Skip to main content

Can We Build A Bigger Bluegill?

Can We Build A Bigger Bluegill?

We have some big bluegills in Illinois, but researchers are studying to see if they can super-size the fish. It looks like it's working!

By Gary Thomas

There is something happening to the bluegills in a number of Illinois lakes. They're growing bigger.

And there is a reason. It's all part of experimental research taking place on lakes for an ongoing study by the Illinois Natural History Survey (INHS). The study intends to find out what makes a lake's bluegill population become stunted and how to reverse that trend. The winners in this study will be the multitude of anglers who fish Prairie State lakes for this feisty battler. And anglers can begin taking advantage of some of the early findings right now.

What are researchers doing? It wouldn't be inaccurate to call it genetic engineering. But it's not cloning fish, tampering with DNA or anything like that. It tends to be more "nuts and bolts" fisheries research - working at a little lower level by manipulating the populations and then just recording what happens.

Initial findings after the first few years show some promise, and if it continues and the experiments are successful, it likely will alter the way fisheries biologists have been managing the populations of this species throughout the Midwest, and perhaps the country.

If you're like the majority of anglers, you probably grew up fishing for bluegills. It's the fish that is sought after by most dads and granddads when they're teaching youngsters how to fish. And it's the perfect fish for the task. Bluegills are easy to catch, so young anglers don't get bored waiting to catch a fish.

Photo by Michael Skinner

It also makes for an inexpensive outing. All it takes is a pole and line, hook and bobber, and you can watch as these fish terrorize worms and crickets from spring through fall. They provide plenty of fight and can also result in a tasty meal, so many anglers call it a "life fish" - one they fish for from cradle to grave.


The principal researchers of this study are doctors David Wahl and David Philipp, fisheries scientists with the INHS, which is a part of the Illinois Department of Natural Resources. The two researchers studied our state's bluegill population, read studies conducted by other researchers in the United States and Canada, and came to the conclusion that there were several possible reasons, or combinations of those reasons, that could contribute or cause bluegill populations to become stunted.

The major theories were these:

  • That overfishing was occurring.
  • That competition for the available resources was so great that it limited the growth of fish.
  • That too many large males were being removed, causing the smaller fish to mature at a smaller size.
Scientists thought each of the three theories might contribute to the overall decline in the size of established bluegill populations, but they suspected the third - the removal of too many large males from the population - to be the main reason for stunted populations.

Overfishing a bluegill population isn't an easy task. These fish reproduce quickly. However, it is possible to remove a high percentage of the larger fish, especially during the yearly spawning cycles, and that, according to the two scientists, could result in a decline in the size of the fish in the bluegill population.

Too much competition for existing resources is just a polite way of saying there are too many fish and not enough food. I can remember many a day of sitting alongside a pond and reeling in small bluegill after small bluegill, and practicing good fisheries management by tossing the little fish onto the bank in order to help thin out the population. I thought I was helping. But was I?

The third theory - the removal of large males - is a little more complicated.

When the study began, Philipp pointed out that fisheries biologists have always believed that the stunting of the bluegill populations was the result of having too many bluegills in the population and that there wasn't enough food for them. The researchers believed their study would show this was not the case.

One thing to keep in mind is that the bluegill is a very social fish. It is a schooling species and spawns in colonies. It's not uncommon to find upwards of 50 bluegill nests in the same spawning area. And there is a definite pecking order in these spawning areas, with fish vying for the more protected nests in the center of the nesting area. Naturally, the larger males tend to get these spots.

Female bluegills know the centrally located nests are the most protected from outside predators, such as predatory fish and crawfish, so when they arrive at these nesting areas to lay their eggs, then tend to place the majority of them in those nests offering the most protection - the ones in the middle of the colony.

To give you an idea of how disproportionate this can become, Phillip pointed out that a centrally located nesting bed could get more than 120,000 eggs, while a nest on the edge of the colony might wind up with as few as 10 to 15 eggs. Therefore, male bluegills want to have the most centrally located nests where they have the greatest chance of fertilizing the most eggs.

The next thing you need to know is that bluegills have the unique ability to become adult fish when they want to. They can mature as early as 2 years of age, or delay maturation for several years if they choose. Further, once a bluegill matures and begins nesting and fertilizing eggs, it doesn't grow much larger, due to the work associated with nesting and guarding the young fish.

Both of these premises are important to the researchers' theory, that being that if large bluegill males are present, smaller males will delay maturation and continue growing until they are large enough to compete for those central nests. But if large bluegill males are removed from a lake's population, the smaller fish will choose to mature at an earlier age - and while they are smaller - therefore reducing the overall average size of the bluegills in the lake.

"We want the research to cover all aspects of bluegill management in Illinois, so we are using both large and small lakes, plus lakes from the northern and southern parts of the state," said Matt Diana, a research biologist for INHS who is running the research project from his office near Lake Shelbyville. "By having different size lakes, plus lakes in different parts of the state, we are more likely to get an accurate gauge as to how different management techniques affect the bluegill in Illinois waters."

Researchers also chose two other categories o

f lakes - half having good existing populations of bluegills, and lakes with a mediocre, or stunted, population of this species.

The research involves 60 Illinois lakes, 32 of which are being manipulated by the study. The other 28 lakes are control lakes, to measure what would take place if no management techniques were applied to the water.

Diana said some lakes are being regulated by just adding more-stringent fishing regulations. This includes requiring that all bluegills and redear sunfish be a minimum of 8 inches in length, and restricting anglers to just 10 fish per day.

Other lakes are being manipulated by adding additional predator fish - in this case, largemouth bass - into the population to help keep the bluegill numbers thinned out.

In still other lakes, the bluegill populations are being manipulated by both stringent fishing regulations and by adding additional predator fish into the lake's population.

And, of course, Prairie State bluegill anglers can benefit by knowing what's going on at different lakes.

Diana said monitoring the lakes is done through electrofishing in the spring and fall, plus researchers try to visit each lake a couple of times a month to analyze lake factors such as food sources and water chemistry to see what effect any changes might have on the bluegill population.

"We monitor all these aspects, and we do see that it affects spawning, growth and nutrition to some extent," Diana said. "But the question is whether it really is an overall factor, and it doesn't appear to be at this stage of the research."

Diana said they also seine lakes to check on smaller fish on occasion.

"We get a lot of help from the DNR fisheries biologists, who keep us up to date on any changes on the study lakes in their districts," Diana said.

He also said they are appreciative of the conservation police officers who are monitoring the lakes closely for any violations of regulations.

"Right now, the most dramatic changes are taking place in those lakes where we've added both regulations and more predator fish to thin out bluegill populations," Diana said. "But we are also starting to see some very positive effects as a result of the study in lakes where only regulations are being used to protect the large male fish."

He said they believe they eventually will find the protective regulations to be the best way to manage for good bluegill populations.

There is one other thing researchers have to factor in.

"We know there will be some fluctuations in a lake's bluegill population every year no matter what we do," Diana said. "You can't predict when we'll have a drought year or flooding during the spawning periods, but things like that will factor into the populations and have a bearing on the study's findings. We have to factor that into the changes we are seeing."

Because of these reasons, researchers are finding that the changes are taking longer than they originally thought they might. As a result, they've decided to let the study continue for a few more years to make sure the final data they gather is as accurate as possible.

"We have found that it is a gradual process, but we're starting to see some positive results taking place in the lakes controlled by just regulations," Diana said. "We're already seeing this to some extent in the populations with medium-sized fish, and we're seeing the beginning of this in lakes with larger sized fish. We believe this eventually will result in an increase in the overall size of the bluegills in a few years."

So how can you, as an Illinois bluegill angler, benefit from the study? Well, it might take a few years, but the study is going to put together the management practices that will result in the best techniques to produce good bluegill populations in lakes throughout our state.

But that's long term. We can do better than that. We can tell you the lakes being used in the study - the lakes that had good populations of bluegills when the study began, and which are now getting even better. And if I were looking for a good place to fish for bluegills, these would be the lakes I would be heading toward. We'll also tell you what researchers are doing to increase the sizes of the bluegills in each of the lakes.

Here's a listing of the lakes that were determined to have good populations of bluegills when the study began, and what researchers are doing there to see if they'll get even better.

In the north, the good large lakes are Busse South Lake, 590 acres, located in the Cook County Forest Preserves, where researchers are using stringent regulations; Spring Lake South, 610 acres, in Tazewell County, where researchers are adding additional predator fish; and Bloomington Lake, 635 acres, McLean County, where researchers are both using stringent regulations and adding additional predator fish.

In the south, the good large lakes are Mermet Lake, 452 acres, located in Massac County, where researchers are using stringent regulations; Lake Murphysboro, 152 acres, located in Jackson County, where researchers are adding predator fish; and Stephen Forbes Lake, 525 acres, located in Marion County, where researchers are both using stringent regulations and adding predator fish.

In the north, the good small lakes are Walnut Point Lake, 59 acres, located in Douglas County, where researchers are using stringent regulations; Woods Lake, 27 acres, located in Shelby County, where researchers are adding predator fish; and Lake Kakusha, 52 acres, La Salle County, where researchers are both using stringent regulations and adding predator fish.

In the south, the good small lakes are Red Hills, 40 acres, located in Lawrence County, where researchers are using stringent regulations; Sam Parr Lake, 180 acres, located in Jasper County, where researchers are adding additional predator fish; and Homer Lake, 81 acres, located in Champaign County, where researchers are both using stringent regulations and adding additional predator fish.

Diana also gave the names of four other lakes with quality bluegill populations that were considered control lakes - those lakes where good populations of bluegills existed when the study began, but where nothing is being done to enhance the fishery. These lakes allow researchers to compare the changes with the lakes where research is taking place. Those lakes are Apple Canyon Lake, 450 acres, a private reservoir in Jo Daviess County, and Siloam Springs Lake, 58 acres, located in Adams County in the north; and Lincoln Trail Lake, 146 acres, located in Clark County, and Gladstone Lake, 27 acres, located in Henderson County in the south.

And just for the record, here are some additional lakes, based on DNR district biologist reports after electrofishing surveys, where they believe anglers will find good bluegill fishing in 2003:

Dawson Lake, 158 acres, McLean County, where bluegills exceeding 1/3 pound are common; Devils Kitchen Lake, 810 acres, Williamson County, where anglers can catch 1/2-pound fish fairly readily; Greenville New City Lake, 775 acres, Bond County, where 1/2-pound fish are not uncommon; Hennepin Canal, more than 900 acres, located in Bureau, Henry and Whiteside counties, where the bluegills range from 1/3 to 1/2 pound and are found throughout the canal and feeder; Ramsey Lake, Fayette County, where you can take an abundance of 1/3- to 1/2-pound fish; and Sam Dale Lake, Wayne County, where you can expect 1/3- to 1/2-pound fish.

"We know a lot of anglers who fish for bluegills don't agree with the new regulations we're using for this research and what we were proposing to do when the study began," Diana said. "But we think they'll change their mind when they see what our research is showing us and how it improves the bluegill populations in our study lakes."

So what should anglers do when they get to one of the study lakes to fish for bluegills? Diana said to just ignore the fact that it's a study lake.

"We're not asking fishermen to do anything any different than they would do on any other fishing trip," he said. "And we're definitely not saying they shouldn't keep any fish. We still want anglers to go out and enjoy a day of fishing. We're just asking them to follow the regulations."

Diana said he expects the study to last another three years.

"We are still looking, of course, but the preliminary data we are seeing is proving our theory of leaving the big male fish in the population is going to be the way we should be managing our bluegill population," Diana said. "It could be we've been managing bluegills wrong for all these many years."

Discover even more in our monthly magazine,
and have it delivered to your door!
Subscribe to Illinois Game & Fish

GET THE NEWSLETTER Join the List and Never Miss a Thing.

Recommended Articles

Recent Videos

Game & Fish Magazine Covers Print and Tablet Versions

GET THE MAGAZINE Subscribe & Save

Digital Now Included!


Give a Gift   |   Subscriber Services


Buy Digital Single Issues

Magazine App Logo

Don't miss an issue.
Buy single digital issue for your phone or tablet.

Buy Single Digital Issue on the Game & Fish App

Other Magazines

See All Other Magazines

Special Interest Magazines

See All Special Interest Magazines

GET THE NEWSLETTER Join the List and Never Miss a Thing.

Get the top Game & Fish stories delivered right to your inbox every week.

Phone Icon

Get Digital Access.

All Game & Fish subscribers now have digital access to their magazine content. This means you have the option to read your magazine on most popular phones and tablets.

To get started, click the link below to visit and learn how to access your digital magazine.

Get Digital Access

Not a Subscriber?
Subscribe Now

Enjoying What You're Reading?

Subscribe Now and Get a Full Year

Offer only for new subscribers.

Subscribe Now