By Tom Eisenhart
Seeing fish swim in laboratory tanks is one thing; watching them hoisted out of the water in nets after being electroshocked is quite another.
This afternoon we are onboard a boat at the upper end of Pool 8 near La Crosse, Wisconsin. Serving as our guide and boat pilot is Brian Ickes, a research ecologist with the U.S. Geological Survey (USGS). We're here to see the USGS-led Long Term Resource Monitoring Program (LTRMP) field work first hand.
Brian slows the boat as we glide up to where Wisconsin Department of Natural Resources (DNR) researchers Andy Bartels, Shawn Giblin and Kraig Hoff are shocking fish off the bank of an island. We don't want to get too close; they are delivering 3,000 watts of current into the water.
On a platform that extends off the boat's bow, Shawn and Kraig stand ready with nets on long poles. In front of them are two orange poles that stick out diagonally from the front of the boat about eight feet. Attached to the end of each pole is a large metal ring; electric probes dangle in the water from the rings.
Andy, who steers while controlling the electric current, eases the boat forward. Shawn and Kraig wait until they see movement and then plunge their nets into the water to scoop up fish. They then dump the fish into the live well behind him. Andy puts the boat into reverse and pulls back, angles the boat slightly to one side and moves forward again.
The process is repeated several times in about 15 minutes. According to Brian, the electroshocking is effective to about 8 feet, which works with most species. Nets are used for fish lying in deeper waters. Today the crew will visit five sites; tomorrow another six. Wisconsin DNR researchers use electroshocking and other collection methods to monitor the abundance, health and diversity of fish species in the river.
Finished at this monitoring site, Andy turns off the electricity and waves us over. We pull up alongside to see what they've caught. Kraig hoists up an impressive flathead catfish weighing about 20 pounds. Shawn and Kraig weigh and measure the fish while Andy enters the data into the computer alongside him.
The fish are then eased back into the river. Brian explains that they use pulsed DC electrical fields to avoid tissue and skeletal damage in the sampled fish. The fish recover quickly and safely, and are released alive and healthy.
Their catch includes an impressive assortment: yellow perch, golden red horse, silver horse, spotted sucker, smallmouth and largemouth bass and flathead catfish. And there are bluegills — lots of bluegills.
Yet as Brian notes, this represents a small sampling of the 90 fish species found here. That's one out of every six species in North America.December 03, 2010