U.S. Fish & Wildlife Service

Invasive Species


Each species evolves in the presence of others and develops a natural pattern of relationships with these other species – as competitors, predators, disease organisms, and so on. Most often species are also limited by physical or other barriers. For example, land is a barrier to the spread of aquatic species just as water can be a barrier to the spread of many land animals. Within these barriers, natural systems (ecosystems) begin to form.

Northern Pike
Northern Pike, Credit: USFWS/Ryan Haggerty

Over geologic time, the world’s major ecosystems developed their own unique assemblages of plants and animals - each accustomed from millennia of adaptation to the others presence. There is always some exchange within and among ecosystems – but humans have dramatically altered this picture by moving species, on purpose or by accident, all over the globe at an unprecedented rate.

Species that evolved in one place are referred to as being “native” to that place; and are called “non-native” if they are moved to another place where they do not naturally occur. Most non-native species (sometimes also called exotic, non-indigenous, or alien species) do not thrive in the new location because their new “home” does not meet their needs. However, many do survive and can become invasive.

Invasive non-native species can harm individual native species or even entire ecosystems, and thus also impact those who depend on natural systems for important resources and products. Unlike other kinds of pollution, these “biological pollutants” can actually increase in abundance over time and force out native species – by competing with them (for space, water, or food), by eating the native species, spreading new diseases, or so altering the habitat that the native species can no longer survive. In fact, the impacts of non-native species are now recognized as second only to habitat alteration as a factor in the decline and extinction of our American flora and fauna.

Photo of submersed aquatic plants (Elodea)
Photo of submersed aquatic plants (Elodea). Credit: USFWS

Water-dependent species and activities are especially threatened because invasive non-native species spread rapidly in water -- e.g., in lakes, rivers and bays. Once the invaders have arrived, it can be extremely difficult to control them without also hurting the native species. The sooner you find them, the better chance there is to control their spread. That is why preventing invasions and keeping a sharp eye out for new invaders is so important – prevention and rapid response are the keys to protecting natural ecosystems and the economic activities that depend upon them.

A weed does not care if it’s growing on private or government property; an invading fish or crab does not care if it is swimming in state or federal waters. Because these aquatic invaders do not recognize political or ownership boundaries, but threaten us all, effective partnerships and coordinated efforts are essential -- everyone has a stake, everyone has a role!

Be on the Look Out!

Species introduced on purpose or accidentally from other places can invade Alaska and harm the economy, environment, and even human health. Once these invaders arrive, it can be extremely difficult to control them without also hurting native species. The sooner you find them, the better chance there is to control them. That is why we keep a sharp eye out for new invaders and work with the State and other partners to prevent invasions.

Atlantic Salmon. Credit: John Volpe.
Atlantic Salmon
Green Crab. Credit: Washington Department of Fish & Wildlife.
Green Crab
Northern Pike. Credit: USFWS/Ryan Haggerty
Northern Pike
Mitten Crab. Credit: W.Lee Mecum, CDFG.
Mitten Crab
Zebra Mussels. Credit: USFWS.
Zebra Mussels
New Zealand Mudsnail. Credit: USGS.
New Zealand Mudsnail


What to Do

If you find one of these aquatic invaders in Alaska, do not throw it back alive! Preserve it in rubbing alcohol or freeze it, note the precise location in which you found it, and contact the Invasive Species Program Coordinator for either the U.S. Fish and Wildlife Service (907-786-3813) or the Alaska Department of Fish and Game at their toll free number: 1-877-INVASIVE (1-877-468-2748)

Report Illegal Northern Pike

Report Illegal Northern Pike



Invasive species “pathways” are the means by which they are moved from one location to another. Natural pathways could include means such as wind or water currents. Other pathways can be enhanced by, or even entirely created through, human activity. Sometimes this is done intentionally, other times quite unintentionally.

Invading species do not recognize political boundaries and often spread very rapidly across jurisdictional lines. This means that responsive partnerships are the only realistic hope for progress. State agencies and citizen organizations are among our most important and effective partners. The links below will take you to the websites of some of our leading partners.

Alaska Dept. of Fish and Game 
Invasive Species in Alaska

Prince William Sound Regional Citizens’ Advisory Council 
Citizens promoting environmentally safe operation of the Alyeska terminal and associated tankers.

Alaska Invasive Species Working Group 
A new partnership whose mission is to minimize the impacts of invasive species in Alaska (all taxa -- from fungus to foxes) by facilitating collaboration, cooperation and communication among AISWG members and the people of Alaska.

Alaska Committee for Noxious and Invasive Plant Management 
Its’ goal is to heighten the awareness of the problems associated with non-native invasive plants and to bring about greater statewide coordination, cooperation and action to halt the introduction and spread of undesirable plants.

Invasive species are increasingly being recognized as a major threat to biological diversity and economic activity. As a result, the network of contacts and information on how best to deal with this menace is also growing. The following links should help you begin to access this network.