Browsing by Subject "anchovy"

Now showing 1 - 5 of 5
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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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    Abrupt environmental shift associated with changes in the distribution of Cape anchovy Engraulis encrasicolus spawners in the southern Benguela
    (2007) Roy, C; van der Lingen, C D; Coetzee, J C; Lutjeharms, J R E
    Cape anchovy Engraulis encrasicolus spawners in the southern Benguela showed an eastward shift in their distribution on the Agulhas Bank that occurred abruptly in 1996 and has since persisted. We assessed whether this shift was environmentally mediated by examining sea surface temperature data from different regions of the Agulhas Bank, which showed that in 1996 the inner shelf of the Agulhas Bank to the east of Cape Agulhas abruptly became 0.5°C colder than in previous years and has since remained that way. In addition, signals, coherent with the 1996 shift recorded in sea surface temperatures, were also found in atmospheric surface pressure and zonal wind data for that region; interannual coastal SST variability is also shown to be correlated with zonal wind-stress forcing. As a result, increased wind-induced coastal upwelling east of Cape Agulhas is proposed as the main driver of the observed cooling in the coastal region. The synchrony between the environmental and biological signals suggests that the eastward shift in anchovy spawner distribution was environmentally mediated and arose from a change in environmental forcing that altered the relative favourability for spawning between regions to the west and east of Cape Agulhas. The results highlight how a relatively minor change in environmental conditions can lead to a drastic spatial reorganisation of the life history of one species in an ecosystem.
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    OMP‐18rev: The revised 2018 Operational Management Procedure for the South African anchovy fishery
    (2021) de Moor, Carryn
    This document details OMP‐18rev, the Operational Management Procedure to be used to recommend total allowable catches for anchovy in South African waters from 2022.
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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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    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.