February 1, 2023

Rock River Sport Fish Surveys

Photos courtesy of the author.

The Illinois Department of Natural Resources (IDNR), Division of Fisheries completes fish community surveys on the small stream basins in Illinois. These basin surveys are completed in conjunction with the Illinois Environmental Protection Agency on an approximate 5-year rotation. Fish population data, stream flow, sediment, macroinvertebrate, water chemistry and fish flesh contaminant samples are collected on these surveys. The data collected from these surveys has been valuable in assessing the health of our streams and has been used to upgrade the IDNR’s strategic plan. It has also proved valuable in helping target stream specific management activities, and to provide the basis for making decisions regarding potential impacts on streams from construction activities, and point and non-point discharges.

A researcher stands in a boat in the middle of a river. The researcher holds a long green, amber fish. In the background is a shoreline full of trees.

The IDNR Fisheries staff also completes targeted sportfish surveys on many of our major stream basins. One of our more interesting stream basins is the Rock River. The Rock River arises in Washington County, Wisconsin and enters Illinois near Rockton. It flows in a general southwesterly direction for approximately 163 miles before entering the Mississippi River near Rock Island. The river drains 10,280 square miles, with about half of this area in Illinois. After the confluence with the Pecatonica River near Rockton, the Rock River is a 7th order stream.

The Illinois portion of the Rock River has major population centers at Rockford, Byron, Oregon, Dixon, Sterling/Rock Falls and Rock Island. The remainder of the Illinois portion of the basin is primarily agricultural. Three major tributaries enter the Rock River in Illinois: 1) The Pecatonica River with a drainage area of 2,641 square miles enters the Rock River near Rockton, 2) the Kishwaukee River with a drainage area of 1,257 miles enters just south of Rockford, and 3) the Green River with a drainage area of 1,131 square miles enters the Rock River almost at the mouth of the river near the Quad Cities. The main-stem has low-head dams at Rockton, Rockford, Oregon, Dixon, two dams at Sterling/ Rock Falls, and a split dam at Milan.

In the falls of 2020, 2021 and 2022, IDNR Fisheries staff completed the Rock River fall sport fish survey and fish flesh contaminate sampling. Boat electrofishing was completed in November on 10 historical sampling sites from South Beloit to Moline. These surveys were part of a 3-year effort to document the population levels and size structure of the sport fish in the Rock River. Walleye, sauger, smallmouth bass, rock bass, white bass, channel catfish, bluegill and crappie were the primary target species. The cool water temperatures in November limit the effective collection of the flathead catfish population in the Rock River by boat electrofishing.

During a snowy winter day, a metal boat is moored to a concrete incline boat launch into the water of a river. In the background is a shoreline with an occasional house interspersed amongst trees near the shoreline.

In conjunction with these surveys, fish flesh samples were taken from a small composite of each sport fish species group and common carp. These flesh samples will be analyzed by the Illinois Environmental Protection Agency lab in Springfield for levels of substances that are considered hazardous for human consumption. In 2021 and 2022, fish flesh contaminate sampling was also completed on the Pecatonica River and Kishwaukee River Basins. When all of these results are completed, we should have updated fish consumption guidelines with the Illinois Department of Public Health for this greater Rock River watershed. Statewide fish consumption advisories can be found here.

Highlights from these fall surveys continued to show high walleye numbers at Fordham dam, Oregon dam, Dixon dam and Lower Sterling Dam tailwaters. A 29-inch walleye weighing 10.8 pounds topped the 2022 survey. Walleye are the only fish annually stocked by the IDNR into the Rock River Basin. Approximately 100,000 walleye that have an average length of 2 inches are stocked each year into the Rock River Basin at five sites on the Rock River and one site on the Pecatonica River.

High catch rates and sizes of smallmouth bass were found from sites at Rockton, Fordham dam, Oregon dam and Prophetstown State Park. Channel catfish continue to be very abundant throughout the entire length of the Rock River with the majority of the fish under 6 pounds and in average body condition.

Six researchers each individually hold up a large fish while standing on a wooden dock that juts out into a river. In the background are both shorelines on either sides of the river filled with trees against a bright blue sky.

These fall surveys have also documented the river redhorse and the American brook lamprey, which are listed as threatened species by the Illinois Endangered Species Protection Board.

Current and future targeted fish studies on the Rock River will focus on the flathead catfish population and the shovelnose sturgeon populations. These studies will require additional sampling techniques and fish tracking techniques to learn more on their population levels, habitat requirements and movements, reproduction ultimate growth, and recruitment to mature fish within the Rock River. Both species are represented by trophy size fish in the Rock River Basin. In October 2022, the new state and world record shovelnose sturgeon was caught and then released alive back into the Rock River!

Rob Hilsabeck has been an Illinois Department of Natural Resouces District Fisheries biologist since 1994 in central Illinois. He received his bachelor and master’s degrees from Western Illinois University with Dr. Larry Jahn as his thesis advisor. Hilsabeck was very fortunate to start his IDNR Fisheries career under the tutelage of the legendary Ken Russell and Wayne Herndon. The Region 1 Fisheries team has tackled fish management in the northwest quarter of Illinois with that zeal for improvement of the aquatic ecosystem for 50-plus years.

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