Browsing by Subject "Management procedure"
Now showing 1 - 5 of 5
Results Per Page
Sort Options
- ItemRestrictedDeveloping and refining a joint management procedure for the multispecies South African pelagic fishery(Oxford University Press, 2004) De Oliveira, J A A; Butterworth, Doug SPilchard (sardine) and anchovy are the main targets of South Africa's pelagic fishery. This fishery is the country's second most valuable in monetary terms, and produces the highest annual yield in terms of landed mass (in recent years, a combined catch of the order of 400 000 t). It is the most dynamic of South Africa's main commercial fisheries, because the species targeted are relatively short-lived, often occur in mixed shoals, and experience large fluctuations in abundance. Mixed shoaling causes operational problems for the fishery, because of the inevitability of juvenile pilchard bycatch (of more value as adults for canning) in the anchovy-directed fishery. This operational interaction implies a trade-off between allowable catches for the two species, and hence necessitates that they are managed together. The development of a joint “management procedure” (sensu IWC) for the two species is described. This provides a framework for quantifying this trade-off, subject to the constraint that acceptable levels of risk of “collapse” are not exceeded for either resource. Important new features incorporated in a revision of the procedure implemented in 2002, which have made appreciably enhanced catches from the resources possible, are described.
- ItemRestrictedIs the management procedure approach equipped to handle short-lived pelagic species with their boom and bust dynamics? The case of the South African fishery for sardine and anchovy(Oxford University Press, 2011) De Moor, Carryn L; Butterworth, Doug S; De Oliveira, J A AWorldwide, small shoaling pelagic fish manifest rapid and substantial natural changes in abundance. Is the application of a management procedure (MP), evaluated using simulation tests [i.e. a MP approach otherwise known as management strategy evaluation (MSE)], to recommend total allowable catches (TACs) with constraints desired by industry on the extent of interannual changes viable for such resources, particularly given the customarily lengthy MP evaluation process? This question is examined by considering the rapid boom and then bust situation that arose for the South African fishery for sardine (Sardinops sagax) and anchovy (Engraulis encrasicolus) across the turn of the century. Novel adaptations to the MP in place at the time of the boom allowed enhanced resource use during the boom period without compromising the risk of unintended depletion of the populations. Importantly a two-tier threshold system allowed the normal constraints on the maximum extent of interannual TAC reduction to be modified when TACs rose above the specified thresholds. The general protocol underlying the application of MPs for South African fisheries proved sufficiently flexible for the approach to continue to be applied, despite the unanticipated rapid fish population boom and then bust experienced.
- ItemRestrictedPurported flaws in management strategy evaluation:basic problems or misinterpretations?(National Inquiry Services Centre (NISC), 2010) Butterworth, Doug S; Bentley, Nokome; De Oliveira, Jose´ A A; Donovan, Gregory P; Kell, Laurence T; Parma, Ana M; Punt, Andre´ E; Sainsbury, Keith J; Smith, Anthony D M; Stokes, Kevin TRochet and Rice, while recognizing management strategy evaluation (MSE) as an important step forward in fisheries management, level a number of criticisms at its implementation. Some of their points are sound, such as the need for care in representing uncertainties and for thorough documentation of the process. However, others evidence important misunderstandings. Although the difficulties in estimating tail probabilities and risks, as discussed by Rochet and Rice, are well known, their arguments that Efron's non-parametric bootstrap re-sampling method underestimates the probabilities of low values are flawed. In any case, though, the focus of MSEs is primarily on comparing performance and robustness across alternative management procedures (MPs), rather than on estimating absolute levels of risk. Qualitative methods can augment MSE, but their limitations also need to be recognized. Intelligence certainly needs to play a role in fisheries management, but not at the level of tinkering in the provision of annual advice, which Rochet and Rice apparently advocate, inter alia because this runs the risk of advice following noise rather than signal. Instead, intelligence should come into play in the exercise of oversight through the process of multiannual reviews of MSE and associated MPs. A number of examples are given of the process of interaction with stakeholders which should characterize MSE.
- ItemRestrictedAn update on the development of a management procedure for the toothfish (Dissostichus eleginoides) resource in the Prince Edward Islands vicinity(2006) Brandão, Anabela; Butterworth, Doug STwo Operating Models (OMs) reflecting an “Optimistic” and a “Pessimistic” current status for the toothfish resource in the Prince Edward Islands region that were developed last year are updated given further data. These models are for use for initial trials of candidate Management Procedures (MPs) which could provide future TAC recommendations for this resource. Deterministic projections under a constant future catch suggest that the two scenarios will only be qualitatively distinguished in the shortterm by an increase in the mean length of longline-caught toothfish over the next five years for the “Pessimistic”, but not the “Optimistic” case. Accordingly the performance of a simple MP control rule based upon recent trends in both CPUE and this mean length is investigated. This MP is able to secure a faster increase in the TAC for the “Optimistic” case, and some recovery in abundance for the “Pessimistic” scenario, but neither is as appreciable as one might wish. Suggestions for future work are made.
- ItemRestrictedWhy a management procedure approach? Some positives and negatives(Oxford University Press (OUP), 2007) Butterworth, Doug SThe origin of the management procedure (MP) approach (sometimes termed management strategy evaluation), with its simulation testing of feedback-control algorithms as a necessary and structured basis for dealing with the inevitable uncertainties associated with fisheries assessments, is briefly reviewed. Also discussed are the advantages that overcome some of the difficulties of the “traditional” approach of coupling an annual “best” assessment to some harvest control rule, such as a failure to consider longer-term trade-offs properly. The MP approach does, however, also have disadvantages, such as the length of time typically required for its development and an argued inflexibility after implementation. Solutions that have been developed to overcome some of these difficulties are discussed.