Nebraskaland

48 Nebraskaland • January-February 2021 On the third and fi nal morning, after scans found numerous fi sh in the east bay, a block net was set to close it off from the main lake. A 1,250-foot seine was wrapped around the bay, and crews pulled in 26,000 pounds of fi sh, 80 percent of which were silver carp, 14 percent bighead carp, and the remainder bigmouth and smallmouth buff alo, common carp, grass carp and gar. Follow-up scans found that some fi sh had found their way under the block net and into the west portion of the lake and others remained in the eastern portion of the main lake, but they estimated that about one third of the rough fi sh biomass was removed. Happy with the results in what was a learning experience for each of the parties involved, they are hoping to try again this winter. "This time, I'm going to bring enough net to make three diff erent blocks and really try to crowd those fi sh into that eastern part of the lake," Havranak said. Eastman said there were noticeably fewer jumping fi sh at the lake this past summer. "If they can get 80 percent of what's left or so, I think that would be a win." Residents are already hopeful they can improve the fi shery, and last year more than tripled their typical budget for fi sh stocking. THE WORK at Hanson Lake was Havranek's fi rst attempt at driving silver and bighead carp with sound. Most of his fi sheries management work involves common carp. Last winter, he worked with the Minnesota Department of Natural Resources and commercial fi shermen on a suburban lake in Minneapolis on a project to remove common carp. With radio tags in fi sh, they knew where a large number of fi sh wintered. Because the shallow bay was strewn with boulders, it could not be seined. They used underwater speakers to drive fi sh from the area, monitoring the movement of tagged fi sh. Weeks later, they used a block net to cut off their escape route and directed fi sh into a seine, capturing 12,000 pounds. Havranek used speakers to move carp at other times during the year, and while there would be substantial logistics and planning involved, he sees potential for use elsewhere to manage carp populations. As for using sound to drive and harvest Asian carp in fl oodplain lakes, "This is a no-brainer that this is going to be an incredible tool," Chapman said. It would be impossible to use it in the Missouri or other large rivers due to the current and debris present, Chapman said. But if suitable netting areas could be cleared of debris, it may be possible to harvest fi sh in tributaries with suffi cient depth and low velocities, like the mouth of the Big Nemaha River. "You could drive these fi sh up and down there like cattle," he said. Like cattle, there will always be fi sh that don't want to cooperate. Unlike cattle, which are easy to see breaking from the herd, it's harder to see fi sh making a break underwater, even with today's high-tech fi sh fi nders. But it's certainly a promising control technique. So, yee-haw! Get along little fi shy! N The fi sh-shaped marks in this side-scan sonar image are large schools of silver carp in Hanson Lake. Tim Adams, part of commercial fi shing crew from Minnesota, checks the contents of a seine.

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