Delineation and Spatial Distribution of Lake Superior's Walleye Stocks

File(s)
Date
2025-01Author
Cristan, Erik
Publisher
College of Natural Resources, University of Wisconsin-Stevens Point
Advisor(s)
Homola, Jared J
Metadata
Show full item recordAbstract
Understanding spatial genetic variation within and among wild populations is a key factor for informing conservation. In fishes, reductions in abundance often result in losses of genetic diversity that can lead to declines in resiliency. In populations where isolation or reduced abundance have occurred, maintaining connectivity can help offset some of these negative consequences. Lake Superior walleye (Sander vitreus; Ojibwe: Ogaa) are a native fish species with cultural, recreational, and commercial importance that have experienced widespread declines in abundance throughout the last century. In recent decades, numerous efforts to restore walleye via habitat improvement, regulation modifications, and stocking have been attempted with mixed success. My objectives were to inform Lake Superior walleye rehabilitation efforts by 1) identifying factors associated with variation in genetic diversity among spawning aggregations, 2) characterizing genetic structure and assessing if influences from stocking exist, and 3) identifying environmental correlates of genetic connectivity. Despite widespread declines, walleye spawning aggregations in Lake Superior have maintained a high degree of genetic diversity, are spatially structured into distinct patterns of diverged populations, but have been influenced by stocking. While geographic distance is likely the most influential environmental factor on connectivity, other factors such as water temperature, relative shoreline exposure to wind and waves, and water currents may also influence gene flow and connectivity among Lake Superior walleye spawning aggregations. The results provided here may serve as a useful guide for identifying walleye spawning aggregations harboring endemic genetic variation, habitats that influence gene flow, and potential broodstock sources suitable for conserving genetic diversity.
In mixed-stock fisheries, knowledge of stock-specific movement patterns, spatial distribution, and the factors that influence them can inform adaptive management strategies. Understanding proportional contributions of distinct stocks to harvest-oriented mixed fisheries allows for regulation that decreases risks from overfishing vulnerable stocks and shifts harvest toward more sustainable stocks. Genomic techniques such as genetic stock identification and mixed stock analysis (MSA) can be used to delineate genetic fish stocks and determine mixing rates across space and time. In walleye fisheries like Lake Superior where subsistence, recreational, and commercial fishing exist, MSA monitoring may help inform strategies for maintaining and restoring once abundant genetic stocks. Walleye movement and genetic structure in Lake Superior has been studied at local geographic scales, but no lake-wide analysis has been conducted. My objectives were to delineate genetically distinct walleye stocks in Lake Superior and characterize genetic stock-specific movement patterns using MSA. I used a recently developed genotyping-in-thousands by sequencing panel for Great Lakes walleye to develop genetic stock assignment baselines from 32 Lake Superior walleye spawning aggregations and broodstock sources to estimate stock-specific contributions to 68 samples representing over 1300 individuals collected during non-spawning times. Self-assignment testing using leave-one-out cross-validation of spawning aggregations resulted in highly accurate genetic stock delineations for MSA (82.7–100%). My results indicate genetic stock mixing rates were variable by region, with greater mixing rates detected in southwestern and southcentral Lake Superior. Measures of alpha-diversity varied regionally, with higher Shannon diversity indices estimated in northwest Lake Superior, and greater genetic stock richness in the southeast. These results may provide useful insights to guide genetic stock-specific management actions that aim to achieve restoration of walleye throughout Lake Superior.
Subject
Genetic Structure
Genetics
Great Lakes
Mixed Stock Analysis
Resistance Surface Modeling
Walleye
Permanent Link
http://digital.library.wisc.edu/1793/90773Type
Thesis