If you thought round gobies and zebra mussels were scary invaders of the Great Lakes, brace yourself for the arrival of Asian carp, a voracious fish that could decimate the lakes' native fisheries. Capable of growing to 4 feet in length and 100 pounds in weight, these carp -- there actually are three species, bighead, silver and black carp -- have the capability to take over ecosystems. According to the Natural Resources Defense Council, 90 percent of the lifeforms in some stretches of the Illinois River are Asian carp.
Filter feeders, Asian carp were introduced to the United States in the 1970s to help keep wastewater treatment facilities and aquaculture ponds clean. Floods in the 1990s enabled them to reach the Mississippi River, and they've been headed north ever since.
According to the Illinois Department of Natural Resources, "Bighead carp are capable of consuming 40 percent of their own body weight in food each day. Silver carp are smaller, but pose a greater danger to recreational users because of their tendency to jump out of the water when disturbed by boat motors. They have severely impacted fishing and recreation on the Illinois River. They can spawn multiple times during each season and quickly out-compete native species by disrupting the food chain everywhere they go."
Against this background, federal authorities on Friday acknowledged that an electric fence that was being counted on to prevent the carp from reaching Lake Michigan has failed, leaving carp just just one lock from being able to swim the final 25 miles to the lake, home to both Indiana Dunes and Sleeping Bear Sand Dunes national lakeshores. Groups worried about the carp reaching the lake have called for the immediate closure of all waterways and locks leading from Chicago into Lake Michigan.
At the Natural Resources Defense Council, Henry Henderson was not surprised by Friday's news.
“Today’s announcement that Asian carp have gotten past the electric fish fence is sobering, but predictable. The responsible federal and state agencies have known about this problem for 13 years, but have utterly failed to act with the urgency that this threat requires," said Mr. Henderson in a statement. "The prospect of 100-pound fish off of Oak Street Beach and leaping out at boaters in the Great Lakes should spur action that should have been undertaken years ago. We have seen how zebra and quagga mussels have literally transformed Lake Michigan, and I fear that the Asian carp could do far worse to the ecosystem.
“The Army Corps of Engineers needs to stop reacting to events, and get ahead of this problem with real solutions. Physical barriers in the waterways need to be put in place quickly, along with a clear plan to move aggressively toward closing off the Chicago Diversion and returning the ecological barriers that used to protect the Great Lakes from these threats. The only thing aggressive about the virtual fish fence has been its multi-million dollar price tag."
In perhaps a last-ditch effort to keep the carp out of Lake Michigan, in early December the Illinois Department of Natural Resource plans to poison the six miles of canal between the electric barrier fence and the Lockport Lock and Dam with rotenone, a fish-killing poison, to prevent the carp from breaching the barrier and traveling some 25 miles upstream to Lake Michigan.
If the carp are able to reach Lake Michigan and then spread to the other Great Lakes, it's feared that they'll quickly overwhelm the lakes' $7 billion sport fishery.
"Once in Lake Michigan, this invasive species could access many new tributaries connected to the Great Lakes," said the Illinois DNR. "These fish aggressively compete with native commercial and sport fish for food. They are well suited to the water temperature, food supply, and lack of predators of the Great Lakes and could quickly become the dominant species. Once in the lake, it would be very difficult to control them."
At the Alliance for the Great Lakes, acting president Joel Brammeier said, “We’ve missed every other opportunity to protect the lakes from these fish and their devastating legacy. It’s imperative we put the health of the Great Lakes -- the world’s largest surface freshwater system -- first.”
The carp are known, along with their appetites, for their aggressiveness. They've been known to leap out of the water and knock boaters into the water. National Park Service officials are aware of the threat the carp pose, and some units have been looking into ways to control the fish.
To gain some understanding of these fish, and the threat they pose, check out this video: