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    Use of a population model to assess the impact of longline fishing on wandering albatross populations

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    Document Number:
    WG-IMALF-94/08
    Author(s):
    Coleen L. Moloney, John Cooper, Peter G. Ryan and W. Roy Siegfried (South Africa)
    Agenda Item(s)
    Abstract

    An age-structured model of a wandering albatross Diomedea exulans population is developed to simulate population trends over time, using demographic parameters from the population at Possession Island Crozets, during 1968 to 1986. The simulation results portray a population decreasing at a rate of 2.29% per year, which concurs with global population trends. Sensitivity analyses of model parameters indicate that both adult and juvenile mortality are contributing to the decrease. Wandering albatross mortality is presumed to have increased as a result of deaths caused by longline fishing vessels; such deaths are likely to be relatively more frequent among young, naive birds. The model is used to investigate the potential impacts of new longline fisheries such as that for Patagonian toothfish Dissostichus eleginoides in Antarctica. Assuming longline fishing operations affect juveniles more than adults, there is a time lag of 5-10 years before further decreases in population numbers are reflected in the breeding population. Also, because wandering albatrosses are long-lived, population growth rates take approximately 30-50 years to stabilize after a perturbation. Consequently, caution must be exercised when interpreting population trend; short-term (<20 yea r) estimates may not provide good indications of long-term trends.

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