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IDNR Goes Fishing for Information


When Rob Miller searches for fish, he doesn’t bring a fishing pole.

Miller, District 8 fisheries biologist for the Illinois Department of Natural Resources (IDNR), has more sophisticated equipment that he uses to see what kind of fish are swimming in a four-county area, including Will County and the lakes owned by the Forest Preserve District.

His boat is equipped with “droppers,” which are flexible metal cables, and alternating current (AC). He uses the equipment for electrofishing to stun fish near his boat so they can be measured and weighed. It is one of several sampling techniques that can be used to evaluate a lake’s fish population, Miller explained. Collecting fish assists in determining trends and helps to guide management decisions, he said.

The Forest Preserve works in cooperation with IDNR to make these management decisions, but deciding which fish will be stocked in Illinois waters is ultimately determined by the state.

Electrofishing also is used to obtain fish that are tested for contaminants. Miller used the electrofishing technique September 8 at Lake Renwick in Plainfield to obtain fish samples to be sent to the Illinois Environmental Protection Agency for contaminant analysis.

In general, he collects fish species that are at the higher end of the food chain because they will be more likely to have ingested contaminants. His samples include bottom feeders (catfish and bullheads), omnivorous fish (carp), and top predators (largemouth bass and walleye).

“From those tests, that is where your contaminant consumption advisories come from,” he said. “We do these on a rotational basis every three to five years and we try to hit all of the lakes.”

Whalon Lake is scheduled to be surveyed September 20-21. This will be a general survey where specimens collected via electrofishing will be measured and weighed and returned to the lake. 

“From that we get a pretty good idea what we have out there,” Miller said. “And I can compare that to my management plan for that lake and see just exactly where that trend is going and if we need to tweak a harvest regulation or if we need to do supplemental stocking.”

There are other ways to obtain fish for analysis, including nets, but electrofishing is the main tool used by IDNR, Miller said.

“It gives you a pretty good idea as far as the fish population,” he said.

Electrofishing isn’t new, Miller said. Fishing with alternating current has been around since the 1950s; and direct current techniques were developed in the last 20-25 years.

The only time it can’t be used is if a lake’s salt content is high and it’s extremely difficult for the charge to be effective, Miller explained.

A fish population survey also will take place later in September at Lake Chaminwood in Minooka. Both a fish population survey and contaminant analysis will occur at Monee Reservoir in Monee Township in October.

To learn more about fishing in Forest Preserve lakes, visit the District’ Fishing Page. The state also has information on lakes and reservoirs throughout Illinois at its Fishing in Illinois page


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