that would likely out-compete many native fish if they become established in the Great Lakes. Silver carp jump out of the water in response to outboard motors and can seriously injure boaters.

TIMELINE

Early 1970s Asian carp are imported from Taiwan to the United States for cleaning aquaculture ponds and sewage treatment facilities. Flooding allows them to escape into the Mississippi River basin.

1995 As Asian carp make their way up the Mississippi River to the Illinois River, an advisory panel forms to aid the U.S. Army Corps of Engineers in finding an environmentally sound method for preventing the spread of the carp and other aquatic nuisance species through the Chicago Sanitary and Ship Canal.

1997 Barrier Advisory Panel recommends an electric barrier as the best approach with the least number of drawbacks. However, the panel notes that no approach relying on animal behavior or a technological solution, as opposed to a physical separation, could be 100-percent effective in stopping the movement of aquatic invasive species through the canal.

April 2002 The Army Corps begins operating the first electrical barrier (Barrier I) as a demonstration of a new technology for preventing the spread of aquatic nuisance species. The barrier operates at a strength of one volt per inch, strong enough to repel most adult fish, but possibly not strong enough to repel smaller juvenile fish.

Based on monitoring and testing of Barrier I, a second, more permanent barrier (Barrier II) is authorized. Barrier II is a similar electric field barrier that covers a larger area within the canal and is constructed to last longer. It consists of two sets of electrical arrays and control houses, known as Barriers IIA and IIB. Each control house and set of arrays can be operated independently, but the ultimate goal is to operate both at the same time.

May 2006 Barrier IIA is completed, but due to safety concerns, it sits idle for nearly three years.

2007 Congress authorizes the Army Corps to complete Barrier II, to upgrade Barrier I and make it permanent, and to operate the barrier system at full federal cost.

September 2008 Flooding in the Chicago region sends water from the Des Plaines River tumbling over the narrow strip of land between it and the Sanitary and Ship Canal at several locations above the barrier site.

October 2008 Barrier I is shut down for maintenance. Repairs are made to allow Barrier I to remain in service for several more years until Barriers IIA and IIB are fully functional.

April 2009 Barrier IIA begins operating full-time at a strength of one volt per inch.

July 2009 Environmental DNA (eDNA) testing detects Asian carp DNA just south of the Lockport Lock, much closer to the barrier than previously believed. The eDNA test detects traces of Asian carp DNA in water samples within a 48-hour period.

August 2009 In response to the eDNA tests, the strength of Barrier IIA is increased to two volts per inch.

September 2009 Asian carp DNA is detected approximately one mile south of the barrier.

October 2009 Asian carp DNA is detected in the Cal-Sag Channel and Calumet River, beyond the electrical barrier.

December 2009 A 5.7-mile section of the canal is closed while scheduled maintenance on Barrier IIA takes place. Barrier I remains active. However, because Barrier I may not be effective in deterring juvenile fish, a fish toxin called rotenone is applied to the canal between the barrier and the Lockport Lock and Dam. At least 450 people from 20 agencies from the Great Lakes states and Canada report to Romeoville, Ill. to assist with the effort.

January 18, 2010 Asian carp DNA is detected in water samples taken Dec. 8, 2009, in the Calumet Harbor in Lake Michigan.

Reproduction in Rivers

If a substantial population of Asian carp establish themselves in the Great Lakes, scientists predict they will have to reproduce in river systems with 100 kilometers or more of open channel. There are 22 such rivers on the U.S. side of the Great Lakes. Four Wisconsin rivers could be especially favorable environments to carp reproduction-the Bad, Manitowoc, Nemadji, and Sheboygan rivers.

Source: April 12, 2005 U.S. Geological Service report submitted to the U.S. Department of Fish and Wildlife