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    A Walleye Pollock (Theragra Chalcogramma) Depletion Estimator For The Eastern Bering Sea

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    Author
    Battaile, Brian Charles
    Chair
    Terrance J. Quinn, II
    Committee
    Kelly, Brendan
    Sigler, Mike
    Adkison, Milo
    Keyword
    Aquatic sciences
    Metadata
    Show full item record
    URI
    http://hdl.handle.net/11122/8771
    Abstract
    The decline of the Steller Sea lion in the eastern Bering Sea over the last 25 years has resulted in increased management of the pollock fishery due to requirements of the Endangered Species Act, as food competition was hypothesized to contribute to the decline. Our research focused on determining if the pollock fishery was causing significant depletion in the eastern Bering Sea, particularly in Steller sea lion critical habitat. DeLury depletion models were fitted to catch and effort data from 1995 to 1999, from the observer program, which required considerable processing to obtain a database at a temporal and spatial scale that is much finer than that used for stock assessment in the eastern Bering Sea. The catch per unit effort (CPUE) data were standardized in a unique way in that the data were stratified in space and time and standardized using separate general linear models for each stratum. A significant amount of depletion was detected in the pollock fishery from 1995--1999. Depletion estimates of fishery mortality tended to be an order of magnitude smaller than those found in traditional stock assessments. Post hoc analyses indicated that depletion is detected more easily in areas of low abundance due to the hyperstable relationship between CPUE and biomass, possibly exacerbated by a lack of search time in the model. Evidence further suggested that dispersing exploitation pressure decreases local depletion, and pollock may repopulate a depleted area within weeks. Finally, a hierarchical spatial Bayesian analysis with a conditional autoregressive model was constructed to unify the analysis. Because the data were relatively clean of outliers and not over dispersed, significant changes in the results between the frequentist and Bayesian based analyses were not found as was little evidence of spatial autocorrelation in the estimates of catchability.
    Description
    Dissertation (Ph.D.) University of Alaska Fairbanks, 2005
    Date
    2005
    Type
    Dissertation
    Collections
    Fisheries

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