Out Of BalanceA Story of Salmon and Lake Michigan

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A fishy tale of how invasive species shaped an ecosystem and a fishery

It all starts with an aquatic food web

Every ecosystem has a food chain – a network of species that rely on each other to maintain a delicate natural balance. Lake Michigan is no exception.

non-native species
native species

A food web is made up of layers of four energy levels: Top Consumers, Primary Consumers, Secondary Consumers, and Primary Producers and Decomposers. Here are some of the cast of characters who fill these roles in Lake Michigan:

Top Consumers

sea lamprey
Sea lampreyPetromyzon marinus
chinook salmon
Chinook salmonOncorhynchus tshawytscha
coho salmon
Coho salmonOncorhynchus kisutch
brown trout
Brown troutSalmo trutta
BurbotLota lota
lake trout
Lake troutSalvelinus namaycush

Piscivorous fish are large predator fish like salmon, trout, burbot, and walleye that eat other smaller fish.

Secondary Consumers

AlewifeAlosa pseudoharengus
rainbow smelt
Rainbow smeltOsmerus mordax
BloaterCoregonus hoyi
deepwater sculpin
Deepwater sculpinMyoxocephalus thompsonii
lake whitefish
Lake whitefishCoregonus clupeaformis
slimy sculpin
Slimy sculpinCottus cognatus
Yellow perchPerca flavescens

Planktivorous fish eat plankton and are eaten by predator fish. They are also called prey species or forage fish.

Primary Consumers

quagga mussel
Quagga musselDreissena rostriformis bugensis
zebra mussel
Zebra musselDreissena polymorpha
AmphipodDiporeia spp

Primary consumers are tiny organisms such as zooplankton and macroinvertebrates that live in the water column or in the sediments at the bottom of the lake and feed on primary producers.

Primary Producers + Decomposers


Primary producers are tiny plants that live in the water column and convert sunlight and nutrients into biomass. Decomposers are tiny animals that feed on detritus and release nutrients for producers to use. Producers and decomposers are the foundation of the food chain.

History of a Changing Ecosystem

Food webs are a delicate balance. One little change can throw the whole system into disarray, Lake Michigan's food web has changed significantly in the last 200 years, all because of a few invasive species with monumental impact.

The little change that started it all was the introduction of two non-native species, the sea lamprey and the alewife into the Great Lakes. By the 1950s, sea lamprey had decimated the native lake trout population. Another non-native species, the alewife, had been kept in check by the lake trout predation. Absent a predator, the alewife population exploded and then crashed, causing massive, stinking die-offs along beaches.

Great Lakes fisheries managers were on the lookout for a new predator to help help keep alewife populations in check. During the 1960s, they started stocking the lakes with Chinook and Coho salmon. This was a spectacular success, for a time. Not only did the salmon help balance the ecosystem in the lower Great Lakes, but it also created a multi-billion dollar sport fishery.

But more changes were in store. During the late 1980s, invasive Zebra and Quagga mussels arrived in the lakes via ballast water discharge from ocean-going lake freighters. The mussels consume much of the primary production in the lake ecosystems, leaving less for higher levels of the food web. Now, prey species are declining and so, too, are the salmon that depend on them.

Today, fishery managers are faced with a decision: Should they keep stocking salmon at high levels and risk a collapse of the alewives in Lake Michigan, or should they reduce salmon numbers?

Click on the timeline below to find out more.


3000 BC

Native Great Lakes peoples fished the Great Lakes from canoes or ice with spears and hooks made of bone, antler and copper. They fished plentiful stocks of native lake sturgeon, northern pike, and suckers.

The Welland Canal connecting Lake Ontario to Lake Erie allows ship traffic to bypass Niagara Falls and access the upper Great Lakes.

Alewives and sea lamprey enter Lake Erie from Lake Ontario via the Welland Canal. Sea lamprey are parasitic, jawless fish that feeds by attaching themselves to their victims. Alewives are small prey fish.

Commercial and charter fishing expand in the Great Lakes.

Native fisheries decline from overfishing. Ciscoes (lake herring and chubs), lake trout, and whitefish populations plummet.

Sea lamprey discovered in Lake Michigan

By the 1950s, sea lamprey decimated the native lake trout population. This caused the alewife population to explode in the absence of a predator.

During the 1960s, Chinook and Coho salmon were introduced into the lake to control the alewives. The experiment was a success, and the result was a multi-billion dollar sport salmon fishery that lasted into the first decade of the 21st century.

Zebra mussels discovered in Lake St. Clair.

Quagga mussel discovered in Lake Erie.

The Round goby discovered in St Clair River.

Since 2002, salmon and alewife populations in Lake Huron have collapsed, and in Lake Michigan, they are on the decline. The main culprit? Another invasive species; this time a primary consumer. The Quagga mussel.

The Zebra and Quagga mussels are efficient filter feeders and consume much of the primary production in the lakes. This leaves little over for prey species and the predators who depend on them. In 2004, alewife and salmon populations collapsed in Lake Huron.

Native lake trout and whitefish have learned to feed on yet another invasive species, the round goby. Chinook salmon, however, have not made the switch. The result is rising populations of native lake trout, cisco and non-native steelhead as Chinook populations decline.

Chinook salmon population in Lake Michigan begins decline.

Great Lakes states consider reduction of Chinook stocking.

The death and life of the

Great Lakes Salmon Sport Fishery

Salmon populations decline

Since 1970, Chinook salmon populations have risen and plummeted in Lake Michigan, while lake trout have rebounded. This graph shows how various populations of salmon species have changed over the past 50 years.

Chart - Abundance of Species Versus Time

Prey Populations at Historic Lows

The biomass of prey species preferred by salmon is at an historic low in Lake Michigan. Fish have less to eat… and what they eat has less to eat. The end result is less salmon.

Chart - Lake Biomass Versus Time

Changes in Lake Michigan

As the density of quagga mussels has increased in Lake Michigan, the density of the zooplankton Diporeia has declined. This means less to eat for prey species that some top predators like Chinook salmon depend upon.

Chart - Lake Biomass Versus Time
Source: National Oceanic and Atmospheric Administration, Great Lakes Environmental Research Lab
Zebra Mussel Density
Quagga Mussel Density
Zooplankton Density
Zebra Mussel Density - 1994 to 1995
Quagga Mussel Density - 1994 to 1995
Zooplankton Mussel Density - 1994 to 1995
Zebra Mussel Density - 1994 to 1995
Quagga Mussel Density - 1994 to 1995
Zooplankton Mussel Density - 1994 to 1995
Zebra Mussel Density - 2000
Quagga Mussel Density - 2000
Zooplankton Mussel Density - 2000
Zebra Mussel Density - 2005
Quagga Mussel Density - 2005
Zooplankton Mussel Density - 2005
Zebra Mussel Density - 2010
Quagga Mussel Density - 2010
Zooplankton Mussel Density - 2010

Slide down the timeline to see changing mussel and plankton density in Lake Michigan

Great Lakes Salmon Sport Fishery

The salmon sport fishery in the Great Lakes is significant, generating millions of dollars in local economies. Anglers spend money on food, gas, hotels and entertainment, which builds local economies and provides jobs in coastal Michigan towns.

Total Economic Impacts: 1990-2009

Chart - Salmon Sport Fisery - Total Economic Impact 1990 to 2009

Proposed Stocking Plans

The current proposal calls for a 25 percent reduction in Chinook salmon stocking across the Great Lakes. The goals are to preserve some fishing opportunities without allowing the prey species to collapse. These efforts are coordinated with fisheries agencies in the other Great Lakes states.

Chart - Proposed Stocking Plans

The tale of invasive species in the Great Lakes is not over. Work goes on to balance ecosystems and prevent future invasions. Find out more here:

National Oceanic and Atmospheric Administration:

Great Lakes Commission:

Find out more about fish stocking in Michigan here

Find out what you can do to prevent the spread of invasive species here

Produced by Second Wave Media

Design and Illustration: Octane Design

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