Under Siege! America’s Most Unwanted Invasive Species
The United States is under an economic and ecological siege by alien invaders — America’s Most Unwanted. More than 6,500 of these harmful non-native species cause more than 100 billion dollars in damage each year to the U.S. economy as the country battles to control the economic, ecological, and health threats these invaders pose. Increased global travel and trade are providing more pathways for both intentional and unintentional introductions of invasive species.
Invasive species affect just about everyone in every State in the country, in urban centers and wilderness areas. And their costs are borne by all of us — farmers, ranchers, businesses, and local, State, Tribal, and Federal governments.
The Cost of Invasives
Costly effects of invasives include crop decimation (cactus and gypsy moths), clogging of water facilities (quagga and zebra mussels) and waterways (hydrilla, giant salvinia), wildlife and human disease transmission (West Nile virus, monkeypox, and diseases in some ships’ ballast water), threats to commercial, native, and farmed fisheries (Asian carp, snakehead fish, sea lamprey, Asian swamp eel, whirling disease, and viral hemorrhagic septicemia), increased fire vulnerability (cheatgrass, brome, and buffelgrass) and adverse effects for ranchers and farmers (leafy spurge and cheatgrass).
Researchers with the USGS Invasive Species Program work on every one of those species mentioned; in fact, our researchers work collaboratively on all significant groups of invasive organisms in terrestrial and aquatic ecosystems in all regions of the United States. Across the Nation, our invasive species experts partner with States, other Federal agencies, businesses, agriculture, and natural resource managers to help solve the problems posed by these invaders.
Key components of invasive species activities include prevention, monitoring and forecasting threats, and control and management of established invaders.
During Invasive Species Awareness Week, we will feature some of America’s Most Unwanted each day to highlight the impacts of invasive species to the nation’s Ecosystems and economy.
In areas where Asian carp are abundant, they have interfered with commercial and recreational fishing, caused reductions in zooplankton (animal plankton, an important food for many aquatic species), and harmed native fish communities. Bighead and silver carp have moved up the Illinois River and are now poised to enter the Great Lakes. Resource managers fear that Asian carp would have ecological impacts and negatively affect the $7 billion–a–year fishery in the Great Lakes. Early USGS research focused on understanding the distribution, abundance, and habitat use of these fish, along with collecting information on their biology and life history from around the globe. USGS researchers are currently examining aspects of risk to the Great Lakes from Asian carp in the Chicago Area Waterways System, as well as conducting studies to develop and test ways to reduce the abundance and distribution of Asian carp.
Q: What are Asian carp?
There are many carp native to Asia, but in North America, “Asian carp” usually refers to bighead, black, grass, and silver carp — all of which are nuisance species in inland waterways. The Asian carp that have garnered the most attention are bighead and silver carp (together, the bigheaded carp), large fish that filter plankton from the water column. Grass carp primarily feed on aquatic vegetation, and black carp feed almost exclusively on mussels, clams, and snails. Grass carp (often sterilized to prevent reproduction) are sometimes stocked to control nuisance aquatic vegetation in lakes and ponds but can be considered a nuisance when they enter waters they were not intended to colonize or when they become established. Bighead, black, and grass carp are still sometimes used in aquaculture in North America.
Q: Why were they brought here?
Bighead and silver carp were imported to the United States in the early 1970s as a method of biological control of nuisance algal blooms in wastewater treatment plants and aquaculture ponds as well as for human food.
Q. How big do they get and what do they eat?
Both bighead and silver carp become fairly large; records of both species approach 100 pounds, but silver carp over 20 pounds and bighead carp over 30 pounds are uncommon. The North American record for bighead carp is a 106-pound fish from Missouri. Both bighead and silver carp feed on plankton, algae, bacteria, and detritus (various small, organic debris) — items that form the base of aquatic food webs.
Q: Where are they in the United States?
Asian carp are found in the great rivers of the central United States, especially in the Missouri, Illinois, and Mississippi Rivers. Bighead and silver carp are not known to be established outside the greater Mississippi and Mobile River basins, though individuals have been captured in many locations. However, experts are quite concerned about the risk of invasion by this species to other waterways in the United States, including the Great Lakes.
Q: How abundant are Asian carp in U.S. waters?
An exponential increase in the population numbers of bighead and silver carp began in the mid-90s and continued through the mid-2000s in parts of the Mississippi and Illinois rivers. The Illinois Natural History Survey has estimated that a population of more than 4,000 silver carp (almost 10 tons) per mile exists between two Illinois River dams that limit their movement. USGS scientists hope to use genetic methods to determine the number of spawning Asian carp in different river reaches that are not bounded by dams.
Q: Do Asian carp affect native species?
Many studies show that bighead and silver carp substantially change ecosystems where they have been introduced. Studies around the world, including a USGS study in the Missouri River, found that zooplankton populations are dramatically reduced when Asian carp are abundant. In the presence of high densities of silver carp, large phytoplankton (plant plankton) species decline, but very small phytoplankton species, too small to be fed on by silver carp, usually become more abundant. The end result is water that appears very green but has little zooplankton. Native fish that eat zooplankton may be negatively affected by Asian carp if food resources are limited. Furthermore, since nearly all fish feed on zooplankton when they are very young, most species have the potential to be affected. There is also evidence of native planktivores being out-competed by Asian carp for food resources in the U.S. as well as around the world.
Q: I’ve seen video footage of Asian carp jumping out of the water. Do people get hurt?
Silver carp have been observed to leap into the air simultaneously as an apparent fright reaction to rocks thrown in the water, passing trains, geese taking off from the water, or when they unexpectedly find themselves in a tight place. Speeding boats seem to especially frighten them, and often dozens of the fish will be airborne at once, sometimes reaching heights of 10 feet off the water. When they collide with boaters or property, injury and damage can result.
Q: Is it possible to eradicate Asian carp once they are in an area?
Eradication of any established population of Asian carp would be extremely difficult and expensive, if possible at all. Effective management of established invasive species that cannot be eradicated usually employs integrated pest management. This approach involves integrating as many feasible methods of control available for a given species into one management and control plan, each focused at the appropriate life stage and each applied most appropriately in time and space to achieve the desired level of control while minimizing economic costs and environmental risk. Generally, possible control methods include the use of fish poisons, physical barriers, physical removal, habitat alteration, or biological controls such as the addition of predators, parasites, or pathogens. Much research to potentially control the distribution or population size of Asian carp is ongoing as part of the Asian Carp Control Strategy Framework.
Q: How might I accidentally spread Asian carp?
The capture and movement of wild-caught baitfish is of special concern for spreading Asian carp. Young Asian carp could easily be transferred, as baitfish, from one body of water to another. In particular, juvenile silver carp sometimes school with gizzard shad and are similar in size, shape, and color. If you catch your own bait, in addition to being familiar with the bait regulations of your State, it is safest to use the bait only where it was caught and not to transport it to new waters, especially above dams.
Q. Can I eat Asian carp?
Asian carp of all types have white, firm, mild flesh, which is excellent table fare, but all Asian carp also have intramuscular bones in the filets that many people find undesirable. Asian carp feed low on the food web, are fast growing, are low in fat in the filets, and are not usually bottom feeders — all properties of fish that are lower in contaminants. Like any fish taken from inland waters, however, be aware of restrictions on consuming fish from any particular water way. For instructions on how to deal with the bones in Asian carp filets, see Flying Fish, Great Dish.