Browsing by Author "van der Lingen, C D"

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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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    Alternative hypotheses of two mixing stocks of South African sardine: initial testing
    (2014) de Moor, Carryn L; Butterworth, Doug S; van der Lingen, C D; Coetzee, J C
    A new assessment of sardine based on data from 1984 to 2014 is planned to commence in a few months’ time. This assessment will eventually form the operating model which will be used to project the sardine population forward in time under alternative future catch scenarios – i.e. it will be used in the development of the next OMP to likely be finalised in 2016. In preparation for this assessment, some initial potential alternative two mixing stock hypotheses are considered using the previous assessment based on data from 1984 to 2011 (de Moor and Butterworth In Review) which has been used in the development of OMP-14. These tests would hopefully highlight any hypotheses that could have a substantial influence on model results and those which might not, and thus aid in prioritisation of future research. This document is a first stage of this process, firstly outlining the alternative hypotheses currently considered plausible, and then refitting the previous assessment at the joint posterior mode for some of these hypotheses.
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    The present agreed hypothesis for South African sardine stock structure
    (2016-11) Butterworth, Doug S; van der Lingen, C D; Coetzee, J; de Moor, Carryn L
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    The use of fish scale deposit records to inform on South African sardine and anchovy recruitment patterns
    (MARAM, University of Cape Town, 2010) De Moor, Carryn L; van der Lingen, C D
    The ERA review during 2009 highlighted the following issue as of “high” priority: “Improved representation of statistical properties of sardine recruitment variation, particularly over periods with abundance peaks.” A review of work on fossil fish scale deposits, particularly those in Namibia, was requested by the SWGPEL in November 2009, to determine if information on recruitment variation of sardine (and anchovy) could be extracted, and how frequently peaks in sardine abundance might be expected to occur in South African waters.