Published May 20, 2011, 09:46 AM

Fending off the fish: Spread of Asian carp could threaten local rivers

Hastings can’t stop Asian carp from spreading upstream, but it, and other sites on the Mississippi River downstream might be sites for alternative technology to deter the invasive fish.

By: Katrina Styx, Northland Outdoors

Hastings can’t stop Asian carp from spreading upstream, but it, and other sites on the Mississippi River downstream might be sites for alternative technology to deter the invasive fish.

In April, a bighead carp – one of four Asian carp species – was caught near Prescott, prompting a new wave of concern for the Mississippi and St. Croix rivers’ ecosystems. Of the four species, two pose a threat to local waterways: bighead and silver carp. The reason for the concern is that Asian carp are “very large fish that eat plankton,” explained Tim Schlagenhaft, Mississippi River Planner for the Minnesota Department of Natural Resources.

Plankton, he added, is the base of the food chain for other aquatic species. As large as they are and as quickly as they grow, breeding populations have been known to push out other native species through competition for food.

“Carp could affect, literally, a billion-dollar fishing industry in Minnesota,” Schlagenhaft said.

That, combined with the effects the fish would have on the overall ecosystem, has environmentalists worried.

“The risk is high, if they get here,” Schlagenhaft said.

The good news is that, even though a few fish have been caught in Minnesota, findings have been sporadic.

“In Minnesota waters, we’ve only had a handful of documented cases of any species of Asian carp,” Schlagenhaft said.

The first fish was reported in 1996. The fish found last month near Prescott was the second found in the St. Croix River.

“They’re not here in large numbers, but they are here individually, and we’re concerned about the potential for them to arrive in large numbers and start reproducing,” he said.

Stopping the spread

The Minnesota DNR, as well as other agencies collaborating on the issue, are taking a proactive approach to Asian carp.

“It’s so hard to get rid of them once they’re there,” said Kelly Baerwaldt of the U.S. Army Corps of Engineers.

One of the options is to create a physical barrier – an option that’s being considered at the Coon Rapids dam, north of Minneapolis. Why so far upstream? Locks and dams from Hastings on down the river are designed to maintain water levels, not control floods, Schlagenhaft explained. During flood season, those dams open up to allow floodwater to pass through. At those times, the fish would have an open door to move farther upstream.

“There’s not really any physical barriers we can do down there,” said Luke Skinner, invasive species program coordinator for the Minnesota DNR.

Lock and Dam 1 and the Upper St. Anthony Falls lock and dam could be better barriers, but fish could still move through the locks just as the boats do. And, those two locations are federally managed, making it more challenging to coordinate improvements.

“The reality of being able to stop these Asian carp downstream is going to be really challenging,” Schlagenhaft said.

There are other technologies that could help discourage the fish from progressing farther north. Researchers are experimenting with bubbles, sound and light technology that would scare fish away from crossing them. Among the potential locations for such technology are Lock and Dam 2, the mouth of the St. Croix River and Lock and Dam 5.

Behavioral barriers wouldn’t be 100 percent effective, Schlagenhaft explained, but could be combined with other removal methods to control carp populations.

“The research is ongoing, but there’s nothing definitive at this point,” Skinner said.

The City of Hastings is officially on board with monitoring and preventative efforts. At its May 2 meeting, the City Council approved a resolution requesting federal and state agencies to take immediate action to implement an ongoing monitoring program and prevent Asian carp populations from moving into the upper Mississippi River. It also requested that the state establish an Asian Carps Task Force for the Mississippi River and its watersheds, and to formalize a plan for mitigating the potential effects of an infestation.

Keeping close watch

While the Minnesota and Wisconsin DNRs, National Park Service, Fish and Wildlife Service, local governments and others work to figure out how to prevent and manage Asian carp, they’re keeping a close eye on the fishes’ progress.

“I think that monitoring is really the heart of what we should be focusing on,” Baerwaldt said.

Much sampling is being done, through fisheries programs throughout the year, commercial fishing and Wisconsin and Minnesota DNR activity.

“If these fish start showing up in larger numbers, we’ll know,” Schlagenhaft said.

Baerwaldt is the program coordinator for a monitoring technique called eDNA (environmental DNA), which is expected to start in the Hastings area this year.

“We call it a genetic surveillance tool,” she said, explaining that it’s a process by which they can survey an area for invasive species.

The concept is that invasive species – carp, in this case – leave behind DNA in the water, whether it’s from feces, scales, mucus or urine. Samples from the surface of the water, where such matter is most likely to found, are tested for the presence of the carp. It’s a sensitive tool, Baerwaldt said, whereas other tools such as netting, are not.

“It’s great for sampling rare populations,” she said.

Because there isn’t as much commercial fishing upstream of Hastings as there is downstream, the Minnesota DNR is looking to start using eDNA sampling at Lock and Dam 1 and 2 and at the St. Croix Falls dam, starting this year. If the sampling shows evidence of Asian carp in those areas, it would trigger more survey work, Schlagenhaft said.

While eDNA sampling can indicate the presence of Asian carp, it’s only an indicator.

“We don’t know where the DNA comes from,” Baerwaldt said. “So we have to put the results in real context.”

The testing does not say whether or not the DNA is from live or dead fish, the number of fish, age, size, how they got there or how long they’ve been there. It’s a powerful tool, Baerwaldt said, but not the only one.

Anyone who thinks they’ve seen or caught an Asian carp should notify the DNR. Schlagenhaft noted that it is illegal for anyone to possess live Asian carp.

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