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    Bioenergetic and economic impacts of humpback whale depredation at salmon hatchery release sites

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    Author
    Chenoweth, Ellen M.
    Chair
    Atkinson, Shannon
    McPhee, Megan
    Committee
    Criddle, Keith
    Friedlaender, Ari
    Heintz, Ron
    Straley, Janice
    Keyword
    Humpback whale
    Food
    Southeast Alaska
    Pacific salmon
    Predators
    Metadata
    Show full item record
    URI
    http://hdl.handle.net/11122/9664
    Abstract
    Since 2008, humpback whales have been documented depredating hatchery-produced juvenile salmon, a novel prey, at points of their release in Southeast Alaska. The objectives of this dissertation are to determine the spatial distribution, seasonal distribution, and frequency of humpback whale foraging at release sites, determine whether whale presence is affecting the economic productivity of hatchery operations, and compare the bioenergetic benefits for whales feeding on juvenile salmon at hatchery release sites relative to typical prey. Five hatchery release sites were monitored over six years during the spring release season for whale presence/absence, numbers, and behaviors. Linear models were used to determine that for coho salmon, cohorts with frequent humpback whale presence had lower marine survival than cohorts with less or no humpback whale presence, but this was not seen for chum or Chinook salmon. Over six years, these sites lost an estimated 23% of revenue from coho salmon totaling almost a million dollars per year in addition to increased rearing costs to mitigate whale predation. A process model was developed to compare the net energy gain for humpback whales foraging on krill, herring and juvenile salmon. Whales were found to feed profitably on krill and chum salmon where they occurred in dense enough distributions and on herring when large coordinated groups impeded the escape of prey. Coho salmon typically distributed too diffusely for humpback whales to recuperate the full energetic costs of engulfment, indicating that behaviors such as bubble net feeding may be essential for increasing prey aggregation to an energetically profitable level, or humpback whales may be feeding to mitigate energetic losses. As intraspecific competition increases due to recovery and or changes to prey resources, generalist humpback whales may expand feeding to exploit new and less profitable prey resources.
    Description
    Dissertation (Ph.D.) University of Alaska Fairbanks, 2018
    Date
    2018-08
    Type
    Dissertation
    Collections
    Fisheries

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