Date of Award
Master of Science
Natural Resource Ecology and Management
Michael J. Weber
Reservoirs are dynamic and differ from natural systems in terms of physical conditions and contain diverse fish communities. Although once thought to be unproductive, reservoirs often contain high abundances of fishes consisting of native riverine species as well as introduced sport fishes that provide unique angling opportunities. As reservoirs are vastly different than natural lakes and rivers, traditional fisheries management strategies are not always applicable, complicating management and understanding. Muskellunge and Walleye are two species often introduced to reservoirs that are sustained by routine stockings due to limited natural reproduction. Previous research has evaluated stocking success and factors regulating Muskellunge and Walleye populations in natural systems; however, little is known about reservoirs populations, although this knowledge is essential for effective management. To address this lack of information, I used radio telemetry to assess behavior and survival of juvenile and adult Muskellunge and Walleye in Big Creek and Brushy Creek lakes, Iowa, USA. My first chapter involved implanting wild and stocked age-0 Walleye with radio transmitters and conducting regular tracking after fall stocking to determine if there were differences in behavior and survival. I found little evidence of behavioral differences between Walleye groups, although home ranges were greater in Big Creek than Brushy Creek. Survival was generally high and was greater for stocked than wild Walleye in Big Creek but did not differ between groups in Brushy Creek. In chapter two, I conducted a similar study on spring-stocked yearling Muskellunge, with a focus on differences in behavior and survival between systems with varying habitat complexity. Movement rates were greatest in both lakes during the first week post-stocking, with greater rates and home ranges in Big Creek. Brushy Creek Muskellunge moved less and were typically associated with coarse woody habitat and aquatic vegetation, while fish in Big Creek exhibited strong selection for limited amounts of complex coarse woody habitat. Muskellunge stocking survival was low but variable; most mortality occurred during the first four days after stocking, survival was greater in Brushy Creek, and post-stocking mortality was significant in both systems during 2018. Mortality in 2018 was likely associated with stocking stressors, while predation also contributed to Muskellunge mortalities in Big Creek. Chapter three involved tagging and tracking adult Walleye for two and a half years to evaluate how harvest, mortality, and escapement regulate populations as well as determine whether individual behavior was related to fish fate. Walleye harvest was greatest from April through July and was greater in Big Creek (annual estimate = 27%) than Brushy Creek (13%). Natural mortality (36-38%) was greater than harvest, similar between systems, and positively related to water temperature. While no escapement occurred at Big Creek, likely due to the presence of a physical barrier, escapement from Brushy Creek ranged from 22-47% and was related to mean water levels during April. Movement rates were greatest in both lakes during spring, but Walleye behavior was largely similar despite fish fate. Similarly, my last research chapter involved tracking adult Muskellunge implanted with radio tags over the same duration as Walleye and assessed behavior and movement as well as factors contributing to fish loss. Muskellunge exhibited seasonal variation in behaviors in Big Creek, with greater movement during spring and use of shallow water during spring and summer. Behavior was similar across seasons in Brushy Creek, and fish ranges were comparable between lakes and encompassed large areas. Additionally, we found no evidence suggesting that previously escaped Muskellunge behaved differently or were more likely to escape than in-lake residents. Several tagged fish in both reservoirs were located in spillway areas during spring and summer; however, no escapement occurred at Big Creek while annual estimates at Brushy Creek ranged from 18-54%, with greater escapement from May through August and at greater maximum lake levels. Natural mortality did not differ by system but was positively related to water temperature, ranging from 15-18% annually. Altogether, these findings indicate that stocked Walleye exhibit similar behavior and survival to wild fish, which suggests that hatchery habituation is not limiting establishment of Walleye populations. In contrast, stocked Muskellunge survival can be low and variable, with system-specific behaviors related to availability of complex habitats as well as mortality. Finally, escapement of adult fishes can be substantial and contribute to greater fish loss than both harvest and natural mortality, though individual behavior does not appear to be related to escapement or harvest probability. Increasing stockings is unlikely to be a cost-effective strategy to mitigate adult fish escapement. Conversely, the physical barrier at Big Creek appears to be effective at preventing adult sport fishes from escaping, and could be a useful tool for improved management of many reservoir fisheries.
Robert Edward Weber III
Weber III, Robert Edward, "Understanding factors regulating Muskellunge and Walleye reservoir populations using radio telemetry" (2020). Graduate Theses and Dissertations. 18245.