126 research outputs found
Age-reading error matrices for Merluccius paradoxus and M. capensis
The revised methodology for hake assessments currently under development requires inputs on the
relative biases amongst different readers of hake ages from otoliths, and the extent of variability of
these readings. This document details the methodology applied to determine these ageing error
matrices
Taking account of the new longline data in the updated Reference Case for the South African hake resource
This paper summarises the assumptions that have been made in previous hake assessments concerning the longline data and makes suggestions for the updated Reference Case
Management procedures for the South African hake resource in the 2000s
Includes bibliographical references.The two-species South African hake fishery (deep-water Merluccius paradoxus and shallow-water M. capensis) has been managed using Operational Management Procedures (OMPs) since 1990. This thesis summarises the development of two OMPs: OMP-2007, which was the basis for the 2007 to 2010 Total Allowable Catch (TAC) recommendations, and OMP-2011, which was first used for the 2011 TAC recommendation and which is intended to extend to 2014. The Operating Models (OMs) used for simulation testing of OMP-2007 were based on the first fully species-disaggregated coast wide assessment of the South African hake resource
Some comments on "Illustration of the role of the pre-1978 species splitting assumptions in hake assessments"
OLRAC (2009) notes the importance of the assumption for the pre-1978 species split of the offshore
trawl catches in the assessment results and suggests that the changeover from a mainly capensis fishery
to a mainly paradoxus fishery occurred later than what is assumed in the Reference Set
An initial attempt at a spatially structured stock assessment for the South African hake resource including movement based on a gravity model.
The movement model for assessing the South African hake populations which was
presented to last year’s review workshop is simplified by applying the “gravity” method to
model movement. This reduces the numbering of movement parameters estimated from
234 to 68. This results in recent biomass estimates which are slightly more precise and
somewhat lower in both absolute terms and relative to estimated pre-exploitation levels.
Areas for possible future research are discussed briefly
2012 Routine update of the South African hake reference case assessment
This paper presents a routine update of the South African hake Reference Case assessment (RS1) (Rademeyer and Butterworth, 2010), including new commercial (catches and CPUE) and survey (abundance estimates and length distribution) data. This analysis does not include post-2009 commercial length distribution data whose finalisation is still in progress
Refinements of the BR CMP as of April 2022
The BR CMP is adjusted in a few respects, most importantly by allowing limited temporal
dependence in the values of the control parameters over the first few years of management, to
allow for smoother transitions in the TACs from 2022 to 2023. This was necessitated especially
by the now higher West area TAC for 2022 included in the updated package. Results are provided
for the four basic development tunings, plus one variant for one of those tunings where the default
maximum TAC decrease constraint is reduced from 30% to 20%. Suggestions are made of areas
for possible improvement in performance, which would require some further refinements of this
CMP
A note on the sensitivity of hake assessments to the choice of the central year for the shift from a primarily M. Capensis to primarily M. Paradoxus fishery
At the February 18 meeting of the DWG, there was a request from Industry for further assessment runs for different choices for the central year for the switch from a primarily M. capensis to a primarily M. paradoxus deep-sea trawl fishery.
This note reports the results from such assessment runs for a set of choices for this central year ranging from 1940 to 1972. Fig. 1 shows time trends of the proportion of M. capensis in the catch for these alternatives. These results are repeated for three different choices for the natural mortality vector assumed: both the high and low options put forward for the Reference Set (RS) in Rademeyer and Butterworth (2010), and also for the intermediate vector chosen for the Reference Case (RC = RS1).
All runs show results for a modified Ricker choice for the stock-recruitment relationship, as for the RC
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