Invasive Species
Methods of Introduction

The means and routes by which invasive species are imported or introduced into new environments are called pathways, or vectors. Globalization has increased long-distance travel and commerce. This and other factors have increased the frequency of introductions of nonnative plants, animals and pathogens to aquatic and terrestrial ecosystems around the globe. Natural pathways (i.e., those not aided by humans), such as marine debris, can also bring harmful species to a new habitat. The ‘harm’ may in fact be outcompeting, and wiping out, native species in areas the newcomer colonizes.

Floatplane pilots: Check out this informative video to learn how to avoid spreading invasive plants and animals. Elodea and other aquatic invasive species can be spread to new lakes when they hitch a ride on your rudder or floats. Remember to Clean, Drain and Dry to remove any visible living plants or animals whenever you move between waterbodies! Take the quiz and receive a certificate.

Human-aided Pathways

Significant human sources of invasive species introduction for Alaska include: 1) contaminated cargo shipments arriving by air, land, or sea; 2) restoration, development or shipping projects that can inadvertently carry seeds, spores or larvae from one place to another; and 3) intentional or unintentional releases or introductions of aquatic species. The latter covers cases where human activity brings discharged aquarium or ballast water, infected fishing gear, fouled hulls, or containers of live bait or seafood into contact with a new waterbody, unexpectedly carrying a “pest” species somewhere it has not existed before.

Sources relating to transportation and shipping are particularly timely to consider. For example, a warming climate is expected to facilitate greatly increased shipping traffic along the Alaska coast. This in turn has the potential to spread a major threat to wildlife, the Norway rat, further north along the state’s coast. Species with low or seasonally concentrated populations (such as ground-nesting migratory birds) can be decimated when rats arrive in previously rat-free areas, especially islands.

More than 100 species of ground-nesting birds used for subsistence in Alaska may be vulnerable to rats, if rats colonize their areas. Rat infestations could be particularly devastating for bird species that may already be facing diminished nesting habitats as a result of climate change. Read more about the threat of rats and what Alaska communities and industries can do about them.

Climate Change Considerations

Climate change could have equally significant effects where aquatic organisms are concerned: For example, higher annual temperatures is likely to mean that species transported in floatplane floats or as hitchhikers in private aircraft find receptive conditions in parts of Alaska where they have not been known to survive before.

Intercept Arrivals, Prevent Releases

Alaska’s and the nation’s interests will be best served by asking citizens, visitors, and local inspectors alike to be vigilant and proactive about invasive species. This will go a long way to preventing accidental or ill-planned releases that harm the state’s native fish and wildlife resources. Help intercept arrivals and prevent releases.

Be especially observant about pathways or vectors that involve transportation (e.g., activities that involve shipping, docking or cargo transfer) or any type of “release” (whether intentional, inadvertent, or accidental). See the following list to better understand the types of actions through which invasive species can be moved from one place to another and colonize new locales.


Contaminated Shipping (or ineffective docking/invasive species containment protocols)

  • Cargo shipments by air, land or sea; Aircraft, including float planes
  • Ship/boat landings, dockings, or groundings (a primary means of spreading rats to and within Alaska)
  • Ballast water/shipping
  • Restoration, highway and construction projects
  • Live food trade and its packing material

Release-related: Intentional but ill-advised

  • Intentional release of species outside their native range/illegal stocking
  • Release of pet species that become invasive in a new environment
  • Live bait releases
  • Aquarium trade/and illegal release of aquaria animals

Release-related: Accidental, or ill-planned

  • Fishing gear and recreational equipment
  • Aquatic farming
  • Fouled hulls of commercial and recreational vessels
  • Dry docks
  • Restoration, highway and construction projects
  • Science lab escapes or introductions
  • Escaped ornamental plants, nursery sales, or disposals
  • Escaped domestic animals

Vectors of Special Concern to Alaska

The following section provides more detail on some of the vectors that pose special risks for introduction of invasive species in Alaska.

Japanese Tsunami Marine Debris

Marine debris is an ongoing global problem. The after affects of the tsunami that hit Japan in March 2011, are now being seen on the western coast of North America. Wind and ocean currents continue to scatter debris, from the ghost ship found sailing off the coast of Southeast, Alaska to the dock that arrived on an Oregon beach. Communities of potentially invasive nonnative species can survive the trip across the Pacific Ocean hitchhiking a ride on marine debris. To read more about this pathway for introducing nonnative species to coastal areas and to find the protocol for responding to marine debris with living organisms, please visit the Aquatic Nuisance Species Task Force website.

If you have found marine debris either at sea or on shore, please report it to the NOAA marine debris program: and if the debris has living organisms please report to the Alaska Department of Fish and Game, Invasive Species HOTLINE: 1-877-INVASIV. You can collect data about the debris and the organisms on the debris by following the instructions on the standard datasheet for collecting and preserving nonnative species from marine debris (PDF 116 kB).


Both private and commercial transportation are major factors in the movement nonnative species throughout the United States. Global markets mean movement of goods from anywhere on Earth in shorter time periods. With shorter transit time there is greater likelihood that nonnative organisms will survive the journey. This category includes transport by planes, float planes, helicopters, and boats of all types; ground transportation, including cars, trucks, and heavy machinery used in land clearing, logging, restoration work, etc.; movement via humans and pets (e.g., on clothing, fishing gear, shoes, stuck to pet’s fur or collar); and livestock and wildlife moving through infested fields.

In Alaska, a major concern is transport and spread of invasive Norway rats to uninfested parts of the state. Rats are known to stow away virtually undetected on aircraft, cargo vehicles, and vessels, and to swim from infected vessels to nearby islands. Because they chew wiring and kill ground-nesting seabirds, their presence can have serious consequences for humans and wildlife alike. Learn more about the Norway rat, including pertinent laws for vessel, aircraft and facility owners.

Ballast Water

All sizes of watercraft, from large commercial ships to smaller recreational boats, use water in tanks for balance (i.e., ballast). When water is taken up in one port and released at a different port, chances are, if the vessel moved any substantial distance, the organisms at the new port are different than where the ballast was brought onboard. These vessels carry live aquatic organisms from fresh, brackish or marine water across and between oceans or along coastlines. Prior to the use of water for ballast, cheap and heavy materials such as rocks, sand, or soil were used. This “dry ballast” introduced thousands of species of insects, other arthropods, mollusks and plants to new locations around the world.

The use of water for ballast introduces organisms from four types of communities: plankton (drifters); nekton (i.e., free-swimming species); benthos (bottom-dwelling organisms such as worms and the resting stages of phytoplankton and zooplankton); and fouling communities (organisms that attach to structures of the ballast compartments). Anchors, anchor chains and lockers can also be sites where larvae or adults of invasive aquatic species hitchhike their way to new waterways.

Live Food Industry

The import of live, exotic foods into Alaska and the United States in general, can result in nonnative organisms being released into the wild. These organisms may be carriers of disease and pathogens, and some of these species may be able to survive in Alaska’s marine and fresh waters. The snakehead fish and the Chinese mitten crab are two species brought into the U.S. for commercial distribution as food. Snakeheads are voracious predators and Chinese mitten crabs are anadromous, meaning they migrate up into freshwater areas to spawn. They burrow in riverbanks causing erosion, potentially endangering Pacific salmon spawning habitat. Crayfish, believed to have been imported into Alaska for food, have in the past been found living in the Kenai River.

Live Seafood Packing and Disposal

Much seafood is packed in seaweed prior to distribution. Because this seafood is often transported long distances, organisms packed in seaweed may reach new waters as an unintended by-product of the live food trade. Don’t dump seaweeds used as packing material, or their raft of hitchhiking organisms, into the waters where you live or work; their fragments, larvae or cysts may persist and hatch, spreading a pest species into new areas.

Illegal Stocking

Although it is prohibited by law in Alaska, people sometimes release fish into new waters for various reasons, including wanting to create a personal fishery. This behavior frequently causes substantial impacts. As an example, northern pike introduced in southcentral Alaska (and outside their native range) have decimated sport fishing opportunities on the Kenai Peninsula, in the Susitna Drainage and in lakes around Anchorage.

Fishing Bait Releases

While current sport fishing regulations prohibit the use of live fish as bait when angling in fresh water, it is advised that the use of any live bait in fresh water can introduce species that disrupt ecosystems and eliminate native species, as well as introduce disease and pathogens. Examples include crayfish and earthworms.

Aquaria Releases

Accidental escape and intentional release of unwanted aquatic pets and aquaria plants are also a source of invasive species. This pathway includes animals imported for educational purposes and then released when they are no longer wanted. Carp (goldfish) are notoriously invasive in many parts of the country and can survive in water temperatures as low as 4° C. Pet goldfish are known to have been released into a pond on the Kenai Peninsula; in order to ensure that all fish were successfully eradicated, the artificial pond containing them was drained. In another Alaska example, an infestation of Elodea nuttallii, a common freshwater aquarium plant, resulted when someone dumped the contents of their aquarium into a slough near Fairbanks. Scientists are trying to determine the full range of effects to the waterway and what treatment, if any, is possible.

Disposal of Solid Waste or Wastewater

Seeds, viable roots and other propagules of invasive plants may also be easily spread to receiving water through wastewater discharge, and then spread by water flow to distant areas downstream. Wastewater can harbor a number of encysted pathogens that are harmful to human health.

Aquatic Farming

Atlantic salmon, mollusks, invertebrates and pathogens associated with aquatic farming generate concern because of their potential to impact aquatic environments if they naturalize to the environment in which they are produced.

Pathogens carried by resistant nonnative animals to vulnerable populations of native species have resulted in assaults on healthy populations. For example, whirling disease has decimated rainbow trout in many western U.S. rivers. It was originally introduced when European brown trout, which are tolerant of whirling disease, were imported to waters and hatcheries of the American West. Although whirling disease has not been detected in Alaska, fragments of its DNA have been found in hatchery trout in Alaska. This leads experts to believe that the disease could arrive at any time.

Hull Fouling

Hull fouling may be the most underestimated pathway for nonnative introductions of aquatic invasive species. The growth and accumulation of unwanted organisms on surfaces such as the hulls and other submerged parts of vessels (including oil rigs and barges), docks, piers and man-made structures in harbors and marinas, equipment associated with fishing, mariculture, diving, even marine debris can transfer and introduce fouling organisms to new freshwater and marine environments.

Roughly 90% of the 343 marine alien species in Hawaii are thought to have arrived through hull fouling. Meanwhile, experts believe that approximately 36% of the nonnative coastal marine species establishing in continental North America could be attributed to hull fouling alone, while ballast water is thought to account for a smaller portion. As more people and goods move from the contiguous U.S. to Alaska, the chances of invasive species traveling with them also increases.

caption follows
Areas on vessels likely to accumulate fouling communities of nonnative organisms.

Recreational Equipment

Fouled boat hulls, fishing gear (including felt-soled waders), dive equipment and other equipment transported between waterways can carry invasive species. Zebra mussels and milfoil are two examples of invasive species that are believed to have been introduced to many freshwater systems in the nation as hitchhikers on boats or boat trailers. Felt-soled waders have been implicated as the vector for translocating New Zealand mudsnails, Didymosphenia geminata (a slimy freshwater diatom), and other organisms by anglers unaware of their role in moving harmful nonnative species.

Science/Lab Escapees, Disposal or Release

Accidental or intentional release of lab animals has introduced some nonnative species into United States waters and lands. Here in Alaska, the red-legged frog was introduced to Chichagof Island by a teacher who thought the act was compassionate. These frogs could prey on native Western toad populations on the island. Ironically, it’s possible that this species could be spread to other islands in Southeast Alaska by children, who often like to make temporary pets of creatures they find in the wild, and then release them when they lose interest.

Escaped Ornamental Plants, Nurseries Sales, or Disposals

Many invasive plant problems began as desirable ornamental plants for sale in nurseries and garden shops. Purple loosestrife, for example, is sold as an ornamental plant but it takes over native vegetation in wetlands, and can clog streams.