Browsing by Author "Rademeyer, Rebecca"

Now showing 1 - 7 of 7
  • Thumbnail Image
    Item
    Open Access
    Can the wide range of resource behaviours evident across the ABFT MSE interim grid of OMS be “tamed” by the feedback control provided by a CMP?
    (ICCAT, 2020) Butterworth, Doug; Rademeyer, Rebecca
    The interim grid of OMs is used to explore the 30-year projection behaviour for catches and the status of the eastern and western ABFT stocks (expressed in terms of their abundance relative to dynamic Bmsy by the Br30 statistic) for both constant future catches and some simple “Fixed Proportion” CMPs. If current TACs continue unchanged, both stocks are rendered extinct for about 20% of the 96 OMs of the interim grid. Fortunately, however, this undesirable feature can be “tamed” through the feedback control mechanism of the CMPs, which can prevent occurrences of extinction. The trade-off between catches and final abundance across the OMs, as the control parameters of the CMPs are varied from lower to higher harvesting intensities, are illustrated. The need to focus on CMP refinement to reduce the spread of the Br30 distributions across the OMs is stressed. Priorities for future work are listed; these include the use of these CMP results to indicate which of the uncertainty axes in the current grid have the greater impacts on MP performance. The interim grid provides a useful framework to continue this work, even though (together with advice on final management objectives and desired trade-offs) it still awaits finalisation.
  • Thumbnail Image
    Item
    Open Access
    Effect of missing values from the Canadian spring and fall surveys of NAFO Divisions 3LNO on the calculation of the TAC using the Greenland halibut HCR
    (2022) Regular, P M; Butterworth, Douglas; Rademeyer, Rebecca
    To test the impact of ignoring recent missing abundance indices for Greenland Halibut in NAFO divisions 2+3KLMNO on applying the accepted HCR for this population to provide a TAC recommendation for 2023, the impact of similar exclusions in the past is examined and found to be small. To further test of the impact of the missing 2021 index from the Canada Fall 3LNO survey, a range of pessimistic to optimistic abundance index values were assumed to assess the plausible range of impact this one value might have on the TAC computation. The range of the resultant TACs is small, and the difference of the impact of TACs at either end of this range on exploitable biomass projections for the next year is found to be negligible. Hence, it is argued, the minimalist and straightforward approach of simply ignoring the missing 2021 Canadian Fall 3LNO result in the four-survey version of the HCR agreed last year would be a defensible and appropriate approach to the required adjustment of the implementation of this HCR to provide a TAC recommendation for 2023.
  • Thumbnail Image
    Item
    Open Access
    Improving communication: the key to more effective MSE processes
    (2019) Miller, Shana; Anganuzzi, Alejandro; Butterworth, Doug S; Davies, Campbell; Donovan, Greg; Nickson, Amanda; Rademeyer, Rebecca; Restrepo, Victor
    The use of management strategy evaluation (MSE) to design and test candidate fisheries management approaches is expanding globally. Participation of managers, scientists, and stakeholders should be an integral component of the MSE process. Open and effective communication among these groups is essential for the success of the MSE and the adoption of the management approach based on it. The highly technical nature of MSE and newness of the approach to many audiences present considerable communication challenges and have, unfortunately, slowed progress in some cases. We draw on diverse experiences with MSE to identify two areas in which the implementation of MSE in multinational fora may be improved: (i) the use of formally constituted “intermediary groups” as a forum for exchange at the management–science interface and (ii) the development of engaging, yet uncomplicated, visual communication tools for conveying key results to different audiences at each stage. While our focus is the MSE processes underway in the regional fisheries management organizations for tunas and tuna-like species, the advice provided is also pertinent for other fisheries, international and domestic alike, pursuing MSE.
  • Thumbnail Image
    Item
    Open Access
    Projections under the selected Management Procedure for Greenland Halibut
    (2018) Rademeyer, Rebecca; Butterworth, Doug S
    Figures 1 to 5 plot the projected 95, 90 and 80% probability envelopes as well as the projected medians under the revised Management Procedure adopted in 2017 for Greenland Halibut for a series of quantities (annual catch, recruitment, and the five survey indices of abundance together with the composite index which combines the five) for the following SCAA-based Operating Models: - OM1 (the Baseline, using data including 2016 and the O3 set of surveys), - OM2 (larger recruitment variability with R=0.6), - OM4 (loRec – the recruitment of the first 8 years of the projections are at 50% of the level predicted by the stock-recruit function), - OM7 (110TAC – future catches are taken as 110% of the TAC) and - OM8 (noplus – zero selectivity for the plus group). The probability envelopes have been computed from a 9-point averaging approach (see Appendix below) from 500 replicates. The 9-point approach was selected as it offered a reasonable trade-off between preserving trend and eliminating “jaggedness” from Monte Carlo variation.
  • Thumbnail Image
    Item
    Open Access
    Refinements of the BR CMP as of April 2022
    (2022) Butterworth, Douglas; Rademeyer, Rebecca
    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.
  • Thumbnail Image
    Item
    Open Access
    Specifications of the South African hake 2019 Reference Case assessment
    (2019) Rademeyer, Rebecca; Butterworth, Doug S; Ross-Gillespie, Andrea
    This document provides the detailed and comprehensive specifications for the 2019 Reference Case assessment model for the South African hake resource, including the algebraic specifications for the assessment model, tables listing the input data and key assessment results for the Reference Case. Note that the RC results presented here do not correspond to the most recent assessment results (as the specification document has not been updated since the last assessment update). Results for the most recent update for the 2019 RC can be viewed in FISHERIES/2019/OCT/SWG-DEM/22rev.
  • Thumbnail Image
    Item
    Open Access
    Updated SCAA Base Case assessment for Greenland halibut
    (2020) Rademeyer, Rebecca; Butterworth, Doug S
    The Statistical Catch-at-Age (SCAA) assessment methodology applied to the Greenland halibut resource in 2017 is updated to take further data now available for the years 2017 to 2019 into account. Results are reported for a Base Case corresponding to that considered in 2017, and some sensitivities related to uncertainties about some recent catch-at-age data. Apart from a slight downward shift in the overall biomass scale, results are essentially unchanged from those in 2017, and the sensitivity runs show little difference from the Base Case. There has been a recent slight downward trend in exploitable biomass, but this is likely to reverse quite soon given that the estimates of incoming recruitment are of above average strength. New data and recent resource trends are consistent with predictions made in 2017 when a revised management procedure for Greenland halibut was adopted.