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Getting the Scoop on Monee Reservoir’s Fish Population

Photo for: Getting the Scoop on Monee Reservoir’s Fish Population

(Photo by Chad Merda)

Dozens of fish were scooped out of Monee Reservoir recently during an electrofishing survey designed to assess the lake's fish population. 

Fish slightly stunned by an electrical current in the water, were netted, measured, weighed and then plopped back into the water to swim swiftly away.

Brennan Caputo, an Illinois Department of Natural Resources fisheries biologist, and Forest Preserve District wildlife ecologist Becky Blankenship served as "dippers" by manning the front of the boat with nets while IDNR fisheries biologist Seth Love piloted the boat.

Low current

The group launched the IDNR boat on a cloudy day with intermittent bursts of sun and cruised around the perimeter lightly shocking the water. The current is set at a low level so it doesn’t harm or stress the fish. Electrofishing is performed every other year during the fall, which is the best time because the fish come up from the deep once the water is cooler.

The survey determines the mix of fish in the lake and the size and health of the various species. The information gathered during the fish foray will help determine how many and what types of fish should be stocked in the future and the proper fishing regulations for anglers.

Fish were netted after a light direct current charge was placed in the water. An onboard generator was grounded to the boat and the boat was grounded to the water, Love explained. The boat also has two booms that are outfitted with rings that put the electricity into the water at a radius of about 10 feet. The rings have metal tubes that look like wind chimes dangling in the water.

“The fish will feel that electrical current and they’ll get shocked and stunned and float to the surface and then the dippers on the front of the boat will dip the fish out of the water and put them in our holding tank which is full of really nice cool water," he said. 

"And then we have an oxygen tank as well to provide oxygen to the fish, so the fish can breathe. A lot of times, as soon as the fish are put into that holding tank, they’ll get lively and try to jump out just because they have so much energy from that oxygen. So, fish are very, very happy to be in that holding tank.”

Some fish wriggled, some flopped a bit and others were almost motionless as they were stretched out on a long board to be measured and weighed on a scale. Fish ranged in size from a tiny bluegill the size of a small goldfish to a 10-pound catfish.

Fish combo

Love was happy with the fish mix he saw during the October outing at Monee Reservoir.

“We got quite a few bass, just about two bass per minute, which is really good,” Love said.

He was less pleased to find yellow perch, which are not stocked in the lake.

“They were likely introduced by anglers who wanted to catch them themselves,” he said. “The yellow perch that we got were really big, which was surprising. Yellow perch will compete with large-mouth bass, so ultimately what can happen is they reduce the forage base for the bass and the bass could become stunted.”

What Love is looking for when he surveys lakes is just the right mix of species.

“In most Illinois lakes and ponds, you’re really looking for the large-mouth bass, bluegill, redear sunfish and channel catfish combo,” he said. “That combo of fish species is really tried and true and works really well. In some bigger lakes, you can stock crappie and walleye."

Love said the four-fish combo works well because the bluegill and redear sunfish provide a forage base for the bass and the bass help to control the bluegill and redear so they do not overpopulate.

“Catfish, they eat a little bit of everything, so they don’t compete with any other species,” he added.

Data entry

After all the lakes are tested, Love said he spends his winter entering the information into a database.

“We’ll look at lengths and weights and body condition, which is an index of how plump the fish are,” Love explained. “That helps us understand fish growth and if there is adequate forage for fish growth.”

The data from electrofishing surveys will be used to set fishing regulations at Forest Preserve lakes, which is a delicate balance. A proper harvest limit keeps fish from getting crowded or stunted and unhealthy by reducing the numbers at the correct ratio. But overharvesting can be a concern if anglers don’t heed the restrictions.

“If fishermen went over the limits, then you could start to fish down the population, which could be really bad, especially if you are harvesting fish that haven’t had a chance to spawn yet. If you’re taking fish that haven’t spawned then you are essentially getting rid of future generations of fish.”

In addition to electrofishing, every two to three years, a small number of fish are sampled for contaminants and the Illinois Department of Public Health reviews the results to see if any fish advisories need to be changed for specific lakes.

“It’s extremely important because there are lot of anglers that still eat fish, so we want to make sure that they are kept safe and they are not eating fish that they shouldn’t be,” Love said.

All the data is important information the Forest Preserve needs to keep its management plans up to date, Blankenship said.

“It’s important for the forest preserve to know the health of our fisheries so that we know that our management plans are working or if we need to make any edits to our plans, based on the results of these surveys, and it also helps us to keep our anglers happy,” she said.

Overall, the surveys are not only critical to managing the Forest Preserve lakes, but they’re also a good way to get out on the water to see what lies beneath, she added.

“It is something that I don’t get to do independently as part of my job,” she said. “So, because we have cooperation (with IDNR) I get to experience a part of fisheries that I wouldn’t normally. It’s a lot of work, but it’s also really fun. It makes you really focus on the flashes of the fish popping up and using your muscles ... to scoop the fish up. It’s a cool perspective that I get to see what the actual fish are that we are pulling up out of these waters.”


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