Browsing by Author "Robinson, William"

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    Claim by Pichegru et al. that marine no-take zone benefits penguins remains premature
    (2010) Butterworth, Douglas; Brandao, Anabela; de Moor, Carryn; Robinson, William
    Pichegru et al. (2010), and a follow up comment by Ryan et al. (2010), make strongly stated claims that closures to pelagic fishing around islands with penguin breeding colonies lead to rapid improvements in those penguin populations. These claims are contested for a variety of reasons, including problems with the analysis method used. Claims that the pelagic fishing stocks are in poor condition, and that this is because of an absence of spatial management, are also contested, as are some other sweeping statements. The data currently available are too limited to be able to confirm or deny the claims made at this stage.
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    Data inputs for the African Penguin Spheniscus demersus model to be coupled to the pelagic OMP
    (2008) Plagányi, Éva E; Robinson, William
    This document serves as an updated compilation of all data currently available as inputs to the African penguin spatial model which is to be coupled to the pelagic OMP. The data are presented here together with some comments as to how they are to be used in the model and notes on their derivation and potential reliability. The model presented thus far is spatial in that different populations of penguins are represented, and different levels of movement between these populations are modelled. The main focus of the model is on Dassen and Robben Islands, which were originally combined for reasons of simplicity and because of their close proximity to each other, suggesting that the effects of external factors such as food availability would be highly correlated between the two. However, data that have recently become available indicate differences between these two colonies which suggest that it may no longer be appropriate to pool the two; hence they are split in the model. The third population is Dyer Island because it has the next largest numbers of penguins, recent declines in the population there are of concern and it is considered an important breeding site for penguins given the eastward shift of sardines. The fourth population is Boulders. Although relatively small, this colony was considered important to include because of its position, its role as the focus of several other studies and because penguins are known to have moved from Dyer Island to Boulders, Robben and Dassen, and hence it is useful to quantify to what extent movement of birds away from Dyer Island could account for observed declines at Dyer and increases at these other colonies. A summary of all the breeding colonies of penguins in so-called area i) is provided in Fig. 1 which also shows the relative abundance of breeding pairs in the different sub-areas, computed from data in Underhill et al. (2006). The regional penguin population is dominated (in terms of numbers) by two large colonies, namely Robben Island and Dassen Island; thus the model here has focused on these two colonies, with the next most important colony being Dyer Island. Fig. 2 maps the extent of strata corresponding to pelagic fish biomass estimates used to link to penguin breeding success in the model. Initially relationships were investigated with the west of Cape Agulhas pelagic spawner biomass and the west of Cape Infanta recruit abundances rather than the total South African pelagic fish abundance. More recently, this has been refined further still to use the Cape Columbine to Cape Point spawner biomass component only since this more accurately depicts the biomass available to penguins in the west coast model area. The west of Cape Infanta recruit estimates are retained because the anchovy and sardine recruits move down the West Coast. The model time step is one year and hence average trends are modelled. Penguins in each subarea are modelled starting from 1986.
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    Modelling the impact of the South African small pelagic fishery on African penguin dynamics
    (2012) Robinson, William
    This paper incorporates a complete description of the penguin–fish interaction model for Robben Island. All data included are described in full in Section 2. The model equations are described in detail in Section 3. Base case results are presented in Section 4.
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    Proposed performance statistics for evaluating the effects of pelagic fishing on African Penguin populations
    (2008) Plagányi, Éva E; Robinson, William
    Given the move towards adopting an ecosystem approach to fisheries in the pelagic sector, the new pelagic OMP needs to be tested in the light of not only the risk parameters as considered previously, along with catch statistics for the anchovy and sardine populations, 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 proposed implementation and suggests performance statistics for use in evaluating the impact on penguins of predicted future pelagic fish trajectories under alternative harvest strategies (OMPs).
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    Update of available data for the African Penguin Spheniscus demersus model to be coupled to the pelagic OMP
    (2008) Plagányi, Éva E; Robinson, William
    This document serves as an updated compilation of all data currently available as inputs to the African penguin spatial model (MCM/2008/SWG-PEL/21b) which is to be coupled to the pelagic OMP. The data are presented here together with some comments as to how they are to be used in the model and notes on their derivation and potential reliability. Note that this is a working group document only and hence should be extended and improved in future, particularly as regards critical evaluation of different data sources.
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    Update to the Robben Island moult count series for 2011
    (2011) Robinson, William
    The 2010/2011 penguin moult season conventionally runs from 1 July 2010 to 30 June 2011. During this period, counts of moulting birds were made on 20 occasions (Table 1). These counts have now been converted to aggregates for the year using the technique of fitting the sum of two Gaussian curves and calculating the area under the function (Robinson and Butterworth 2010).
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    Updating the Dassen Island and Robben Island penguin moult series with data from the 2011/2012 season
    (2012) Robinson, William
    The moult count time-series for Dassen Island and Robben Island, historically the two most important African penguin colonies in the Western Cape, are updated with data collected during the 2011/2012 season (1 july 2011 to 30 June 2012). The counts made over this period have been converted to aggregates for the season using the technique of fitting the sum of two Gaussian curves and calculating the area under the function (Robinson 2012).