St. Croix River gets a second chance

Zebra mussels in sharp decline, NPS report says

A researcher, photo left, collects data as part of a National Park Service study on the zebra mussel population in the St. Croix River. The study showed the river's zebra mussel population is in a steep decline. (Photo courtesy of National Parks Service)

A researcher, photo left, collects data as part of a National Park Service study on the zebra mussel population in the St. Croix River. The study showed the river’s zebra mussel population is in a steep decline. (Photo courtesy of National Parks Service)

The zebra mussel population in the St. Croix River continues a steep decline according to research released by a National Park Service Aquatic biologist done for the Army Corps of Engineers earlier this week.

NPS Aquatic biologist Byron Karns, author of the research paper, said the zebra mussel population has dramatically decreased in the Lower St. Croix. Data comes from test sites in Stillwater all the way down to Prescott with researchers finding only 22 zebra mussels in their sampling this year. According to Karns, none of the eight river test sites needs more attention going forward.

“We’ve gone from millions of mussels to probably thousands,” he said. “They’re not completely eliminated but they’ve certainly crashed.”

Karns’ believes predation and a higher, faster river flow are probable causes of the zebra mussel population crash.

“Our guess is that the common carp have made the mussels their preferential meal. We’ve also had some fairly unusual conditions the last couple of years and may have had this effect due to higher temperatures,” he said.

Zebra mussels are not well-adapted to living in rivers, according to Karns. The

(Graphic courtesy of the national park service)

(Graphic courtesy of the national park service)

invasive mussels are especially not adapted to sticking to soft surfaces such as sand, found on the bottom of the lower St. Croix River. When zebra mussels invade an environment, they stick to hard surfaces like native mussel populations. That makes native mussels vulnerable to environmental stressors and impact the environmental food chain.

“They’re (zebra mussels) more likely to be found in a lake. Reproduction is done by spewing out babies which then settle into the river or lake. But these are constantly being flushed downstream and don’t really seem to settle until they get to the Mississippi River.” Karns said.

Peak reproduction time for zebra mussels is June and July when the St. Croix River experienced high water flow in 2011 and 2012. The reduced zebra mussel population presents a unique opportunity for recreational river users to prevent a future zebra mussel invasion.

“We want to get the word out to the public that we have the unique opportunity to dodge the first bullet and not bring zebra mussels to the river. There are lots of lakes in Wisconsin and Minnesota that are infested with them which allows people more opportunities to bring them from today’s lakes,” Karns said. “What we can do to prevent invasive species — not only zebra mussels but milfoil and a host of other things — is to not transport them.”

Transporting zebra mussels can be prevented by:

  • Removing any visible vegetation from items that were in the water, including the boat, trailer and all equipment.
  • Flush a boat engine cooling system, live wells and bilge with tap water. If possible, use hot water.
  • Do not re-use bait if exposed to infested waters.
  • Dry the boat and other equipment for at least 48 hours before using in uninfested waters.
  • Examine the boat exterior for mussels if it has been docked in infested waters. If mussels are found or the exterior is heavily fouled by algae, individuals can clean fouled surfaces or leave the boat out of the water for at least five days before entering uninfested waters.

Karns said the prevention guidelines are important to follow when the new bridge goes in as well.

“When it comes to the barge traffic associated with the bridge construction the fact is we’re going to have huge barge traffic, probably more than we’ve had in 15 or 20 years. We’d like the barges coming up to be clean when they get here versus sitting here and being contaminated,” he said. “MnDOT has been working with the Fish and Wildlife Service to put protocols in place for bridge construction. MnDOT will put in regulations for their contractors to follow and though I’ve been working with fish and wildlife I’m pretty far removed from MnDOT. But I understand they’ll have the equipment taken out and cleaned and some new equipment as well.”

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