Ridge Lake Station
Ridge Lake Station
Impoundments, or artificially created lakes, are important fisheries resources in Illinois. Almost half of the surface waters in Illinois are impoundments, and of these, 38 percent are 40 acres or smaller in size, representing almost 100,000 acres of water. Because these impoundments receive high angler use (up to 1,000 hours per acre per year), it is important to study ways in which fish populations and angling opportunities in these systems can be maintained. Ridge Lake Station, a Survey fisheries research laboratory located at 14-acre Ridge Lake south of Champaign in Coles County, was constructed in 1941 for the purpose of investigating fisheries management alternatives for small impoundments.
Over the years, investigations at Ridge Lake have covered a variety of topics important to the management of small impoundments. From the beginning of operations through the 1960s, studies at Ridge Lake included determination of the effect of water level management, harvesting strategies, and artificial feeding regimes on bass and bluegill populations. Investigations during the 1970s focused on factors influencing the catchability of largemouth bass. In the 1980s, the influence of predator fish (other than largemouth bass) on bluegill populations was investigated by introducing tiger muskellunge and later walleye. All of these projects included a public angling program, with Survey biologists collecting information on catch, harvest, diet, and growth of fish from all anglers using the lake.
Current research under way at Ridge Lake Station is aimed at determining how fish managers might manipulate forage fish populations (primarily gizzard shad) to improve populations of predator fish such as largemouth bass and walleye. Forage of the appropriate size and type can be important to the survival and growth of predator fish. Fish managers can manipulate forage populations by introducing new species or by taking steps to alter the size structure of existing forage populations.
Introductions have been used with mixed success, and the reasons for failures are not fully understood. Adult gizzard shad were accidentally introduced into Ridge Lake from an upstream impoundment in the fall of 1989, and Ridge Lake researchers took that opportunity to assess the influence of gizzard shad on the growth, survival, catch, and harvest of largemouth bass, bluegill, black crappie, and walleye in the lake. Information gathered in this study also will lead to a better understanding of basic ecological concepts related to "food web" interactions.
The introduction of gizzard shad has had a mixed effect on fish populations in Ridge Lake. Gizzard shad had little influence on walleye survival; density of forage fish other than gizzard shad (e.g., young bluegill) appeared to be a more important factor. In contrast, gizzard shad had a substantial impact on largemouth bass and bluegill survival, possibly through competition for planktonic food among young fish or interference with spawning activities. Growth of walleye increased dramatically following the introduction of gizzard shad, whereas growth of bass, bluegill, and crappie did not appear to be affected.
With the introduction of gizzard shad to Ridge Lake, researchers expected to see increases in the size and number of fish caught and harvested due to the presence of an additional food source. Contrary to these expectations, both catch and harvest of largemouth bass declined markedly to about one third of previous levels. Catch of walleye and bluegill differed little between pre- and post-shad introduction time periods, whereas catch of black crappie more than doubled. With the exception of black crappie, size of fish caught also did not change following the introduction of gizzard shad to Ridge Lake
Current research at Ridge Lake has shown that the effects of introducing gizzard shad may be positive or negative, depending on the species of fish and population characteristic of interest. Introduction of forage fish to improve game fish populations should be done only with caution and after careful consideration of management objectives. Future fisheries investigations at Ridge Lake will continue to include work that will help fishery managers develop angling opportunities on the important small impoundment resources of the state of Illinois.
Dave Clapp and David H. Wahl, Center for Aquatic Ecology.
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Subject: INHSPUB-2148
Last Modified 3/19/96