OpenUCT :: Browsing by Author "de Moor, Carryn L"

Browsing by Author "de Moor, Carryn L"

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Open Access
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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A 2-stock hypothesis for South African sardine: two discrete stocks
(2009) de Moor, Carryn L; Butterworth, Doug S
A 2-stock, 2-area hypothesis for the South African sardine resource is being developed, with the following boundaries: i) A “western” stock distributed throughout the “western area”, defined as the area west of Cape Agulhas ii) An “eastern” stock distributed throughout the “eastern area”, defined as the area east of Cape Agulhas As previously discussed (de Moor 2009) two separate scenarios are to be considered for this 2-stock hypothesis: i) No mixing between these stocks. ii) Movement of 1-year-olds from the “western” stock to the “eastern” stock and movement of 2+-year-olds from the “eastern” stock to the “western” stock. Recruitment to the “western” stock will be dependent on the SSB of both the “western” and “eastern” stocks. Recruitment to the “eastern” stock will be dependent on the SSB of the “eastern” stock only. This document gives the results of fitting the assessment model to data under the first of these scenarios: two discrete “western” and “eastern” stocks of the South African sardine resource.
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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.
Open Access
An alternative two mixing stock hypothesis for South African sardine
(2016-10) de Moor, Carryn L
The results of the two mixing stock hypothesis for South African sardine presented in de Moor and Butterworth (2016) assumed recruitment to each coastal management unit was dependent only on the spawner biomass (SSB) of that coastal management unit. In this document some contribution from the south coast SSB to the effective west coast SSB is considered as an alternative two mixing stock hypothesis.
Open Access
Are South African administrative law procedures adequate for the evaluation of issues resting on scientific analyses
(Juta Law, 2012) Butterworth, Doug S; de Oliveira, Jose A; de Moor, Carryn L
This article traces, from a critical perspective, the way in which the various courts that were seized of the matter reviewed the scientific approaches to the allocation of fishing quotas for sardine and anchovy in Foodcorp (Pty) Ltd v Deputy Director General, Department of Environmental Affairs and Tourism: Branch Marine and Coastal Management & others. The article explains the scientific basis that underpinned the allocations (Total Allowable Catches) made by the Department of Environmental Affairs and Tourism in terms of the Marine Living Resources Act 18 of 1998 in the early 2000s. It then considers the approach adopted by both the Cape High Court and the Supreme Court of Appeal to these allocations. In all except the first of these cases, the courts found the allocations to have been irrational in terms of the requirements of administrative law. The authors argue that this occurred because of a failure on the part of the respective courts to understand the science behind the quota allocations. The authors argue that there is a need for courts to be more open to seeking guidance from experts in the scientific community to ensure that these issues are properly understood in the future.
Open Access
Assessment of the South African anchovy resource using data from 1984 - 2015: results at the posterior mode
(2016-10) de Moor, Carryn L
The operating model (OM) for the South African anchovy resource has been updated from that used to develop OMP-14 given four more years of data. The model has been altered from previous assessments to now fit directly to length frequency data, removing the earlier need for estimates of proportions of anchovy-at-age 1 during the annual November hydroacoustic survey. A Beverton Holt stock recruitment relationship is used for the base case. Time-invariant natural mortality is assumed to be 1.2year^(-1) for both juvenile and adult natural mortality as before; this provides a better fit to the data than other options considered. The resource abundance is estimated to be near the historical (1984-2014) average, with a total biomass of 3.3 million tons in November 2015. Recruitment reflects three major peaks over the past 20 years, although the lowest points in these fluctuations were still large, being similar to the maximum recruitment prior to 2000.
Open Access
Excluding survey estimates of recruitment on the South Coast from the two mixing stock hypothesis for South African sardine
(2016-11) de Moor, Carryn L
The international panel from the annual Stock Assessment Workshops have recommended that the sensitivity of the two mixing stock hypothesis to the inclusion of hydroacoustic survey estimates of recruitment on the South Coast be tested. This time series of data does not cover the full time period modelled, and these data have large CVs (Smith et al. 2013; Dunn et al. 2015). This document explores an alternative where these data are excluded from the two mixing stock model.
Open Access
Final Anchovy and Sardine TACs and TABs for 2017, Using OMP-14
(University of Cape Town, 2017) de Moor, Carryn L
As the November survey estimate of sardine abundance was less than 300 000t, the Exceptional Circumstances rule was used resulting in an initial directed >14cm sardine TAC being recommended at the beginning of the year.
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Fisheries management under climate and environmental uncertainty: control rules and performance simulation
(Oxford University Press, 2014) Punt, Andre´ E; A’mar, Teresa; Bond, Nicholas A; Butterworth, Doug S; de Moor, Carryn L; De Oliveira, Jose´ A A; Haltuch, Melissa A; Hollowed, Anne B; Szuwalski, Cody
The ability of management strategies to achieve the fishery management goals are impacted by environmental variation and, therefore, also by global climate change. Management strategies can be modified to use environmental data using the “dynamic B0” concept, and changing the set of years used to define biomass reference points. Two approaches have been developed to apply management strategy evaluation to evaluate the impact of environmental variation on the performance of management strategies. The “mechanistic approach” estimates the relationship between the environment and elements of the population dynamics of the fished species and makes predictions for population trends using the outputs from global climate models. In contrast, the “empirical approach” examines possible broad scenarios without explicitly identifying mechanisms. Many reviewed studies have found that modifying management strategies to include environmental factors does not improve the ability to achieve management goals much, if at all, and only if the manner in which these factors drive the system is well known. As such, until the skill of stock projection models improves, it seems more appropriate to consider the implications of plausible broad forecasts related to how biological parameters may change in the future as a way to assess the robustness of management strategies, rather than attempting specific predictions per se.
Open Access
Further work on a risk analysis of the impact of harvesting sardine on the west coast of South Africa
(2016-08) de Moor, Carryn L
de Moor and Butterworth (2016a) undertook an initial risk analysis to consider the risk to the sardine resource for the 2016 season, in terms of the west coast harvest proportion. This analysis was to assist in discussions regarding the implementation of the "Gentleman’s agreement" that the South African pelagic industry self-regulate fishing pressure west of Cape Agulhas to ensure the spread of fishing west compared to east of Cape Agulhas is similar to that observed during recent November surveys (further details provided in de Moor and Butterworth (2016a)).
Open Access
OMP-13: Initial Results Assuming a Two Sardine Stock Hypothesis
(2013) de Moor, Carryn L; Butterworth, Doug S
Further work in the development of OMP-13 has continued with modifications to the documentation and code, mostly to allow for a generalisation towards one or two sardine stocks and one or two directed sardine TACs (de Moor and Butterworth 2013a). This document provides updated results for no catch scenarios and candidate MPs assuming a single sardine stock hypothesis, with different levels of variability about the stock recruitment relationship. Initial results are also presented for a no catch scenario and candidate MPs assuming a two sardine stock hypothesis; risk under this two stock hypothesis is discussed. Results are presented for candidate MPs which set a single sardine TAC only. The split of the sardine catch between the “west” and “south” stocks, in the case of the two sardine stock hypothesis, is based on a relationship with the ratio of the directed sardine TAC to the “west” stock 1+ biomass in the previous November (de Moor and Butterworth 2013a).
Open Access
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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Progress in checking the code used to condition the operating models for the South African hake resource to be used in OMP-2010 testing
(2010) de Moor, Carryn L; Rademeyer, Rebecca A
The code used to condition these Operating Models, the results for which have been reported in documents such as MCM/2010/FEB/SWG-DEM/05, has been subjected to careful independent checking by the first author. This checking has focused on aspects leading to the computation of the likelihood upon which this conditioning is based. It has not (as yet) extended to the specification of outputs and all aspects of the computation of projections which are also part of the software in question. This checking is now about 90% complete. This checking process has not yet revealed anything that would result in the computation of the likelihood (and hence the consequent results) by this software differing from what was intended. However it has revealed a few omissions and typos in the documentation of the Operating Models, as set out in Appendix II of MCM/2010/FEB/SWG-DEM/05. The consequent corrections are shown in track changes in an updated version of that Appendix which is attached hereto.
Open Access
Progress report on recommendations from the International review panel report for the 2013 International Fisheries Stock assessment workshop:sardine
(2014) de Moor, Carryn L; Butterworth, Doug S; Coetzee, Janet C; van der Lingen, Carl D
The international review panel report (MARAM/IWS/DEC13/General/4 Final Report) contained the following recommendations pertinent to sardine in response to key questions put to them at the annual stock assessment review meeting held at UCT from 2-6 December 2013. Comments on any progress in response to these recommendations are inserted in italics. As a general point of background information, the Small Pelagic Scientific Working Group agreed earlier in 2014 to finalise OMP-14 based on a single sardine stock operating model only, but coupled with some spatial management, the spirit of which is to be a “warm up period” with the expectation that the next OMP will quite likely require spatial management components. The development of new operating models and a new OMP is to be brought forward, commencing in early 2015 with the aim of being finalised before the end of 2016.
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The quantitative use of parasite data in multistock modelling of South African sardine (Sardinops sagax) 1
(NRC Research Press, 2017) de Moor, Carryn L; Butterworth, Doug S; van der Lingen, Carl D
Differences in parasite infection have previously been used to distinguish between fish stocks. We demonstrate a novel use of parasite prevalence-by-length data to inform quantitatively on stock mixing. An initial two mixing stock hypothesis proved consistent with biological and survey data, suggesting that there are different stocks of sardine off the west and south coasts of South Africa. That hypothesis assumed that only recruits moved from the west to the south stock. However, new “tetracotyle”-type metacercarian parasite bio-tag data indicate a need to allow older fish to move between the stocks as well. We demonstrate extension of bio-tagging to inform on the plausibility of population structure hypotheses by including parasite prevalence-by-length data in the model’s likelihood. Our method enables the estimation of the magnitude of mixing between semidiscrete stocks, providing more precise estimates of annual movement. Such improved precision may be important in better informing future movement hypotheses and thereby management. Our research provides a framework to use to inform quantitatively on stock structure and movement hypotheses for other fish species with bio-tagging data.
Open Access
Response to MCM/2010/PEL/48: Suggestions for improving the penguin modeling framework
(2010) Butterworth, Doug S; Robinson, William M L; Plagányi, Éva E; de Moor, Carryn L
As general background, it should be noted that the brief for document MCM/2010/SWG-PEL/35 was to combine into a single convenient reference a number of documents that contributed to the discussion and decision on the issue of possibly amending the pelagic OMP to take explicit account of impacts of removals by the fishery on penguin dynamics that was taken at the December 2008 meeting of the PWG. No attempt was made in that document (PEL/35) to revise the calculations available at that time in the light of further work which has been ongoing – some of that work and associated future plans have been reported in the latter part of MCM/2010/SWG-PEL/36. Furthermore, it should be noted that those calculations had to be finalized rapidly to meet that December 2008 deadline, taking account of elements were not reported upon in as full a manner as might otherwise have been the case.
Open Access
The simulation testing framework used during the development of OMP-13
(2012-11) de Moor, Carryn L; Butterworth, Doug S
This document details the framework used to simulation test candidate MPs during the development of OMP-13. A summary of assumptions made in this simulation testing framework are listed below, with yellow highlights indicating updates since de Moor and Butterworth (2012f). Appendix A provides the full details, with data used listed in the tables at the end of the Appendix.
Open Access
Testing robustness of the two mixing stock hypothesis for South African sardine to parasite prevalence data between 20 and 22 degrees
(2016-12) de Moor, Carryn L
The baseline two mixing stock assessment of South African sardine has been conditioned on parasite prevalence data on the south coast east of 22◦E only (Dunn et al. 2015, de Moor and Butterworth 2016). Data between 20 and 22◦E were excluded from the baseline assessment to ensure no age-1 sardine from the west stock that were not permanently moving to the south stock were included in south stock prevalence data. This document explores the sensitivity of the assessment results to including the parasite prevalence data between 20 and 22◦E.
Open Access
When would a survey estimate be considered "appreciably outside the bounds predicted in the OMP testing"
(2009) de Moor, Carryn L; Butterworth, Doug S
Anon. (2009), outlining the procedures for deviating from or initiating an early review of the pelagic OMP, was discussed at the Scientific Working Group (Pelagic) on 26th February 2009. The document lists examples as to what might constitute Exceptional Circumstances in the case of sardine and anchovy. One such example was: “Survey estimates of abundance that are appreciably outside the bounds predicted in the OMP testing.” A request was made to develop a rule to determine what determines when a survey estimate is “appreciably outside the bounds predicted in the OMP testing.”

Browsing by Author "de Moor, Carryn L"

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