Our Great Lakes

How are Non-Native Species Affecting the Great Lakes?

Humans have deliberately or accidentally introduced more than 160 new species - from alewives to zebra mussels - into the Great Lakes basin, forever changing the species mix in it. Non-native species range from tiny plankton that float in the water to shellfish and fish. Some, like coho and chinook salmon and rainbow and brown trout, were released intentionally to provide sportfishing fun and to keep alewife populations under control. Most, like the spiny water flea, zebra mussel, and sea lamprey, entered the lakes unobserved and are wreaking havoc on native species. Usually the conflict takes place underwater, and we see only small signs of it: we may find a beach covered with tiny, striped zebra mussel shells, or we notice that a native species, such as lake trout, is not where it used to be.

What is happening?

Non-native species are one of the most serious threats to the natural balance of life in the Great Lakes. The newcomers can displace native species by either eating them or outcompeting them for food.

One of the most dramatic invasions began in the early 1800s when the eel-like sea lamprey moved into Lake Ontario from the Atlantic Ocean and later, using shipping canals, upstream past Niagara Falls. The parasitic lamprey, which feeds on the body fluids of other fish, clinging to its victim with a suction cup mouth and rasping though the scales and skin with a sharp tongue, devastated many native fish populations. A series of control measures are holding the lamprey in check, but invasions by other species continue.

Since zebra mussels were discovered in Lake St. Clair in the late 1980s, the small, fast-breeding shellfish have spread throughout the Great Lakes and into surrounding inland lakes and rivers. In the process, this species has displaced most native freshwater mussels and may also be causing the disappearance of the small, freshwater shrimp known as scud, a key part of the Great Lakes food chain. Historically, parts of the lakes had several thousand scud for every square meter of lake bottom. A decade after zebra mussels arrived, some areas are devoid of scud.

The effects of invasive species are unpredictable. Lake Erie’s increasing clarity has been attributed to billions of zebra mussels gobbling up algae that normally cloud the water. There is also concern that zebra mussels are fostering an abundance of toxic blue-green algae by eating only the other algae. As well, the mussels are thought to play a role in the creation of a “dead zone” of low oxygen found in parts of the bottom of Lake Erie. These actions are changing living conditions for a wide range of other species. Another invader, a small fish called the round goby, is suspected of being involved in increased outbreaks of type E botulism, which has killed thousands of fish and birds, including ducks, gulls, mergansers, and loons, that live in or migrate through the Lake Erie region.

Invasive species are not confined to the water. Purple loosestrife, a flowering plant, is displacing many native plants in wetlands. Two insects, the emerald ash borer and the Asian longhorned beetle, threaten to devastate forests around the Great Lakes.

Invasive species impose an economic toll, as well as an ecological one. It costs municipalities and industries tens of millions of dollars a year just to keep zebra mussels from clogging up water intake pipes around the Great Lakes. Governments currently spend more than $12 million a year on sea lamprey controls. Invasive species threaten a sport and commercial fishing industry that is valued at almost $4.5 billion annually and that supports more than 80,000 jobs.

Stopping the invasions is no easy task. At least one-third of the new species arrived in ballast water carried by the more than 500 ocean-going ships that enter the lakes each year. While in a foreign port, a ship draws water into its ballast tanks to give it stability for an ocean crossing, and in doing so often takes in local species. That water, along with its imported species, is discharged into the Great Lakes when the ship takes on cargo or navigates through shallow waters. Since the Great Lakes basin is an international destination, new organisms from around the world keep invading. Although not all species arriving in ballast water flourish in local conditions, successful invaders tend to be fast-breeding and voracious eaters. Once established, they are virtually impossible to eradicate.

Some invasive species are released into the lakes when people dump the contents of aquariums, water gardens, and bait buckets, not realizing that doing so can disrupt the environment. Sometimes invaders have escaped from fish farm ponds where they were being used in food production for people.

Cumulative number of invaders

Figure 10:
Since the 1830s, more than 160 species of non-native fish, animals, and plants have entered the Great Lakes basin.

Nonindigenous Animals Established in the Great Lakes Drainage Basin Since the mid-1980s

Common Name	Year of Discovery	Endemic Region	Mode of Transfer	Probable Donor Region
Rouffe	1986	Ponto-Caspian	Ballast Water	Danube River
Zebra Mussel	1988	Ponto-Caspian	Ballast Water	Baltic Sea
Quagga Mussel	1989	Ponto-Caspian	Ballast Water	Black Sea
Rudd	1989	Eurasia	Ballast Water	--
Round Goby	1990	Ponto-Caspian	Ballast Water	Black Sea
Tubenose Goby	1990	Ponto-Caspian	Ballast Water	Black Sea
New Zealand mudsnail	1991	New Zealand	Ballast Water	Baltic Sea
Blueback Herring	1995	Atlantic N.A.	Canal	Atlantic N.A.
Echinogammarus	1994	Ponto-Caspian	Ballast Water	Baltic Sea
Acineta noticrae	1997	Eurasia	Ballast Water	Baltic Sea
Cercopagis	1998	Ponto-Caspian	Ballast Water	Baltic Sea
Daphnia lumholtzi	1999	Eurasia	Boat?	Ohio Reserviors
Schizopera borutzkyi	1999	Ponto-Caspian	Ballast Water	Danube
Heteropsyllus nr.nunni	1999	Atlantic N.A.	?	Atlantic N.A.
Ricciardi and MacIsaac, 2000.

What is being done?

Governments use a combination of regulations and guidelines requiring ships entering the Great Lakes to first exchange their ballast in open salt water, where there should be no organisms that can survive in fresh water. However, even a change of water is not guaranteed to purge everything because ballast tanks retain a certain amount of sludge that can hide foreign organisms.

In 2002, an underwater electric barrier was installed in the Chicago Sanitary and Ship Canal, which links Lake Michigan with the Des Plaines, Illinois, and Mississippi rivers. The barrier was designed to keep non-native carp that escaped into the Mississippi River system from moving north into the Great Lakes, and to prevent the invasive ruffe from moving from the lakes into the Mississippi.

The long struggle against the sea lamprey shows that the fight to control even a single invader can be extremely costly and probably never finished. For more than half a century, Great Lakes fishery managers have been using barriers, traps, the release of sterile males, and, mainly, the pesticide known as TFM to hold the sea lamprey in check. Even this barrage of measures cannot eliminate the lamprey from the lakes, but it has reduced them to less than 10 percent of their previous numbers. If we want native fish such as the lake trout to make a comeback, the fight against the lamprey must continue. In Hamilton Harbour, Lake Ontario, a carp barrier was built at the entrance to the Cootes Paradise Marsh. This barrier keeps carp out of the marsh, allowing marsh vegetation, no longer uprooted by carp, to regenerate.

	Figure 11: First discovered in Lake St. Clair in 1988, zebra mussels rapidly spread throughout the Great Lakes basin. The thumbnail-sized shellfish probably entered the lakes in ballast water discharged by a European freighter. The striped mollusk attaches itself to boat hulls, thereby being spread further. The maps here show the spread of zebra mussels from 1988 through to 2003.