Browsing by Subject "pelagic OMP testing"

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    Illustrative outputs of the age-structured model of African penguin populations for linking to the pelagic OMP testing process
    (2008) Robinson, William M L; Plagányi, Éva E; Butterworth, Doug S
    Given the move towards adopting an ecosystem approach to fisheries in the pelagic sector, the new joint OMP needs to be tested in the light of not only the risk parameters as considered previously, along with catch statistics, but also parameters denoting risk to the African penguin population(s) Spheniscus demersus. Penguins have been chosen as a key predator species to consider because of their conservation status, and because of their potential sensitivity to changes in pelagic fish abundance and distribution as a consequence of their land-based breeding sites. A model of penguin dynamics has been developed for use as a penguin Operating Model to be coupled to the pelagic fish OMP. This paper summarises the base-case penguin model and proposed method for use in evaluating the impact on penguins of predicted future pelagic fish trajectories under alternative harvest strategies (OMPs).
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    Updated results from a Spatial Age-Structured Model of African Penguin populations for use in linking to the pelagic OMP testing process
    (University of Cape Town, 2008) Robinson, William M L; Plagányi, Éva E
    Updated results of an earlier penguin model are presented. The model focuses on four colonies 1) Robben Island; 2) Dassen Island; 3) Boulders and 4) Dyer island, although projections will narrow the focus further to the first two of these. Some progress has been made in terms of fitting the model adequately to historic data. However, there are still problems with the fits such that the current model is not yet at the stage where it can be linked to the pelagic OMP (Operational Management Procedure) testing process to take account of the relationship between the breeding success and also natural mortality of African penguins and the abundance of both anchovy Engraulis encrasicolus and/or sardine Sardinops sagax. Despite extensive investigations, in many cases no overly strong functional relationships between penguin breeding success and pelagic abundance have been found. As a result, functional relationships are being investigated between the natural mortality of African penguins and pelagic abundance, with results suggesting that a relationship exists at Robben Island, but not at Dassen Island. Dassen and Robben Islands are split and modelled separately for these and other reasons.