Browsing by Subject "Sardine"

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    The 2004 re-assessment of the South African sardine and anchovy populations to take account of revisions to earlier data and recent record abundances
    (National Inquiry Services Centre (NISC), 2009) de Moor, Carryn L; Butterworth, Doug S
    Hydroacoustic surveys off the coast of South Africa over the early years of the 21st century indicated that both the sardine Sardinops sagax and anchovy Engraulis encrasicolus populations had simultaneously reached record abundances. The South African pelagic fishery is regulated using an Operational Management Procedure (OMP). The OMP in use at that time had been developed using data from the two populations prior to this rapid and substantial increase in abundances. This paper documents the revised assessments that were urgently required to provide a basis to update the OMP. These assessments resulted in a changed perception of the status and productivity of these populations. In particular, estimates of the stock-recruitment relationships and the extent of variation about them, which play a key role in evaluating risk when developing OMPs, altered substantially from estimates derived from earlier assessments.
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    Developing and refining a joint management procedure for the multispecies South African pelagic fishery
    (Oxford University Press, 2004) De Oliveira, J A A; Butterworth, Doug S
    Pilchard (sardine) and anchovy are the main targets of South Africa's pelagic fishery. This fishery is the country's second most valuable in monetary terms, and produces the highest annual yield in terms of landed mass (in recent years, a combined catch of the order of 400 000 t). It is the most dynamic of South Africa's main commercial fisheries, because the species targeted are relatively short-lived, often occur in mixed shoals, and experience large fluctuations in abundance. Mixed shoaling causes operational problems for the fishery, because of the inevitability of juvenile pilchard bycatch (of more value as adults for canning) in the anchovy-directed fishery. This operational interaction implies a trade-off between allowable catches for the two species, and hence necessitates that they are managed together. The development of a joint “management procedure” (sensu IWC) for the two species is described. This provides a framework for quantifying this trade-off, subject to the constraint that acceptable levels of risk of “collapse” are not exceeded for either resource. Important new features incorporated in a revision of the procedure implemented in 2002, which have made appreciably enhanced catches from the resources possible, are described.
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    Is the management procedure approach equipped to handle short-lived pelagic species with their boom and bust dynamics? The case of the South African fishery for sardine and anchovy
    (Oxford University Press, 2011) De Moor, Carryn L; Butterworth, Doug S; De Oliveira, J A A
    Worldwide, small shoaling pelagic fish manifest rapid and substantial natural changes in abundance. Is the application of a management procedure (MP), evaluated using simulation tests [i.e. a MP approach otherwise known as management strategy evaluation (MSE)], to recommend total allowable catches (TACs) with constraints desired by industry on the extent of interannual changes viable for such resources, particularly given the customarily lengthy MP evaluation process? This question is examined by considering the rapid boom and then bust situation that arose for the South African fishery for sardine (Sardinops sagax) and anchovy (Engraulis encrasicolus) across the turn of the century. Novel adaptations to the MP in place at the time of the boom allowed enhanced resource use during the boom period without compromising the risk of unintended depletion of the populations. Importantly a two-tier threshold system allowed the normal constraints on the maximum extent of interannual TAC reduction to be modified when TACs rose above the specified thresholds. The general protocol underlying the application of MPs for South African fisheries proved sufficiently flexible for the approach to continue to be applied, despite the unanticipated rapid fish population boom and then bust experienced.
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    Refined estimates of South African pelagic fish biomass from hydro-acoustic surveys:quantifying the effects of target strength, signal attenuation and receiver saturation
    (National Inquiry Services Centre (NISC), 2008) Coetzee, J C; Merkle, D; De Moor, Carryn L; Twatwa, N M; Barange, M; Butterworth, Doug S
    The biomass of small pelagic fish species off the coast of South Africa has been monitored since 1984 using hydro-acoustic survey techniques. These time-series of spawner biomass and recruitment estimates form the basis for management of both the South African sardine Sardinops sagax and anchovy Engraulis encrasicolus resources and are central to the setting of annual total allowable catch levels. However, these survey estimates have, for the most part, been treated as relative indices as there are several biases inherent in acoustic survey methodology that remain difficult to quantify. Advances in acoustic technology together with an improved understanding of the major sources of survey errors have enabled estimation of and correction for biases such as receiver saturation, acoustic signal attenuation and target strength. Incorporation of these corrections over the entire time-series has resulted in an improved accuracy of acoustic survey estimates and substantial changes to the biomass estimates of both species, without jeopardising the requirement that the time-series remains comparable throughout its duration. Furthermore, the resultant decrease in the level of uncertainty associated with these abundance estimates has rendered improved utilisation of these resources possible.
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    Open Access
    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.