ODNR uses electrofishing to collect fish data
PORT CLINTON – At varying times throughout the year, local fishermen can be found wading waist-deep in the Sandusky River hoping to hook white bass, shooting grass carp with bows in the canals near Pickerel Creek, or cutting chunks of ice out of Lake Erie in search of winter perch.
But Zak Slagle catches his fish with a unique method: He shocks them with electricity.
Slagle is a fisheries biologist with the Ohio Department of Natural Resources Division of Wildlife who oversees the department’s nearshore electrofishing surveys. Electrofishing is a nonlethal method of surveying the fish in Lake Erie and surrounding waters. Electricity temporarily stuns the fish, which are retrieved with nets, placed in a live tank, and studied before they are returned unharmed to the water.
Slagle and his crew work on an ODNR electrofishing boat equipped with a generator. Electricity from the generator travels to probes which release electricity into the water surrounding the boat. The electricity stuns the fish for about 30 seconds, long enough to get them to the live tank before they revive.
There are 20 shock sites in Slagle’s territory, and on June 29, he and his crew shocked along the shoreline near Catawba Island State Park. With him were field technician Frank Depalma and research associate Heather Luken. While Slagle drove the electrofishing boat, Depalma and Luken stood on sensor mats – designed to stop the flow of current if someone falls overboard – and caught stunned fish with nets.
“We shock about 500 meters of shoreline and collect everything we can get,” Luken said.
It was a light fishing night. The team collected 23 fish, including eight different species. Among them were unusually bright blue gill, largemouth bass, and a single pumpkinseed fish, one of Ohio’s most colorful sunfish. On an earlier survey in June, the team caught 18 different species, including a bowfin.
When they reach the end of the shock site, Slagle shutters the boat, and the crew identifies, weighs and measures each fish.
“We can learn a lot. Live fish tell us about the lives of the active fish community,” Slagle said.
The survey data informs biologists of fish populations, pollution sensitivities, invasive species and more. Most of the fish are returned to the water, but a few largemouth bass are kept for later dissection
so biologists can learn more about their reproduction, diet and age, which is determined by viewing the fish’s otolith, or ear bone.
“They are small and fragile, like a fingernail. They have rings like a slab of wood which tell us how old it is,” Slagle said.
Although most surveys are conducted to collect data, the electrofishing boat has been used for other projects, such as tagging smallmouth bass with acoustic transmitters and catching invasive grass carp on the Sandusky River.
Slagle chose to do an electrofishing survey at Catawba on June 29 because the weather conditions were favorable for the work. A light wind is crucial, and electrofishing surveys gain the best results on early summer nights. Slagle begins the surveys a half hour after sunset.
“Early summer nighttime electrofishing is the easiest way to determine how many fish are at a given site,” he said. “At
night, they come up in the water table and are less wary.”
All of the information collected from the electrofishing surveys are available in a multipage data report to anyone, but it is most often utilized by biologists and university students.
In an effort to get essential data from the surveys into the hands of fishermen, the ODNR Division of Wildlife has released the 2021 Annual Angler Report, which condenses practical information on Lake Erie fish. Fishermen can view data on topics such as catch rates, estimated weight of fish at known lengths, and the percentage of prey species found in fish stomachs.
The Angler Report can be found at ohiodnr.gov. For more information, visit ohiodnr.gov.
Contact correspondent Sheri Trusty at sheritrusty4@gmail.com.