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Minnesota Department of Natural Resources research biologist Doug Dieterman lugs a net full of fish into a small freshwater corral for tagging and the implantation of electronic transmitters on the Mississippi River below the Ford Dam in St. Paul, Minn. on Wednesday, May 15, 2013. (AP Photo/The St. Paul Pioneer Press, John Doman)

Fight to stop spread of Asian carp goes high tech

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ST. PAUL, Minn. (AP) — Minnesota's fight to stop the spread of invasive Asian carp is going high tech.

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Scientists launched a new underwater spying campaign this week. They plan to implant 120 ordinary local fish with transmitters to track their movements and gain knowledge that will better prepare them for when the exotic species inevitably arrive in significant numbers, the St. Paul Pioneer Press reported Thursday (http://bit.ly/10AVrJd ).

“There are a lot of things we don't know,” said Minnesota Department of Natural Resources biologist Joel Stiras, talking loudly over the sound of water cascading over the Ford Dam on the Mississippi River.

A corner of an island below the dam was converted into a makeshift surgical suite Wednesday.

Before the first operation, Stiras checked the transmitter. It was about the size of his index finger. Each one costs $400 and sends signals for 10 years. Smaller fish take a smaller version that lasts 18 months. Stiras picked a catfish out of a holding area, then inserted a 4-inch flame-orange tag into the upper fin, which dangled like a piece of string. He then slipped the fish into a brownish bath of a fish anesthetic. After a few minutes, the fish was comatose.

Then DNR biologist Andy Carlson cradled the catfish in a net over an ice chest, placing it belly-up. Kneeling on the rocky shore, Carlson grabbed a curved scalpel, and slowly cut into the fish's white belly. He put a gloved finger into the opening to clear a path, and inserted the 4-inch sonar transmitter. Then he sewed four stitches.

During the surgery, an assistant used a hose to keep a gentle stream of water flowing over the fish’ gills. Afterward, Carlson released it into the river.

Waiting for that fish and others it is an underwater network of about 50 receivers, scattered in the Mississippi, Minnesota and St. Croix rivers. When any tagged fish comes within a third of a mile of a receiver, the transmitter's sonar signals will be picked up and recorded. Then, when DNR researchers dredge up the devices, they'll know which individual fish passed by, and when.

That will tell them about how fish interact with locks and dams — crucial information for the fight against Asian carp.

Downstream, hundreds of Asian carp have been implanted with the same devices, so when the first ones migrate upriver, their signals will serve as a calling card.

Asian carp rapidly became an environmental nightmare after escaping from southern fish farms into the Mississippi. They eat so much they wipe out native species. They have been advancing steadily up the Mississippi River system. Left alone, they could eventually reach many of Minnesota's premier lakes and damage the fishing industry.

The narrow part of the river at the Ford Dam is seen as perhaps the best hope for stopping them. But officials need to know more about fish behavior before spending millions on some kind of barrier.

Anyone who catches a fish in metro area with a 4-inch orange tag is asked to immediately release it if the fish is alive. If the fish is dead or appears likely to die, call the DNR at 651-259-5806 so officials can retrieve and reuse the sonar transmitter.

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Information from: St. Paul Pioneer Press, http://www.twincities.com

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