The U.S. Geological Survey confirmed that four grass carp (a species of Asian carp) taken from the Sandusky River in Ohio are the result of natural reproduction within the Lake Erie basin.
Grass carp can threaten native
fish populations and could be detrimental to ducks, geese and other large
aquatic birds that rely on the vegetation that these carp destroy. Grass carp were brought to the U.S. to control aquatic
plants in the 1960s. They eat large quantities of aquatic plants, which
could degrade areas important for spawning and early development of
Fish captured by a
commercial fisherman in October 2012 were examined by USGS scientists and determined that they were at
least one year in age and had the capacity to become spawning adults.
Bones in the heads of fishes, called otoliths, are useful to biologists
because they provide a history of the chemistry of the water the fish
inhabited over its life. Analysis of those bones indicates that the four
captured grass carp had lived in the Sandusky watershed their entire
lives. Scientists ruled out the possibility that the fish originated
from a fish farm by comparing their otoliths to those from reference
"These findings are significant because they confirm recent USGS research
indicating that shorter rivers, like the Sandusky, are potential
spawning sites for grass carp and other Asian carps as well," said USGS
scientist Duane Chapman. "The study may also provide resource managers
an opportunity to address the spread of grass carp before it becomes
Successful reproduction of grass carp in the Great Lakes is an
indication that other species of Asian carp—silver, bighead and black
carp—might be able to reproduce there. Silver, bighead, and black carps
have spawning and development requirements similar to grass carp.
Bighead and silver carps have reached extremely high densities in the
Mississippi River Basin and there is great concern that they may invade
the Great Lakes Basin.
Scientists are confident that these grass carp are the result of
natural reproduction for a number of reasons. The Sandusky watershed has
a naturally occurring high ratio of strontium to calcium, and fish
inhabiting the Sandusky River have strontium to calcium ratios in their
otoliths that reflect this unusual chemistry. The otoliths of the
Sandusky River grass carp were not only higher in strontium to calcium
ratio than pond fish, but also reflected the Sandusky River’s natural
fluctuations in this ratio, which are caused by rainfall. Pond fish
otoliths reflected the stable and low strontium to calcium concentration
This study was done in cooperation with Bowling Green State University and the Ohio Department of Natural Resources.
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