DNR battling unwanted fish invasions

While imported invaders like carp are often badmouthed for adversely affecting rivers and lakes, two native species have caused much recent damage to southern Iowa fisheries.

Infestations of gizzard shad, a desirable forage fish in Lake Rathbun, the Mississippi River and many other waters, has forced the Department of Natural Resources to eradicate them in three southeast Iowa lakes.

Infestations of yellow bass, a fish esteemed in Clear Lake and other northern Iowa waters, has caused similar trouble and expense in more than a half dozen southwest Iowa lakes.

“I would say we are on top of the yellow bass now, but it has been a costly battle,” said DNR fisheries biologist Gary Sobotka, who has overseen the draining, poisoning and restocking of several lakes.

The average rehabilitation project costs at least half a million dollars, and that does not include the lost economic activity in nearby communities during the several years in which the fishery is declining and then recovering, Sobotka said.

The DNR is still engaged in an effort to eliminate shad from Lake Sugema, a popular fishing destination in Van Buren County.

Fisheries technician Bruce Ellison said a tricky procedure involving the application of enough poison to kill the shad, without killing desirable fish like bluegills, crappies, walleye and largemouth bass, appears to be succeeding.

In earlier shad-eradication efforts, the DNR had drained and poisoned all the fish in lakes Wapello and Hawthorn. Since the shad infestation at Sugema had only begun last spring, they opted for a measure that would avoid the years of down time inherent in total eradication programs, Ellison said.

“We killed some desirable fish, but the losses were acceptable. Anglers should not notice the difference this spring,” he said.

Careless or misguided anglers are typically responsible for the unwanted and illegal introduction of shad and yellow bass.

State law forbids the introduction of any live fish, except for bait, into public waters.

Sobotka said the DNR has undertaken public education initiatives to discourage the practice.

Biologists, he said, are not sure why southern Iowa lakes are so susceptible to damage from shad and yellow bass.

“We know they multiply rapidly and out-compete desirable species for food and space. Eventually the desired species are gone, and the lake is filled with stunted, unwanted fish,” he said.