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

Top Consumers

sea lamprey
Sea lampreyPetromyzon marinus
chinook salmon
Chinook salmonOncorhynchus tshawytscha
coho salmon
Coho salmonOncorhynchus kisutch
brown trout
Brown troutSalmo trutta
burbot
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

alewife
AlewifeAlosa pseudoharengus
rainbow smelt
Rainbow smeltOsmerus mordax
bloater
BloaterCoregonus hoyi
deepwater sculpin
Deepwater sculpinMyoxocephalus thompsonii
lake whitefish
Lake whitefishCoregonus clupeaformis
slimy sculpin
Slimy sculpinCottus cognatus
yellowperch
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
amphipod
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

phytoplantkton
PhytoplantktonPhytoplantkton
zooplankton
ZooplanktonZooplankton

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. Here's how Lake Michigan's food web has changed

Lake Michigan has been transformed since humans first began exploiting it for shipping, industry and recreational and commercial fishing.

The changes began in the 1830s with the first shipping channels connecting the Great Lakes with the St. Lawrence Seaway and the Atlantic Ocean. These pathways allowed exotic species to enter the Great Lakes. Humans introduced Chinook salmon in the 1960s as a way to rebalance the local food web while creating a sport fishery.

The effort was successful for a time. But the entrance of exotic mussels into the Great Lakes in the early 2000s changed everything. Now, the salmon population is declining and the lake is transforming again.

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
1830
1830
1860
1900-1920
1920-1950
1936
1950s
1960s
1988
1989
1990
2002
2004
2012
2005-present
2017

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.

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.

Logging of most of Michigan's virgin forest resulted in loss of fish habitat and dammed tributaries.

Commercial and charter fishing expand in the Great Lakes.

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

Sea lamprey discovered in Lake Michigan

In the 1950s, the sea lamprey, a parasitic, jawless fish that feeds by attaching itself to its victims, decimated the native Lake Trout population. This caused the alewife (another invasive species) 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.

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? Yet another invasive species; this time a primary consumer,the Quagga mussel, has altered the lake ecosystem once again.

The Zebra and Quagga mussels are super-efficient filter feeders and consume much of the primary production biomass in the lakes. This leaves little over for secondary consumers, or prey species, and hence the predators who depend on them. IN 2004, Alewife and salmon populations collapse in Lake Huron.

Chinook salmon population peaks in Lake Michigan and begins decline.

Native Lake Trout and Whitefish have learned to feed on yet another invasive species, the Round Goby, a bottom feeder that depends less on the primary consumers in the water column for its diet. Chinook salmon, however, have not made the switch. The result is rising populations of native Lake Trout, Cisco and non-native steelhead, even as Chinook populations decline.

Great Lakes states weigh reduction of Chinook stocking.

Abundance of Species Vs. Time

The population dynamics of salmonid (salmon and trout) species in Lake Michigan since 1970 have seen the rise and fall >of Chinook salmon and the rebound of the Lake Trout.

Chart - Abundance of Species Versus Time

The death and life of the

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

Historic Low Prey Biomass

However, that fishery is on the decline. The biomass of prey species preferred by salmon is at an historic low in Lake Michigan.

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
Zebra Mussel Denisty
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 denisity in Lake Michigan

Proposed Stocking Plans

The current proposal calls for a 50 percent reduction in Chinook salmon stocking across Michigan. 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

Presented by: Michigan DNR | Editor: Nina Ignaczak
Design and Illustration: Octane Design | Programming: Steve Fogg

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