Asian Carp: A Growing Threat

“Asian carp” refers to several species of related fish originating from Asia. Two species of Asian carp—the bighead and silver carp—were imported into the southern United States to keep aquaculture facilities clean and to provide fresh fish for fish markets. Bighead and silver carp escaped into the wild in the 1980s and have been swimming northward ever since, overwhelming the Mississippi and Illinois River systems. In some areas, the Asian carp now comprise more than 95% of the biomass (MICRA 2002).

The Great Lakes are at serious risk from Asian carp. An artificial connection—known as the Chicago Waterway System—connects the Great Lakes to the Illinois River, which connects to the Mississippi River. This waterway system provides the pathway for Asian carp to enter the Great Lakes.

Biologists, policy makers, and citizens have grown deeply concerned about the prospects of Asian carp entering the Great Lakes through the Chicago Waterway System. The probability of bighead and silver carps surviving and reproducing in the Great Lakes is high (Mandrak and Cudmore 2004). If these fish enter the Great Lakes, they will likely spread throughout the basin due to the natural and man-made connections and the widespread distribution of suitable habitat. While the fish will not find all parts of the Great Lakes to be hospitable habitat, the lakes contain ample areas where the fish will thrive, reproduce, and cause harm (Kolar et al. 2005; Mandrak and Cudmore 2004; Lodge 2010; Hansen 2010)

A Trail of Destruction

Asian carp have left a trail of destruction in the Mississippi River system that has harmed the ecosystem, the economy, property, and boaters. The people of the Great Lakes basin do not want to see history repeated in their region.

Bighead and silver carp are voracious eaters. They consume plankton—algae and other microscopic organisms—stripping the food web of the key source of food for small and big fish. Asian cap can grow to large sizes: some as large as 110 pounds (Hoff 2004), though the average size is around 30-40 pounds. An Asian carp is capable of eating 5-20% of its body weight each day. The diet of Asian carp overlaps with the diet of native fishes in the Mississippi and Illinois Rivers (Chick and Pegg 2001), meaning the carp compete directly with native fish for food.

Between 1991 and 2000, as scientists watched the Asian carp spread in the Mississippi and Illinois Rivers, Asian carp abundances surged exponentially (Chick and Pegg 2001). Between 1994 and 1997, for instance, commercial catch of bighead carp in the Mississippi River increased from 5.5 tons to 55 tons between (Chick and Pegg 2001). Today, commercial fishers in the Illinois River regularly catch up to 25,000 pounds of bighead and silver carp per day (Irons et al. 2007); a half acre of river can often yield thousands of pounds of Asian carp (Chapman 2003), a remarkably large amount of fish. The commercial value of Asian carp is quite low and much less valuable than the native fish they replaced.

In addition to causing ecological harm, the silver variety of the Asian carp has caused direct harm to people. The silver carp is skittish and easily startled by the sound of a boat motor. The sound causes the fish to leap as high as ten feet out of the water, earning them the nickname “the flying fish.” Some of these fish weigh more than twenty pounds. They land in boats, damage property, and injure people. Boaters are routinely injured and one woman was almost killed near Peoria (Meersman 2004). Said one biologist working on the waterway: “You may imagine it would be quite novel for a 20-pound fish to jump into your boat, but being hit by a large Asian carp would be similar to being hit by a bowling ball. Even if the fish don’t hit you, they can break fishing rods, windshields, electronics or anything else in your boat. As if adding insult, the carp will leave slime, blood and excrement on everything it touches” (Chapman 2010).

Potential Impact on the Great Lakes Economy

The establishment of Asian carps could cause great economic impact to the Great Lakes’ commercial, tribal, and sport fisheries, today valued at more than $7 billion annually (ASA 2008).

Reduced abundance of native fishes will result in reduced harvest by sport and commercial fishers. Reduced harvest will cause reduction in angling quality and economic impact to those whose livelihood depends on sport and commercial fisheries.

The potential impact of Asian carps on the Great Lakes’ sport, tribal, and commercial fisheries can be seen now along the Mississippi River basin, where in just a few short years following introduction of Asian carp into an area, many commercial fishing locations have been abandoned, as native fish have nearly disappeared from the catch, replaced by Asian carp.

Potential Impact on the Great Lakes Food Web

The presence of Asian carp in the Great Lakes could cause declines in abundances of native fish species. Asian carp will compete with native fish for food—native fish like ciscos, bloaters, and yellow perch, which in turn, are fed upon by predator species including lake trout and walleye (Hansen 2010). Under the conditions found in some areas of the Great Lakes (such as water temperature and food abundance), Asian carp could outnumber all other native species, as is happening in parts of Illinois, Mississippi, and Missouri Rivers.

The Great Lakes are home to federally and/or state listed threatened or endangered fish, mollusks, plants, mammals, insects, and reptiles. Other Great Lakes invasives have been implicated in adverse effects upon up to 46% of the local federally listed endangered plant and animal species. Introduction of Asian carp to the region could further harm these organisms and perhaps lead to their disappearance from the Great Lakes.

Risk assessments carried out by officials from the U.S. Department of Interior (Kolar et al. 2005) and the Department of Fisheries and Oceans Canada (Mandrak and Cudmore 2004), and overall experience with biological invasions, provide ample reason for considerable concern. First and foremost, these assessments conclude that the carp will certainly tolerate the Great Lakes basin’s climate, as the basin is well within the fishes’ native climate range. Mean annual air temperatures range between -2ºC and 22ºC for bighead carp and -6ºC and 24ºC for silver carp, a temperature span that would support Asian carp populations in much of the United States and Canada, including the Great Lakes.

These risk assessments also suggest that the Great Lakes would offer the carp an abundant and varied food supply. Bighead carp would consume zooplankton in the Great Lakes and silver carp would prey heavily on phytoplankton. This feeding would place the carp in direct competition young and mature native species (Hansen 2010). More troubling is that Asian carp appear to be highly opportunistic when it comes to feeding. For instance, bighead carp diet in the Mississippi River is more varied than in their native range, showing the carp take advantage of the food that is present. By feeding on plankton, the Asian carp feed on the “low end” of the food web, and few people doubt that the carp would have significant negative impacts on the food web (Hansen 2010; Lodge 2010).

The Great Lakes also offer the Asian carp suitable spawning habitat. The risk assessments show that the Asian carp require 30-60 miles of unimpeded rivers to spawn (Kolar et al. 2005; Mandrak and Cudmore 2004). The carp also thrive in areas with vegetated shorelines; areas that provide habitat for feeding. The Great Lakes basin contains numerous streams with suitable spawning habitat and large areas of vegetated shorelines, particularly large bays, wide river mouths, connecting channels (e.g., the Saint Marys River), wetlands, and lentic areas (areas of still waters). The carp certainly will not thrive in all portions of the basin—for example, in the deep, cold, open waters of the lakes. However, ample habitat for spawning and feeding exists in all five of the Great Lakes, including Lake Superior.

Injury to Boaters

The Asian carp invasion of the Mississippi and Illinois Rivers has indicated that recreational users are at risk. The “flying carp” have caused serious bodily harm. The Great Lakes is a haven for boaters, water-skiers, and others who take to the water for pleasure or work. Indeed, the Great Lakes Commission estimates that nearly 1 million boats and personal watercraft operate on the lakes (GLC 2003), which means millions of people will be in direct contact (literally) with the silver carp, should the fish become abundant. Knowing the hazards of boating, Jet-skiing, waterskiing, and biological work on the Illinois River system, the risk to people would be compounded on the Great Lakes by a significantly larger boating population in the region.

References

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Risk Assessments

• Columbia River Basin Asian Carps Risk Evaluation (205 KB PDF)
  U.S. Fish & Wildlife Service (February 2008)
• Asian Carps of the Genus Hypophthalmichthys: A Biological Synopsis and Environmental Risk Assessment (4.8 MB PDF file from offsite link)
  Cindy S. Kolar, Duane C. Chapman, Walter R. Courtenay, Jr., Christine M. Housel, James D. Williams, (USGS) and Dawn P. Jennings (USFWS) (April 2005)
• Risk Assessment for Asian Carps in Canada (2.1 MB PDF from offsite link)
  Nicholas E. Mandrak and Becky Cudmore, Great Lakes Laboratory for Fisheries and Aquatic
  Department of Fisheries and Oceans Canada (2004)
• Biological Synopsis of Grass Carp (1 MB PDF from offsite link)
  Becky Cudmore and Nicholas E. Mandrak, Great Lakes Laboratory for Fisheries and Aquatic Sciences, Department of Fisheries and Oceans Canada
• Asian Carp Status Report (205 KB PDF from offsite link)
  Department of Fisheries and Oceans Canada (March 2005)