An expansion of nonlethal tools for use on juvenile pallid sturgeon in the upper basin of the Missouri River
Djokic, Matea Asahi
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Pallid sturgeon (Scaphirhynchus albus) are an endangered species endemic to the Missouri and Mississippi drainages in North America. Mitigation activities including conservation spawning and stocking programs were implemented to prevent extinction of the species. Monitoring of growth, survival, and condition are conducted annually to determine efficacy of managerial efforts to recover pallid sturgeon. My thesis aimed to establish a knowledge base of juvenile pallid sturgeon physiological bioindicators that can supplement field monitoring of growth, size, and condition measurements. Ultimately, I aimed to resolve mechanisms underlying population fluctuations (e.g. growth rate) caused by environmental changes or management actions. Fisheries managers have observed reduced growth rates of recently stocked hatchery origin pallid sturgeon (HOPS) relative to earlier cohorts. Based on high survival rates of historic stocked HOPS, some fisheries biologists hypothesize that growth rates of recent HOPS cohorts reflect compensatory density dependence in growth caused by overstocking. However, size, growth, and condition metrics commonly tracked on wild-captured sturgeon cannot assess underlying mechanisms driving trends in population growth rate. The purpose of this hatchery-based research was to explore nonlethal physiological measurements to expand the toolset available to managers to assess the status of physiological processes within HOPS that may reflect ecosystem effects on these fish. I investigated a suite of physiological bioindicators that could reflect key physiological processes (nutrition, tissue damage, and chronic stress) expected to respond to common ecosystem stressors. I determined reference intervals for 13 blood biochemical analytes on a population of healthy hatchery-reared juvenile pallid sturgeon (n = 41). Inter-individual variation in blood biochemical analytes and five additional physiological variables were analyzed to determine composite variables predictive of growth. To investigate nonlethal tools to quantify whole-body energetic reserves of juvenile pallid sturgeon, I determined best-fit predictive models to estimate whole-body energy (df = 33; R 2 = 0.40; p < 0.001) and lipid (df = 33, R 2 = 0.45, p < 0.001) content using Distell Fatmeter and mass measurements. Research presented in this thesis aims to provide a preliminary understanding of expected ranges of various physiological bioindicators and methods for nonlethally measuring these bioindicators in hatchery-reared juvenile pallid sturgeon.