Making management procedures operational—innovations implemented in South Africa
Marine Resource Assessment and Management Group, Department of Mathematics and Applied Mathematics, University of Cape Town, Rondebosch 7701, South Africa
Correspondence to É. E. Plagányi: tel: +27 21 6503200; fax: +27 21 6860477; e-mail: eva.plaganyi-lloyd{at}uct.ac.za
Plagányi, É. E., Rademeyer, R. A., Butterworth, D. S., Cunningham, C. L., and Johnston, S. J. 2007. Making management procedures operational — innovations implemented in South Africa. – ICES Journal of Marine Science, 64: 626–632.Operational management procedures (OMPs) have become an indispensable fisheries management tool in South Africa in light of their ability to consider the consequences of the main sources of assessment uncertainty. An overview is provided of the MP approaches applied to the major South African fisheries for hake, sardine and anchovy, and west coast rock lobster. As these are among the first OMPs to be implemented worldwide, some for periods longer than 10 y, they provide useful examples of some of the successes and problems encountered with the approach. Particular emphasis is given to some recent innovations and adaptations. These include moves to (i) joint two-species OMPs for the hake and sardine/anchovy resources; (ii) a reference set of weighted operating models for primary testing and tuning in preference to a single model; (iii) consideration of a "research-conditional" approach for hake to allow greater catches in the short term, conditional on research being implemented to resolve a key uncertainty; and (iv) incorporation of some ecosystem considerations by developing appropriate robustness tests (which link with moves towards an ecosystem approach to fisheries). Key lessons gained from experience over the past decade of OMP implementation in South Africa are summarized.
Keywords: management procedure, operating model, operational management procedure applications, research-conditional approach, uncertainty
Received 30 June 2006; accepted 12 January 2007.
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Introduction |
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One of the major challenges facing fisheries management systems is the need to develop and refine techniques for effectively addressing uncertainties related to scientific understanding, the environment, and the decision-making process. Management procedure (MP; Butterworth and Punt, 1999) or the analogous management strategy evaluation (MSE; Smith et al., 1999) frameworks are key examples of formal methods for addressing uncertainty issues, given their focus on identifying and modelling uncertainties as well as on balancing different resource dynamics representations (Sainsbury et al., 2000). The prefix "operational" (OMP) is customarily used in South African applications to emphasize that the MP is of a form ready for implementation to provide quantitative advice, rather than representing a concept only. A review of the MP approach is given in Rademeyer et al. (2007); but briefly, it involves an evaluation of the implications, for both the resource and the industry using the resource, of alternative combinations of monitoring data, analytical procedures, and decision rules to provide advice on management measures that are robust to inherent uncertainties in all inputs and assumptions used (Cooke, 1999). The simulation-testing frameworks used consist of operating models (OMs) that simulate alternative plausible scenarios for the "true" dynamics of the resource and generate "data" that are used by the MP modules. The final choice of an MP seeks to ensure reasonably robust performance in terms of expected catches and risk to the resource, given prevailing uncertainties about resource status and dynamics (De Oliveira and Butterworth, 2004).
The development of MPs has played a central role in the management of South African fisheries since the early 1990s (Punt, 1992; Butterworth et al., 1997; Cochrane et al., 1998; Geromont et al., 1999; Rademeyer, 2003; Johnston and Butterworth, 2005). Considerable success has been achieved in putting the approach into practice, OMPs being used systematically to regulate all three major fisheries: the demersal hake fishery (consisting of the deepwater Merluccius paradoxus and shallow-water M. capensis); the pelagic fishery focused on sardine (Sardinops sagax) and anchovy (Engraulis encrasicolus); and the fishery for west coast rock lobster (Jasus lalandii). In addition, they are being developed for Patagonian toothfish (Dissostichus eleginoides) in the Prince Edward Island EEZ, as well as for South African squid (Loligo vulgaris reynaudii) and south coast rock lobster (Palinurus gilchristi).
We present a brief overview of the three OMPs as currently applied (Table 1), the main focus being on recent innovations and adaptations. These include moves to (i) an OMP for the hake species combined and for the short-lived anchovy and sardine resources; (ii) a "reference set" of several (weighted) OMs for primary testing and tuning in preference to a single model; (iii) consideration of a "research-conditional" approach (Donovan and Hammond, 2004; Punt and Donovan, 2007) for hake to allow greater catches in the short term, conditional on research being implemented to resolve a key uncertainty; and (iv) incorporation of ecosystem considerations by developing appropriate robustness tests (linking with moves towards an ecosystem approach to fisheries; EAF).
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OMP case studies |
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Hake
Since 1990, the hake fishery has been managed (except for transitional periods) through an OMP with catch per unit effort (cpue) and research trawl survey abundance indices as input. The first OMP was applied to the resources along the west and south coasts separately until 1995. At that time, a revision proved necessary because a new GLM-standardized cpue series did not show the same (positive) trend as the less sophisticated cpue series formerly used as input. Also, changes in selectivity over time (as a consequence of the phase-out of illegal use of small-mesh net liners in the late 1980s) had to be accounted for because, as a consequence, the cpue series did not provide a consistent index over the full 1978–1995 period for which detailed data were available (Geromont et al., 1999).
In 1998, a revised OMP to provide recommendations for the total allowable catch (TAC) of the west coast component of the hake stocks was adopted with three main objectives for the following 10 y: (i) a high probability for the resource to recover to the MSYL, the level estimated to provide maximum sustainable yield (MSY); (ii) a low probability of a net decline in spawning biomass over this 10-y period; and (iii) a low probability of a decline in TAC early during the period. The two hake species remained aggregated for the west coast, but they had to be disaggregated for the south coast following the development of a longline fishery, primarily targeting the shallow-water M. capensis in that region. The previous justification for aggregating the two species had been based upon simulation tests that assumed that the species- and age-based selectivity of the fishery would remain unchanged (Punt, 1992). The development of the longline fishery invalidated this assumption.
A revised OMP for the south coast M. capensis component was adopted in 2000. The objectives were somewhat different from those for the west coast hake resource, because the shallow-water hake resource was assessed to be in a healthy state, well above the estimated MSYL. Therefore, the choice of a candidate MP primarily involved a trade-off between catch and catch rate, rather than between catch and resource recovery, as had been the case for the west coast component.
Both OMPs were based on f0.n (0.n controls the slope of the yield-per-recruit function associated with different exploitation rate strategies; values were 0.075 and 0.3 for west and south coasts, respectively) harvesting strategies coupled to a Fox (1970) production model (Geromont and Glazer, 1998; Augustyn, 2000), and were used until 2003. The intent to substitute these OMPs with fully species-specific versions has been overtaken by other considerations, including the realization that distinguishing stocks by coast was inappropriate. This has necessitated an interim approach, while the split between species is being fully accounted for, and one OMP is being developed for west and south coasts combined.
Sardine and anchovy
The anchovy fishery has been regulated using an OMP since 1991, and the first joint sardine and anchovy OMP was implemented in 1994 (De Oliveira et al., 1998), with TACs calculated based on abundance estimates from hydroacoustic surveys of recruitment each May and spawning biomass each November. The two species have to be managed jointly because the two fisheries interact. It is not possible to catch anchovy without an accompanying bycatch of juvenile sardine. In the first joint OMP, the total allowable bycatch (TAB) of sardine was based on the anchovy TAC, but the latter was otherwise unaffected by the sardine TAC (calculated as a proportion of the observed biomass) or sardine TAB.
The anchovy fishery encountered problems in operating within the constraints of the sardine TAB during a period of particularly low abundance of anchovy when the sardine bycatch proportion rose to unprecedented levels. To account for the interaction, the pelagic fishery OMP was updated in 1999 to allow a more workable sardine TAB to be set, dependent upon the estimated relative recruitments of the two species at any point in time. The rationale was to avoid loss of potential catch through early closure of the anchovy fishery because an unnecessarily low TAB limit had been reached. However, with the preference of industry for larger directed sardine catches, this meant that the total bycatch of juvenile sardine had to be kept low. Hence, lower TACs had to be set for anchovy than dictated by considerations of risk to anchovy alone. A trade-off curve was used to show explicitly the inverse relationship between the projected average anchovy catch, with its associated juvenile sardine bycatch, and the directed sardine catch, to facilitate the selection of what became known as OMP-99 (Geromont et al., 1999).
Since then, two further refinements have been necessary. OMP-02 (implemented in 2002) included a further 3 y of data and an additional within-season adjustment of the anchovy TAC, introduced to utilize the resource better by allowing additional catches late in the year when sardine bycatch proportions were very low. The simulation testing incorporated implementation uncertainty by making allowance for the sardine TAB not always being fully utilized. In addition, OMP-02 was constructed to allow individual rights-holders in the fishery to select their own preferred anchovy–sardine trade-off, rather than impose a fixed value universally (De Oliveira and Butterworth, 2004). However, unanticipated record levels of both sardine and anchovy recruitment shortly after the turn of the century prompted a refinement of OMP-02 earlier than planned, to allow the industry to take advantage of the (expected short-term) record biomass levels. The resulting OMP-04 was implemented in 2004 (Cunningham and Butterworth, 2005). Another new feature is that OMP-04 allows for upward adjustment to the sardine TAB set at the start of the year when sardine abundance is high. Therefore, the anchovy fishery is not unduly hindered by reaching the initial sardine TAB well before the final TAB, as well as the final anchovy TAC decided upon in midyear, based on the results from the annual May recruitment survey. The underlying problem is that the anchovy fishery depends primarily on recruits of the year, and year-class strength is not known before the pelagic fishing season commences. Hence, a conservative initial anchovy TAC, associated with an initial sardine TAB, is specified at that time, only based on the results from the November spawning biomass survey. This TAC and TAB may be increased (but not decreased) in midyear in light of results from the annual May recruitment survey.
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West coast rock lobster |
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The west coast rock lobster resource has been managed using an OMP since 1997, with two revisions (for details, see Johnston and Butterworth, 2005). Because the parameters for a population dynamics model could not be satisfactorily estimated at that time, the first OMP had a fairly simple empirical form, with TACs computed directly from three resource indices and tuned to provide a 20% biomass recovery over the period 1996–2006, with a 20% increase in the 1997 TAC relative to the 1996 TAC (the numerical choices were selected from a set of options presented to managers). The longer cpue and survey data time-series available in 2000 allowed a move from an empirical to a population model-based OMP. Updated stock assessment results revealed that the resource biomass was somewhat larger than previously estimated. Therefore, the 2000 OMP that was selected allowed for a lower target rebuilding rate of 14% over the period 1996–2006, with a 6% increase in the 2000 TAC over that of 1999.
The most recent (2003) revision is similar to the 2000 OMP, although the process undertaken to choose between alternative candidates involved consideration of performance statistics integrated over a "reference set" of different OMs (reflecting a plausible range of historical recruitment trends and predicted future trends in somatic growth and recruitment), weighted by their relative plausibilities based on expert judgement. The 2003 OMP also included features allowing refinement of the shape of the anticipated TAC trajectory, as well as a year-dependent parameter constraining interannual changes in TAC.
All three OMPs were based on commercial cpue, a fishery-independent monitoring survey index of abundance, and data on somatic growth rate. The general rationale for each input has been that, when the observed trend is positive, the TAC should be increased, and vice versa. The OMPs had an implicit feedback structure (and hence the ability to self-correct), and also incorporated constraints on the maximum interannual rate of change in TAC. In addition, "exceptional circumstances" were specified under which the OMP-generated TAC could be modified if necessary to offset the consequences of an unexpectedly "bad" or "good" event (Johnston and Butterworth, 2005). This is particularly important because this resource is known to have experienced a large reduction in somatic growth rate around 1990 and to be occasionally subject to sizeable "walkouts", during which lobsters emerge on beaches in response to low-oxygen events (usually dying in the process). In particular, the OMPs have emphasized the trade-offs between resource recovery and future catch levels. It is also important that they were able to respond rapidly to any evidence that somatic growth was returning to its earlier higher level, by way of increasing TACs in sympathy with such increased productivity.
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Recent innovations and adaptations |
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TopIntroductionOMP case studiesWest coast rock lobsterRecent innovations and...Summary of some key...References |
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Some of the more recent innovations provide clear examples of ongoing efforts to improve the applications of OMPs in South Africa and to address problems encountered, which might be borne in mind when developing MPs for other systems.
Joint two-species OMP
Whether as a consequence of fishing practices or ecological associations, the species taken by a fishery cannot always be managed effectively on an individual basis, in which case one OMP is required that combines information on more than one stock. Sardine and anchovy shoal together as juveniles, so any catch of juvenile anchovy is unavoidably accompanied by a bycatch of juvenile sardine. A larger anchovy TAC in one year could therefore have a negative effect on the potential (directed) catch of adult sardine some years later, and the industry is faced with a choice between the anchovy catch and the directed sardine catch. The two fisheries are managed jointly to account explicitly for this trade-off. The OMP was chosen from a trade-off curve (Figure 1), depicting the average predicted directed sardine catch against the average predicted anchovy catch and corresponding to the threshold values for risk criteria, to ensure that neither of the resources would be severely depleted (De Oliveira and Butterworth, 2004).
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The OMP for the South African hake resources has not always distinguished between the two species involved, because commercial catch records make no distinction between them. More recently, the two species have been assessed separately, but still within a single assessment framework. This has been accomplished by disaggregating past commercial catches based on the proportion-at-depth of various size classes of the two species in research surveys (Rademeyer and Butterworth, 2006).
To accommodate this additional information, the new OMP being developed is species-disaggregated and computes appropriate TACs for M. paradoxus and M. capensis separately, based on the updated data in combination with an updated assessment of each species. However, the species split in the overall TAC recommended by the MP module is not implemented by the OM, because in reality the industry cannot cope with species-specific TACs (Figure 2). Therefore, the OM uses the overall TAC and apportions this quantity between species by assuming a fixed fishing mortality ratio (no change in fishing patterns), although this likely means a different split of the TAC by species than suggested by the MP. This OMP is considered the most realistic way to proceed, given the practical difficulties of setting species-specific TACs and then monitoring compliance, with each catch having to be split by species on landing. This is an example of a method for including up-to-date information, but nonetheless tailoring the approach to account for limitations arising from the practicality of certain management options.
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A reference set of weighted OMs
The robustness of the final performance of any candidate MP is tested across a broad range of alternative plausible "states of nature" that are compatible with the available data and reflect uncertainties about resource dynamics and future data. Nevertheless, earlier testing has typically been dependent on replicate projections arising from a so-called reference case OM. Subsequently, it became apparent that a single OM is not always satisfactory, because different views may exist with regard to the specific OM that currently reflects the "best assessment" of the resource and the "best set of assumptions" for projections. The choice of OM may have important consequences for future catch performance, if managers opt for an MP selection criterion such as a particular probability of abundance not falling below a certain level in the projections. A workable solution is to select the major (typically 3–5) sources of uncertainty, to consider 2–3 alternative OM specifications for each, and to treat the resultant combination of OMs as a reference set, with tuning and performance measures evaluated across this set. Within the set, each member may be weighted by the product of the weights chosen to reflect the relative plausibility associated with the alternative specifications for each separate source of uncertainty, based on expert judgement.
This approach is taken in the current revision of the hake OMP, focusing on three aspects of the assessment, accounting for most of the key uncertainties regarding resource status and productivity (Rademeyer et al., 2007). A similar approach was applied in the selection of the 2003 OMP for west coast rock lobster, the reference set spanning three major sources of uncertainty and including 18 different OMs, with a different weight applied to each (Johnston and Butterworth, 2005).
Consideration of a research-conditional approach
During the current revision of the hake OMP, a problem arose: to satisfy risk criteria across the full range of possible bias in the estimates of the commercial offshore trawl catch by species (based upon survey ratios) would have required the selection of a conservative MP with relatively low catches. To solve this problem, thinking was guided by the innovative approach suggested by Donovan and Hammond (2004) and discussed further by Punt and Donovan (2007). This research-conditional approach would allow for a formal sidetrack within the OMP, provided specific uncertainties were diminished if a suitable research programme were carried out. Although this approach has yet to be formally adopted in this case, it illustrates how progress can be made by incorporating feedback not only within an MP, but also by being able to move between different MPs.
In the case of hake, consultation with the industry led to the following process being outlined.
- Provided the deep-sea trawling industry carried out a sampling programme of the species composition of catches taken at sea, then the question might be satisfactorily answered after a minimum of 2 y whether or not the existing basis for indirectly estimating the catch by species by extrapolating results from research surveys provided results that were close to the actual situation.
- OMP1 would be implemented immediately, which provided satisfactory performance on risk for scenarios, assuming that, currently, the species split in the offshore trawl catches is estimated correctly.
- OMP2 would come into effect after 3 y of operation of OMP1 if the planned on-board sampling programme had not been carried out satisfactorily, or if the data collected indicated that the current assumptions were invalid. OMP2 would be more conservative in its TAC recommendations in the longer term, because the combination of 3 y of OMP1 followed by OMP2 must achieve the same performance in terms of risk-related statistics as would OMP1 for the full projection period (Figure 3).
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In addition, exploratory simulations have been carried out to determine what the effect might be of adding measures to the management controls that secure the potential for adjustment of the fishing mortality ratio between the two species each year. These simulations suggested that substantial increases in overall catches could be achieved for the same risk level by broadly regulating the depths at which fishing takes place. This can be visualized (Figure 4) as a choice between options (i) and (ii), with a move to the latter indicated if management could indeed adjust the future ratio in the catches of the deepwater fleet. Although this approach is not considered a realistic option at present, the simulations proved useful in providing an incentive for investigations of new approaches to increase future catches without increasing risks to the resource.
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Incorporating ecosystem considerations
MPs also provide a strategic and practical framework for developing an operational EAF. However, data limitations are likely to restrict the number of multispecies models that reach the stage of being considered viable OMs to assist in the management of target species. Butterworth and Plagányi (2004) posit that, whereas there is an immediate role for ecosystem models as OMs to reflect and test alternative possibilities for the true underlying dynamics of a resource (or the utility of alternative forms of management), the development of tactical ecosystem models as the basis for computing specific harvest limits within MPs still seems some time off. Nevertheless, given the much larger uncertainties in ecosystem models, associated for example with appropriate choices for the functional forms and the large number of parameters to describe species interactions, there is no guarantee that scientifically defensible and practically useful conclusions concerning management advice can be drawn in all cases where this is attempted (Cochrane, 1998; Sainsbury et al., 2000).
Several ecosystem models for potential use within MP (and MSE) frameworks have recently been developed. For instance, the Atlantis modelling framework (Fulton et al., 2005) has been closely aligned to efforts to evaluate ecosystem indicators using a MSE approach. It can be configured flexibly to many different degrees of process detail for simulating "real world" dynamics. Within the South African sphere of influence, multispecies models are also being used in association with the MP approach. For instance, a spatial and multispecies MP is being developed for the Antarctic Peninsula krill-predator-fishery system (Plagányi and Butterworth, 2006a, b).
In general, the level of development of ecosystem models cannot yet provide quantitatively reliable predictions. Therefore, their implementation in MP evaluation exercises generally has been implicit only, by means of interim solutions. Rather than developing complicated multispecies testing models to contribute to the revised MP development process, IWC (1989) adopted a simpler method allowing for time dependence in the intrinsic growth rate and carrying capacity parameters of a single-species OM. This served to mimic the typical impacts on the modelled population of changing levels of predator and prey species. Similarly, MP testing procedures for the South African hake resource have used changes in single-species parameters (such as carrying capacity, K) as a surrogate for ecosystem effects (Rademeyer et al., 2005). Technical ecosystem effects such as bycatch concerns are also included in robustness tests. Attempts to incorporate bycatch, stock structure, and spatial aspects are increasingly being documented elsewhere (Punt et al., 2002; Dichmont et al., 2005).
Recently, there has been increasing pressure on the management system for the South African purse-seine fishery to ensure adequate escapement of anchovy and sardine by setting some threshold on stock abundance below which no catch can be taken to avoid excessive negative impacts on the breeding success of vulnerable predator species such as the African penguin Spheniscus demersus (Crawford et al., 2006; Cunningham and Butterworth, 2006). The development of the next pelagic OMP will be subject to diagnostic testing by considering, for example, the risk to penguin populations associated with different levels of pelagic fish catch. Attempts are being made to incorporate functional relationships between predators and prey into the OMs for sardine and anchovy, augmented by population dynamics model(s) for the predator(s) of concern.
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Summary of some key lessons learned |
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TopIntroductionOMP case studiesWest coast rock lobsterRecent innovations and...Summary of some key...References |
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Drawing on the relatively long and successful history of implementing OMPs in South African fisheries management, some key lessons learned are listed below.
- When difficulties arise in agreeing on a single OM, a pragmatic way forward is to select the major sources of uncertainty, consider alternative specifications for each, and treat the resultant combination of OMs as a reference set, with tuning and evaluation of meeting risk-related criteria across this set. This approach easily extends to EAF and is being used elsewhere in the multiple use management context (Little et al., 2006).
- The research-conditional approach appears to be a promising way forward when satisfying risk criteria across a full range of possible bias would require the selection of a conservative MP with an anticipated relatively poor performance. This approach allows a less risk-averse MP to be implemented provided that experiments are scheduled to resolve the current key uncertainties.
- MP testing procedures can use changes in single-species parameters as surrogates for ecosystem effects that are difficult to incorporate explicitly in OMs. Technical ecosystem effects can also be included in the robustness tests. These additions constitute a first step towards incorporating ecosystem aspects into practical fisheries management advice.
For almost 10 y now, TAC recommendations for all three major South African fisheries have been based on the outputs from OMPs, except when, on occasion, interim approaches have been applied. It is noteworthy that over this period, the responsible Minister has not deviated from any TAC recommendation arising.
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Acknowledgements |
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We gratefully acknowledge support from the National Research Foundation and Marine and Coastal Management, South Africa. We also thank many colleagues and associates, particularly Trevor Branch, André Punt, and Anabela Brandao, for useful discussions related to the work. The manuscript was greatly improved following inputs from Beth Fulton and an anonymous reviewer.
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References |
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R. A. Rademeyer, E. E. Plaganyi, and D. S. Butterworth Tips and tricks in designing management procedures ICES J. Mar. Sci., May 1, 2007; 64(4): 618 - 625. [Abstract] [Full Text] [PDF]
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