Just as anglers can fill their tackle boxes with everything from jigs and crankbaits to sinkers and bobbers, biologists also depend on different “gear types” to sample Oklahoma’s fish communities. Electrofishing – the practice of sampling live fish by temporarily stunning them with an electrical current – has long been the recommended gear for studying the state’s blue catfish. But biologists have had doubts about its ability to bring up big fish.

“There’s an abundance of 30-inch-plus fish getting checked in at lake tournaments,” said Austin Griffin, a fish biologist with the Oklahoma Department of Wildlife Conservation. “But when we sample the same lakes with our shock boats, we’re just not seeing those fish.”

To find out if additional gear should be used to monitor the state’s blue catfish, Griffin teamed up with other Wildlife Department biologists to intensively sample three lakes using three common catfish gear types. They found electrofishing may catch the largest numbers of blue catfish but misses a “shocking” number of big fish.

Blue catfish are considered “preferredsized” when they reach at least 30 inches in length. These catfish grow slowly relative to many other sport fishes and may take 12-14 years to reach this size class.

The Nuts and Bolts of Electrofishing

The idea of using electricity to capture fish has been around since at least 1863, when a patent for an apparatus using a battery and electrified hooks was unsuccessfully filed in England. But the practice didn’t take off until the 1940s when technology adequately caught up to the concept. Now, fisheries biologists can use a direct current at either a high frequency – 60120 pulses per second – to sample bass, sunfish, and other centrarchids, or at a low frequency – about 15 pulses per second – to sample catfish. In general, electrofishing is used when water temperatures are at least 60 degrees Fahrenheit. High-frequency electrofishing is typically conducted in April and May while low-frequency is used throughout the summer months.

“Electrofishing is the best way to momentarily stun and capture fish; collect length and weight data; and return the fish to the water unharmed,” Griffin said.

For the blue catfish study, Griffin’s team used