Roger L. Knight

Piscivory by Walleyes and Yellow Perch in Western Lake Erie

Abstract We examined stomach contents of 906 age-0 and older walleyes Stizostedion vitreum vitreum and 1,575 age-2 and older yellow perch Perca flavescens, collected from western Lake Erie in 1979–1981, to measure preferences for prey type and size and diet overlap among different size groups of these two percids. Seasonal diets closely followed changes in forage-fish availability. Walleyes ate age-1 shiners Notropis atherinoides and N. hudsonius in spring, but switched to age-0 clupeids Dorosoma cepedianum and Alosa pseudoharengus in summer and autumn. Diet selection was governed by abundance of appropriate-size prey and preferences for forage species. Yellow perch ate invertebrates in spring but clupeids and shiners thereafter; electivity values for prey were low compared with those of walleyes, indicating that yellow perch were the more opportunistic feeders. Diet overlap was greatest among walleye age groups (0, 1, and 2-and-older) and least between walleyes and yellow perch. We hypothesize that densi...

LIFE AFTER DEATH IN LAKE ERIE: NUTRIENT CONTROLS DRIVE FISH SPECIES RICHNESS, REHABILITATION

Support for this work was provided by (1) Federal Aid in Sport Fish Restoration F-69-P (to R. A. Stein), administered jointly by the U.S. Fish and Wildlife Service and ODNR-ODW, (2) the Department of Evolution, Ecology, and Organismal Biology at The Ohio State University, and (3) a Presidential Fellowship awarded to S. A. Ludsin by The Ohio State University.

First-Year Growth, Recruitment, and Maturity of Walleyes in Western Lake Erie

Abstract In some lakes, first-year growth of walleyes Stizostedion vitreum has been identified as an important factor governing recruitment of juveniles to the adult population. We developed a regression model for walleye recruitment in western Lake Erie by considering factors such as first-year growth, size of the spawning stock, the rate at which the lake warmed during the spring, and abundance of gizzard shad Dorosoma cepedianum. Gizzard shad abundance during the fall prior to spring walleye spawning explained over 40% of the variation in walleye recruitment. Gizzard shad are relatively high in lipids and are preferred prey for walleyes in Lake Erie. Therefore, the high degree of correlation between shad abundance and subsequent walleye recruitment supported the contention that mature females needed adequate lipid reserves during the winter to spawn the following spring. According to the regression analysis, spring warming rate and size of the parental stock also influenced walleye recruitment. Our reg...

FUZZY COGNITIVE MAPPING AS A TOOL TO DEFINE MANAGEMENT OBJECTIVES FOR COMPLEX ECOSYSTEMS

Defining objectives for ecological rehabilitation requires consideration of how an ecosystem responds to management. Validated quantitative models of physical, chemical, and biological processes are the best way to project such impacts; however, time, data, and model limitations often make these approaches impractical. An alternative is to encode expert knowledge about interactions among ecosystem components in a fuzzy cognitive map (FCM), which then translates that subjective, qualitative information into predictions of the effects of management on an ecosystem. Herein, we present the steps involved in constructing an FCM of an ecosystem, interpreting FCM output using multivariate statistics, and portraying the information in an easily communicated fashion. To illustrate these ideas, we rely on a complex (>160 variables) ecosystem model built for the Lake Erie watershed under the auspices of the Lake Erie Lakewide Management Plan (LaMP). Based on our experiences in building this model, we also offer recommendations for increasing the efficiency of the model-development and interpretation process. Use of the FCM method in this case promoted constructive interaction among dozens of scientists, managers, and the public, as well as providing insights concerning the potential effects of broad classes of management actions upon the Lake Erie ecosystem. The analysis focused the attention of participants on four broad alternatives for the Lake. One represents present conditions, and another results from a decrease in nutrient inputs but an increase in stresses from land use and human disturbance. The two others involve reduced stress from nutrients and land use, with one having relatively more nutrients and less human disturbance and fishing. The latter ecosystem alternative was tentatively endorsed by LaMP management, and all four alternatives will be reviewed by the public.

Response of Yellow Perch to Changes in the Benthic Invertebrate Community of Western Lake Erie

Abstract In the western basin of Lake Erie, benthic invertebrate abundance and community composition have changed dramatically over the past five decades, as have abundance and growth of yellow perch Perca flavescens. Before 1950, large benthic invertebrates dominated the benthic community of the western basin. Yellow perch readily consumed Hexagenia larvae, caddisfly larvae, amphipods, chironomids, and zooplankton. From 1960 through 1980, large-bodied benthic invertebrates were eliminated from the western basin, and yellow perch relied primarily on smaller chironomids and zooplankton as forage. Growth rates and abundance of yellow perch declined through this period in the western basin, in part because of food limitation. From the late 1980s through the 1990s, large benthic invertebrates, including Hexagenia spp., caddisfly larvae, and amphipods recolonized the basin, and yellow perch again readily consumed them. Additionally, daily food consumption by adult yellow perch in the 1990s was marginally more ...

Reduction in recruitment of white bass in Lake Erie after invasion of white perch

Abstract Recruitment to the adult population of white bass Morone chrysops in Lake Erie sharply declined during the early 1980s. To explain this phenomenon, we formulated the following four hypotheses: (1) the biological characteristics of adult spawners changed during the early 1980s, so that the ability to produce eggs decreased; (2) the decrease in phosphorus loadings to Lake Erie during the 1970s resulted in a lower abundance of crustacean zooplankton and thus in reduced survival of age-0 white bass; (3) the increase in the population of adult walleyes Stizostedion vitreum in Lake Erie during the 1970s and 1980s led to reduced survival of age-0 white bass; and (4) establishment of the white perch Morone americana population in Lake Erie during the early 1980s led to reduced survival of the early life stages of white bass. The growth, maturity, and fecundity of adults during the period 1981–1997 were compared with the same characteristics found by earlier studies. The mean length, weight, and condition...

Removal of Walleye Eggs from Reefs in Western Lake Erie by a Catastrophic Storm

Abstract We document the removal of walleye Stizostedion vitreum eggs from reefs in western Lake Erie by a gale-force storm event during April 1998. From April 8 to April 10 of that year, the western basin reefs were exposed to sustained winds exceeding 80 km/h and originating from the east-northeast. This storm produced waves in excess of 4 m on the reefs and caused extensive flooding along the Ohio and Michigan shorelines owing to seiche activity. We sampled eggs on Cone, Crib, Locust Point, Niagara, Round, and Toussaint reefs on April 6, the day before the storm, and on April 10, the day after the storm. We found approximately 80% fewer eggs in the samples collected on April 10, a difference that was significant. Shallow sites on reefs lost significantly more eggs (87%) than deep sites (50%). The lower loss rate of eggs from deep sites was thought to be related to reduced wave energy at greater depths. The results of this study emphasize the importance of physical processes in structuring walleye early...