Aquatic Invasive Species Management

Typically three to six inches in length, round gobies are small fish—but they are aggressive and prolific breeders.

Where are they from? The round goby is native to Eurasia, specifically the Black and Caspian Seas. They were first spotted in the Great Lakes in the early 1990s and are believed to have gotten here by riding in the ballast waters of ocean ships.

Ecological and economic impact: Round gobies have caused declines in native fish populations and negatively impacted the fishing industry. They aggressively compete with native fish for food, and they also eat the eggs and fry of native fish and many of the bugs and critters that native fish rely on for food. In addition, anglers complain that gobies steal bait off their lines.

As with many invasive species, the impact of round gobies is not always clear cut. On the positive side, round gobies eat invasive zebra and quagga mussels and are now an important food source for some Great Lakes fishes, native water snakes and water birds. However, round goby can pick up botulism from the mussels, passing this disease to birds and causing mass mortality events.

Outlook: Efforts are now focused on limiting further spread of round gobies into the inland rivers and streams in the Great Lakes basin. Scientists are also trying to identify how and whether to suppress round goby numbers on some critical habitats, such as native fish spawning reefs.

Where are they from? Native to Eastern Europe, zebra and quagga mussels got into the Great Lakes via ocean ships. These fingernail-sized creatures likely rode in the ballast waters of ocean ships and were then released into the lakes.

Ecological and economic impact: Quagga and zebra mussels consume massive amounts of phytoplankton and zooplankton, which are tiny plants and animals that many fish and larger zooplankton rely on for food. The mussels have dramatically disrupted the entire food web in the Great Lakes basin, reducing the movement of nutrients into offshore open waters. The mussels have also altered native habitats, smothering the habitats in clumps of live mussels or dead shells.

Importantly, by outcompeting larval fish for an increasingly limited zooplankton resource, the mussels have contributed to declines in some of the region’s important fisheries. They have also contributed to the loss of many species of native pearl mussels, which were an important part of the basin’s native communities but are now only a distant memory for older generations.

On the positive side, the mussels have been credited with cleaning up the waters of some Great Lakes. However, invasive mussels also contribute to toxic, foul-smelling, blue-green algae blooms in Lake Erie. The invasive mussels preferentially filter out the healthy algae in water and leave behind the harmful blue-green algae. In addition, the mussels’ excrement (pseudo-feces) can provide a flush of nutrients that can promote blooms.

The mussels also wreak havoc on industrial and city water (municipal) users by attaching themselves to the insides of pipes and water collection structures, resulting in expensive cleanup operations.

Outlook: Quagga and zebra mussels are widespread across the Great Lakes basin and the United States. Nationally, prevention efforts are trying to keep the mussels out of the few uninvaded major river systems, especially in the western United States. Scientists are trying to identify how to best suppress invasive mussels in the Great Lakes and elsewhere. Visit the Invasive Mussel Collaborative for more information.

Where is it from? Invasive common reed is from Europe and was likely introduced in the eastern United States via ballast waters on ocean ships in the 1800s. The nonnative plant spread into the Great Lakes basin and across most of the country.

Ecological and economic impact: There is both a native and an invasive common reed. The two plants look alike, but the invasive species is darker in color and grows in denser stands than the native species, and today is far more common. Because of its jam-packed growing patterns, invasive common reed tends to crowd out other plants. The reed also has deep roots and releases a chemical into the soil, which further prevents other plants from growing. Phragmites have taken over shorelines and nearby wetlands, decreasing wildlife diversity and reducing recreational opportunities for birders and anglers.

Outlook: There are a number of control methods that can be used to suppress invasive common reed, including prescribed fire and herbicides and some promising new tools in development that offer more selective and effective management. Visit the Great Lakes Phragmites Collaborative for more information. 

Where are they from? Native to the Ohio River Basin, rusty crayfish were likely transported to the Great Lakes by fishers who use this animal as bait.  

Ecological and economic impact: Rusty crayfish tend to outcompete native crayfish for habitat and food. They are omnivores and eat a lot of invertebrates, fish eggs and aquatic plants, even to the extent that submerged plant habitats or algal forests are lost.

Outlook: Scientists are evaluating various control methods, including trapping rusty crayfish, to see if short-term suppression can benefit native fish spawning. New methods are being tested to respond to the recent spread of another crayfish species (red swamp crayfish), which might have potential in the management of rusty crayfish.

The U.S. Fish and Wildlife Service and state and provincial resource management agencies encourage anglers to dispose of unwanted bait in the trash and not release them into lakes and other waterways.

Non-native fish, animals and plants that are sold in pet stores, aquariums and bait shops have the potential to become invasive species if accidentally or deliberately released into the Great Lakes.

For example, a pet store may sell a non-native plant that looks beautiful in a home aquarium. But when water from that home aquarium is emptied into a local river or stream, it carries the plant along, increasing the risk that this species could take root and become invasive in the Great Lakes.

To prevent scenarios like this, TNC and partners have developed science-based risk assessment tools to identify nonnative organisms that are likely to become invasive if released. The tools are intended to help state, provincial and federal lawmakers determine when it is appropriate to prohibit the sale of a particular organism because it would likely harm native ecosystems.

Historically, there has been significant variation in the species each state or province prohibits for sale. Without rules to prevent interstate transport and sale, the regulations of individual jurisdictions were only as strong as their weakest neighbors. TNC and partners are working with the Great Lakes Aquatic Nuisance Species Panel to develop lists of invasive species that have the greatest potential to arrive, spread and cause harm in the Great Lakes.

As a result of these efforts, the National Oceanic and Atmospheric Administration (NOAA) Great Lakes Environmental Research Laboratory has developed a risk-assessment clearinghouse to make this data available. Armed with this science-backed information, management agencies and legislators are working together to consistently manage the trade of these organisms across shared waters.

As a result, the number of species regulated by at least half of the Great Lakes states and provinces increased from 10 to 44 between 2008 and 2020. (Blue Accounting provides more information on this work.)

Recreational boating is an important part of life on the Great Lakes. Unfortunately, invasive species can spread through our region by hitchhiking on boats and other recreational watercraft, as well as on equipment such as fishing gear or waders.

As boaters travel and move their vehicles between different bodies of water, invasive mussels, plants and other organisms can cling to the craft’s hull, anchor, motor props, bilge and even the trailer itself.

Large boats aren’t the only vehicles of transportation. Invasive species can also be introduced into new habitats on jet skis, wave runners and non-motorized crafts such as canoes and kayaks.

While some invasive species may be large enough to see and remove by hand, other invasive microorganisms that travel on watercraft may be invisible to the naked eye or hide in places that can only be observed by deliberate inspection.

This is why TNC actively promotes the Stop Aquatic Hitchhikers campaign, which encourages people to follow a three-step process before moving boats and other watercraft from the water: Clean, Drain, and Dry.

In addition, Natural Resource Management Agencies across the basin encourage anglers to dispose of unwanted bait, worms and fish parts in the trash. When keeping live bait, drain the bait container and replace it with spring or dechlorinated tap water. Never dump live fish or other organisms from one water body into another.

Some agencies have also adopted regulatory-based inspection and decontamination policies for recreational watercraft, and all have ongoing outreach and education programs, as described by Blue Accounting.

Across the basin, regulatory programs vary in the specific activities they regulate (e.g., possession and transport of plants and animals, draining bilge and livewell water) as well as the agency authorities (e.g., mandatory inspection) and associated penalties.

To aid travel and commerce, people built locks and canals to connect the Great Lakes with other river basins, such as the Mississippi, Ohio and Hudson/Mohawk rivers or to allow ships to bypass natural barriers like the Niagara Falls.

Historically, these natural barriers prevented the movement of species between these waterways. Unfortunately, while they facilitate the transport of goods and recreational vessels, these canals provide artificial connections that have enabled the movement of many aquatic invasive species into and out of the Great Lakes. In fact. They're one of the reasons why the Great Lakes basin has been referred to as a beachhead for the invasion of North America.

The Great Lakes region has a long history of using barriers to help manage invasive species. For example, dams are a cornerstone of the sea lamprey control program, and a set of electric barriers are maintained in the Chicago Area Waterway System to prevent invasive carp from entering the Great Lakes.

There is renewed interest in developing smarter barrier methods that can prevent the movement of aquatic invasive species through canal systems or waterways while still allowing for commerce and the movement of native species. For instance, the U.S. Army Corps of Engineers is fortifying the Brandon Lock and Dam on the Des Plaines River, south of the electrical barriers in Chicago, to block invasive carp from getting into Lake Michigan.

A new locking mechanism is being added that will create a strong current to flush any fish downstream before a boat can enter the canal. Research is also underway to test a variety of other deterrents, including sound waves, electricity and bubbles. The goal is to stop invasive carp without harming the migration of important native fishes.

TNC has been working to raise awareness of the need for additional solutions to curb the spread of invasive species in canals. For example, we have historically worked with our partners and federal and state agencies to track the spread of invasive carp through the Chicago Area Waterway System.

In addition, TNC participated in a New York State task force that recommended barriers as the most effective way to address the longstanding problem of invasive species movement in the Erie Canal, which has often been referred to as a “superhighway” for invasive species.

More recently, we have been conducting research at our preserves on new methods that could eventually be used on the Great Lakes. For instance, at Emiquon Preserve in Illinois, TNC installed a state-of-the-art water-control device that allows conservation staff to manage the flow of water into and out of the preserve. 

Scientists have used the structure to test various methods for deterring invasive carp. Currently, a project is evaluating a fish identification and sorting apparatus driven by artificial intelligence that could eventually be used to recognize any invasive carp trying to get into the preserve via the waterway and automatically route those carp into a storage container while allowing passage of native fish species.