Browsing by Subject "sardine"

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    The 2018 Operational Management Procedure for the South African sardine and anchovy resources
    (2018) de Moor, Carryn
    The Operational Management Procedure (OMP) to be used to recommend total allowable catches and bycatches for sardine and anchovy in South African waters has been updated and is detailed herein
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    Comparisons between single area management and various forms of two area management for directed sardine TACs off South Africa
    (2017) de Moor, Carryn
    Relatively simple Harvest Control Rules which recommend either a single directed sardine Total Allowable Catch (TAC) for the whole western and southern coastline of South Africa are compared with some alternatives which split the TAC between the west and south coasts. These provide some insight into the possible impact of spatial management – or lack thereof - on the sardine resource under the next Operational Management Procedure.
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    Does parasite infection definitely increase for sardine aged 2 and above on the south coast
    (2014) Ross-Gillespie, Andrea; Butterworth, Doug S
    The trend with length in parasite prevalence in sardine on the South Coast is modelled in a manner that isolates behaviour at larger lengths to enable a determination of whether the trend continues to increase from age one to ages of two and above. The results indicate that a continued increase is robustly confirmed at the 5% level of significance, and hence that there must be some movement of sardine of ages greater than one in at least one direction between the West and the South Coasts under the hypothesis that infection by the parasite can occur only on the West Coast.
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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
    (2008) Coetzee, J C; Merkle, D; de Moor, C 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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    Risk-related aspects of the west coast rock lobster and of the joint sardine and anchovy OMPs to be developed this year
    (2007) Johnston, Susan J; Cunningham, Carryn L; Plagányi, Éva E; Butterworth, Doug S
    In 2006, the west coast rock lobster scientific working group moved from assessing the resource as a single stock, to assessing the stock at a spatially disaggregated “super-area” level, to take better account of different resource monitoring trends in different areas which indicated area-specific dynamics. The resource was divided into five super-areas by combining the existing eights areas (A1 to A8): A1-2, A3-4, A5-6, A7 and A8. Stock assessment updates at the super-area level have now been completed, and work is underway in developing a new OMP for the resource which inputs data on an area-disaggregated basis. This OMP is scheduled for finalisation early during the second half of this year.
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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
    (2009) De Moor, C; 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.