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    Ocean and stream ecology of adult hatchery and wild pink salmon

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    Author
    McMahon, Julia
    Chair
    Westley, Peter
    Committee
    Gorman, Kristen
    McPhee, Megan
    Rand, Peter
    Keyword
    Pink salmon
    Ecology
    Prince William Sound
    Pink salmon fisheries
    Spawning
    Hatchery fishes
    Metadata
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    URI
    http://hdl.handle.net/11122/12626
    Abstract
    In this thesis I investigate potential interactions of hatchery and wild pink salmon (Oncorhynchus gorbuscha) at sea and on the spawning grounds, in the context of the ecological and economic importance of modern Alaskan hatcheries. Although hatchery and wild salmon are known to interact, the nature and outcome of those interactions remain unclear. Here, I identify potential mechanisms of competition and hatchery salmon fitness with two datasets from Prince William Sound, Alaska, home to the largest pink salmon hatchery program in the world. First, I compared fitness-related traits such as body length, return timing, instream lifespan, and egg retention between straying hatchery and homing wild pink salmon to identify potential barriers or bridges to gene flow with over 120,000 individuals sampled over six years (2013-2018). Predicted lengths of hatchery and wild fish depended on the even or odd year lineage, return timing, and sex. Odd year pink salmon were smaller on average than even year pink salmon, odd year hatchery fish were smaller than wild fish, odd year length decreased over the season, and odd year males tended to be larger than females. In even years, hatchery pink salmon were larger on average than wild pink salmon, length increased over the season, and hatchery females were larger on average than any other group. I found no statistically significant differences in instream lifespan (2017: t-test (₂₀.₅₄), P = 0.41; 2018: t-test(₆.₂₆), P = 0.556) or egg retention (x²₍₂₎= 4.5, p = 0.11; 2017 and 2018 combined) between hatchery and wild fish. In contrast, I detected significant differences in stream life of the wild fish between two different sized streams in a manner consistent with observed black bear (Ursus americanus) predation; specifically stream life was shorter in the smaller stream with markedly higher predation. Second, I used stable carbon and nitrogen isotope analysis to test the hypothesis that hatchery and wild pink salmon have distinct foraging niches during their last months at sea, which could underpin observed differences in length between hatchery and wild pink salmon. Using data from 2015, I fit linear models and detected no difference in broad-scale foraging locations (delta¹³C values) of hatchery and wild pink salmon. However, trophic positions (delta¹⁵N values) for hatchery and wild pink salmon were inversely related to size where large wild salmon and small hatchery salmon tended to have the highest delta¹⁵N values. Because delta¹³C values and delta¹⁵N values of wild fish were positively associated with body size, it is likely that hatchery and wild pink salmon have size-dependent, yet still overlapping foraging niches. Overall, these results are consistent with the potential for hatchery and wild pink salmon to compete for resources on the spawning grounds and at sea to the extent that resources are limiting.
    Description
    Thesis (M.S.) University of Alaska Fairbanks, 2021
    Table of Contents
    Introduction -- Chapter 1: Do fitness-associated reproductive traits differ between hatchery strays and wild pink salmon (Oncorhynchus gorbuscha)? A large-scale empirical test in Prince William Sound, Alaska -- Chapter 2: Stable isotopes suggest foraging niche overlap between adult hatchery and wild Alaskan pink salmon during their last summer at sea -- Conclusions.
    Date
    2021-08
    Type
    Thesis
    Collections
    New theses and dissertations

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