Invasive carp closer to threatening Lake Superior
While most eyes have been on the Great Lakes as the likely route for an Asian carp invasion into the Northland, the creatures already may be making a back-door move into the region up the St. Croix and Mississippi rivers.
State and federal officials announced last week that silver Asian carp DNA has been found in 22 of 50 St. Croix River water samples taken as far north as St. Croix Falls, Wis.
No actual carp have been found that far upstream, but scientists say some of the fish are probably in the area because there's no other plausible source of the DNA.
"It's hard for people to get excited about one more invasive species that is supposed to wreak havoc," said Dave Zentner, Duluth angler and conservation activist. "But this one has the ability to absolutely remove huge amounts of biomass from the system," making it unavailable to native species.
The big carp don't eat other fish, but instead feed by filtering small organisms out of the water, the very organisms that are the base of the food chain for native fish.
"We're in a mess, there's no doubt about that," Zentner said. "I think it's 50-50 if we can do anything now that would stop them."
He criticized both state and federal agencies for moving too slowly and politicians for dragging their feet and balking at spending the money and enacting regulations necessary to curb invasive species both in the Great Lakes and inland waters.
Bighead carp, native to southern and central China, can weigh up to 110 pounds. Silver carp, known for jumping into the air at the sound of boat motors, can weigh up to 60 pounds and are native to waters in far eastern Russia.
Both species have exploded in number and range in recent decades and are potentially devastating to some Northland ecosystems. The carp were brought to the U.S. decades ago to help fish farmers clean the pools where catfish are raised. But floods inundating the pools allowed the carp to escape into the Mississippi River.
Since then they have moved up and down the Mississippi system all the way up the Illinois River system to Chicago, where there has been great concern that they will enter Lake Michigan. In some areas they have become the dominant fish, outnumbering native species.
DNA test results on the Mississippi River in the Twin Cities showed no signs of Asian carp, although the fish are believed to be able to swim as far north as the Ford Dam in St. Paul on the Mississippi.
No bighead Asian carp DNA was found in the June tests of either river.
The tests, using incredibly sensitive DNA-sensing devices only available in recent years, were made in late June by a private contractor. They are designed to detect the presence of DNA left by Asian carp through their skin mucous and excrement.
The recent findings come after eight live Asian carp were found in Minnesota waters of the Mississippi system in recent years, including the most recent finding in April in the lower St. Croix.
"Our immediate goal is to mobilize as much effort as possible to confirm the presence of live silver carp in the St. Croix," Tom Landwehr, Minnesota Department of Natural Resources commissioner, said in statement. "The (DNA test) results raise the profile and the level of urgency around the Asian carp issue - not just for the DNR, but for all agencies, conservation groups, municipalities and river users who have a stake in the health of the St. Croix and the Mississippi."
Both rivers reach far into the region - the St. Croix into northwestern Wisconsin and Minnesota, including large tributaries such as the Namekagon and Knife. The Mississippi River system runs through the heart of Minnesota's resort region, including some of the state's most popular fishing lakes.
"The further spread of this invasive species could have a disastrous economic and ecological impact and harm Minnesota's recreation and fishing industries that contribute $4 billion annually to our state's economy," U.S. Sen. Amy Klobuchar, D-Minn., said in a statement.
It's unclear if natural barriers such as waterfalls might stop the big fish or if man-made barriers can be built in time. But even if the fish can't swim directly into Northland lakes, their proximity in nearby rivers makes it more likely they could be moved by people.
DNR officials said they will proceed with development of a bubble or sonic barrier at the mouth of the St. Croix River at Prescott, Wis. Scientists believe such a barrier would not be a 100 percent deterrent to Asian carp, but if the populations are low, the barrier could help keep additional carp out of the river while other population-control methods are developed.
Meanwhile, the DNR will contract with commercial fishing operators to begin using nets on the St. Croix to try to capture live silver carp in the same areas where DNA tests were positive. DNR staff also will use nets and boats outfitted with electric shocking capabilities to search for fish. DNR operations could start this month; commercial netting operations are expected to start by the end of August.