Exploration of spatiotemporal patterns in recruitment and community organization of Lake Erie fishes: A multiscale, mechanistic approach

To explore factors that influence fish community organization and recruitment in Lake Erie, I used three approaches. First, I collaborated on an ecosystem modeling project that explored how anthropogenic disturbance might cause the Lake Erie ecosystem to take on several configurations (e.g., pristine, degraded) (Chapter 2). Analysis of differences among these configurations suggest that both protecting natural land from development and limiting phosphorus inputs are critical to maintaining healthy fish communities. Second, by merging bottom trawl data from western and central Lake Erie with species-specific life-history information (e.g., tolerances to environmental degradation), I demonstrate that reduced phosphorus inputs (i.e., oligotrophication) have driven fish community rehabilitation during 1969--1996, whereby intolerant species have begun to replace tolerant species (Chapter 3). In turn, species turnover has caused species richness to decline in the west basin, but increase in the central basin. Given that several recovering intolerant species are desired sport or commercial fishes, these analyses support some of the hypotheses generated from the ecosystem model. Third, using multiple regression modeling, I explored ecological mechanisms underlying yellow perch growth and recruitment in western and central Lake Erie during 1969--1998 (Chapter 4). During this time, recruitment appears to have switched from dependence on temperature to dependence on factors that influence system productivity (e.g., precipitation, river discharge, phosphorus loading), likely owing to oligotrophication. Although productivity was unrelated to growth, interspecific competition with white perch (Morone americana) appears to have negatively influenced yellow perch growth. Conversely, warm temperatures appear to enhance growth by stimulating early spawning or by increasing zooplankton availability to fish. Finally, I combined recent (1994--1998) larval yellow perch growth, diet, and hatch date data with temperature, zooplankton, and potential competitor (e.g., white perch) abundance information to test the relative importance of temperature and interspecific competition to yellow perch growth (Chapter 5). Temperature, through both hypothesized pathways, does indeed regulate larval growth, whereas interspecific competition with white perch appears unimportant. Ultimately, this work exemplifies how multi-scale, mechanistic investigations of fish population and community dynamics can enhance the ability of resource managers to understand and anticipate changes in their fisheries.