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Five Invasive Species That Harm Salmon and Their Habitats

Invasive species either hunt native plants and animals — or starve them of food or oxygen. CIAA is watching five of these invasive species.

by | March 2, 2022

A European green crab covered with barnacles was caught in Vancouver. As it works its way up the Pacific coast, this species has the potential to become one of most harmful invaders in Alaska waters. ADF&G

An invasive species is any plant, animal, or fungus that’s non-native to a new ecosystem that harms native organisms or human beings. An invasive species can damage an ecosystem by preying on native plants and animals. They can also overpopulate an ecosystem, choking off food, oxygen, and other vital resources.

Several invasive species create problems for young salmon in Cook Inlet, whether they are born in natural streambeds or in a hatchery. Working with other organizations, the Cook Inlet Aquaculture Association (CIAA) protects salmon habitats by reducing the impacts of these species and helping the public understand how to prevent their spread.

Here are five invasive species that causes the most concern for salmon aquaculture in the Cook Inlet region:

1. Northern Pike

Native to waters in northern Alaska, biologists consider northern pike an invasive species in the southcentral region because it preys upon juvenile salmon. ADF&G

Northern pike are native to the lake and streams north of the Alaska Range. Over the last several decades, people illegally introduced northern pike to the Susitna River watershed. On the Kenai Peninsula, they were first spotted near Soldotna Creek in the 1970s and subsequently colonized 23 bodies of water on the peninsula. Since then, regulatory agencies, with the help of organizations such as CIAA, have almost completely eliminated these invasive fish from the peninsula. 

Northern pike are ambush predators, which dart out from the weeds to catch prey. They prefer the same habitats as many species of salmon fry. Fishermen have seen the bellies of northern pike literally stuffed full of juvenile salmon. 

Since 2012, CIAA has removed more than 20,000 northern pike from the Cook Inlet region. These fish eat at least one juvenile salmon a day. Based on this behavior CIAA lead biologist Andy Wizik estimates this effort may have saved more than 2.25 million salmon over three years.

CIAA continues to monitor and suppress northern pike at Shell, Whiskey, and Hewitt Lakes along the Susitna River and water systems near Tyonek on the west side of Cook Inlet.

2. Elodea

Elodea is an invasive plant that forms thick underwater mats. Elodea spreads easily from place to place because a small fragment of the plant can multiply into a new infestation.

Elodea is a hardy aquatic plant that can quickly infest a lake or stream. It can also grow in the winter, under ice, when other plants around it die off during the winter. Scientists believe the Alaska Elodea infestations may have first started when people dumped their aquarium plants into nearby waters. Thick mats of Elodea block out light, gobble up nutrients, and prevent other plants from surviving. Elodea can become so thick, it slows the flow of streams. As the water slows down, sediment drops from the water column and covers gravel where salmon spawn. 

It only takes a fragment of the plant for Elodea to take root. Floatplane pontoons and outboard engines have the potential to carry small stems from one place to another and start new infestations. 

Elodea threatens the state’s most productive salmon habitats. An economic study predicts that Elodea could reduce the value of commercial fisheries by $159 million a year. This is roughly 16% of the statewide value of sockeye salmon over the last ten years.

CIAA surveys Cook Inlet area lakes and streams for Elodea. It also participates in eradicating the plant by funding programs and providing staff support.

3. Reed Canarygrass

Reed canarygrass can overwhelm streambeds and reduce prey species for young salmon. ADF&G

Reed canarygrass is another aquatic plant that multiplies in wetlands. Infestations of the plant choke tributary streams thereby reducing prey species for young salmon. People remove reed canarygrass by cutting it down, mowing repeatedly, applying herbicide, or laying down a sheet of plastic or fabric to block out light. Alternatively, people can plant native willows and other shady trees and shrubs that deprive reed canarygrass of sunlight.

CIAA works to eradicate reed canarygrass in the Cook Inlet region by monitoring all of our field sites for its presence.

4. European Bird Cherry

European bird cherry blossoms are beautiful, but the they edge out native willows and attract fewer of the insects young salmon depend upon.

These trees are deceptively beautiful, with delicate white flowers and bright red fruit beloved by birds. They do well in Alaska because moose avoid eating bird cherry leaves in favor of other trees and shrubs. Eventually, bird cherry trees outcompete native willows, which creates a problem for salmon.

Juvenile salmon depend on insects that thrive in native plants. When European bird cherry dominates an ecosystem, young salmon have less food to eat.

5. European Green Crab

Fisheries biologists on the alert for the European green crab, a highly-invasive species that has been making its way up the Pacific coast to British Columbia. It has nearly made its way to Alaska.

European green crab is on the “watch list” as a possible future danger to juvenile salmon. These predators feast on juvenile salmon, destroy seagrass, and could outcompete our native Dungeness crab. Scientists consider European green crab one of the most harmful invasive species in the marine environment. European green crab first showed up in California in 1989. They flooded into Washington and British Columbia in July 2020.

The National Oceanic and Atmospheric Administration (NOAA) is teaming up with Alaska Sea Grant. Together, they will monitor Alaskan waters for European green crab DNA. If this genetic material shows up in seawater samples, it could tell Alaskan scientists that these invading crabs have arrived. 

In CIAA’s service region, several organizations have teamed up to monitor for green crabs and engage citizen scientists.

Cook Inlet Region Invasive Species Partners

CIAA works with the following organizations on invasive species in the Cook Inlet region.

  • Alaska Department of Fish and Game — Protects native fish and wildlife and habitats from invasive species, except terrestrial and freshwater plants 
  • Alaska Department of Natural Resources — Protects natural resources from invasive species, specifically terrestrial and freshwater plants
  • U.S. Fish and Wildlife Service — The mission of the U.S. Fish and Wildlife Service is working with Others to conserve, protect, and enhance fish, wildlife, plants and their habitats for the continuing benefit of the American People.
  • Kenai Peninsula Cooperative Invasive Species Management Area — A volunteer partnership dedicated to preventing the introduction and managing the spread of non-native, invasive species.
  • Alaska Invasive Species Partnership — A volunteer partnership that provides statewide leadership in the prevention and reduction of the impacts from invasive species in Alaska
  • Tyonek Tribal Conservation District — A nonprofit organization that conserves, enhances, and encourages the wise use of natural resources in the Tyonek Tribal Conservation District, including the prevention and management of invasive species.
  • Mat-Su Basin Salmon Habitat Partnership — A volunteer group that is part of a network of fish habitat partnerships in the U.S. Work includes the prevention and management of invasive species in the Matanuska-Susitna Basin. 
  • Kenai Watershed Forum — A nonprofit, regional watershed organization of the Kenai Peninsula. Provides education, outreach, and project work focused on invasive species.

CIAA’s Invasive Species Work

To learn more about how CIAA works to eradicate invasive species in the Cook Inlet region, visit our website.

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