Fisheries Research in Illinois

Throughout the State of Illinois, fisheries professionals are working hard to better understand fish populations and the factors that combine to create and maintain a healty fishery. This knowledge directly impacts management strategies (such as daily bag limits, size minimums, etc.) and makes a great contribution to a healty Illinois fishing resource. Many of these projects are conducted directly by the Department of Natural Resources, either through the Division of Fisheries or by the Illinois Natural History Survey (a division of the Illinois DNR).

Below is just a sample of the kinds of projects conducted in the state. In the near future, more projects will be highlighted here, so come back and visit often!

Factors affecting age-at-maturity in bluegill populations

We are examining life-history decisions of bluegill in populations of different size structures. Specifically, we are examining factors that influence age-at-maturation in stunted and non-stunted bluegill populations. Previous research (conducted as part of the state-wide bluegill project) has demonstrated that stunted bluegill mature at younger ages and smaller sizes than non-stunted individuals. We are examining several potential mechanisms associated with early maturation in stunted populations, including differences in resource availability (which affects juvenile and adult growth rates), mortality rates, and influences of social interactions between mature and immature male bluegill. This research provides insight into reasons that populations become stunted, which should help fishery managers decide appropriate actions to return stunted populations to a normal size structure.

Factors determining yellow perch year-class strength in Lake Michigan

Ongoing research is exploring some factors that may affect yellow perch year class strength. In particular, we are trying to determine whether larval yellow perch are suffering from severe food limitation and/or vulnerable to predation. To explore these hypotheses, we are sampling larval yellow perch, zooplankton, and alewife (a major predator of larval fish). Age-0 yellow perch were sampled with a bottom trawl to assess survival of larvae to the juvenile stage. Results to date suggest that zooplankton density is positively related to survival of yellow perch during their first year of life. This relationship appears to have changed over the last decade, with similar densities of zooplankton now yielding fewer yellow perch than was the case during the late 1980s. This shift may be due to changes associated with reduced nutrient loading or the recent influx of exotic species like zebra mussel, spiny water flea, and fishhook water flea.

Spatial Variability in Nearshore Fish Recruitment

Recruitment success of fishes in large systems may depend on favorable conditions at local or regional scales. To explore possible variation in conditions, we are sampling larval fish, zooplankton, invertebrates, and water temperatures at four locations along a 100 km stretch of southwestern Lake Michigan during May-July 1999-2001. Water temperatures increased faster, reached greater peaks, and were more stable at two southern sites. Densities of larval fish and zooplankton began increasing 1-2 weeks earlier at the two southern sites. Furthermore, the composition of both zooplankton and larval fishes differed between northern and southern sites. More zebra mussel veligers and larval fish taxa associated with warm water were present at the southern sites. These patterns suggest that mechanisms influencing recruitment may operate at regional scales (i.e. <100 km) in large systems.

Potential importance of the main channel to fishes in the Mississippi and Illinois rivers

The main channel is a largely overlooked habitat when considering the function of large floodplain rivers. Our research with collaborators at the USGS-BRD Upper Mississippi Environmental Science Center has sampled the main channel for fishes during the late 1990s. Research results to date reveal that a diverse assemblage of larval, juvenile, and adult fishes use the main channel, with eight larval taxa and 24 species of larger fish collected during 1996. Furthermore, the main channel supports large numbers of benthic invertebrates and zooplankton. These results suggest that a food web develops in the main channel, but that the ultimate sources of the energy supplying this food web is not yet clear.

Growth and Survival of Larval Yellow Perch

Yellow perch recruitment has declined dramatically during the last decade in Lake Michigan. Concurrent with this decline, zooplankton (an important prey item of larval yellow perch) density has decreased and the zooplankton taxonomic composition has shifted. This suggests that food availability may be a factor shaping yellow perch recruitment. By conducting experiments that quantify the relationship between zooplankton species and size on the growth and survival of larval yellow perch we hope to determine how food availability affects recruitment of larval yellow perch. We will also quantify aspects of feeding behavior (search time, capture success, handling time, etc) to more explicitly understand why food availability affects recruitment.

Factors effecting bluegill population size structure

Stunted bluegill populations are viewed as a major problem by many Illinois anglers. Factors that control bluegill population size structure include growth rate, life span, and age at maturation. Stunted bluegill populations can result from overharvest, density dependent growth limitations, large portions of the population maturing at early ages, or from an overabundance of cuckolders. We categorized Illinois bluegill populations based on adult size structure using existing creel surveys and standardized sampling to determine which factors are controlling size structures in each of these populations. We then developed an adaptive management experiment to assess the ability of several management alternatives (regulations, predator manipulations) in altering bluegill size structure. The management experiment is divided into four treatments across 32 lakes in Illinois. The four treatments consist of a control, an 8-inch minimum bluegill size limit, largemouth bass stocking, and a combination of the latter. We plan to use the results from this experiment to improve stunted bluegill populations by implementing appropriate management strategies.

Long-term monitoring in Lake Shelbyville

Long-term data collection is important for detecting large scale temporal trends. In addition, these samples can be valuable for use as pre-data in evaluating the effects of a disturbance. We have been collecting data from Lake Shelbyville since the 1980's and are currently using this data set for answering and developing new research questions. All of the data is collected at fixed sites throughout the lake at regular time intervals. Variables that are being sampled include adult and juvenile fish assemblages, zooplankton, invertebrates, water level, and nutrients. In the future we will continue to develop this long-term data set in order to gain a better understanding of the interactions among measured variables and the factors determining community structure in this important reservoir system.

Largemouth bass recruitment in Illinois

Recruitment of largemouth bass in Illinois is highly variable and most likely depends upon a variety of biotic (e.g., food availability, predation, population structure, etc.) and/or abiotic factors (e.g., spring water levels and temperature, spawning habitat, angling pressure, etc.). This research will examine recruitment dynamics among reservoirs representing a gradient of conditions in Illinois in order to evaluate which factors are most consistently important in determining year-class strength in largemouth bass. An understanding of largemouth bass recruitment mechanisms will help to guide management decisions, such as supplemental stocking, designed to enhance the largemouth bass fishery in Illinois.