Browsing by Author "de Moor, Carryn"

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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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    The acceptable level of risk for the South African sardine resource.
    (2019) de Moor, Carryn
    An acceptable maximum level of risk for the South African sardine resource has been calculated by comparing the depletion of the effective west component spawner biomass from the recent Operating Model being used to develop OMP-18 with the total spawner biomass from previous Operating Models used to develop earlier OMPs. This results in a risk level of approximately 15%. This risk level is higher than that considered acceptable in other countries, but may be argued to be acceptable given the risk to the sardine resource expected even under a no future catch scenario.
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    Assessment of the South African sardine resource using data from 1984-2018: Initial results at the joint posterior mode for the two mixing-component hypothesis.
    (2019) de Moor, Carryn
    The assessment of the South African sardine resource is in the process of being revised and updated using data available up to November 2018. While some data are yet to be finalised and robustness to some key model assumptions is still to be considered, the initial results presented here are expected to be sufficiently accurate such that they can reliably form the basis of simple constant catch projections for short-term management decisions. The assessment model considers the sardine population to consist of two mixing ‘components’, with a west component distributed west of Cape Agulhas and a south component distributed south-east of Cape Agulhas. Mixing occurs via movement from the west to the south component in November each year and via some contribution from the south component spawning biomass towards west component recruitment.
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    Calculating an informative prior distribution for the bias of hydro‐acoustic survey estimates of the biomass of the South African anchovy
    (2020) de Moor, Carryn; Coetzee, Janet; Butterworth, Doug
    A prior distribution for the bias of the hydro‐acoustic survey estimates of the biomass of the South African anchovy is developed by considering the bias associated with the individual sources of error.
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    A case for a higher critical biomass threshold in the anchovy‐only OMP‐ 18rev than in OMP‐18
    (2021) de Moor, Carryn
    de Moor (2021a,b) has provided a number of results for alternative candidate Management Procedures for an anchovy‐only OMP‐18rev. The SWG‐PEL TTG has suggested that the shape of the anchovy HCR should remain the same as that for OMP‐18 (de Moor 2018a) ...
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    Claim by Pichegru et al. that marine no-take zone benefits penguins remains premature
    (2010) Butterworth, Douglas; Brandao, Anabela; de Moor, Carryn; Robinson, William
    Pichegru et al. (2010), and a follow up comment by Ryan et al. (2010), make strongly stated claims that closures to pelagic fishing around islands with penguin breeding colonies lead to rapid improvements in those penguin populations. These claims are contested for a variety of reasons, including problems with the analysis method used. Claims that the pelagic fishing stocks are in poor condition, and that this is because of an absence of spatial management, are also contested, as are some other sweeping statements. The data currently available are too limited to be able to confirm or deny the claims made at this stage.
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    Comparing the 2018 survey estimated sardine biomass to carrying capacity.
    (2019) de Moor, Carryn
    This document details a calculation noted during the December 2018 Small Pelagic Scientific Working Group meeting which compared the recent survey estimate of sardine biomass to estimated carrying capacity, showing the survey biomass west of Cape Agulhas corresponded to approximately 3-4% of carrying capacity. A comparison between the alternative biomass “currencies” of total, spawner, effective spawner and survey estimated biomass is also given.
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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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    Considering alternative constraints to the anchovy Harvest Control Rule
    (2018-04) de Moor, Carryn
    As part of the development of OMP-18, alternative constraints in the anchovy Harvest Control Rule are investigated.
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    Considering the variability in directed sardine catches for the current OMP-18 reference case HCR
    (2018-03) de Moor, Carryn
    As part of the development of OMP-18, alternative ‘stable’ TAC and minimum TAC thresholds for the sardine HCR are explored.
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    The data used in the 2019 sardine assessment.
    (2019) de Moor, Carryn; Merkle, Dagmar; Coetzee, Janet; van der Lingen, Carl
    Data to which the 2019 assessment of the South African sardine resource is to be conditioned are listed
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    Density dependent movement of South African sardine
    (2018-03) de Moor, Carryn; Bergh, Mike; Butterworth, Doug S; Coetzee, Janet; van der Lingen, Carl
    A hypothesis that the movement of South Africa sardine from the west to the south coast is dependent on west coast biomass is revisited and a relationship proposed for use in future projections.
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    Developing informative prior distributions for the bias of hydro-acoustic survey estimates of the biomass of the South African round herring population
    (2022) de Moor, Carryn; Coetzee, Janet; Butterworth, Douglas
    Prior distributions for the bias of the hydro‐acoustic survey estimates of the biomass of the South African round herring are developed by considering the bias associated with the individual sources of error
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    Examination of redeye roundherring size and age data - towards developing a growth curve for the redeye stock assessment
    (2010) Durholtz, Deon; de Moor, Carryn; Geja, Yonela
    Redeye roundherring (Etrumeus whiteheadi) in South African waters is exploited by the pelagic purse seine fishery, which primarily targets anchovy (Engraulis encrasicolus) and sardine (Sardinops sagax). In spite of a relatively large adult biomass (averaging 1.3 million tons over the last 10 years), redeye catches have been low, averaging 50 000 tons per annum over the last 10 years. The redeye fishery is currently managed with an annual Precautionary Upper Catch Limit (PUCL) of 100 thousand tons. Furthermore, the Operational Management Procedure for sardine and anchovy (de Moor and Butterworth 2008) makes provision for some by-catch of adult sardine [3500 t] with redeye. Only once in the history of the fishery, has the industry managed to come close to this PUCL (92 thousand tons in 1997). In view of the under exploitation of the redeye resource and possibility of expanding the fishery, work has been directed at assessing the status of the redeye to support the management of the resource. Implicit in such an assessment is the requirement for information on the age and growth of the species.
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    Final Anchovy TAC and small pelagic TABs for 2018
    (2018-07) de Moor, Carryn
    The final anchovy TAC and associated small sardine TAB quotas depend on outputs from the pre-agreed Harvest Control Rules. However, these require observations from a winter hydro-acoustic survey which did not take place during May/June 2018. Final recommended quotas for 2018 are therefore calculated based on some reasonable assumptions.
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    Final anchovy TAC for 2019, using OMP-18.
    (2019) de Moor, Carryn
    Following the recruit survey results, the anchovy TAC for 2019 is revised to a final value of 350 000t.
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    Final baseline assessment of the South African sardine resource using data from 1984‐2018
    (2020) de Moor, Carryn
    The quantitative assessment of the South African sardine resource, using data from 1984 to 2018 has been finalised. This two mixing‐component model assumed no stock recruitment relationship during conditioning. The west component abundance was estimated to be about 12% of the historical (1984‐2018) average, with a biomass of 51 thousand tons in November 2018. The south component abundance was estimated to be about 95% of the historical (1984‐2018) average, with a biomass of 560 thousand tons in November 2018. Results are only given at the joint posterior mode.
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    Further results towards finalising HCRs for OMP-18.
    (2018-11) de Moor, Carryn
    The baseline Operating Models to be used to tune a new Operational Management Procedure for South African sardine and anchovy have been updated, and the performance statistics from a Candidate Management Procedure (“CMP5”) assuming only implicit spatial management are given. This “implicit” spatial management of the sardine fishery will be linked to ‘red flags’. Preventative red flags introduce corrective measures when the survey estimated biomass west of Cape Agulhas is low. Penalty red flags, with corresponding benefit green flags, are intended to introduce corrective measures if the future spatial distribution of catches differs from that seen historically and assumed when tuning the CMP. Results in this document should allow a selection of preventative and penalty/benefit flags in order to finalise OMP-18.
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    Generating the future proportion of directed sardine catch taken west of Cape Agulhas in the absence of explicit spatial management
    (2018-04) de Moor, Carryn; Butterworth, Doug S
    The relationship governing the proportion of directed sardine catch simulated to be taken west of Cape Agulhas during projections underlying the development of OMP-18 is updated. The relationship now differs for each draw from the posterior distribution.
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    Initial Directed Anchovy TAC and Sardine and Anchovy TABs for 2019, Using OMP-18
    (2018-12) de Moor, Carryn
    OMP-18 is used to calculated a TAC for the anchovy fishery and an associated small sardine TAB.