STATE OF THE GREAT LAKES
WHAT IS THE STATE OF GREAT LAKES TOP PREDATOR FISH?
Native and non-native fish at the top of the Great Lakes food web are maintained in part through stocking
programs. Habitat alteration, invasive non-native species, changing food supply, fish harvesting, and
contaminants exert negative pressures on these fish.
The Issue
• Top predator fish are important components of
the Great Lakes food web and they provide food
to both human and wildlife consumers.
Currently, top predator fish populations are not
self-sustaining in all Great Lakes and are
impacted by habitat loss and alteration, non-
native aquatic species, food web condition,
fishing, and contaminants.
The Indicators
Native top predator fish include lake trout in Lakes
Superior, Huron, Michigan and Ontario, and walleye
in Lake Erie. Abundant, self-sustaining populations
of lake trout or walleye are a good indication of a
healthy open water ecosystem.
Non-native coho salmon, Chinook salmon, rainbow
trout, and brown trout (hereafter referred to as
salmonids) were introduced to the Great Lakes in
the 1960s as top predator fish primarily to control
populations of alewife and rainbow smelt (both
non-native preyfish), and they now also provide
recreational fishing opportunities. The size of the
salmonid population should be maintained in
balance with the food supply to ensure its
continued success.
A diversity of prey species is needed to support
populations of predator fish. Dominant preyfish
include non-native alewife and rainbow smelt, and
native species such as bloaters, lake herring, and
deepwater sculpin. At high abundance, alewives
and rainbow smelt indicate poor ecosystem health
due to a lack of top predators and impoverished
native prey species.
Additional pressures on top predator fish include
parasitic attacks by sea lamprey and various effects
of contaminants. Sea lamprey abundance is a direct
measure of their potential to impact populations of
large fish, especially lake trout. Assessment of levels
of contaminants in top predator fish helps to
determine the potential for adverse health or
reproductive effects on fish communities and the
risks to human and wildlife consumers of these fish.
The Assessment
Naturally-reproducing lake trout disappeared from
most of the Great Lakes by the 1950s, primarily due
to sea lamprey predation and overfishing. Today, self-
sustaining populations exist in Lake Superior, and
some natural reproduction occurs in Lake Huron and
Lake Ontario. For all Great Lakes except Lake
Superior, however, populations are maintained
through annual stocking programs. Sea lamprey
continue to inhibit lake trout recovery in northern
Lakes Huron and Michigan. Throughout the Great
Lakes, a predominately alewife diet is associated with
thiamine deficiencies that inhibit survival of young
lake trout.
Walleye suffered major declines in abundance in the
1960s and 1970s, primarily due to poor water quality.
Improved water quality and spawning and nursery
habitat quality, along with fishery management
programs, led to a dramatic recovery of walleye in
many areas of the Great Lakes. Populations have
generally been declining from the mid-1990s to
present, however.
Lake trout. Photo: Fisheries and Oceans Canada.
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WHAT IS THE STATE OF GREAT LAKES TOP
PREDATOR FISH?
Non-native salmonids in the Great Lakes have
helped suppress non-native alewife and rainbow
smelt populations. Although the salmonids also
provide a valuable sport fishery, they potentially
have negative effects including direct competition
with native fish species for food and habitat,
genetic alteration through hybridization, and
transfer of pathogens and parasites.
Preyfish abundance in all the Great Lakes has
declined since the early 1990s. In Lakes Ontario,
Michigan, and Huron, the offshore preyfish
community remains dominated by non-native
alewives.
Sea lamprey abundances have been greatly
suppressed from pre-control levels in all the Great
Lakes, although their abundances are above targets
in the three upper Great Lakes.
Levels of legacy contaminants such as PCBs, DDT,
and mercury have declined in monitored Great
Lakes lake trout and walleye since the 1970s, but
they may still be high enough to impair fish-eating
birds such as the bald eagle and to restrict
consumption by humans.
Current Actions
U.S. and Canadian federal, state, provincial, and
tribal agencies work together to conduct fish
population estimates and analyze fisheries yields.
This information, along with established fish
community objectives for each Lake, is used to
determine stocking and harvest targets for lake
trout, walleye, and non-native salmonids. Effective
management of commercial and sport fishery
harvests contributes to increased survival of lake
trout and increased abundance of walleye.
Stocking of salmon and lake trout in Lakes
Michigan, Huron and Ontario has recently been
reduced in recognition of significant reductions in
preyfish populations.
Suppression of sea lamprey continues in all five
Great Lakes through treatment of streams with
lampricides and alternative control efforts.
Walleye. Photo: Fisheries and Oceans Canada.
Actions Needed
To restore a self-sustaining Great Lakes top predator
fish community, the following actions are needed:
• Research to reestablish self-sustaining lake trout
populations throughout the Great Lakes
• Research to determine the optimal stocking
amounts of non-native salmon and prey species
to support self-sustaining top predator fish
communities
• Improvements to watersheds, substrate
enhancement, and dam removal to help
remediate impacted walleye spawning and
nursery habitats
• Protection or reestablishment of native preyfish
species
• Aggressive sea lamprey treatment efforts and
further research in sea lamprey-prey interactions,
population dynamics, and alternative control
methods
For More Information
For further information related to Great Lakes top
predator fish, refer to the State of the Great Lakes
2005 report which, along with other Great Lakes
references, can be accessed at
www.epa.gov/glnpo/solec.
02/06
EPA 905-F-06-906
IISG-05-32
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