Seven species of carp native to Asia have been introduced into the U.S. Two of these species, silver and bighead carp, are considered a pressing threat to the Great Lakes.
Hypopthalmichthys molitrix (Silver carp)
Hypopthalmichthys nobilis (Bighead carp)
- Weigh up to 60-110 pounds.
- Have low-set eyes, situated far forward, and large, upturned mouths.
- Both species are planktivores, feeding on microscopic plants (phytoplankton) and animals (zooplankton).
- Silver carps, like their name suggests, are light in color.
- Bighead carps are darker grey with dark blotches all over their bodies.
- Bighead and silver carps do not have barbells, like those of the common carp.
- Bighead carps consume up to 140% of their body weight when very young but eat far less as they become adults.
- Silver carps can leap out of the water when disturbed by boat motors.
How they arrived in the U.S.
Silver and bighead carp were brought into the U.S. in the 1970s to improve water quality in aquaculture ponds and water treatment systems, and to boost harvests from catfish ponds. They are believed to have entered the Mississippi River system by means of the ponds flooding in the 1990s.
Despite the operation of electric barriers on the Chicago Sanitary and Ship Canal, a man-made connection between the Mississippi River system and Lake Michigan, a live bighead carp was caught on the Lake Michigan side of the barriers in June 2010. Environmental DNA (eDNA) testing found evidence of silver carp in Lake Michigan, and suggests that silver carp and bighead carp are present between Lake Michigan and the electric barriers.
Threats of Invasion
There are several ways the carp could infiltrate the Great Lakes ecosystem. One of the primary pathways is through the Chicago Canal that connects the Mississippi River system and Lake Michigan. Improper bait-bucket release is a potential risk because young bighead or silver carp are easily mistaken for shad or minnows and could be accidentally released by anglers. Flooding and intentional release of fish bought from live fish markets are other possible paths of introduction.
Problems Carp May Pose
If silver and bighead carp become established in the Great Lakes, they are believed to pose a serious threat to native species at multiple levels of the food web. Silver carp also pose a physical threat to boaters in the connecting waterways of infested lakes and rivers as they jump out of the water when disturbed by boat motors.
The U.S. Army Corps of Engineers (USACE), along with several other agencies, installed electric barriers along the Chicago Sanitary and Ship Canal to prevent invasive fish from moving between the Great Lakes and Mississippi River watersheds. The EPA, USACE and the Great Lakes Commission are exploring complete ecological separation, as well as other strategies to reduce the spread of Asian carp and other invasive species.