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Browsing Reports by Faculty "Faculty of Science"

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2018 GLMM-standardised Tristan lobster CPUE compared with the current OMP target levels (Itar)

Author: Johnston, Susan ; Butterworth, Doug S Date: May 2018 This document reports the 2018 GLMM-standardised Tristan lobster CPUE compared with the current OMP target levels that are in place for each island. Read more
The 2018 Operation Management Procedure for the South African Merluccius paradoxus and M. capensis Resources

Author: Ross-Gillespie, Andrea ; Butterworth, Doug S ; Glazer, Jean ; Fairweather, Tracey Date: 2019 Specifications and projection results for the 2018 Operational Management Procedure used for setting South African hake Total Allowable Catches are provided along with various background information, including details of the metarule processes. Read more
The 2018 Operational Management Procedure for the South African Merluccius paradoxus and M. capensis resources.

Author: Ross-Gillespie, Andrea ; Butterworth, Doug S ; Glazer, Jean ; Fairweather, Tracey Date: Oct 2018 Specifications and projection results for the 2018 OMP used for setting SA hake TACs are provided along with various background information, including details of the metarule process. Read more
The 2018 Operational Management Procedure for the South African sardine and anchovy resources

Author: de Moor, Carryn Date: 2018 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 Read more
The 2018 south coast rock lobster reference case operating model

Author: Johnston, Susan ; Butterworth, Doug S Date: 2019 This document details the current 2018 Reference Case Operating Model which is to be proposed to be used for simulation testing of a new OMP for South Coast rock lobster. Read more
2018 Updated horse mackerel assessments

Author: Johnston, Susan ; Butterworth, Doug S Date: Oct 2018 The assessments for the two hypotheses (reduced catchability and a one-off additional mortality event) for the recent reduced Desert Diamond catch rate are updated to take one further year’s data into account. The 2017 CPUE somewhat increased ... Read more
2018 updated south coast rock lobster assessment results

Author: Johnston, Susan ; Butterworth, Doug S Date: 2019 The 2017 assessment of the resource for South Coast rock lobster is updated given the two further years of catch-at-length data and one further year of CPUE data now available. Recruitment is estimated to have decreased over the last two ... Read more
2018 updated west coast rock lobster assessments

Author: Johnston, Susan ; Butterworth, Doug S Date: Nov 2018 A new set of 2018 assessments for all five super-areas for the west coast rock lobster resource has recently been completed. These provide the bases for projecting the resource forwards (in each super-area) under alternative future catches ... Read more
2020 sole dynamic Schaefer production model results

Author: Glazer, Jean ; Butterworth, Doug Date: 2020 The sole resource is modelled by a dynamic Schaefer production model which allows for a drop in the value of the intrinsic growth rate parameter from 2000 onwards. The model is fit to the available CPUE and survey abundance indices. These ... Read more
A summary of the South African sardine (and anchovy) fishery. MARAM/IWS/2019/Sardine/BG1

Author: Coetzee, J C ; de Moor, C L ; Butterworth, Doug S Date: 2019 The sardine fishery is an important component of the South African purse-seine fishery, the largest commercial fishery in South Africa (by landed mass). This fishery, initially established on the West Coast, but with some subsequent infrastructure ... Read more
The acceptable level of risk for the South African sardine resource.

Author: de Moor, Carryn Date: 2019 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 ... Read more
Addendum to: Further 2018 west coast rock lobster assessment and associated biomass projections results

Author: Johnston, Susan ; Butterworth, Doug S Date: Aug 2018 This Addendum provides further results for the two-step TAC phase down option, where the distribution of the TAC amongst the Super-areas is changed. The shifts from A8+ are to either or both of A34 and A7. The Results are shown in the Tables ... Read more
Adjustments made to recent catches and CPUE for West Coast Rock Lobster in Areas 3+4 and 5+6

Author: Butterworth, Doug S ; Glazer, Jean ; Johnston, Susan ; van Zyl, Daniel Date: Aug 2018 During the 2017/18 fishing season, some catches made in Area 3+4 by trapboats were landed in Area 5+6 as hoopnet catches. This document reports the methodology used and the results obtained from an attempt to correct the catches reported for ... Read more
Age-Structured Production Model (ASPM) assessments of the Alfonsino (Beryx splendens) resource in the SIOFA area of the Southern Indian Ocean

Author: Brandão, Anabela ; Butterworth, Doug ; Johnston, Susan Date: 2020 An Age-Structured Production Model is applied to assess the Alfonsino (Beryx splendens) resource in the West and East SIOFA areas of the Southern Indian Ocean. Data limitations restrict these applications to deterministic variants, which ... Read more
Analysis of tagging data of the toothfish (Dissostichus eleginoides) resource in the Prince Edward Islands vicinity

Author: Brandão, Anabela ; Butterworth, Doug S Date: Mar 2018 Some simple analyses of the tag-recapture data available for the PEI toothfish resource are undertaken. Somatic growth rate seems to be less than that in Subarea 48.3 which has previously been assumed for assessments of the PEI resource. ... Read more
Application of a minor variant of OMP-2014 to the updated base case operating model for the SCRL resource

Author: Johnston, Susan ; Butterworth, Doug S Date: 2019 Projected TAC outputs for OMP-2014 at that time are compared to those that subsequently eventuated. A minor variant of OMP-2014 is applied to the adjusted base case SCRL operating model for a number of values for the central parameter CPUE_targ. Read more
An approach to weighting the various Operating Models in a Reference Set in inverse relation to the similarity of their results

Author: Vrancken, Candysse ; Butterworth, Douglas Date: 2017 How to weight results from different OMs in getting a “best” representation across their differing results is a problem not only in fisheries but also in Climate Change. We attempt here to borrow an approach from the latter field and compare ... Read more
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.

Author: de Moor, Carryn Date: 2019 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 ... Read more
Assessment of the toothfish (Dissostichus eleginoides) resource in the Prince Edward Islands vicinity to include data from 1997 to 2017

Author: Brandão, Anabela ; Butterworth, Doug S Date: Oct 2018 The assessment of the Prince Edward Islands (PEI) toothfish (Dissostichus eleginoides) resource carried out by Brandão and Butterworth (2017) is updated to take further data now available for 2017 into account. This update also incorporates ... Read more
Basis suggested, following task group discussions, for determining the 2019 sardine directed TAC and by-catch TAB

Author: Butterworth, Doug S ; Coetzee, Janet Date: 2019 A list is put forward of suggestions and criteria to provide a basis for developing a sardine directed TAC and by-catch TAB for 2019 Read more

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