Factors effecting bluegill population size structure.
M.J. Diana, J.E. Claussen, R.W. Oplinger, J. Stein, D.P. Philipp, and D.H. Wahl
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.

Evaluation of largemouth bass stocking program.
M.J. Diana and D.H. Wahl
Although largemouth bass are stocked extensively in Illinois, little is known about the long-term contribution of hatchery fish to the natural population. Factors that influence stocking success include prey availability and predation or abiotic factors such as water temperature and water level. Prey availability and predation are dependent on the size of stocked largemouth bass. As a result, the current study is examining lakes and reservoirs throughout Illinois to determine factors affecting growth and survival of stocked largemouth bass. Evaluations are being made of small and large fingerling bass to determine appropriate stocking size. In addition, we are evaluating the contribution of stocked fish to future reproductive success and harvest. These results will be used to develop management strategies that optimize use of these important stocked sportfish.

Largemouth bass recruitment in Illinois.
J.J. Parkos, D.H. Wahl, and D.P. Philipp
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.

Evaluation of a Dam Removal on the Fox River.
K.O. Maloney, S.E. Butler, and D.H. Wahl
From an environmental perspective, low-head dams cause habitat loss and fragmentation and block fish from moving upstream to reach critical spawning, nursery, or feeding habitats. Further, impounded areas upstream of these dams have low water quality and lack the habitat diversity needed to support the variety of life stages of many lotic fauna. As such, dam removal has become an important issue for natural resource agencies across the country and in Illinois. In our study, we are evaluating the effects of a low-head dam removal on restoring physical habitat, water quality, macroinvertebrate communities, and fish assemblages. We are also monitoring seasonal fish movements and habitat selection of three fish species. Documentation of the positive effects of dam removal/modification on river communities will help justify and guide future dam removal projects in Illinois.

The Illinois Pilot Watershed Program: effects of best management practices on stream quality.
H.R. Dodd, J.W. Niesler, and D.H. Wahl
Many lotic systems in Illinois remain in a degraded condition as a result of nonpoint sources of pollution. Best Management Practices (BMPs), which include both on-field and off-field techniques, can be used to improve stream quality. The Pilot Watershed Program is designed to examine the effects of BMPs on physical/chemical water quality and stream biota. Four Illinois stream basins were selected for this study with each basin containing a “pilot” watershed, which will have extensive BMP implementation, and a nearby reference watershed without extensive BMPs. During this ten year study, we will be monitoring changes in habitat/water quality, macroinvertebrate, and fish assemblages before and after BMP implementation. Results will be used to guide watershed management efforts throughout Illinois.

Effects of dam removal on fish passage, movements, and habitat utilization
S.E. Butler, H.R. Dodd, V.J. Santucci, Jr., and D.H. Wahl
Dams drastically alter aquatic habitats, making them unsuitable for many riverine fish species. Additionally, they obstruct fish movements and fragment populations. Removing a dam is hypothesized to enhance the physical habitat, creating new areas appropriate for lotic species. It is also predicted to restore the ability of fishes to move unrestricted throughout a section of river. This study seeks to determine how dam removal affects fish movements and how habitat selection is influenced by the changes resulting from such an impact. We are monitoring the ability of eight species of fish to pass dam sites using mark/recapture techniques. Seasonal movements of three species ­ smallmouth bass, channel catfish, and common carp ­ will be monitored intensively using radiotelemetry. Habitat data will be collected at each location a fish is found at in order to determine selection relative to available habitat.

Exploring fish community dynamics in Illinois reservoirs
M.P. Carey and D.H. Wahl
The goals of community ecology include an understanding of organism distribution and abundance patterns and the structuring processes within fish communities. Numerous studies have explored what factors are important in determining patterns, but the current need is to understand the context in which processes are important and to encompass multiple trophic levels. Data on fish communities and aquatic food webs in Illinois reservoirs provides a unique comparative field test by incorporating gradients of abiotic and biotic factors to explore the context of important processes across a large number of aquatic systems. Fish species richness, relative abundance, and biomass estimates are being collected across 32 reservoirs throughout the state. Concurrently with fish sampling, relevant abiotic and biotic variables are measured including temperature, dissolved oxygen, total phosphorous, chlorophyll a, vegetation, and zooplankton community characteristics. Quantifying fish community patterns across systems and the relationship between patterns and environmental variables begins to resolve some of the goals of community ecology. Additionally, an understanding of key structuring processes will suggest more focused questions to understand the overall food web dynamics.

Bluegill and largemouth bass populations in the Chicago area forest preserves.
M.J. Diana and D.H. Wahl
Chicago area forest preserve lakes provide many angling opportunities for local residents, however, factors effecting growth and survival of fish in urban settings have recieved little attention. The effects of angling can be dramatic in this area given the unusually high fishing pressure. We are currently studying bluegill size structure along with largemouth bass recruitment and stocking strategies in several Chicago area forest preserve lakes. We will eventually develop and test several management strategies to improve bluegill size structure. The results from this study should give us a better understanding of factors effecting growth and survival of largemouth bass and bluegill, and how to manage for quality fisheries in metro areas.

Long-term monitoring in Lake Shelbyville.
M.J. Diana and D.H. Wahl
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.

Evaluation of yellow perch movements in Lake Michigan
D.C. Glover, J.M. Dettmers, and D.H. Wahl
In Lake Michigan, yellow perch have suffered from poor recruitment since 1989. However, the mechanisms driving poor recruitment still have not been identified. Until a mechanism(s) affecting recruitment can be identified, it is essential to properly manage the existing adult populations. Delineation of yellow perch stocks will be an integral element for successful management of the yellow perch fishery so as to determine the best allocation of catch between the competing fisheries, recognize potential protection zones of spawning areas, monitoring strategies and future research. We will use recaptures from a lake-wide yellow perch tagging project to provide us with information about locations of fish throughout time. Evaluating movement patterns of adult yellow perch from mark-recapture data will provide a way to quantitatively determine dispersal distance, directional preference, and spawning site fidelity. This information will be used to infer the range and pattern of movement, spawning aggregations, degree of mixing among the populations, movements across jurisdictional boundaries and degree of spawning site fidelity.

Assessment of the relationships between size-specific growth rates of fish and physical habitat and biotic community variables in Illinois streams.
J. W. Neisler, H. R. Dodd, and D. H. Wahl
Growth rates of fish are widely used as indicators of ecosystem quality in lentic systems, but have only recently been applied to streams. Knowledge of the factors affecting growth rates and their relative contribution would be useful in attributing changes in fish growth to implementation of management and rehabilitation practices. Results of this study could be used to aid the development of management plans and stream remediation projects, such as the Illinois Pilot Watershed Program. Habitat and prey availability will be examined to determine how resource abundance affects fish feeding guilds in stream environments. Because most species undergo ontogenetic diet and habitat shifts as part of their life history, we will also analyze size-specific growth rates. To take a holistic approach to food web examination, we will link fish growth rate to physical habitat, invertebrate community, and fish community parameters to better understand stream ecosystems.

Effects of abiotic and biotic factors on gizzard shad growth.
K.G. Ostrand, J. M. Dettmers, D. H. Wahl, J. Kalas, and C. L. Pierce
Gizzard shad (Dorosoma cepedianum) are important forage fish for game species; however, variable growth rates limit many management options. Many factors, operating independently or concurrently can effect growth rates of forage fish species. These factors include (1) environmental conditions, (2) food availability during the early life stages and throughout the growing season, (3) predation and competition for food, (4) availability of adequate habitat, and (5) timing of predator and prey spawning. We are quantifying the variation in growth rates of gizzard shad in the midwest and southern U.S. and exploring the relationship with important biotic and abiotic factors. Development of a model to predict shad growth will help guide future management efforts.

Largemouth bass diet and growth in bluegill and gizzard shad dominated reservoirs.
J.J. Parkos, and D.H. Wahl
Two somewhat different approaches to the study of growth rates have emerged: (1) growth rate is independent from spawning, in that growth rates are primarily controlled by the timing and availability of size-structured prey communities, and (2) the earlier a piscivore spawns in relation to its prey fish communities, the sooner it can switch to piscivory and maximize growth. Both approaches are underlain with the assumption that piscivores are gape-limited predators and pass through distinct ontogenetic diet shifts. We are evaluating the importance of largemouth bass spawning date and ontogenetic niche shifts on their growth and recruitment and comparing these processes in reservoirs that are dominated by either bluegill or gizzard shad.

Effect of temperature and food availability on overwinter survival in age-0 bluegill.
D.E. Shoup and D.H. Wahl
Fish with protracted spawning often have high variability in length of age-0 fish in fall. Several studies from northern climates have found that early-spawned bluegill, which are larger and therefore have greater energy reserves going into winter, have greater overwinter survival than their smaller late-spawned cohorts. However, other studies investigating bluegill populations at lower latitudes have found that overwinter survival is not size-selective. Using both laboratory and field experiments, we are examining the influence of food availability and winter severity (mean temperature and winter duration) on the overwinter survival of different size classes of age-0 bluegill.

Factors influencing vulnerability to angling in largemouth bass.
M.Nannini, S.J. Cooke, D. P. Philipp, and D.H. Wahl
Largemouth bass are an important game fish species. Previous research has demonstrated that vulnerability to angling varies among individuals, and that this differential vulnerability is hereditable. We are examining behavioral and ecological differences between low and high vulnerability fish from to determine why angling vulnerability differs. We are considering habitat use, prey type preferences, and predatory strategies of both genetic types.

Effect of turbidity on prey selection in largemouth bass.
D.E. Shoup and D.H. Wahl
Turbidity is known to reduce foraging return in many fish species. However, little is known about how turbidity affects the predatory behavior of piscivores. We are examining how prey selection and predation strategy of largemouth bass are modified by changes in turbidity. We are combining behavior studies in the laboratory that quantify specific predator and prey behaviors (bluegill, gizzard shad, and crayfish) at different turbidity levels with field diet analysis to determine if prey selection varies with turbidity and, if so, what mechanisms are likely responsible.

Evaluation of fish diversity and reproduction in seven oxbow lakes of the Lower Kaskaskia River, Illinois.
D.E. Shoup and D.H. Wahl
Oxbow lakes provide important spawning and nursery habitat for main river channel fishes. Many large river systems in North America are altered through channelization, impoundment, and land use practices. These alterations may reduce connectedness between oxbow lakes and the main channel. Little is known about the role of floodplain systems in the northern temperate zone, so it is difficult to predict what impacts alterations to main river channel have on floodplain ecosystems. We are examining fish community structure, abundance, and diversity of seven oxbow lakes on an unchannelized reach of the lower Kaskaskia River in order to relate these fish community characteristics to physical and chemical characteristics of the oxbow lakes. This research will provide a better understanding of the importance of oxbow lakes to main river channel fish populations and help determine the impact that main river channel alterations may have on floodplain ecosystems.

Diel littoral-pelagic habitat changes in bluegill.
D.E. Shoup and D.H. Wahl
It has been previously demonstrated that juvenile bluegill have a tradeoff between foraging in open water where both predation risk and foraging return are high and foraging in littoral habitat where both predation risk and foraging return are low. This leads to an ontogenetic shift in habitat based on size-specific predation risk. Little attention has been given to the potential for diel habitat changes that would allow bluegill to stay in littoral habitat during the day, but forage in the open water at night when predation risk is decreased and zooplankton abundance is increased. We are using horizontal hydroacoustics to track the movement of juvenile bluegill into and out of the littoral zone in Ridge Lake. Using modeling techniques and diel diet data from the field, we will also investigate the implications of diel littoral-pelagic habitat changes to nutrient dynamics in lakes and the possibility of a fish-mediated littoral-pelagic nutrient flux in systems where this diel habitat change takes place.

Effects of angling on largemouth bass reproduction
M. J. Siepker, M.J. Diana, D. H. Wahl, and D. P. Philipp
Increases in competitive and recreational black bass fishing has placed greater pressure on fishery managers to produce quality, sustainable bass fisheries. Besides stocking, successful reproduction and recruitment are the only way to ensure we have sustainable bass fisheries. We are examining the effects angling has on the fitness of largemouth bass, and how these may affect recruitment levels. Egg health, male nest guarding ability, abandonment rates, and nest predator effects are being examined for undisturbed fish, catch and release angled fish, and tournament angled fish. An understanding of angling effects on the reproduction of bass will allow us to manage these fisheries in a sustainable way.

Angler-applied livewell treatments to reduce largemouth bass initial and delayed mortality during live-release tournaments.
M. J. Siepker, K. G. Ostrand, and D. H. Wahl
Competitive fishing for largemouth bass in Illinois has increased in recent years. Fish captured in these events are held in livewells for extended periods of time before being weighed and released. During confinement, these fish are subjected to increased levels of sublethal stress leading to about 30% mortality. We are currently working with bass tournament directors and participants to determine the usefulness of angler-applied treatments at reducing mortality. Treatments that are effective, but simple to apply, are being examined in actual tournament situations. By reducing mortality rates, we will reduce the biological impact tournaments have on largemouth bass.

Quantifying the sublethal effects of catch-and-release angling.
S.J. Cooke, C.D. Suskie, D.P. Philipp, and D.H.Wahl
Traditional catch-and-release studies have focussed on hooking mortality associated with different handling and environmental conditions and biochemical indicators of stress response and recovery. These methodologies do not permit the collection of real-time data on the sub-lethal effects and recovery period associated with the angling event. The advent of hard-wired and telemetered technologies capable of collecting information on heart rate, stroke volume, cardiac output, and axial electromyogram activity provides researchers with a powerful methodology for monitoring the response of individual fish to different stressors. We are conducting studies on several freshwater fish species (rock bass, smallmouth bass, largemouth bass, Atlantic salmon) to examine the effects of different angling and handling practices on their physiology and behavior. This unique approach has many advantages over traditional methodologies and will provide managers with better information on the true effects of catch-and-release angling.

Locomotory dynamics as indicators of stress in fish ­ remote measures utilizing activity transmitters.
S.J. Cooke, J.F. Schreer, D.H. Wahl, and D.P. Philipp
Stress related physiological disturbances can result in either locomotory impairments or hyperactivity. These behavior-altering disturbances, however, are difficult to quantify. Devices capable of remotely monitoring and quantifying the locomotory activity of free-swimming fish have been developed and have been applied widely within fisheries science, particularly for the determination of activity patterns and the calibration of bioenergetics models. The application of these devices to the measurement of environmental or anthropogenic stressors provides the opportunity to link behavior and physiology in an effort to understand the influences of these stressors from both an energetic and ecological framework. We are currently using activity transmitters in the areas of aquaculture production research, thermal effluent monitoring, and handling and angling related disturbances. The approach of coupling behavior and physiology provides detailed information on how stress manifests itself at the organismal level.

Individual-based model for walleye.
T.L. Galarowicz, D.H. Wahl, and R. Herendeen
Size-dependent mechanisms and physical factors influence fish growth and population dynamics. Individual-based models, which follow individuals of a species rather than an "average" individual, provide additional insight into these relationships. By modeling foraging, daily growth and mortality using an individual based approach we hope to predict growth and survival of young-of-year walleye. Parameters for the model are based on extensive field data and laboratory foraging experiments.

Effect of light intensity and habitat complexity on predator-prey interactions in fishes.
L.M. Einfalt and D.H. Wahl
Many predators visually forage for prey. Light intensity and availability of habitat are important abiotic factors influencing predator-prey interactions. In a series of laboratory experiments, we evaluated the effect of these factors on foraging for a fish predator (walleye) and two prey (bluegill and golden shiner). Previous studies indicate walleye forage in low light or turbid conditions. The two prey differ in morphology and anti-predator behavior. We found walleye were better foragers in low light conditions due to increased activity and decreased prey vigilance. Prey, however, can compensate for decreased light and lack of habitat by modifying antipredator tactics. Future research will use a comparative approach by repeating these experiments with a predator adapted to daytime foraging.

Effects of predator size and prey characteristics on piscivory of juvenile largemouth.
L.M. Einfalt, J.J. Parkos, and D.H. Wahl.
Piscivores experience ontogentic diet shifts as juveniles, and the development of foraging behavior may be a crucial bottleneck in their growth and survival. Foraging success can depend on the size and species of prey. In a series of laboratory experiments, we examined the effects of predator and prey size on piscivory by juvenile largemouth bass (25-75mm; Micropterus salmoides). Ontogenetic changes in size preference were determined in aquaria experiments using different sizes and species of prey (bluegill, fathead minnow, gizzard shad) differing in behavior and morphology. Sizes of prey selected by bass varied according to prey morphology. Predators chose slightly larger prey al all three prey species than sizes predicted by an optimal foraging model. To investigate differential prey vulnerability and development of predator behavior, observations of predator and prey behavior were conducted in a 750-L tank. Prey developed antipredator behaviors as they grew, and vulnerability differed by prey species. Regardless of size, largemouth bass used a similar foraging strategy, but changes in prey behavior and morphology influenced predation success.

Food web dynamics in sunfish communities
S.R. Chipps and D.H. Wahl
Evidence for trophic cascades provides a foundation for understanding food web dynamics in aquatic ecosystems. "Top-down"or " middle-out" interactions help describe direct and indirect linkages among trophic levels. In these cases, predation plays an important role in structuring aquatic food webs. Among sunfish communities, phenotypic plasticity allows species to utilize different resources in the presence of congeners. However, effects of these behavioral niche shifts on food web structure is not clear. Using sunfish communities as a model, this research is evaluating the role that behavior plays on food web configuration in ponds and shallow lakes.

Aquaculture of walleye
S.R. Chipps, T.L. Galarowicz and D.H. Wahl
Walleye are popular as food and sport fish through out the country, but commercial harvesting is not allowed in the United States. As a result, there is an increased interest in culturing walleye to market size to meet this demand. In response, the North Central Regional Aquaculture Center funded a multi-research group including the Natural History Survey, to focus on developing techniques for commercial culture of walleye by evaluating growth, feed efficiency, and stress response under various culture conditions. Researchers from INHS will use a bioenergetics model to study different components affecting culture success.

Establishment of Daphnia lumholtzi in Illinois
M.A. Nannini, C.S. Kolar, and D.H. Wahl
The exotic zooplankter, Daphnia lumholtzi, was recent discovered in Illinois. Studies conducted by INHS scientists have determined that D. lumholtzi has a competitive advantage over native Daphnia spp. by avoiding predation by young bluegill. At present, long-term effects of this exotic species on aquatic ecosystems in Illinois are unknown. To assess potential changes in zooplankton communities, researchers are examining data from Lake Springfield that characterize the lake before and after establishment of D. lumholtzi. In addition, food habits of planktivorous fish are being examined to assess the contribution of D. lumholtzi to fish diets before and after their introduction. Results of these investigations will help quantify changes that have occurred as a result of the establishment of D. lumholtzi in Illinois waters.

Hydroacoustics: a tool for understanding fish-habitat association in rivers.
R.M. Claramunt, J.M. Dettmers, D.H. Wahl, D.A. Soluk, and S. Gutreuter
Large floodplain rivers, such as the Mississippi and Illinois, are composed of a variety of different habitats (e.g., backwater, side channel, main channel). The majority of sampling done to understand the importance of these different habitat types to fish occurs outside the main channel because high current velocities. As a result, present knowledge on fish abundances, species composition, and habitat utilization in the main channel is lacking. Through midwater and bottom trawls, we have found that the main channel supports an abundant and diverse fish assemblage. A digital 200-kHz single beam hydroacoustic system is being used to investigate questions such as how do fish survive in high-current velocities that are typical of the main channel? and Where exactly are fish located in the main channel? Fish targets have been found to be strongly associated with sand dunes in the echograms from the Mississippi River. However, when dunes are not present (as in the Illinois River), fish targets are more evenly distributed, both vertically and horizontally. Sand dunes may be a critical habitat river fishes that have adapted to the conditions in the main channel of large rivers.

Evaluation of commercial navigation and indirect effects on fish behavior in large river systems
E. J. Gittinger, D.A. Soluk, D.H. Wahl, and J.M. Dettmers
Barge traffic has the potential to directly increase mortality of fishes. Alternatively, fish may exhibit avoidance behaviors and move away from barges in large river systems. If this is found to be true then the costs associated with these behaviors should be evaluated, as well as how an increase in barge traffic may impact the fishes of large rivers. This study is being conducted in reach 26 of the Mississippi River and the lower 35 miles of the Illinois River. Hydroacoustics are being used to observe fish movements before, during and after barge passage.

Observing fish movements using a phased array hydroacoustic unit
E.J. Gittinger, D.A. Soluk, D.H. Wahl, and J.M. Dettmers
Both the River Continuum Concept and the Flood Pulse Concept suggest that fish do not reside in the main channel of large rivers, concluding instead that fish utilize the main channel simply as a corridor to go from one place to another. Although recent studies have found significant populations of fishes in the main channel, this alone is not contradictory because it is not known whether the fish are transient or persistent. To address these questions, a hydroacoustic unit was used to horizontally scan large areas of the main channel in reach 26 of the Mississippi River and the lower 35 miles of the Illinois River. In spite of high current velocities (often > 1 m/s), fishes do persist in the main channel. These results demonstrate the importance of main channel habitats to fishes in large floodplain rivers.

Stable isotope analysis of large river food webs.
B.R. Herwig, D.A. Soluk, D.H. Wahl, and J.M. Dettmers
To more fully understand the trophic basis of production in large rivers (e.g., Mississippi and Illinois River) we are examining how resource use changes both seasonally and in relation to the amount of intact floodplain area within a river reach. To determine the sources of organic matter assimilated by consumers in large river food webs we are determining naturally occurring stable isotope ratios (del 13C and del 15N ratios) of resources and consumers (invertebrates and fish). Determining the sources of organic matter assimilated by consumers is critical for understanding resource-consumer dynamics, trophic relationships among consumers, and the inter-relationship of the lotic, lentic, and terrestrial habitats that comprise large floodplain river ecosystems.

Differences in macroinvertebrate communities between gizzard shad and bluegill dominated systems: effects on growth rates of young of the year largemouth bass.
J. L. Kline and D. H. Wahl
Gizzard Shad (Dorosoma cepedianum) have been shown to have a major effect on trophic interactions in reservoirs and may influence macroinvertebrate populations. The resulting macroinvertebrate community may, in turn, effect growth rates of young of the year largemouth bass (Micropterus salmoides) prior to the switch to piscivory. We are evaluating the role of macroinvertebrates in influencing the growth of largemouth bass by sampling in six Illinois reservoirs, three of which are gizzard shad dominated and three are bluegill (Lepomis macrochirus) dominated. Our results will help clarify the role of macroinvertebrate and fish community interactions in influencing the growth of YOY largemouth bass.

Predictive model of juvenile gizzard shad abundance for Lake Shelbyville, Illinois
T.B. Smith and D.H. Wahl
Gizzard shad dominate the fish communities and are the primary diet item of most piscivores in Midwestern and Southern reservoirs in the continental US. We recently devised a model to predict the annual abundance of gizzard shad in a flood control reservoir from characteristics of spring water-level rises. For the past three years, this model has provided successful a priori predictions of juvenile gizzard shad abundance. These results demonstrate the utility of water level manipulations as a tool to regulate trophic dynamics in systems with managed flows.

Top predators regulate both rooted and pelagic primary producers through crayfish assemblages in shallow aquatic systems
T.B. Smith and D.H. Wahl
Linear food chain models such as the trophic cascade hypothesis (TCH) state that top predators reduce the abundance of grazers and thus indirectly regulate primary producers. Pond habitats contain many violations of linear food chain models including omnivory, spatial subsidies between habitats, and predator-resistant taxa. Despite these complexities, we have shown that predator fish in ponds indirectly increase the abundance of rooted plants and reduce phytoplankton by removing omnivorous crayfish. Our results contrast with the TCH model by demonstrating that predator effects are enhanced by the a reduction of nutrients cycled by crayfish from the benthos into the water column. Additionally, many of the indirect effects we observe from predation on crayfish appear similar to indirect effects resulting from predation on planktivorous fish. This research adds to the list of top-down and bottom-up mechanisms that stabilize macrophyte abundance when large predator fish are abundant in shallow aquatic systems.

Evaluation of esocid stocking program
D.H. Wahl and L.M. Einfalt
The stocking program for muskellunge and tiger muskellunge is being evaluated to determine optimal stocking strategies for these fish in Illinois. Mechanisms of survival and growth of various sizes of esocids after impoundment stockings are being compared and used to develop a bioeconomic model. Second, the effect of rearing method in determining susceptibility to largemouth bass predation is being evaluated in impoundment stockings, as well as pond and laboratory experiments. Finally, an assessment of different genetic stocks of muskellunge throughout North America, and their performance characteristics are being evaluated in physiological experiments.

The effect of common carp on aquatic ecosystems.
M.D. Wolfe, J.J. Parkos, V.J. Santucci, Jr., and D.H. Wahl
The common carp is an excellent example of an exotic species that can invade and dominate aquatic systems. Since its introduction into North America during the early 1800’s, the common carp has invaded and adapted to almost every type of freshwater habitat. Most of the methods used in attempts to eliminate these fish from aquatic systems are either very costly or ineffective. Even though this large benthivore is prevalent, little research has quantified the effect of common carp on aquatic ecosystems. In association with the Max McGraw Wildlife Foundation, we have been assessing the effects of carp on the trophic ecology of lentic freshwater systems and compared these impacts of those of other large benthivores. Current studies are examining the effects that the common carp have on growth, survival, and reproduction of largemouth bass and bluegill in pond experiments.

Largemouth bass parental care behavior, nest success, and recruitment.
J.J Parkos, D.H. Wahl, and D.P. Philipp.
Variation in mortality rates during early life stages has a large effect on recruitment in fish populations. Species with parental care, such as largemouth bass, influence mortality rates of the earliest life stages by providing protection from predators. Our research uses molecular markers to investigate the relative contribution of individual nests to recruitment and to test if differences between parental males in care behavior affect nest-specific contribution. This research has important implications for management of largemouth bass fisheries that are often active during nesting periods.

Effects of turbidity and cover on prey selection of smallmouth bass.
M.W. Carter, J.M. Dettmers, D.Shoup, and D.H. Wahl
Smallmouth bass, a clear-water predator, is not typically found in turbid environments. We are investigating how increasing turbidity levels affect prey selectivity of smallmouth bass in tank experiments with three prey species (round goby, golden shiner, and crayfish). Additionally, the interaction between turbidity and cover will be investigated to determine its affect on prey selectivity of smallmouth bass. These experiments will provide insight into the predatory behavior of smallmouth bass, the effects of turbidity on piscivory, and the degree to which round goby (a recent invasive species to the Great Lake) are preferred by smallmouth bass.

Smallmouth bass post-spawn movements in Lake Michigan.
M.W. Carter, J.M. Dettmers, and D.H. Wahl
Smallmouth bass seasonal movements in Lake Michigan are not well understood. Marinas and harbors are common smallmouth bass spawning areas because they are warmer than the main lake and provide proper spawning habitat. Previous data suggests that fish may not leave these harbors directly after spawning, which is not consistent with other systems. We are using radio telemetry to help determine why nesting males stay in the harbors after spawning, and also to determine summer and fall home ranges.

Recruitment of yellow perch in southwestern Lake Michigan.
M.J. Weber, J.M. Dettmers, and D.H. Wahl
Recruitment of yellow perch in Lake Michigan has declined dramatically since the late 1980s. As with many species, recruitment of yellow perch in Lake Michigan is set during the first year of life. Therefore, we are studying the early life history of yellow perch to evaluate mechanisms that shape recruitment. Through the use of otoliths, we are determining growth rates and hatch date distributions of newly hatched near shore larvae, pelagic larvae captured up to 15km off shore, and benthic juveniles that return nearshore. This will allow us to determine how biotic and abiotic factors influence yellow perch recruitment, which cohorts are contributing greatest to recruitment, and when year class strength is determined. This information will contribute to a greater understanding of recruitment of fishes in large systems.

Examining evidence for behavioral syndromes in largemouth bass.
M.A. Nannini, J. Parkos, and D.H. Wahl
Behavioral syndromes are characterized by individuals expressing correlated suites of behaviors across different contexts. For example, we might expect an aggressive individual to express relatively aggressive behaviors independent of the context under which that behavior is expressed. We are examining largemouth bass for the existence of a bold/shy behavioral syndrome, under which certain individuals are relatively bold while others are relatively shy. If the behavior of individuals is predictable based on these behavioral syndromes it should provide insight into how individuals manage important tradeoffs and how these behavioral tendencies may structure the evolution of a population under different environmental parameters.

Evaluation of growth and survival of various stocks of muskellunge.
C.P. Wagner, M.J. Diana, and D.H. Wahl
Muskellunge are an important sport fish and the fishery often depends on a successful stocking program because native stocks have been extirpated from major areas. The current brood stock used in Illinois has been developed since the early 1980s and is comprised of fish obtained from throughout the native muskellunge range. The F1 offspring of this mixture of distantly related stocks may not be as well suited to same waters as a specific pure stock. We are currently conducting pond and lake stocking experiments comparing the growth and survival of populations from the three recognized stocks of muskellunge, the Ohio River drainage stock, the upper Mississippi River drainage stock, and the Great Lakes drainage stock, as well as the current Illinois population used in the hatchery system. In addition, we are examining ecological life-history characteristics such as thermal preference, movement rate, and habitat selection variation among the stocks. We plan to develop a stock-specific bioenergetics model to predict growth and consumption for juvenile muskellunge. Identifying physiological and behavioral differences among the recognized stocks of muskellunge will provide insight as to the best performing brood stock for use in Illinois and throughout the Midwestern United States.

Influence of Maternal Effects and Predators on the Age of Maturation and Growth of Bluegill.
R.W. Oplinger and D.H. Wahl
In many lakes, the total catch of bluegill, by mass and numbers, exceeds that of all other sportfish combined. Despite the large number of bluegill that are harvested, anglers are often concerned about the lack of large fish in their catch. As a result, managers seek strategies that can be used to help alleviate stunted body size in bluegill. First, this project seeks to determine whether a maternal effect exists in bluegill. A maternal effect occurs when the phenotype of a female or the environment that she lives in somehow influences the fitness of her offspring. In order to determine whether a maternal effect exists in bluegill, we will conduct two experiments. The first experiment is a small-scale tank experiment that will look to see if there is a maternal effect with respect to egg size and fry growth. The second experiment is a pond experiment that will look to see if there is a maternal effect that influences the timing of when a bluegill becomes sexually mature. The second part of this project seeks to determine whether predators influence the growth rate and timing of sexual maturation of bluegill. This will be accomplished using a pond experiment. The results of these experiments will be compared to data collected from a number of Illinois lakes. These findings will assist in the development of management strategies that will increase the size of bluegill harvested throughout North America.

Morphological differences between bluegill populations in lotic and lentic systems.
M R. Harrington, M.J. Diana, and D.H. Wahl.
Bluegill inhabiting littoral and pelagic habitats in lakes display differing morphological characteristics that affect feeding efficiency and vulnerability to predation. We hypothesized differences in available prey, predators, cover, and other abiotic variables between lotic and lentic systems could cause substantial morphological variation among bluegill populations. We are measuring morphological characteristics of fish size (e.g. total length, body depth, caudal peduncle depth) and individual characteristics of feeding morphology (e.g. gape width, fin length). The morphological variations between lotic and lentic bluegill may influence foraging, predator avoidance, and mating success.

Exploring plankton dynamics in three major habitats of large floodplain rivers.
M. Nannini, J.L. Goodrich, J.M. Dettmers, D.A. Soluk, and D.H. Wahl
Although off-channel (floodplains, backwaters, and side channels) habitats in large river-floodplain ecosystems are recognized as being important to the riverine plankton community, the role they play in structuring this community is poorly understood. Off-channel habitats can be important nursery grounds for larval and juvenile fishes. Furthermore, these habitats are often thought to be a source of zooplankton and phytoplankton for the main river channel. We have initiated a study of the Illinois and Mississippi Rivers to examine how the plankton community differs and to quantify the biotic fluxes of plankton between habitat types.

An Experimental Test of Habitat Complexity and Sunfish Diversity on Food Web Structure in Lentic Systems.
M.P. Carey, K.O. Maloney, S.R. Chipps and D.H. Wahl
Examining the function, indirect effects, and interactions of fish diversity and habitat complexity is necessary to understand aquatic food web dynamics. Changes in fish diversity can transform food web dynamics through trophic and indirect interactions altering energy pathways through the food web. Habitat complexity is a key driver of food web dynamics, because the physical structure dictates resource availability to the aquatic community. We are exploring the effects of fish diversity, habitat complexity, and their interactions on phytoplankton, zooplankton, periphyton, and benthic invertebrates using a replicated mesocosm experiment. There is a need to understand how abiotic and biotic processes interact to understand food web dynamics and determine management strategies for biodiversity conservation and habitat restoration.

Exploring the influence of fish diversity as a determinant of ecosystem properties in aquatic food webs.
Michael P. Carey and David H. Wahl
Dramatic changes in biodiversity globally from species loss and invasion has made research linking community and ecosystem processes particularly relevant. Exploring the potential for biodiversity to govern ecosystem process through species traits and interactions has developed the biodiversity ecosystem function paradigm. This area of research seeks to predict how changes to community structure influences ecosystem properties. Studies exploring biodiversity as a determinant of ecosystem function are sparse in freshwater systems despite their unique characteristics. Linear food webs, greater material exchange, steeper physical and chemical gradients, and rapid biological processes are all more common within aquatic communities. Biodiversity patterns have been dramatically altered in aquatic systems. Changes in fish diversity are of particular interest due to their ability to modify biodiversity ecosystem linkages through trophic interactions. Thus, this project is experimentally exploring the influence of fish diversity on food web dynamics at multiple spatial scales. We are first testing the null hypothesis that fish diversity does not influence ecosystem processes. We will then explore the relationship between fish diversity and the ecosystem properties of productivity and zooplankton dynamics and examined the mechanisms responsible for these relationships. Understanding the functional consequences of changing community structure will provide insights into community and ecosystem interactions.

Evaluation of Woody Debris as a Habitat Restoration Tool for Stream Biota: Assessment of Macroinvertebrate Communities.
J. Weidner, H. Dodd, and D. H. Wahl
Illinois streams experience flash floods which drastically change the appearance of the stream. As the streams recede back into their banks, deposition of new woody debris takes place, forming complex logjams and snags which are utilized by a number of stream biota. In streams with little or no woody debris, introduced woody structures have been placed into the stream to create habitat for fish and macroinvertebrates. In our study, we are examining macroinvertebrate colonization of introduced woody debris seasonally and comparing this to naturally deposited woody debris. We are also examining the effects of temperature and stream geomorphology on colonization by comparing colonization in four streams in the northern portion of Illinois and four in the southern portion. As part of the Pilot Watershed Program, this study will aide in the evaluation of restoration practices to improve Illinois streams.