Doctor of Philosophy, University of Toledo, 2017, Biology (Ecology)

This work was motivated to improve understanding of Lake Erie walleye (Sander vitreus) distribution and abundance. Lake Erie walleye are large migratory fish that are ecologically and economically important within the Great Lakes region. The population is monitored partly through a fishery independent gill net survey carried out by the Ohio Department of Natural Resources - Division of Wildlife (ODNR-DOW). However, high variation in annual CPUE has interfered with this survey's ability to identify changes in walleye abundance. Therefore, the ODNR-DOW was interested in the potential of coupling hydroacoustic sampling with the existing gill net survey to quantify Lake Erie walleye distribution and abundance. In this dissertation I address four major questions that helped optimally couple hydroacoustic and gill net surveys. In Chapter 1, I evaluated the impact of beam compensation on surveyed target strength (TS) data. I found that using an intermediate beam compensation (18 dB), greater than conventionally suggested (6 dB), provided a higher quantity of TS data with minimal impact on TS data quality. Increased beam compensation led to higher encounter rates and more TS data per fish, which ultimately provided a better characterization of the low density walleye population. In Chapter 2, I evaluated the influence of vessel size and day-night period on the availability of the walleye population to a hydroacoustic survey. I found that walleye were less likely to avoid smaller sampling vessels, but the vessel size effect decreased with depth. Also, during the fall period of the gill net survey, walleye were more available to hydroacoustic sampling at night. Finally, although vessel size and day-night sampling period are important logistical consideration, capturing spatial distributions across the survey should be prioritized in future surveys. In Chapter 3, I compared gill net catch-per-unit-effort (CPUE) and hydroacoustic abundance estimates from across a larg (open full item for complete abstract)

Committee: Christine Mayer PhD (Committee Co-Chair); Song Qian PhD (Committee Co-Chair); Jonathan Bossenbroek PhD (Committee Member); Patrick Kocovsky PhD (Committee Member); David Warner PhD (Committee Member) Subjects: Aquatic Sciences; Biology; Biostatistics; Ecology; Environmental Science; Freshwater Ecology; Natural Resource Management

Master of Science, University of Toledo, 2011, Biology (Ecology)

The population genetic structure of three of the largest walleye spawning groups in Lake Erie is tested for consistency over time and space spanning 14 years, based on nine high-resolution nuclear DNA microsatellite loci. Previous genetic studies focused on a one-time genetic “snapshot”, with an earlier study by our laboratory finding that the genetic structure of three Lake Erie spawning groups along the southern shore - Maumee River, Sandusky River, and Van Buren Bay reefs - appeared similar in 2003, whereas most other spawning groups across Lake Erie were genetically distinctive. The present study analyzes the stability of genetic similarity patterns within and among 726 walleye spawning at these three sites across years and age cohorts in 1995, 1998, 2003, 2007, and 2008. Genetic patterns are evaluated using pairwise FST analog and contingency tests, AMOVA partitioning, and Bayesian assignment tests. Results reveal overall year-to-year consistency in genetic structure of walleye spawning at the three sites, with some annual variation in the Van Buren Bay reef group. Greater genetic divergence from the other groups is detected in the Van Buren Bay spawning group, which reflects greater geographic separation. Walleye spawning in the Sandusky and Maumee Rivers are genetically distinguishable from each other when data from all years are combined, which suggests possible sample size effect (i.e., annual sample sizes likely were not large enough to detect their genetic differentiation). No significant differences occur among age cohorts, between the sexes, or among sampling dates within spawning runs. Results demonstrate the importance of sampling over several years of walleye spawning runs in order to resolve fine-scale genetic relationships within an open lake system.

Committee: Carol Stepien PhD (Committee Chair); William Sigler PhD (Committee Member); Patrick Kocovsky PhD (Committee Member) Subjects: Biology; Conservation; Ecology; Environmental Science; Genetics; Natural Resource Management

Master of Science (MS), Ohio University, 2006, Biological Sciences (Arts and Sciences)

Walleye (Sander vitreus) is a heavily managed fishery, the genetic integrity of which has been affected by introductions of nonnative stocks via hatchery supplementation. DNA analysis on walleye has revealed highly divergent populations of walleye in the Ohio and New rivers. The focus of this project is to identify the distribution and assess the introgression of native walleye populations in West Virginia. PCR-RFLP analysis of mtDNA reveals native walleye are distributed throughout West Virginia, with higher frequencies in the Kanawha/New River system. Analysis of microsatellite DNA markers suggests native walleye stocks within the Ohio and Monongahela Rivers have introgressed with introduced walleye populations. Native walleye stocks in the Kanawha and New Rivers are relatively uninfluenced. The stocks in the Kanawha/New River system should be used for future hatchery supplementation and restoration of a native population of walleye in West Virginia.

Committee: Matthew White (Advisor) Subjects: