Mute Swan

Origin  |  Habitat  |  Introduction and Spread  |  Impacts  |  Identification  |  Prevention and Control  |  Occurrences  |  New York Distribution Map


Mute swans (Cygnus olor) are non-migratory waterfowl. They were first introduced in the United States in the 1870s as a decorative, captive waterfowl because of their impressive appearance. In the early 1900s, some swans escaped captivity in New Jersey (1916) and in New York (1919). Mute swans are now found throughout the Atlantic Flyway. These birds are very aggressive and threaten many native waterfowl species.

Adult mute swan.  Photo: Jim Occi, BugPics,


Mute swans are native to Europe and parts of Asia.


Mute swans thrive in aquatic habitats including bays, rivers, wetlands, lake inlets, and ponds where there is ample emergent and submerged vegetation. The swans utilize dense phragmites and cattail stands for nesting areas. A mated pair of mute swans typically stays in the same territory year-round, moving only for food shortages or if their habitat ices over.

Introduction and Spread

The swans were first brought to the United States and used in zoos and private estates because of their flashy appearance. A small number of birds escaped into the wild in New Jersey (1916) and New York (1919) and successfully created wild breeding populations. The birds then expanded into Rhode Island in the 1920s and are now found from southern Ontario, Canada to North Carolina. The release in the 1910s started with a wild population of about 500 birds. The population of mute swans in New York has increased in size to about 3000 birds.

The swans are capable of reproducing between the ages of two and five years old. They build large nests (4 – 5 feet in diameter) in March or April. Mute swans produce on average 6 eggs per clutch, but could produce as many as 11 per clutch. The eggs hatch in early June, approximately 35 days after being laid.


Mute swans pose a threat to aquatic plant communities and other organisms that rely on the vegetation to survive. Swans can reach vegetation up to 4 feet deep. In the Chesapeake Bay, it is estimated that 4,000 swans could consume 12% of the aquatic vegetation each year (Avery and Tillman 2005). Aquatic plants found both above and below the water’s surface are affected by mute swans with the majority of damage occurring below the water’s surface (Stafford et al. 2012). Flocks of mute swans cause considerably more damage than those found in pairs (Tatu et al. 2007). Additionally, vertebrate and invertebrate species that rely on the vegetation cover are indirectly negatively impacted by mute swans. Ecosystems are under greater pressure from mute swans than from native migratory tundra swans (Cygnus columbianus) because the mute swans do not migrate and may be present year-round at the same location.

Some mute swans are very aggressive and territorial and will chase off and sometimes kill other waterfowl species that enter their territory. With the swan’s large breeding territories in wetlands, they displace many native birds for breeding habitat. Swans tend to be most aggressive during the nesting and brood-rearing stages.

Mute swans feeding on aquatic vegetation.  Photo: Jim Occi, BugPics,


An adult mute swan is all white with an orange bill and black face with a black, fleshy knob on the forehead just above the nares. It is a large waterfowl that has a long, curved neck. Juvenile mute swans have dirty gray to white bodies, gray to pink legs, and a tan to pinkish bill. Adult mute swans weigh on average 25 lbs. The adults of native trumpeter and tundra swans have a similar body shape as mute swans, but may vary in overall size, facial markings and bill color. For more information about mute swans visit:

Adult mute swans have an orange bill and black facial markings.  Photo: Jim Occi, BugPics,

Prevention and Control

The New York State Department of Environmental Conservation (DEC) conducts surveys and research to gain more information on nest distributions, clutch sizes, hatching and survival rates, and numbers of breeding birds in a population. Understanding more about the population dynamics and behavior of mute swans will help for developing efficient management strategies. If a collared mute swan is found in New York, report it to the DEC to help with their tracking efforts. (For more information visit:

In many states, egg addling, culling, and euthanasia have been performed to control mute swan populations.  However, mute swans are protected by the New York State Environmental Conservation Law.  Do not handle or harm the swans, their nests, or any eggs without DEC authorization. If you have a problem with controlling mute swans, contact the DEC for more information.


Mute swans are currently found from Ontario, Canada to North Carolina, throughout the Atlantic Flyway region.  In New York State, Long Island and the Hudson Valley have the highest population of mute swans. Areas around Lake Ontario have been increasing in population size as well.

New York Distribution Map

This map shows confirmed observations (green points) submitted to the NYS Invasive Species Database. Absence of data does not necessarily mean absence of the species at that site, but that it has not been reported there. For more information, please visit iMapInvasives.

Northern Snakehead

Origin  |  Habitat  |  Introduction and Spread  |  Impacts  |  Identification  |  Prevention and Control  |  Occurrences  |  New York Distribution Map


The northern snakehead fish (Channa argus) has been identified as an invasive aquatic fish across the United States.  Snakehead fish got their name because of their long, cylindrical body plan and large scales on their head that give them a snake-like appearance.  In the United States, there are four species of snakeheads: Channa argus (northern snakehead), Channa micropeltes (giant snakehead), Channa marulius (bullseye snakehead), and Channa maculate (blotched snakehead).  The northern snakehead fish has succeeded in establishing breeding populations in the wild.  This species is of concern because it is a top predator and disrupts the natural aquatic feeding structure in ecosystems.

Northern snakehead fish. Photo: U.S. Geological Survey Archive, U.S. Geological Survey,


The snakehead fish family is native to parts of Asia and Africa.  The northern snakehead fish species is native to China and possibly Korea and Russia.


Snakeheads are an aquatic fish that live in freshwater streams, rivers, wetlands, or ponds. They prefer low moving to stagnant waters.  Snakeheads can survive the cold winters and low oxygen environment.  Some snakeheads are capable of breathing atmospheric oxygen and may be able to jump out of the water to be found on terrestrial land near aquatic systems.  During the spawning season, northern snakehead fish prefer shallow waters with macrophyte cover (Lapointe et al. 2010). Nests are made by first clearing an area and then weaving aquatic vegetation into a column to hold and protect eggs.

Introduction and Spread

It is believed that the northern snakehead fish entered the United States when aquarium owners discarded their unwanted exotic captive species into local waterways.  The fish is also an important food source in other countries and could have been intentionally released into waterways to create a local food source for fisherman here in the United States.  Even though it is illegal in some states to possess a snakehead fish, they are utilized in some restaurants and are available for purchase online.  Northern snakehead fish can spread by swimming underwater and are also capable of breathing out of the water to move short distances on land.  Snakehead fish breeding occurs during the summer months (June to August).  However, there is not a full understanding of the details of the snakehead fish reproductive cycle yet as their nesting behaviors in their introduced habitat differ from those in their native range (Gascho Landis and Lapointe 2010).  Gascho Landis and Lapointe (2010) did find that parent fish will stay with their young up to 4 weeks to increase juvenile survival.


Northern snakehead fish are strong predators at the juvenile and adult stages of their life cycle.  Many native species are outcompeted for food resources.  Small prey, such as zooplankton, larvae, and small fish and crustaceans populations may be threatened by feeding juvenile snakehead fish.  Adults devour fish, crustaceans, small amphibians, reptiles, and some birds and mammals.  During the spawning season and after the young are born, snakehead fish may become very aggressive towards trespassing species.  If the northern snakehead fish becomes established in the United States, it could cost millions of dollars in management, and ecological and recreational damages.

The mouth of a northern snakehead fish is filled with many sharp teeth.  Photo: U.S. Geological Survey Archive, U.S. Geological Survey,


Northern snakehead fish have long, narrow bodies with long dorsal and anal fins.  They have a large mouth and protruding jaw with canine-like teeth.  The fish get their name from the enlarged scales, shape and irregular, blotchy coloration on their head that give a snake-like appearance.  Snakehead fish may vary size depending on their age and location, but grow to be up to 4 feet in length.  Invasive northern snakehead fish are easily confused with the native bowfin and burbot. Check out a U.S. Fish and Wildlife Service factsheet for a comparison of the northern snakehead fish to the burbot and bowfin here:

Northern snakehead fish.  Illustration: Susan Trammell,
Immature northern snakehead fish in the center with two adults. Photo: Brett Billings, US Fish and Wildlife Service,

Prevention and Control

All snakehead fish have been assigned injurious wildlife status.  Under the Federal Lacey Act, these fish and viable eggs cannot be moved through importation or interstate transport. Once populations are found, efforts are made to eradicate and control snakehead fish.

Waters with snakehead fish presence can be treated using chemicals.  Previous control efforts have found that Rotenone has been successful in lakes and ponds.  However, chemical control methods should be done by professionals since the chemicals may effect or kill non-target fish species and also may require permits for use.  If approved to work with chemicals, always follow the instructions on the label.

If you catch a snakehead fish, do not release it back into the water. Kill it, freeze it in a double bag and then report the fish and its location to a local natural resource agency for documentation.  To prevent more occurrences from happening, it is important to control the current populations and also to educate others on the importance of not releasing or transporting exotic species to new ecosystems.


The northern snakehead fish was first discovered in the United States in California in 1997.  This species is considered established in Virginia, Maryland, Pennsylvania, New York and Arkansas.  Individual fish have also been collected in California, Florida, Illinois, Massachusetts, Delaware and North Carolina.  Established breeding populations in the Potomac River in Maryland and Virgina were discovered in 2004.  Genetic evidence shows that the introduction in the Potomac was unrelated to previous infestations in Maryland (Starnes et al. 2011).  In New York, the first documentation was reported in 2005 at Meadow Lake in Queens and then again in 2008 in a stream in Wawayanda, New York.  For the USGS interactive distribution point map visit:

New York Distribution Map

This map shows confirmed observations (green points) submitted to the NYS Invasive Species Database. Absence of data does not necessarily mean absence of the species at that site, but that it has not been reported there. For more information, please visit iMapInvasives.

Asian Clam

Origin and Spread   |   Maps   |   Identification   |   Biology   |   Ecology   |   Ecological Impacts  |  Economic Impacts   |   Control and Management  |  New York Distribution Map

Additional Common Names

Asiatic clam, Prosperity clam, Pygmy Clam, Golden clam, Good luck clam


Origin and Spread

The Asian Clam Corbicula fluminea (Müller) is native to the fresh waters of eastern and southern Asia. It was likely introduced to the West Coast of North America around 1930, initially assumed to have been imported as a food source for the immigrating Chinese population (USACE ERDC 2007). Alternatively, it may have come in with the importation of the Giant Pacific oyster also from the Asia (Foster 2012). Live Asian clams were first detected in US waters in 1938 in the Columbia River, Washington; the species quickly spread across the continent and is currently found in 44 states. Corbicula was detected in the Ohio River in 1957 and continues to spread through drainages in the Midwest and Northeast. In New York State, the Asian clam has been collected in the running waters of central and western portions of the state, the Erie Canal from Lockport east to Clyde (shells only, colonization status unknown), Canandaigua Lake Outlet (shells only, colonization status unknown), Canandaigua, Keuka, Otisco, Owasco, and Seneca Lakes in the Finger Lakes, the Hudson River from Troy to Newburgh, the Wallkill River (colonization status unknown), the Champlain Canal near Fort Edwards, Lake George, and in Massapequa Lake and a number of other ponds and streams and the Massapequa Reservoir on Long Island.

The exact mechanism for secondary dispersal of Corbicula throughout North America is unknown, but likely involves human activity, including bait bucket introductions, accidental introductions associated with imported aquaculture species, and intentional introductions by people who buy them as a food item in markets (Foster 2012). Larval clams can attach to vegetation, floating debris for long distance dispersal. There is no peer-reviewed data demonstrating long distance overland travel by juveniles as a result of byssal attachment to trailered boats (McMahon 2012). Juvenile Corbicula are more likely to be carried in bilge and livewell water in boats and on vegetation attached to anchors and trailers or in sediments left on anchors (McMahon 2012).The only other significant dispersal agent is thought to be passive movement via water currents. There remains some question regarding transport by waterfowl. Based upon Foster (2012), birds are not considered to be significant distribution vectors. Sousa, et. al. (2008) cites a number of credible peer-reviewed sources indicating that transport on the feathers and feet of water birds is a secondary transport vector.


The species has a typical oval-triangular clam shape, with a dorsal “beak” or umbo at the peak of the shell. The outside of the shell (periostracum) is olive, or yellowish to black-brown in color, with 1-3 brown/purple colored radial bands (particularly in juveniles) and white erosion rings near the umbo. As the clam ages, the periostracum becomes darker in color. There are also distinctive, thick, concentric growth rings on the periostracum. The inside layer of the shell, the nacre (or “mother of pearl layer) is typically white-bluish white in color. Inside each shell half (or valve), there are also 1-2 pair of small, elongated  and , finely serrated lateral “teeth” that extend on either side from the umbo part way  down on the inside edge of each valve. Also, the interior of each valve, immediately under the umbo, there are 3  cardinal “teeth” (MacNeill 2012). The clam most closely resembles native sphaerid (fingernail) clams, however, sphaerid clams are smaller (6-14 mm), more oval in shape, cream colored, have fine growth rings, lack serrations on the lateral teeth and are found completely buried in the sediment. These relatives of Corbicula are also found in slow flowing waters with poorer water quality.

Corbicula fluminea External (left valve) and Internal (right valve) body features

Corbicula fluminea identication key


Corbicula burrows into the bottom sediments of streams and lakes and has the ability to feed from both the water column and the substrate. It uses its siphon to filter feed suspended particles (particularly phytoplankton) from the water and its fleshy foot appendage to pedal feed on detritus in the sediment. Corbicula can live in a variety of substrates, but prefers sand and gravel, over silt hard surfaces (McMahon 1999).

Corbicula is less tolerant than native mussels to environmental fluctuations. It is extremely sensitive to low oxygen conditions, and consequently its distribution is restricted to well‐oxygenated streams and lake shallows. In its native semi‐tropical/tropical habitat, the Asian clam is rarely exposed to temperature extremes. Its northern distribution in North America is thought to be limited by a 2°C lower lethal limit, and reproduction requires sustained water temperatures of 15°‐16°C. Asian clams have been known to find temperature refuges in cooler waters heated by power plant discharge. Upper lethal limit is believed to be 30°-35°C (Foster 2012, MacNeill 2012). Corbicula has been found to be resistant to desiccation and can survive periods of low water in damp sand or mud (USACE ERDC 2007).

Adult Corbicula are simultaneous hermaphrodites (both male and female) that are capable of both cross and self‐fertilization; thus, it takes only 1 individual to start a population. [Note: some literature indicates that Corbicula also exists as male and female sexes; this idea might be a result of observation of cross fertilization between hermaphrodites.] Adults can live 3‐4 years, and typically reproduce two times a year, although some populations have been observed reproducing more often under optimal situations. A single adult can produce 1000 – 100,000 juveniles per year. Egg fertilization is internal and the larval clams are brooded on the gill where they transform into juveniles in about 4-5 days (MacNeill 2012). Juveniles are tiny (0.25mm) and are capable of long distance dispersal via stream transport and water currents (using a mucous “balloon” or “parachute” {MacNeill 2012}), or hitchhiking on animals, floating objects, or vegetation (to which they can attach via a byssal thread). The juveniles transform into a pediveliger (shelled juvenile equipped with a foot) and settle to the bottom at about 0.25 mm in size. Pediveligers can crawl around along the bottom and seek firm substrates where they attach (at about 1.0 to 1.5 mm in size) using a temporary byssus which eventually disappears (MacNeill 2012). Juvenile clams can reach maturity in 3‐6 months or about 6-10 mm in size, and reach 10 to 30 mm in size during their first year depending on food availability and temperatures (MacNeill 2012).

Corbicula can rapidly grow into dense populations (> 2,000 per square meter), but are prone to rapid die‐offs with sudden changes in temperature (hot or cold) and low oxygen. However, their life history traits (i.e., quick maturity, high fecundity) enable rapid re‐colonization and population recovery, even after near extirpation. Additionally, these traits allow the Asian clam to successfully colonize habitats disturbed by human activity (e.g., channels and impoundments) that are unsuitable for native mussels.


Like other bivalves, Corbicula is a filter-feeder on microscopic plants, animals (including bacteria) and in the water column or in the sediments. Among other freshwater bivalves it has the highest rates of filtration rates (up to 1.3 liters/hr/clam), food consumption and growth of any species (MacNeill 2012). It is also extremely efficient in channeling consumed food for growth and reproduction. Its ability to reproduce rapidly, coupled with low tolerance of cold temperatures, can produce wide swings in population sizes from year to year in northern water bodies. Both yellow and brown morphs are simultaneous hermaphrodites and brood their larvae in the inner demibranchs (Foster 2012). The life span is about one to seven years. No large-scale geographic features function as dispersal barriers.


Ecological Impacts

Like other invasive mussels (e.g. zebra and quagga mussels), Corbicula is highly successful coupling the nutrient and energy flows that occur in the water column and bottom sediments. With a high filtering capacity and population density, Corbicula filters out phytoplankton and other particles suspended in the water that are also important food sources for other filter‐feeding organisms. Unlike zebra and quagga mussels, Corbicula also uses its pedal foot to feed on organic material and tiny organisms (microbes, protists, meiofauna) in the sediment (Hakenkamp et al. 2001). Whether Corbicula depletes these food resources to the extent that it negatively affects other organisms (particularly native unionid and sphaeriid mussels) remains an open question (Strayer 1999).

Corbicula can affect aquatic ecosystem processes in other ways. Bivalves, particularly when in dense populations, excrete significant amounts of inorganic nutrients, particularly nitrogen that, in turn, can stimulate the growth of algae and macrophytes (Lauritsen and Mozley 1989, Sousa et al. 2008). Additionally, Asian clam mass mortality events that occur in the summer followed by the release of nutrients via decomposition may also have negative effects on water quality. The shells of dead Asian clams can also provide a hard substrate on soft sediments, creating new habitat for other species that prefer hard substrates (e.g., zebra mussels).

It should be noted that to date, there are few studies on the ecological impacts of the Asian clam on native biota (McMahon 1999). In fact, most studies examine a water body after Corbicula invasion, with no comparable information on the biota or environmental conditions pre‐invasion.

Moreover, recent justifications for expensive and intensive management actions (e.g., Lake Tahoe Asian Clam Response) overstate evidence in the scientific literature. For example, in “Asian clam (Corbicula fluminea) of Lake Tahoe: Preliminary scientific findings in support of a management plan,” Wittman et al. (2008) state that:

Asian clam is known to aggressively outcompete native invertebrate communities.”

Here the report authors incorrectly interpret and cite the findings of Karatayev et al. (2003). Karatayev and colleagues studied Corbicula in a Texas reservoir. Although the Asian clam dominated the total animal biomass of the reservoir sediments (up to 95%), it was not associated with declines in native biodiversity. In fact, it was found to co‐occur with an abundant population of native unionid mussels.

Studies claiming that the Asian clam has an impact on native bivalves (particularly unionids) are often anecdotal and only report the spatial distribution of bivalves after invasion (Strayer 1999). They assume that non‐overlapping distributions of Corbicula and native mussels indicate that Corbicula have outcompeted the native species. As Strayer (1999) points out, this is just one possible explanation. Corbicula could also prefer different habitat than native mussels (e.g. sandy vs. silt/gravel). Native mussels have long experienced declines due to human‐induced changes to habitat (pollution, land use change, channelization), and it is difficult to tease apart these changes versus direct impacts of invading Corbicula that also happen to do well in disturbed habitats. Thus, while it is quite possible that in some cases Corbicula has a direct, negative impact on native biota, more studies that monitor changes in mussel populations over time and that directly evaluate competitive interactions are warranted.

Economic Impacts

Asian clams can colonize the intake pipes of water treatment systems and power stations. Unlike zebra mussels, Corbicula do not attach to the hard substrate. Rather, juvenile clams pass through filter screens/strainers and settle on the floors of intake pipes where low flow allows silt and sand to settle. The clams reproduce in situ and continue to accumulate in pipes and are transported deeper into the system. Corbicula fouls the pipes, blocking structures with shells, altering flow, and increasing sedimentation rates (McMahon 1999).

Asian clam shells that accumulate in beach or swimming areas will also impede recreation and tourism.

Control and Management

Little to no research regarding control practices have been published in the peer‐reviewed scientific literature. The Lake Tahoe team has submitted a manuscript for publication to the journal Biological Invasions on the use of bottom barriers to control Corbicula and it remains in the peer review process. Additionally, the New York Invasive Species Research Institute had difficulty locating research-based Best Management Practices for Corbicula.

To date, given the life history traits of Corbicula that make it a successful invader and the widespread distribution of the species in North America, eradication is typically not a viable option. As with many aquatic invaders, emphasis ought to shift from eradication to containment and spread prevention.

New York Distribution Map

This map shows confirmed observations (green points) submitted to the NYS Invasive Species Database. Absence of data does not necessarily mean absence of the species at that site, but that it has not been reported there. For more information, please visit iMapInvasives.


New York Invasive Species Information wishes to acknowledge the work of Dr. Holly Menninger, former director of the New York Invasive Species Research Institute. Dr. Menninger’s literature review formed the basis for this species profile and provided much of the text published above.

Zebra and Quagga Mussel

Ecosystem impacts | Physical Impacts | Quagga Mussels | New York Distribution Map

Zebra Mussel (Dreissena polymorpha)

This clam-like bivalve mollusk, commonly called the zebra mussel, Dreissena polymorpha, is a native of the Ponto-Caspian region of Eastern Europe and western Asia—the Black, Caspian, and Aral Seas, and the Ural River drainage. It was introduced into several European freshwater ports during the late 1700s; within 150 years Dreissena was found throughout European inland waterways. Dreissena was first found in the Great Lakes in Lake St. Clair in 1988, where it is believed to have been introduced as the result of the discharge of freshwater international shipping ballast water.

Map of Zebra and Quagga Mussel Distribution, 2008
Mussel grouping. Scott Camazine, New York Sea Grant

While there is still some disagreement as to whether the zebra mussel was introduced in a single location or whether the North American population is the result of multiple introductions in various locations over a number of years, what is certain is that once established in the Great Lakes, the zebra mussel spread rapidly across the eastern half of the continent, reaching 23 states and two provinces in only 15 years. Once established in the lakes, the mussel spread via intra- and interbasin ballast water movement; attachment to commercial ship and recreational boat hulls and boat trailers; movement of construction equipment; larvae carried by currents, in bait buckets and in recreational boat live wells; commercial bait and aquaculture shipments; and, natural movement in lake and river currents and flows. Zebra mussels have now crossed the 100th Meridian and are now found in 25 states nationwide.


Zebra Mussel
Zebra Mussels.

Ecosystem Impacts

Zebra mussels are small (generally under 5 cm), with elongated shells typically marked by alternating light and dark bands. Eggs (as many as one million per season per female) are fertilized outside the body in the spring or summer. Larvae (veligers) are free-swimming for up to 30 days, being dispersed by currents. Juvenile mussels settle to the bottom and attach to suitable hard substratum (rock, wood, shells of native mussels, and human-made surfaces such as concrete, steel, fiberglass, etc.) by secreting durable elastic strands called byssal threads; if no hard substrate is available, zebra mussels will also attach to vegetation. The mussels are generally found within 2 to 7 meters of the water surface but have been found as deep as 50 meters. Zebra mussels will colonize lakeshores and riverbanks where they attach to rock or gravel substrates, forming broad mats up to 10 to 15 cm in thickness. Colony densities may reach 20,000 per square meter. Extensive colonization of shoal areas could impair reproduction of species of fish (such as walleye and lake trout) that spawn only on rocky-bottomed areas.

Zebra mussels are filter feeders, capable of filtering up to two liters of water per day per adult, feeding on phytoplankton, small zooplankton, detritus, and even bacteria down to approximately the one-micron size range. Such filtration can dramatically increase water clarity and significantly reduce lake productivity, changing aquatic plant and animal habitat value. It has been estimated that the zebra mussel population of the western basin of Lake Erie has the capability of filtering the entire volume of the basin daily. Since phytoplankton and detritus are major food sources for pelagic lake and riverine food webs, fisheries-related impacts can result from zebra mussel filtration activity. Excessive removal of phytoplankton, detritus and small zooplankton from the water column can result in a decline in zooplankton species that feed upon those food particles. Larger zooplankton species and larval fish of all species preying on smaller zooplankton face reduced survival as mussel populations expand. Changes in water transparency can favor a shift towards increased production of benthic algae.

Physical Impacts

Because of an affinity for water currents, zebra mussels extensively colonize water pipelines and canals, such as those in drinking water treatment plants, industrial facilities and electric power generation plants. Once inside an intake, the mussels are protected from predation and the ravages of the weather, resulting in very large densities of mussels (one Great Lakes power plant canal had up to 750,000 mussels per square meter). Such mussel growth can severely reduce water flow, result in a loss of intake head, obstruct valves, clog condensers and heat enchangers, result in noxious tastes and smells in treated water, produce nuisance methane gas, and increase electro-corrosion of steel and cast iron pipelines. Zebra mussels attached to a commercial or recreational vessel’s hull increase drag and fuel consumption. Recreational use of beaches is impacted by colonization of cobble in nearshore areas and by littering of beaches by shells washed up by storm waves. Bathers on Great Lakes beaches have adopted the use of beach/bathing footgear to prevent cuts from zebra mussel shells. It has been estimated that since their introduction into North America, zebra mussels have caused $1 billion to $1.5 billion worth of economic harm.

Zebra Mussels in pipe
Clogged pipe. Photo: Don Schloesser, USGS, Biological Resources Division

Quagga Mussel (Dreissena rostriformis bugensis)

Originally thought to be a variant of the zebra mussel (D. polymorpha, see species profile, above), the quagga mussel (nicknamed after a now-extinct zebra-like quadruped), is now known to be genetically a separate, distinct species. For the general description of introduction, range expansion, and ecological and physical impacts, see the discussion in the profile of D. polymorpha. Zebra mussels possess a distinctly flattened ventral (hinge) surface as compared to the same side on quagga mussels, which presents a smoothly rounded surface. A simple field test to distinguish the two as large adult specimens is that a zebra mussel will usually sit upright on its ventral side, whereas a quagga mussel will tip over. On smaller mussels, with shells that have not finished forming, this is not a definitive test. A second test is that the valves (shell halves) on zebra mussels are symmetrical with the two valves meetings along a straight line, whereas on quagga mussels they are asymmetrical, with the two valves meeting along a curved line.

Zebra and Quagga Mussels
Shell shape comparison of zebra mussel (D. polymorpha) on left and quagga mussel (D. bugensis) on right. USGS

Quagga mussels have been found to be able to survive and colonize in areas of soft substrate, such as sandy or silty lake bottoms, whereas zebra mussels that settle onto such bottoms usually do not survive. D. polymorpha is more tolerant of warm temperatures than is D. bugensis, capable of sustaining water temperatures of 30°C for extended periods of time and up to 39°C for several hours, while D. bugensis has an upper thermal tolerance limit of approximately 25°C. D. bugensis appears more efficient at growing under lower water temperatures than D. polymorpha. Quagga mussels can filter and incorporate food down to the sub-micron level, thereby including bacteria too small for zebra mussels or native clams and mussels to consume, giving the quaggas a competitive advantage over zebra mussels and native species when levels of larger plankton are too low to sustain large populations. There are no apparent salinity tolerance differences between the two species, each having chronic salinity tolerance levels of approximately 2 parts per thousand, allowing some, but not much, range expansion into tidal estuaries.

A marked distribution replacement of D. polymorpha by D. bugensis is taking place in the Great Lakes; since the mid-1990s, D. bugensis has almost totally replaced D. polymorpha in Lakes Erie and Ontario, to the extent that the original zebra mussels are now very rare in most of eastern Lake Erie and throughout Lake Ontario. It is theorized that this might be due do the quagga mussel’s ability to colonize softer substrates than zebra mussels, to the quagga’s ability to grow more efficiently in colder water temperatures than zebra mussels, particularly in deeper waters, and to the quagga’s more efficient feeding capability.

New York Distribution Map: Zebra Mussel

This map shows confirmed observations (green points) submitted to the NYS Invasive Species Database. Absence of data does not necessarily mean absence of the species at that site, but that it has not been reported there. For more information, please visit iMapInvasives.

New York Distribution Map: Quagga Mussel

This map shows confirmed observations (green points) submitted to the NYS Invasive Species Database. Absence of data does not necessarily mean absence of the species at that site, but that it has not been reported there. For more information, please visit iMapInvasives.

Spiny Waterflea

Background | Biology & Impacts | New York Distribution Map


This predatory cladoceran zooplanktor, commonly known as the spiny waterflea (Bythotrephes longimanus; formerly identified as Bythotrephes cederstroemi), is a crustacean, a relative of crayfish and shrimp. A native of the Ponto-Caspian region of Eastern Europe and Western Asia, Bythotrephes was first found in North America in December 1984 in Lake Huron. Spread through the Great Lakes was rapid, with the species being found in Lake Ontario in September 1985, Lake Erie in October 1985, Lake Michigan in September 1986, and Lake Superior in August 1987.This species is believed to be an international shipping ballast water introduction. Its rapid spread throughout the lakes most likely is the result of currents, inter- and intra-lake ballast transfers, and recreational boating on the lakes.


Biology & Impacts

Bythotrephes is planktivorous, consuming up to 20 prey zooplanktors per day. One major target species of Bythotrephes is Daphnia (another small water flea). Research has shown that a dramatic decrease in Daphnia abundance coincided with the introduction of Bythotrephes in Lake Michigan. Density of a native predatory zooplanktor, Leptodora, also dropped off coincident with the appearance of Bythotrephes, possibly because Bythotrephes was outcompeting it for Daphnia. It has been theorized that declines in the abundance of Daphnia and other Bythotrephes prey may alter the food web in the Great Lakes, reducing the number of young plankton-eating fish which survive their first year. Researchers have observed that chinook salmon, walleye, white bass, alewife, yellow and white perch, emerald and spottail shiner, and lake whitefish consume Bythotrephes. It is not known, however, how nutritional this water flea is for fish, given the amount of its mass made up by exoskeleton and the long tail spine. It is too soon to know the ultimate impact of Bythotrephes on Great Lakes ecosystems. If the water flea is found to be a preferred (and nutritious) food source for perch and other fishes, its impact on fish populations may be beneficial. If predation by Bythotrephes results in reduced populations of preferred prey, such as Daphnia, the water flea may result in negative consequences to native Great Lakes fish populations. Is has been theorized that the decline of alewife in Lakes Ontario, Erie, Huron, and Michigan may be related to the introduction of Bythotrephes.

New York Distribution Map

This map shows confirmed observations (green points) submitted to the NYS Invasive Species Database. Absence of data does not necessarily mean absence of the species at that site, but that it has not been reported there. For more information, please visit iMapInvasives.

Sea Lamprey

Biology | Life cycle | Impacts | Control | New York Distribution Map


Adult sea lamprey
Adult sea lamprey

The sea lamprey (Petromyzon marinus) is one of four lamprey species found in the Lake Champlain Basin. Lamprey are eel-shaped fish with a skeleton made of cartilage and they belong to a relic (primitive) group of jawless fishes called Agnathans. The sea lamprey has smooth, scaleless skin and two fins on its back (dorsal fins). The sea lamprey is parasitic; it feeds on other fish, using a suction disk mouth filled with small sharp, rasping teeth and a file-like tongue. These are used by the sea lamprey to attach to a fish, puncture its skin, and drain its body fluids.

Life cycle

Sea lamprey have a complex life cycle. The first four years of their life are spent as ammocoetes [am-mah-seats] – a blind worm-like larval stage – in the soft bottom and banks of waters that flow into Lake Champlain. They then transform into the parasitic adult stage and enter the lake to feed on landlocked Atlantic salmon (salmon), lake trout and many other fish species; which they prefer due to their small scales and thin skin. After twelve (12) to twenty (20) months in the lake the adults migrate back into the streams flowing into the lake to spawn, after which the adults die.

Lampreys in Lake Champlain

Moderate numbers of sea lampreys were first noted in Lake Champlain in 1929. The sea lamprey has been considered a non-native invasive species that entered Lake Champlain during the 1800s through the Hudson/Champlain Canal. Recent genetic studies indicate that the sea lamprey may be native to Lake Champlain.

Three other lamprey species are found in the Lake Champlain Basin. Two species are non-parasitic, and while the third species is parasitic, it does not have a significant impact on the Lake Champlain fish community.

Whether the sea lamprey is native to Lake Champlain or not, it is having detrimental impacts on the Lake Champlain fisheries, ecosystem, and human residents that are very significant.


Sea lamprey have a major detrimental impact on the Lake Champlain fish community, the Lake Champlain Basin ecosystem, the anglers that fish Lake Champlain, and the many people throughout the watershed whose livelihood is directly or indirectly supported by the fishing and tourist industry.

Lake trout with sea lamprey attached.
Lake trout with sea lamprey attached.

Adult sea lamprey attach to a host fish, rasp and puncture its skin, and drain its body fluids, often killing the host fish. Their preferred hosts are salmon, lake trout and other trout species, however they also feed on other fish species, including lake whitefish, walleye, northern pike, burbot, and lake sturgeon. The lake sturgeon is listed as a threatened species in New York and an endangered species in Vermont and it is likely that sea lamprey are affecting their survival.

Impacts on Host Fish

Most sea lamprey hosts are native fish species that have been part of the Lake Champlain Basin ecosystem for thousands of years. Additionally many of these fish species are important sportfish, highly prized and sought after by local and visiting anglers.

Prior to any control measures, angler catches of lake trout and salmon in Lake Champlain were a fraction of catches in similar lakes, despite intensive stocking efforts. High wounding rates indicated that sea lamprey were having a significant impact on the lake trout and salmon populations, and were preventing the restoration of these native fish species to Lake Champlain.

Fresh lamprey wound on a fish and the lamprey that was removed from the fish.
Fresh lamprey wound on a fish and the lamprey that was removed from the fish.

Studies on the Great Lakes show a 40 to 60 percent mortality rate for fish attacked by sea lamprey. Other studies found that a single sea lamprey can kill 40 or more pounds of fish during its adult life. The abundance of sea lamprey were obviously having significant impacts on Lake Champlain’s fishery and ecosystem.

Impacts on Local Economy

Poor fishing caused many anglers to seek fishing opportunities elsewhere. A study estimated that 29.4 million dollars in economic benefits to businesses and residents of the Lake Champlain Basin were lost due to the impacts of sea lamprey.


Liquid TFM applied to a stream during a lamprey control treatment.
Liquid TFM applied to a stream during a lamprey control treatment.

Due to the severity of the impacts that sea lamprey have on the Lake Champlain fishery and ecosystem, and the social and economic impacts on the people who live in the Lake Champlain Basin, it has been determined that sea lamprey populations should be controlled. The federal and state governments, the agencies that manage Lake Champlain, the various organizations that are concerned with Lake Champlain and the people that live in the Lake Champlain Basin generally agree that it would be irresponsible not to control the sea lamprey population.

The New York State Department of Environmental Conservation, the Vermont Department of Fish and Wildlife and the United States Fish and Wildlife Service formed a cooperative and began an integrated control program to reduce the sea lamprey population in Lake Champlain to an acceptable level. The program is not attempting to eliminate the sea lamprey from Lake Champlain, but rather to reduce the impacts of sea lamprey on the lake’s fishery and restore balance to the ecosystem.

Control Efforts

Physical methods of control include the use of barriers to prevent adult sea lamprey from migrating up waterways to spawn and traps to capture adult sea lamprey before they can spawn.

Bayluscide being distributed from boat during a lamprey control treatment on a delta.
Bayluscide being distributed from boat during a lamprey control treatment on a delta.

However, the most significant and effective form of control has been the treatment of tributaries and deltas with lampricides – TFM in tributaries and Bayluscide on deltas. The lampricides target the larval sea lamprey, killing them before they can transform into their parasitic adult form.

It should be noted that after years of study in Lake Champlain, the Great Lakes, and other places where sea lamprey are controlled by using lampricides, fisheries managers have concluded that the lampricides have little or no known permanent effect on populations of non-target species present in the treatment areas.

Control Program

Evaluation of an eight year experimental sea lamprey control program that took place in Lake Champlain in the 1990s documented significant benefits for fish and anglers. These benefits included decreases in wounding rates on trout and salmon, increases in weight and survival rates of lake trout, increases in angler catch rates of lake trout and a benefit to cost ratio of 3.5 to 1.

At the end of the eight year experimental sea lamprey control program, a limited, three-year interim sea lamprey control program was undertaken from 1998 to 2000. After a thorough environmental review, a long term sea lamprey control program began in 2002.

Fish sampling programs, salmon returns to fish ladders, angler surveys and sampling of larval sea lamprey are used to measure the effectiveness of the control program. The control program may be expanded to other streams and delta areas if significant sea lamprey populations develop in them.


Fisheries staff wading through stream using an back electroshocker to locate larval lamrpey.
Fisheries staff wading through stream using an back electroshocker to locate larval lamrpey.

Assessments of sea lamprey populations are made before any control measures are undertaken and afterwards to assist in determining the effectiveness of the controls. Field staff, using a variety of capture methods, sample both adult and larval sea lamprey from streams and deltas to determine the presence and density of sea lamprey populations. This information is used to determine which streams or deltas are in need of control measures and which control measures to use.

Scientists and fish managers have considered, and continue to consider, other methods to reduce sea lamprey impacts. These include the use of pheromones (chemical attractants naturally produced by lamprey) to capture adult sea lamprey, the release of sterile males to disrupt spawning, and the stocking of lamprey-resistant strains of fish.

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New York Distribution Map

This map shows confirmed observations (green points) submitted to the NYS Invasive Species Database. Absence of data does not necessarily mean absence of the species at that site, but that it has not been reported there. For more information, please visit iMapInvasives.

Fishhook Water Flea

Background | New York Distribution Map


Cercopagis pengoi, known in North America as the “fishhook water flea,” is an aggressive, predatory zooplankton that preys on smaller zooplankton. It belongs to the same family as Bythotrephes (Cercopagididae), and, like Bythotrephes, has a long caudal process (“tail”) with up to three pairs of barbs near its end. Also like Bythotrephes, Cercopagis is a native of the Ponto-Caspian region of eastern Europe/western Asia (the area of the Caspian, Azov, and Aral seas). As with the spiny water flea, the fishhook water flea is believed to be an international shipping ballast water introduction.

Photo: Igor Grigorovich, University of Windsor

Since its first discovery in Lake Ontario in August 1998, copagis spread inland to six of New York’s Finger Lakes (Seneca, Cayuga, Otisco, Canandaigua, Owasco and Keuka) within a year, possibly on fishery sampling gear, in bait buckets, or on recreational angling equipment. In these inland lakes, Cercopagis now dominates the offshore zooplankton community during the summer and fall. This species has also been found in Grand Traverse Bay and southern Lake Michigan and in western Lake Erie and the Detroit River. It is expected to spread throughout the Great Lakes by means of currents, inter- and intra-lake ballast transfers and recreational boating and angling. The fishhook water flea, like the spiny water flea, fouls fishing lines, downs rigger cables and fish nets, in many cases to an extent that anglers have had to cut their lines and lose fish because of reel clogging. The species’ length, including body and spine, can exceed 1 cm.

The species has been observed at densities of 170 to 600 individuals per square meter. In addition to sexual reproduction, Cercopagis most commonly reproduce parthenogenically (asexually), which allows them to quickly establish new populations with a relatively small seed population without the need for a large number of the smaller males along with females. Eggs produced in the early part of the season are delicate and very susceptible to damage, with low recruitment rates. Later in the season, as surface water temperatures decline, Cercopagis females produce over-wintering or resting eggs (the species is also known to produce resting eggs anytime during the year when environmental conditions become inhospitable). Such resting eggs can successfully overwinter in an inactive state and replenish the population after hatching in the spring. Resting eggs are also resistant to desiccation, freeze-drying and ingestion by predators (such as other fish). They can be easily transported to other drainage basins by various vectors, particularly if they are still in the female’s body (the barbed caudal spine allows attachment to ropes, fishing lines, waterfowl feathers, aquatic gear, vegetation, and mud). Resting eggs can hatch regardless of whether the carrier female is alive or dead.

It is unknown what the future impacts of Cercopagis are going to be. It is possible that the high population densities of the species will create significant predation pressure on smaller cladocerans to impact the size and composition of native phytoplankton communities. Furthermore, Cercopagis may compete with native, young-of-the-year fish populations for small prey. It is also possible that the species may become prey itself for larger fish. It is not known, therefore, whether Cercopagis will ultimately be an energetic source or sink in the Great Lakes.

New York Distribution Map

This map shows confirmed observations (green points) submitted to the NYS Invasive Species Database. Absence of data does not necessarily mean absence of the species at that site, but that it has not been reported there. For more information, please visit iMapInvasives.



Chinese Mitten Crab

Background | Planned Response | How to Identify a Mitten Crab | What to do if you Find a Mitten Crab | New York Distribution Map

Christian Fischer [CC BY-SA 3.0 ], from Wikimedia Commons


The first Chinese mitten crab documented in Chesapeake Bay was collected June 9, 2006 at the mouth of the Patapsco River, Maryland by a commercial waterman fishing crab pots. This was the first confirmed report of a Chinese mitten crab (Eriocheir sinensis) in the Eastern United States. The species is native to East Asia, and is a potential invasive that could have negative ecological impacts. The Chinese mitten crab occurs in both freshwater and saltwater. It is catadromous, migrating from freshwater rivers and tributaries to reproduce in salt water. Young crabs spend 2-5 years in freshwater tributaries and can extend over 50 miles inland, potentially above fall lines. Mature male and female crabs migrate downstream to mate and spawn in salt water estuaries.

Under the Federal Lacey Act, importation and interstate transport of this animal is prohibited.

On June 23, 2007 a mature female mitten crab was captured in a commercial crab pot off Kent Point in the Maryland portion of Chesapeake Bay. This was the fourth mitten crab captured in the Bay in 3 years, and the first mature female. As of that date, no mitten crabs had been confirmed in upstream, freshwater habitats where they spend the bulk of their lives, burrowing in tributary banks. In late May 2007, four mature male mitten crabs were captured in commercial crab pots in Delaware Bay, and one mature male was reported from a commercial crab pot in the Hudson River, New York. There are several possible transfer mechanisms that could result in the delivery of these crabs to local waters, without the species becoming established. However, due to the documented ability of this species to invade and to establish itself in new areas, Maryland Department of Natural Resources (MD DNR), the Smithsonian Environmental Research Center (SERC), the US Fish and Wildlife Service (USFWS), and the National Oceanic and Atmospheric Administration (NOAA) established a joint effort to investigate the status of this species.

Planned Response

MD DNR and partner agencies are taking these encounters seriously. This watch statement has been circulated to federal, state, county, municipal and private agencies and/or organizations that are conducting sampling programs in the Chesapeake Bay watershed and potential mitten crab habitat. MD DNR is also networking with commercial watermen, fish passage monitoring programs, and with power companies that monitor species captured on cooling water intake screens. This broad based monitoring is the first step to assessing if additional mitten crabs are present in the Bay habitat.

How to Identify a Mitten Crab

Chinese mitten crab. Note the notch between the eyes and four lateral spines on each side of the carapace. Source: California Department of Fish and Wildlife
    • Only crab in fresh waters of North America
    • Claws equal in size with white tips and “hair”.
    • If you find a crab without hair on the claws, it is NOT likely to be a mitten crab.
    • Carapace up to 4 inches wide; light brown to olive green in color.
    • No swimming legs. This crab has eight sharp-tipped walking legs.

Correctly Identifying Mitten Crabs

There is another species of crab found in Maryland, which has been mistakenly identified as a Mitten Crab.
Small mitten crabs may be confused with the Harris mud crab, because of their similar size and appearance


Harris Mud Crab Characteristics

  • no notch between the eyes
  • non-hairy, white-tipped claws
  • ridges on back
  • dull greenish-brown color
  • maximum carapace width is 19 mm (¾ inch)

Juvenile Mitten Crab Characteristics

  • notch between the eyes
  • claws may not be hairy if carapace width is less than 20 mm (¾ inch)
  • claws are hairy by 25 mm (1 inch) carapace width
  • four lateral carapace spines (fourth spine is small)
  • smooth, round carapace or body shape
  • legs over twice as long as the carapace width
  • light brown color

What to do if you Find a Mitten Crab

  • Do not throw it back alive!
  • Freeze the animal, keep on ice, or preserve it in rubbing alcohol, as a last resort.
  • Note the precise location where the animal was found.
  • If possible, take a close-up photo, as above.
  • Photos can be emailed to for preliminary identification. Please include your contact information with photo.
  • If you cannot take a photo, contact the Mitten Crab Hotline (443-482-2222). REMEMBER THE LAW!

Never transport a live Mitten crab except to deliver to proper authorities.

Mitten crab specimens are needed to confirm sightings, so please follow the instructions above, if you find a mitten crab.

To learn more about mitten crabs see:

With special thanks to our partners, USFW, NOAA, and SERC.

New York Distribution Map

This map shows confirmed observations (green points) submitted to the NYS Invasive Species Database. Absence of data does not necessarily mean absence of the species at that site, but that it has not been reported there. For more information, please visit iMapInvasives.


Asian Carp

Ecological Impacts & Risks     Economic Impacts     Prevention

Introduction and Spread

In North America, the term “Asian carp” typically refers to two species of invasive fish introduced from Asia: the bighead, or “bigheaded” carp (Hypopthalmichthys nobilis) and the silver carp (Hypopthalmichthys molitrix). These carp are native to China. They were originally imported into the southern United States in the 1970s to provide an inexpensive, fast-growing addition to fresh fish markets. They also served to help keep aquaculture facilities clean.  By 1980 the carp were found in natural waters in the Mississippi River Basin. As they have moved north through the Basin they have overwhelmed the Mississippi and Illinois River systems where Asian carp now make up more than 95% of the biomass in some areas. Silver carp can now be found in 12 states. Bighead and silver carp are currently in the Illinois River, which is connected to the Great Lakes via the Chicago Sanitary and Ship Canal.

Key bighead carp identification indicators (David Riecks, University of Illinois/Illinois-Indiana Sea Grant)


Key silver carp identification indicators (David Riecks, University of Illinois/Illinois-Indiana Sea Grant)

Two other species of carp imported to the United States from Asia can also become invasive in the wild, the grass carp (Ctenopharyngodon idella) and the black carp (Mylopharyngodon piceus). The herbivorous grass carp, indigenous to eastern Asia where it is cultivated for food, was introduced to the United States to control aquatic weeds in lakes and waterways. The molluscivorous black carp (i.e., feeding on snails, clams, mussels, and other mollusks) is a native of China where it is cultivated for medicinal purposes and as a food source. It was introduced to the United States to provide snail control in aquaculture settings. By the 1990s the grass carp had escaped from cultivation into the wild and can now be found in waters within or adjacent to 45 states where they are considered a threat to natural vegetation. Black carp have also escaped and are now in several locations along the Missouri and Lower Mississippi River Basins.

Grass carp (Texas Dept. of Parks & Wildlife)
Black carp (U.S. Geological Survey, SESC)


Ecological Risks and Impacts of Asian Carp

Silver and bighead carp are filter-feeders which feed on plankton (drifting animal, plant, or bacteria organisms that inhabit the open waters of waterbodies), with an apparent preference for bluegreen algae). Asian carp can dominate native fisheries in both abundance and in biomass. Bighead carp can reach 110 pounds, although 30 to 40 pounds is considered average (silver carp are generally smaller). Bighead carp can live over 20 years, maturing at about 7 years. Asian carp can consume 5 to 20 percent of their body weight per day. As most native fish feed on plankton during their larval and juvenile life stages (and some native fish remain planktivorous for life), this high level of feeding on plankton by Asian carp can have serious impacts on the stability of the food web, with bighead carp potentially outcompeting native fish while eliminating the main source of food for larval fish and native planktivorous fish. Native fish considered most at risk include ciscos, bloaters, and yellow perch, which serve as prey to important predatory sportfish including lake trout and walleye.

The Great Lakes provide a wide range of habitat types which would serve as good spawning, recruitment, and maturation areas for Asian carp. Spawning habitat could be provided in the flowing waters of Great Lakes tributaries, while young Asian carp prefer warm, biologically productive, backwaters and wetlands. When not feeding on plankton, Asian carp have been known to feed on detritus and root in the bottom of protected embayments and wetlands. This disturbance could have significant impacts on Great Lakes wetlands and shoreline vegetation which provide spawning habitat for native fish and breeding areas for native waterfowl.

Black carp, being molluscivores, are not a threat to plankton. Should black carp reach the Great Lakes from the Mississippi Basin, however, they could become a threat to native Great Lakes native clam, snail, and mussel populations (particularly those that are rare or endangered), as well as to lake sturgeon (another molluscivore). Black carp can grow to more than 100 pounds and a length of up to seven feet.

In their native habitats, populations of Asian carp are held in check by natural predators. Unfortunately, there are no native Great Lakes fish species large enough to prey on adult Asian carp. White pelicans and eagles have been observed feeding on juvenile Asian carp in the Mississippi Basin. The pelicans, found in the western reaches of the Great Lakes and eagles throughout the Basin may be expected to do the same. Native predatory fish such as largemouth bass may feed on juvenile Asian carp. Given the growth rates of Asian carp, many juveniles can be expected to grow too large too quickly for fish predation to be a significant pressure to hold down carp populations.

Once populations of Asian carp become established with recruitment of young fish exceeding mortality, eradication is considered to be difficult if not impossible. Populations might be minimized in some areas by denying access to spawning tributaries via construction of migration barriers, but this is an expensive proposition which may inadvertently result in negative impacts on native species. The best control of Asian carp is to prevent their introduction into the Great Lakes.


Economic & Recreational Impacts

When frightened by the sound of a boat or personal watercraft motor, silver carp have been known to jump up to ten feet out of the water. The sound of boat motors can cause entire schools of silver carp to jump simultaneously. It is not unusual for 20 to 30 pound silver carp to jump into boats, sometimes resulting in damage to equipment or even injury to occupants. The Great Lakes Commission estimates that almost one million motorboats and personal watercraft are in use the Great Lakes. If the silver carp gets into the lake, around one million recreators could be placed in jeopardy. This could have a negative impact on the $4.5 billion annual Great Lakes commercial and recreational fisheries. Unlike the silver carp, the bighead carp does not jump in response to boat traffic.

School of jumping silver carp
A school of silver carp jumping in response to passing motorboat. Photo:Jason Jenkins

if Asian carp feed (and root) extensively in Great Lakes shoreline wetlands, degradation of the water quality and damage to wetland vegetation in native waterfowl breeding areas could threaten the $2.5+ billion annual waterfowl hunting industry.



The main pathway through which Asian carp are expected to enter the Great Lakes is the Chicago Sanitary and Ship Canal (CSSC).

Silver Carp Distribution
Silver carp distribution as of January 2012 [US Geological Survey]
Bighead carp distribution
Bighead carp distribution as of January 2012 [US Geological Survey]
This manmade waterway directly connects Lake Michigan to the Mississippi River system. A series of three electrical barriers of underwater electrodes has been placed across the canal about 25 miles downstream of the lake. The electrodes create a pulsating field of direct electric current in the water of the canal, intended to deter the carp from swimming through the canal and into Lake Michigan.

Electric field carp dispersal barriers on the Chicago Sanitary & Shipping Canal (U.S. Army Corps of Engineers)
Electric field carp dispersal barriers on the Chicago Sanitary & Shipping Canal (U.S. Army Corps of Engineers)

The barriers may prove not to be 100% effective but are currently the main defense against introduction of the carp into the Great Lakes. In 2011, individual carp had been found as close as 22 miles from the barrier. The nearest known breeding population of Asian carp was 50 miles downstream of the barrier; no carp were known to be living above the barrier.

There is also the possibility that Asian carp may get into the Great Lakes through release of live bait into the CSSC above the barrier or directly into the lakes. Live Asian carp being transported to fish markets could also be accidentally or intentionally released into the lakes or their tributaries. The Asian carp has recently been added to the Federal Lacey Act as an injurious species and transport and possession of the fish has been banned.


Additional Asian Carp Information

Asian Shore Crab

Identification  |  Impacts  | New York Distribution Map

Photo: USGS,

The Asian shore crab, Hemigrapsus sanguineus, a native of the western Pacific Ocean from Russia to Hong Kong and the Japanese archipelago, is also known as Japanese shore crab and Pacific crab. Its known New York range includes the Hudson River and its lower tributaries and Oyster Bay National Wildlife Refuge on the north shore of Long Island. The crab’s means of introduction to the U.S. Atlantic coast is unknown, but it is theorized that adults or larvae were introduced via ballast water discharge from international shipping.


This shore crab has a square-shaped shell with 3 spines on each side of the carapace. Males have a fleshy, bulb-like structure at the base of the moveable claw finger. Carapace colors can be green, red, orangish brown or purple. Claws have red spots; legs are light and dark banded. Adult carapace width ranges from 1.4 inches to 1.7 inches. This species is highly reproductive, breeding from May to September, with females capable of producing three to four clutches per season, each containing up to 50,000 eggs. Free-floating larvae can be transported over long distances during the month that it takes them to develop into juveniles and settle out of the water column.

Photo: USGS,


Owing to this crab being an opportunistic omnivore (it feeds on macroalgae, salt marsh grass, larval and juvenile fish, and small invertebrates), it could potentially negatively impact populations of such native species as fish, shellfish and other crabs by predation and by general food web effects. It could also out-compete native mud crabs, blue crabs and lobsters.

New York Distribution Map

This map shows confirmed observations (green points) submitted to the NYS Invasive Species Database. Absence of data does not necessarily mean absence of the species at that site, but that it has not been reported there. For more information, please visit iMapInvasives.