Fight continues against yellow bass in some of Iowa’s lakes

Want to start an argument? Ask a group of people what their thoughts are concerning yellow bass in Iowa lakes.

Some people are huge proponents and enjoy their fight, their willingness to bite and their table fare. Others believe they can ruin a fishery, become overpopulated and stunted, while at the same time squeezing out other game fish by outcompeting native fish for food sources. 

A little history

Yellow bass is a native species that has historically inhabited the Mississippi River drainage until the last few decades. Through undetermined means they have made their way across the state to inhabit a number of natural and constructed public lakes. Yellow bass are very prolific spawners and their populations can increase extremely quickly and, as a result, have no bag limits.

Since the early 2000s, the Iowa DNR has battled infestations in several lakes in southern Iowa.

“We’ve actually been dealing with the yellow bass issues going back to the late 1990s,” said Chris Larson, Southwest Iowa Fish Management Supervisor at Iowa Department of Natural Resources.

Yellow bass got into many of these bodies of water by unknown means, but quite possible through anglers, who dumped yellow bass into the lake. The fisheries in these lakes did not respond well and became overrun with slow-growing, high-density yellow bass populations.

“These constructed lakes in southern Iowa are not good choices for yellow bass,” Larson said.

Studies show that lakes like these with a more simple species diversity have issues with yellow bass explosions, and in a few short years, they overpopulate, and they do not reach angler acceptable sizes. The only answer for these lakes has been a total fish renovation and restocking.

“Over the years we have renovated several lakes because of nuisance yellow bass populations,” Larson said.

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Lake Anita in 2003; Viking, 12 Mile, Icaria and Afton in 2007; and 3 Mile in 2016, are all examples of lakes that have had to be re-set because of yellow bass.

Larson believes that education has begun to have an impact with anglers.

“The DNR has worked really hard to get the word out, and as a result angler transfer is significantly down,” he said. “Anglers seem to have gotten the message that these transfers are not good for the lakes or other anglers.”         

Five-year study

A recent five-year research study compiled by DNR Fisheries Biologist Jonathan Meerbeek examined yellow bass and their impact on Iowa’s lakes.

“It is largely unknown how natural lakes of varying physical and biological characteristics will respond to introduced populations of yellow bass,” Meerbeek said.

For instance, at Clear Lake, a natural lake where yellow bass were introduced in the 1920s, yellow bass populations widely fluctuate. Periods of overabundance have not caused significant declines in the fishery. 

Iowa Great Lakes

In 2005, yellow bass were found in East Okoboji and are now prevalent throughout the Okoboji chain of lakes. Not a native fish of the Iowa Great Lakes, yellow bass were most likely introduced by an angler.

As an invasive, the yellow bass have the ability to upset the balance in a lake as they compete for food and resources. If a lake’s fishery is healthy, it may be resilient enough to absorb the species without causing too much harm. Biologists believe that is what has happened in the Iowa Great Lakes. Yellow bass are present, but their numbers seem to be in check.

Yellow bass numbers quickly increased shortly after they arrived in the Iowa Great Lakes, and it looked like they might start causing major issues. However, a disease hit the fishery, wiping out many of the yellow bass.

This fish disease also impacted the yellow bass’ cousin, the white bass. Since that time, yellow bass have persisted, but their numbers have never recovered to that of those early days.

Other natural lakes in the region haven’t been so lucky, with populations swelling to the point that other gamefish populations are being harmed. Yellow bass populations are being monitored in several northwest and north-central Iowa lakes, and the DNR is actively looking for solutions to this manmade problem.

Iowa’s smaller lakes can be especially susceptible. The yellow bass can become stunted, making them angler unacceptable, and their resulting overabundance, can negatively affect these fisheries and be tough to overcome. 

A different strategy

Lake Cornelia, a 242-acre lake by Clarion, Iowa, was just such a lake.

According to Meerbeek, 385 pounds of yellow bass per acre were estimated in population assessments conducted from 2020-2021. That’s about a million yellow bass in this 242-acre lake. They were taking up the biomass of fish and showed very poor growth, and the fishery suffered.

The DNR worked with local constituents and determined that a low dose rotenone application could hopefully improve the fishery. In November of 2022, several DNR fisheries teams performed a low dose rotenone experiment at Lake Cornelia.

Then, last November, the DNR fisheries management team decided to do a low dose Rotenone application. Rotenone is often used to target all fish in a system and simply start over. However, it has been found that at certain levels, Rotenone can be used to target certain species of fish to provide a partial renovation of the fishery. 

“In this case, we were looking at eight parts per billion, a very small amount, but it was enough to eradicate rotenone sensitive species such as yellow bass,” Meerbeek said. 

After the treatment, the DNR returned and found some dead yellow bass but not the number they had expected to find. The yellow bass had sunk to the bottom. Several times over the past year the lake was sampled, and no yellow bass were caught.

Besides reducing yellow bass abundance, restocking the fishery with predator diversity was also an important tool used by the DNR to combat reestablishment of the yellow bass population.

In 2023, Lake Cornelia was stocked with a variety of predators: muskies, blue catfish, largemouth bass and walleyes.

“We will be evaluating this system over the next few years, but it appears this can be a helpful management tool for lakes that have been overrun with yellow bass,” Meerbeek said.

If so, the re-set will be quicker and cheaper than having to treat the entire water body with a heavier dose of rotenone.