DES MOINES - Iowa Department of Natural Resources fisheries biologist Gary Sobotka was shocked last spring when he collected a 13-inch yellow bass during a routine fish survey at Three Mile Lake. The reason for his alarm is that yellow bass have upset the fish populations in nine lakes in southwest Iowa making those lakes unattractive to anglers, and Three Mile Lake is one of the most popular fishing lakes in Iowa.
"There is at least 1,800 acres of water in southwest Iowa that have been negatively impacted because of yellow bass," Sobotka said. "Our hope is to get some of those systems back on line within a couple of years, which means total renovation."
An example of how yellow bass can impact a lake is underway at Twelve Mile Lake, near Creston.
"Three to four years ago, we would have 25 to 30 bass fishing tournaments at Twelve Mile Lake," Sobotka said. "This year there is only one. The bass anglers know the situation at Twelve Mile and it's not good. You can't even fish for bluegills or use small bait because you can't get past the yellow bass."
Yellow bass is a small panfish that, once introduced to a lake, can completely take over the fish population within a few years. These fish are able to reproduce when they reach five to six inches and aggressively feed on the eggs of nest laying fish, like largemouth bass and bluegills. They will also eat the newly hatched larvae of those species as well as crappies.
"I have seen a school of yellow bass follow a female crappie and feed on her eggs as she deposits them," said Chris Larson, fisheries biologist at Cold Springs, near Atlantic.
Yellow bass can get so numerous in a system that no other fish can grow. They negatively impact other species through competition or even direct predation. Yellows can get so thick, in fact, that the food in the system cannot support their own population, causing the yellow bass to become stunted, rarely getting to angler acceptable size of 8 inches.
Larson has seen first hand how yellow bass can destroy a lake. He eradicated the entire fish population at Lake Anita last fall to get rid of yellow bass. The lake has been restocked with largemouth bass, bluegill, crappie and channel catfish. Unfortunately, it will take a few years for the fish to grow large enough before anglers will return. Before yellow bass took over Lake Anita, the lake had an estimated impact of $750,000 each year to the state and local economy.
"The only way I know how to manage yellow bass is at the bottom of a Rotenone barrel," Larson said. "And you will basically lose your fishery for a couple of years."
At Lake Icaria, largemouth bass are outnumbered 2,000 to 1. "At those numbers, largemouth bass can't protect a nest to get a spawn off. Bluegills face the same problem," Sobotka said. Sobotka has surveyed Icaria and estimates there are 392 largemouth bass, 668 walleye, 12,600 bluegill, and 784,000 yellow bass.
"Domination doesn't do justice to describe what yellow bass do to these southern Iowa lakes," Sobotka said. "It's worse than domination."
Sobotka and Larson have been talking with neighboring states to see what they are trying to address the yellow bass problem. Nebraska tried over-stocking largemouth bass in affected lakes and all they found was skinny largemouth bass and no impact on yellow bass.
Larson and Sobotka have studied predator species - largemouth bass, walleye, channel catfish - and although these fish are eating a few yellow bass, they are looking elsewhere for the primary food sources. A stomach analysis of more than 200 largemouth bass at Viking Lake this past summer reveled that largemouth bass do not feed effectively on yellow bass. In fact no, yellow bass were consumed by largemouth bass even though they are the dominant prey species in the lake.
Part of the problem may be that yellow bass and these predators do not frequent the same habitats in a lake. Another may be the spiny make up of the yellows. Or another may be the fish simply don't like the taste of them. Whatever the reason is, predator stockings is not the answer.
So far, there is no solution other than total renovation.
"There are a lot of systems that maybe on the verge of crashing because of yellow bass," Sobotka said. Bender Lake, near Corning, is one. So is the Afton City Reservoir. Other lakes include Viking, Manawa, and Arrowhead, in Pottawattamie County.
Larson has a special project underway involving walleye stockings at Viking Lake to help control the yellow bass, but he is not optimistic. "Twelve Mile has a good walleye population with lots of big fish, and it is still choked with yellow bass," he said. He is also stocking wipers, a cross between the ocean striped bass and white bass, in Manawa to see if that species can have an impact. Wipers cannot reproduce in the wild.
"I know yellow bass are popular at Clear Lake, but in southern Iowa they are the top nuisance species - even above carp," Larson said. "Clear Lake is really the exception to the rule when it comes to yellow bass populations, and in a majority of the years at Clear Lake, yellow bass have been too small to keep."
Larson was horrified to hear reports of anglers using live yellow bass as bait for channel catfish. "That is a sure way for yellow bass to find their way into a new system."
Iowa law makes it illegal to transport live fish from one public body of water to another, unless written permission is granted by the DNR.
"Please, by no means, transport these fish to other waterbodies," Larson said. "You might think you are establishing another fishery, but are more likely leading that lake down the road to renovation."
The DNR has already renovated Lake Anita and East Hackelbarney Lake because of an excessive yellow bass population. Plans are underway to renovate Lake Icaria, Binder Lake, and Old Corning Reservoir this fall. Renovating a lake to get rid of yellow bass is expensive and will impact local economies for up to three years and possibly longer.
Back at Three Mile Lake, Sobotka is keeping an extremely close eye on the fish population. He has surveyed the lake many times since finding that one yellow bass last spring using different methods and, so far, has not found another one. The economic impact Three Mile Lake has on local communities is in the millions of dollars each year. It is a destination lake drawing anglers from all over Iowa and surrounding states.
"I'm hoping it is the only yellow bass I ever find there," he said.