What Anglers Need to Know About Aquatic Invasive Species

Aquatic invasive species are plants, animals, and microbes that have been introduced into a body of water outside of their native range, causing ecological and economic harm. Once they become established in a water body, they can quickly displace native species, disrupt food webs, and cause environmental degradation. The cost of controlling an established invasive species and the loss of revenue from diminished fishing, boating, tourism, and other recreational opportunities can be substantial compared to the cost of preventing introductions and monitoring aquatic invasive species. When the ecological and economic damage caused by an invasive species warrants its listing as “injurious wildlife,” it becomes illegal to import, export, or transport the species between states without a permit.

Asian Carp: There are four invasive species from Southeast Asia – bighead, black, grass, and silver – that are commonly called Asian carp. Fast-growing, aggressive and adaptable fish, they are outcompeting native fish species for food and habitat in much of the mid-section of the United States. Voracious filter feeders, they consume up to 20% of their bodyweight per day in plankton and aquatic vegetation. Silver carp pose a particular threat to boaters, as they are known to jump out of the water when startled by boat engines.

Adult Asian carp have no natural predators in North America and females lay approximately half a million eggs each time they spawn. As a result, they can change aquatic food webs, modify habitat, and directly compete with forage fish, larval fishes, and native mussels for food.

It is crucial to prevent Asian carp from entering the Great Lakes. Once established in an ecosystem they are virtually impossible to eradicate.

Northern Snakehead: The northern snakehead has been described as a voracious predator of fishes, freshwater crustaceans, and amphibians. Because of their feeding style, they could outcompete popular sport fish such as largemouth bass. Biologists are also concerned that they could introduce parasites and diseases that could harm native species.

In 2002, a reproducing population of northern snakeheads was discovered in a pond in Crofton, Maryland. In 2004, northern snakeheads were found in the Potomac River near the nation’s capitol and have since established a reproducing population. Northern snakeheads have also been found in Arkansas, Pennsylvania, and New York.

Lionfish:  Lionfish are native to the Indo-Pacific, but are now established along the southeast coast of the U.S., the Caribbean, and in parts of the Gulf of Mexico. Since lionfish are not native to Atlantic waters, they have very few predators. They are carnivores that feed on small crustaceans and fish, including the young of important commercial fish species such as snapper and grouper. Lionfish have venomous spines which make them unappetizing to predator species.

They were first reported in U.S. waters in 1985 but since 2000, sightings have rapidly increased. People are encouraged to remove lionfish which can be speared, caught in hand-held nets, or caught using hook and line. Though their flesh is safe to eat and considered by many to be delicious, be cautious of the venomous spines while handling the fish.

Sea lamprey: Historically,i t is the most devastating invader in the Great Lakes. It is an aggressive parasite with a toothed, funnel-like sucking mouth and rasping tongue which is used to bore into the flesh of other fishes to feed on their blood and body fluids. A single sea lamprey can kill 40 lbs. of fish during its adult lifetime. They are so destructive that, under some conditions, only one out of seven fish attacked will survive. Anglers might see wounds or scars on sport fish they catch as a result of lamprey bites.

Before control efforts, sea lamprey populations became excessive in the Great Lakes, which contributed significantly to the collapse of fish species that ere an economic mainstay of a vibrant Great Lakes fishery. Ongoing control efforts have been very successful, as a 90% reduction of sea lamprey populations in most areas has been achieved. This has created a healthier environment for fish survival and spawning.

Zebra and Quagga Mussels:  Zebra mussels and quagga mussels are virtually identical both physically and behaviorally. Originally from Eastern Europe, they entered U.S. waters from ship’s ballast discharges in the late 1980s.  These invasive mussels quickly colonize any submerged hard surface and reach incredible densities. They crowd out native bivalves, harm fish populations, and impact aquatic food chains. They can also clog the inside of pipes and water-cooled boat engines and can be dangerous to unwary swimmers.

Now, both quagga mussels and zebra mussels have spread to 29 states by attaching themselves to boats and gear moving between the Great Lakes and Mississippi River Basins. Their microscopic larvae, called veligers, are easily spread in infected water or equipment.


New Zealand Mudsnail:  These tiny invaders (3 to 6 mm or 1/8 inch) have brown or black cone-shaped shells with five whorls. In the late eighties, New Zealand mud snails were found in the Snake River in Idaho and the Madison River in Montana. In 1994, additional discoveries were made in the Madison River near the boundary of the Yellowstone National Park. Snails have also been found in Lake Ontario, near the mouth of the Columbia River and in the Owens River in California.

This snail has the ability to reproduce quickly and mass in high densities which has been a cause for concern in western trout streams. There is concern that the mudsnails will impact the food chain of native trout and alter the physical characteristics of the streams themselves.

Research indicates that anglers will probably be the group most impacted by the New Zealand Mudsnail. If this species does have a long-term impact, western trout fisheries could become devastated.

Invasive Crabs:  At least three species of invasive crabs –  the European green crab, Chinese mitten crab, and Asian shore crab – threaten native ecosystems. All three were introduced through the release of ballast water though there is some evidence of intentional introduction.

The European green crab was first discovered on the East Coast in 1817 but more recently started appearing on the West Coast in the 1980s. It preys on bivalves and other crustaceans, such as soft-shell clams and scallops.

The Chinese mitten crab is native to the Pacific coasts of China and Korea. It was found on the West Coast in 1991 and, more recently, on the East Coast in 2005. It is particularly troublesome as it has been known to interfere with fish salvage operations, fish passage facilities, water treatment plants, power plants, and other facilities.

The Asian shore crab is a native of the western Pacific and was discovered in New Jersey in 1988. It is known to compete with native crustaceans and prey on other native species.

Asian Tiger Shrimp:  Originally found in Indo-Pacific, Asian, and Australian waters, the territory of tiger shrimp now includes saltwater areas from North Carolina to Texas. They are not yet well-established in the U.S. but sightings have notably increased over the past few years.

These shrimp are hearty, capable of withstanding broad temperature and salinity ranges, and grow rapidly sometimes reaching 30 cm in length. They predate heavily on native organisms like crab, mussels, and other shrimp.

Much remains uncertain about the source and impacts tiger shrimp have on new ecosystems but there are concerns over the potential for transmission of foreign diseases and competition with native shrimp stocks.


Hydrilla: Hydrilla is naturalized and invasive in the United States following release in the 1950s and 1960s from aquariums into waterways in Florida. It is now established in Canada and the southeast from Connecticut to Texas, and also in California. By the 1990s control and management were costing millions of dollars each year.

Aquarium dealers shipped live Hydrilla from Sri Lanka under the common name “Indian star-vine.” After these plants were considered unsatisfactory, they were dumped into a canal near Tampa Bay, where they flourished. It is believed that several undocumented cases of accidental or careless releases followed, as there was extensive spread of the Hydrilla throughout Florida and the southeastern U.S.

Eurasian Milfoil:  Eurasian milfoil is a fast-growing aquatic plant with feathery underwater foliage native to Europe and Asia. It was introduced to the United States in the early 1900’s through the aquarium trade and is now found in many waterways throughout the U.S.  Eurasian milfoil can form dense mats of vegetation, shading out native plants, clogging water-intake and drainage pipes, and interfering with boating, fishing, and other recreational activities.  It is difficult to completely remove Eurasian milfoil once it has become established in a waterbody but herbicide treatments and manual removal have been successful at controlling growth in some small waterbodies.

Didymo (“Rock Snot”):  The invasive alga Didymosphenia geminata is a microscopic diatom that can form thick mats on river bottoms and stream beds. Thick, slippery mats of Didymo can make fishing difficult and crowd out the native algae and aquatic insects that form the base of the food chain in many streams and rivers.

Although Didymo is considered native in nutrient-poor streams in Canada, Europe, and Asia, it is expanding its range to nutrient-rich rivers in the United States.

Viral Hemorrhagic Septicemia (VHS):  VHS is a viral disease that affects freshwater and saltwater fishes, causing hemorrhages on the body surface and within internal organs.  Although contact or consumption of fish with VHS is not dangerous to humans, VHS has been known to cause large-scale fish kills in some waters of Great Lakes states. Currently the virus that causes VHS has been detected in each of the Great Lakes, the St. Lawrence River, and inland lakes in New York, Michigan, Minnesota, and Wisconsin, but it is easily spread through the transport between waterbodies of infected fish, bait, or water.

State and National actions

ANS Task Force:  The Nonindigenous Aquatic Nuisance Prevention and Control Act of 1990 established the Aquatic Nuisance Species (ANS) Task Force, an intergovernmental organization tasked with preventing and controlling the spread of introduced aquatic nuisance species.  The Task Force is co-chaired by the U.S. Fish and Wildlife Service and the National Oceanic and Atmospheric Administration.  The goals of the Task Force are to reduce the risk of harmful aquatic species being introduced into U.S. waters, to minimize the negative effects of established aquatic invasive species, to facilitate aquatic invasive species research, and to educate the public about the introduction, spread, and impact of aquatic invasive species.  More information about the ANS Task Force can be found here.

100th Meridian Initiative:  The 100th Meridian Initiative is a national cooperative effort between non-governmental, state, and federal agencies led by the ANS Task Force to prevent the spread of zebra mussels and other aquatic invasive species to waters of western states.  The main objectives of the Initiative are educating boaters, anglers, and the general public about preventing the spread of aquatic invasive species and conducting voluntary boat inspections for aquatic invasive species at highway stops and boat ramps.  The Initiative is also involved in monitoring and eradicating aquatic invasive species in western states, as well as supporting aquatic invasive species research.  More information about the 100th Meridian Initiative can be found at http://100thmeridian.org/.  Some states and specific lakes may have stricter inspection requirements to prevent the spread of aquatic invasive species than voluntary inspections through the 100th Meridian Initiative.  Check with local authorities for up-to-date inspection requirements when planning your next boating or fishing trip.

Felt Bans: With increasing concern about the spread aquatic invasive species, parasites, and pathogens, many states have moved to ban the use of wading gear with absorbent felt or fiber soles.   Research has shown that absorbent fibrous materials such as felt-soled wading boots can transport microscopic pathogens and hard-to-see invasive species, such as Didymo.  This type of gear is also harder to disinfect and dry than footgear with non-felt soles.  In 2011, Maryland became the first state to implement a ban on felt soles, soon followed by Alaska, Missouri, Nebraska, Rhode Island, South Dakota, and Vermont.  Other states including Idaho, Maine, Montana, New Mexico, New York, and Oregon have also considered similar bans.  Up-to-date information on felt restrictions in the United States can be found at the Invasive Species Action Network website, or by contacting state wildlife authorities.

Angler Actions

Stop Aquatic Hitchhikers is another national campaign led by the ANS Task Force aimed at educating the public about aquatic invasive species prevention.  The Stop Aquatic Hitchhikers campaign recommends that everyone follow the general procedure of Clean, Drain, and Dry to remove aquatic hitchhikers from equipment when leaving a body of water.

  • Clean all visible mud, plants, other organisms, and debris from your boat, trailer, clothing, and equipment before transport. Some invasive species that are too small to see can be attached to visible debris.
  • Drain all water from bait buckets, live wells, bilges, etc. before transport.
  • Clean equipment with hot or high-pressure water. Disinfect any items that cannot be exposed to hot or high-pressure water. Allow all equipment to dry thoroughly before entering new waters.
  •  Do not transport bait between water bodies, or release unused bait. Be aware of local bait regulations.

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