"One Fish Two Fish Red Fish Blue Fish"
The receiver stops on each fish’s frequency for several seconds, then moves on to the next one. This allows us to listen for many fish at one time.
Ultrasonic receivers emit a sound signal, rather than a radio signal. We use special listening devices placed in the water to hear these signals. All of the ultrasonic transmitters we use are on the same sound frequency, but the rhythm of the pulse is different. This allows us to listen for many fish at one time, but still allows us to identify individual fish as we get closer to them.
Where Did Goober Go?
Rather than always referring to them by number, staff working on this project sometimes name lake sturgeon tagged with ultrasonic transmitters after characters that appear in the books of Dr. Seuss. Thing One, Thing Two, and the Lorax are just a few of the names used. Radiotagged fish are named after characters from the old Andy Griffith Show. Barney, Opie, Aunt Bea and their friends have been teaching us a lot about the lives of lake sturgeon.
Goober, a 23-pound male we caught and tagged just south of Hannibal in late March 2005, has been an especially interesting fish to follow.
After tracking him for a little over a week, he disappeared. Although we searched for him nearly every day, we didn’t find him until 10 days later. He’d moved 18 miles downriver, to the town of Louisiana. Then, for some reason, he decided to head back upstream.
Over the next six days we tracked him for another 80 miles as he made his way to Keokuk, Iowa. During that time he navigated around submerged rock dikes, through the fishing lines of shoreline anglers, and passed through three dams that break the river into large flowing pools.
This upstream movement couldn’t have been easy for Goober. During most of the year, it’s almost impossible for fish to go upstream through a dam. However, when the river is at or near flood stage, dam gates are raised. Although the water rushing through the gates is fast and turbulent, fish can dash through the gates with a burst of energy. Goober must have really wanted to go upstream to have passed through three dams.
He’s not likely to go any further upstream than Keokuk, though. The only way to move past the hydroelectric dam there is to enter a lock, a specially designed chamber that helps river boat