Counting Fish

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Published on: Jul. 2, 2007

Last revision: Dec. 1, 2010

One night in April, two bass anglers on Lake of the Ozarks are pitching jigs and spinnerbaits around sunken brushpiles. Using an electric trolling motor, they quietly make their way around a rocky point and approach a craft with three people in it, all of whom are hovering around a tank in the middle of the boat.

As they get closer, they can hear one person speaking while another seems to be taking notes. They hear subtle splashes as the speaker slips objects over the side of the boat. The anglers then watch as the boat starts its engine and moves to the other side of the cove.

Curious, but still fishing, the anglers are surprised to hear a gasoline generator start and see the area in front of the boat suddenly bathed in bright light. They also notice two people standing in the bow of the boat dipping nets into the water.

They keep an eye on the boat, and when the generator shuts down and the lights go out, they slide up close to the boat to find out what its occupants are doing.

“I’m a fisheries biologist with the Missouri Department of Conservation,” the driver responds to their question. “We are conducting our spring electrofishing survey to collect data about the black bass population in the lake.”

Fisheries biologists use electroshocking to survey fish populations in Missouri rivers and lakes. Biologists often work at night because many species of fish tend to be closer to shorelines after dark, and the fish are less likely to be spooked by a boat. The fish are only stunned by the electric current and recover quickly.

Electrofishing, Trap nets and Hoop nets

Electrofishing works well for counting some, but not all, species of fish. We also use trap nets and hoop nets for surveying populations. What’s important is that we collect each species at the same time of the year and using the same method so that we can compare our data with other years.

For example, we survey largemouth bass with electrofishing gear in April and May once the surface water temperature reaches 65 degrees. We collect crappie in trap nets in October. We survey channel catfish in the summer by using hoop nets baited with aged, foul-smelling cheese. We set gill nets below wing dikes in the Missouri River during late winter for sturgeon.

Our knowledge of when and how to survey fish populations was not accumulated overnight. Present-day

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