Browsing by Subject "Spatial model"

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    Investigating the consequences of Marine Protected Areas for the South African deep-water hake (Merluccius paradoxus) resource
    (Oxford University Press (OUP), 2009) Edwards, Charles T T; Rademeyer, Rebecca A; Butterworth, Doug S; Plagányi, Éva E
    Protected areas are often touted as important management tools to mitigate the uncertainty inherent in marine ecosystems, and thereby improve the long-term prospects for sustainable resource use. However, although they certainly play an important role in conservation, their usefulness in improving fishery yields is contentious. We present a simulation model that explores spatial closure options, and apply it to the demersal hake trawl fishery off South Africa. The model is based on the age-structured approach used for current assessments, representing the dynamics of the deep-water hake Merluccius paradoxus within a zonally disaggregated spatial system. Fitting the model to two zones, which demarcate a potential closed area from the remaining fished area, we investigate the consequences that such a protected area could have for the fishery. Our model suggests that area closures would have a negligible benefit for the fishery, regardless of the level of hake movement between areas. This is likely the result of the model's simplicity, and we suggest additional factors that should be considered to quantify the impact of Marine Protected Areas on the fishery more reliably.
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    A spatial model of African penguin Spheniscus demersus populations in the Western Cape
    (2007) Plagányi, Éva E
    A number of questions have recently been raised regarding the status and management of the African penguin Spheniscus demersus. The PWG penguin task team agreed that it would be useful to develop a dynamic model to assist in understanding the population dynamics as well as in an attempt to reconcile the various data sources. This document describes the development of such a model. Although still preliminary only, the model is of a form that can readily be linked to the pelagic OMP (Operational Management Procedure) to take account of the relationship between the breeding success of African penguins and the abundance of both anchovy Engraulis encrasicolus and/or sardine Sardinops sagax (e.g. Crawford et al. 2006). The aims of the current model are as follows: 1) To provide a dynamic representation of penguin dynamics; 2) To fit to available data to provide estimates of important demographic parameters such as survival rates, which can then be compared to other available estimates; 3) To attempt to reconcile some apparent contradictory trends in the different data series; 4) By gradually increasing the complexity of the model to represent different plausible hypotheses, the model should assist in identifying the most parsimonious hypothesis to explain the observed trends in the population; 5) To quantify and provide additional substantiation for the relationship between penguin breeding success and pelagic fish abundance; 6) To dynamically project the penguin population assuming various future scenarios to assist in providing advice regarding the management of the penguin population (and possibly pelagic fish populations as well).