Common carp were intentionally introduced into Illinois rivers
in the late 1800s to provide more fish for the dinner table.
Within a few decades, this successful invasive species became
abundant because they are tolerant of a wide range of
According to Daniel Gibson-Reinemer, post-doctoral researcher
with the Prairie Research Institute at the University of
Illinois, problems arose when large numbers of carp rooted
through submerged vegetation, muddying the water and decreasing
availability of sunlight to aquatic plants, as well as
outcompeting other fish for river resources.
With funding from the Illinois Department of Natural Resources,
Gibson-Reinemer and colleagues accessed data from two
river-monitoring programs dating back to the 1950s to study carp
population trends. A total of 84,381 common carp specimens were
sampled from the two monitoring programs.
The researchers discovered that steep population declines
started in the 1970s and persisted throughout the Illinois and
upper Mississippi rivers. By the 1990s, carp numbers had fallen
by more than 90 percent in some areas. Smaller, younger fish
suffered higher rates of mortality, while many older fish
“The demographics clearly show that common carp populations were
faltering, and that they had experienced decades of erratic
spawning,” Gibson-Reinemer said.
Interestingly, most other fish species were increasing in
numbers during the same time, indicating that poor water
quality, native predators, and a lack of food did not cause the
Instead, diseases, particularly two herpes virus strains that
infect fish, were identified as the likely cause of fish
mortality. Since the 1990s, outbreaks of the viruses have been
observed in common carp around the world without affecting other
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Gibson-Reinemer’s study suggests that, in some situations, natural
factors can curb populations of invasive species more effectively
than diligent human initiatives. Previous management efforts to
decrease common carp populations were largely unsuccessful.
“Management activities aimed at eradicating or severely reducing
invasive species over large-scale, connected river systems are not
impossible,” Gibson-Reinemer said. “However, we are unaware of any
large-scale management program that could have produced such a
About the Prairie Research Institute: The Prairie Research
Institute (PRI) at the University of Illinois at Urbana-Champaign
comprises the Illinois Natural History Survey, Illinois State
Archaeological Survey, Illinois State Geological Survey, Illinois
State Water Survey, and Illinois Sustainable Technology Center. PRI
provides objective natural and cultural resource expertise, data,
research, service, and solutions for decision making, the
stewardship of Illinois’ resources, and the public good.
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