Browsing by Author "Coetzee, Janet"

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    Basis suggested, following task group discussions, for determining the 2019 sardine directed TAC and by-catch TAB
    (2019) Butterworth, Doug S; Coetzee, Janet
    A list is put forward of suggestions and criteria to provide a basis for developing a sardine directed TAC and by-catch TAB for 2019
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    Calculating an informative prior distribution for the bias of hydro‐acoustic survey estimates of the biomass of the South African anchovy
    (2020) de Moor, Carryn; Coetzee, Janet; Butterworth, Doug
    A prior distribution for the bias of the hydro‐acoustic survey estimates of the biomass of the South African anchovy is developed by considering the bias associated with the individual sources of error.
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    The data used in the 2019 sardine assessment.
    (2019) de Moor, Carryn; Merkle, Dagmar; Coetzee, Janet; van der Lingen, Carl
    Data to which the 2019 assessment of the South African sardine resource is to be conditioned are listed
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    Density dependent movement of South African sardine
    (2018-03) de Moor, Carryn; Bergh, Mike; Butterworth, Doug S; Coetzee, Janet; van der Lingen, Carl
    A hypothesis that the movement of South Africa sardine from the west to the south coast is dependent on west coast biomass is revisited and a relationship proposed for use in future projections.
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    Developing informative prior distributions for the bias of hydro-acoustic survey estimates of the biomass of the South African round herring population
    (2022) de Moor, Carryn; Coetzee, Janet; Butterworth, Douglas
    Prior distributions for the bias of the hydro‐acoustic survey estimates of the biomass of the South African round herring are developed by considering the bias associated with the individual sources of error
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    Proposal for an interim initial anchovy TAC for 2020
    (2019) de Moor, Carryn; Coetzee, Janet
    As only part of the small pelagic hydroacoustic survey has been analysed thus far, an interim initial anchovy TAC is proposed to enable the 2020 anchovy fishing season to begin timeously.
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    Summary of issues pertinent to a decision on possible adjustment of the maximum directed sardine catch allowance west of Agulhas for 2016
    (2016) Coetzee, Janet; Butterworth, Douglas; van der Lingen, Carl; de Moor, Carryn
    This paper summarises proposals on the many and varied issues that need to be addressed in reaching a decision on a possible increase in the maximum directed sardine catch that may be taken west of Cape Agulhas during 2016. It also includes a list of associated issues on which further information is required, both for the short and the longer term.
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    A summary of the method used to provide 2019 catch limit advice for South African sardine
    (2019) de Moor, Carryn; Coetzee, Janet
    Following the declaration of Exceptional Circumstances for sardine, a TAC and TABs for sardine for 2019 were recommended based on short-term projections rather than on OMP-18. The methods used to obtain those projections are described. The Small Pelagic Scientific Working Group (SWG-PEL) focused primarily on the simulated multiplicative increase in biomass from November 2018 to 2019 under alternative 2019 catch scenarios when compared to a no catch scenario.
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    A summary of the South African sardine (and anchovy) fishery
    (2018-11) Coetzee, Janet; de Moor, Carryn; Butterworth, Doug S
    The sardine fishery is an important component of the South African purse-seine fishery, the largest commercial fishery in South Africa (by landed mass). This fishery, initially established on the West Coast, but with some subsequent infrastructure development on the South Coast, is currently under pressure because of recent low biomass levels, reduced TACs and frequent changes in the spatial distribution of the resource. The current low biomass followed from prolonged poor recruitment, whereas the distributional changes are plausibly linked to processes related to spatial structuring of the population, which is now hypothesized to comprise multiple components (western, southern and eastern), with interchange amongst them. Given the predominantly west-coast-based location of sardine processing infrastructure, exploitation levels on the western component is high relative to other components, particularly when most of the biomass is located on the south coast. This has sparked debate about whether there is need for spatially differentiated management to ensure both a healthy ecosystem and a more soundly managed resource. This document summarises the history of the fishery, the current status of the resource and data used in its assessment and management.
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    Uncertainties and associated concerns relating to using short-term projections to advise on the 2020 sardine TAC and TABs
    (2019) de Moor, Carryn; Coetzee, Janet; Butterworth, Doug S
    The analyses undertaken to provide a scientific recommendation for the 2019 sardine TAC and TAB, under Exceptional Circumstances were subject to a number of more serious uncertainties than would normally apply. Given the critically low level of the sardine resource, care should be taken to either recommend catch limits that are robust to these uncertainties, or to undertake further research to minimise such uncertainty. One key uncertainty is how survey (and commercial) length frequencies should be weighted given that concerns frequently arise that one or other (or both) may be unrepresentative of the population length structure. Future recruitment to this short‐lived resource is another key uncertainty. While the primary uncertainty surrounding the weight‐at‐length has been alleviated, and the growth curve adjusted, some uncertainty surrounding the choice of growth curve remains. Finally, under Exceptional Circumstances, the decision‐making process involves a greater degree of subjectivity. While the Small Pelagic Scientific Working Group aimed at making this as objective as possible to recommend 2019 sardine catch limits, that approach could possibly be further improved. This document is aimed at providing current research and analyses to assist discussion on the key questions to the panel at the MARAM International Stock Assessment Workshop.