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

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

Initial applications of statistical catch-at-age assessment methodology to the Greenland halibut resource

In this initial report of the application of SCAA to the assessment of the Greenland halibut resource, a Baseline case with temporally invariant selectivity-at-age vectors is considered together with four variants which allow for serial correlation in survey residuals, temporal variability in commercial selectivity-at-age, and force asymptotically flat commercial selectivity. Only catch- and survey-based data are taken into account, as for the standard NAFO XSA-based assessment. In terms of recent trends, results vary greatly amongst these variants. Two are similar (though slightly above in absolute terms) to the recent negative prognosis indicated by the XSA assessment. Others however (including what reflects the best fit to the data obtained thus far) suggest more optimistic results, in particular indicating increases in abundance over the last decade

SCAA/ASPM assessments of white hake incorporating data to 2007

The preliminary SCAA/ASPM assessment of white hake presented to the previous GARM meeting is refined and updated, being advantaged by the greater availability of catch-at age information for the surveys and now also for commercial catches. Six assessment variants are presented, which reflect whether or not to take survey catchat-length information into account in fitting the assessment models, whether to use a Ricker or a Beverton-Holt form for the stock-recruitment relationship, and whether or not to constrain the multiplicative bias factor for the autumn NEFSC survey sweptarea estimates of biomass to preclude the possibility of herding. Imposing this last constraint leads to an appreciable deterioration in the overall likelihood of the model; the likelihood also indicates a slight preference for the Ricker over the Beverton-Holt form. Inclusion of the survey catch-at-length data in the likelihood leads to a considerable improvement in estimation precision, but also shows a marked overestimate by the model of the proportion of white hake of 20 cm and less in the autumn NEFSC surveys. Both variants are put forward as candidates to provide the basis for scientific management advice. The variant which includes the catch-at-length information reflects lesser abundance in absolute terms, a greater retrospective pattern, but also current abundance at a greater proportion of the MSY level, when compared to its counterpart. The estimation of current resource status in relation to the MSY level is critically dependent on the determination of the parameters which specify the starting (1963) numbers-at-age vector for the assessment.

Further CPUE-based assessments of the Greenland halibut resource using SCAA

Earlier CPUE-based SCAA assessments of the 2+3KLMNO Greenland halibut resource by Butterworth and Rademeyer are updated by taking account of some data adjustments and adjusting methodology for consistency with refinements of the SCAA methodology now applied to survey based. Results are qualitatively unchanged, indicating a resource currently at an intermediate level of depletion, and increasing over recent years in line with recent increases in CPUE