© 2004 by ICES/CIEM International Council for the Exploration of the Sea/Conseil International pour l'Exploration de la Mer
Developing and refining a joint management procedure for the multispecies South African pelagic fishery
a CEFAS Lowestoft Laboratory Pakefield Road, Lowestoft, Suffolk NR33 0HT, England, UK
b MARAM (Marine Resource Assessment and Management Group), Department of Mathematics and Applied Mathematics, University of Cape Town Rondebosch 7701, South Africa
*Correspondence to J. A. A. De Oliveira: tel: +44 1502 562244; fax: +44 1502 524511. e-mail: j.deoliveira{at}cefas.co.uk.
Pilchard (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.
Keywords: anchovy, management procedure, pelagic fishery, sardine, simulation testing, trade-off curves
Received 5 January 2004; accepted 9 August 2004.
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Introduction and background |
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 Top Introduction and background Methods of developing management...Results: comparing alternative...DiscussionReferences |
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Since their development within the International Whaling Commission in the late 1980s (Kirkwood, 1992, 1997), management procedures (MPs) have been developed (though not always implemented) for a number of disparate fisheries, from short-lived pelagic species exploited with purse-seine nets (e.g. anchovy) to long-lived demersal species captured by bottom trawls (e.g. orange roughy), and are steadily gaining wider acceptance (Butterworth and Punt, 1999; Kell et al., 1999; McAllister et al., 1999; Smith et al., 1999). In South Africa, MPs currently form the basis for the regulation of the three major fisheries (Geromont et al., 1999), the demersal trawl fishery for Cape hake (Merluccius capensis, M. paradoxus), the purse-seine fishery for pilchard, or sardine (Sardinops sagax), and anchovy (Engraulis encrasicolus, formerly E. capensis), and the fishery for west coast rock lobster (Jasus lalandii).
Butterworth et al. (1997) define an MP as a set of clearly defined and possibly quite simple rules, which translate data from the fishery into a regulatory mechanism (e.g. total allowable catch, TAC, or maximum fishing effort) each year. These rules are first tested by simulation to ensure reasonably robust performance in terms of expected catches and risk to the resource, given prevailing uncertainties about resource status and dynamics. The rules should be agreed upon by all parties concerned (scientists, industry, managers) before being implemented, and should specify exactly how the regulatory mechanism is to be calculated and what data are to be collected and used for this purpose. Once implemented, MPs should be left to operate "automatically" for periods of 3–5 years (i.e. scientists should not seek to alter the recommendations that they provide, unless very strong evidence pointing to such a need becomes available). After such a period, MPs should be reviewed and modified as necessary in the light of any changes in understanding of the resource or fishery that may have occurred in the interim (Butterworth et al., 1997; Cochrane et al., 1998).
MPs have been implemented in the South African pelagic fishery since 1991, although initially only for anchovy (De Oliveira, 2003, provides a historical overview). A joint MP was first implemented in 1994 to provide TAC recommendations for pilchard as well as for anchovy. This was necessary because, for reasons detailed later, there is an operational interaction between the catches of the two species (essentially, juvenile pilchard are taken as a bycatch in the anchovy fishery). The joint MP of 1994 accounted for this operational interaction by setting low TAB (total allowable bycatch) levels for pilchard bycatch, in order to ensure reasonable future TAC levels for the directed pilchard fishery, thus introducing a trade-off between pilchard bycatch and directed catch (Geromont et al., 1999). At this stage, the anchovy TAC was only used to calculate the pilchard TAB, and TAC calculations for anchovy were otherwise unaffected by TAC/B calculations for pilchard. It was soon clear, however, that attempting to control pilchard bycatch by setting low levels of pilchard TAB was causing the industry difficulty, because they were not able to fill the anchovy TAC without exceeding pilchard TAB levels. This led to the approach of setting realistic levels for pilchard TAB (related to both the anchovy TAC, and the pilchard–anchovy mix present in the fishing area), and using the anchovy TAC instead as a means of ensuring sufficiently small (but nevertheless realistic) pilchard TAB levels to make a more viable directed pilchard fishery possible (Geromont et al., 1999). Pilchard and anchovy exploitation levels were explicitly linked through trade-off curves, which allowed an overall trade-off choice to be made between desired average TACs for the two species. The resultant MP, introduced during 1998, but fully implemented from 1999 onwards, is referenced here as OMP99. (The "O" in "OMP" reflects Operational, to emphasize that the MP is implementable, not merely conceptual.)
OMP99 has since been refined and implemented as OMP02 in 2002. Refinements were necessary to permit the enhanced utilization of both resources (as demonstrated below). The associated analyses took account of a further 3 years of data, an additional within-season adjustment of the anchovy TAC (although implemented in practice, this had not formally been incorporated into OMP99), implementation error (necessary to address the fact that the pilchard TAB had not always been filled in practice, allowance for which could admit larger TACs for the directed pilchard fishery – the development of the OMP99 formulae had assumed that the pilchard TAB was always fully caught), and the introduction of a scheme whereby rights-holders in the pelagic fishery could each select their own preferred pilchard–anchovy trade-off. This paper provides a brief background to the pelagic fishery, and a description of OMP02, which explains the refinements introduced to allow enhanced utilization of both resources. Particular focus is given to the construction of trade-off curves, with details of some of the problems encountered and how they were addressed.
The fishery, and pelagic fish biology
Pilchard and anchovy form the mainstay of the South African pelagic fishery, and together with round herring (Etrumeus whiteheadi) have accounted for more than 90% of the mass of all small pelagic fish landed annually since the mid-1970s (Figure 1). The rapid rise of the pilchard fishery in the mid- to late 1950s, targeting mainly adult fish for canning, was followed by a collapse by the mid-1960s, and a move to anchovy through the introduction of nets with smaller mesh (Crawford et al., 1980). The anchovy fishery targeted mainly juveniles, which were processed in reduction plants (to provide fishmeal, oil, and fertilizer). Pilchard and anchovy are the only small pelagic species currently managed by a TAC, with separate TACs set for each.
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The close similarity between the spawning behaviour and movement of pilchard and anchovy has been attributed to their response to the environment (Crawford et al., 1980). Spawning by both species appears to be almost entirely confined to the austral spring and summer, the main upwelling season (Shelton, 1986; Hutchings et al., 1998). Spawning is concentrated on the western Agulhas Bank, with the spawning products of both species subsequently transported to food-rich nursery areas along the west coast by a shelf-edge frontal jet system (Figure 2; Shelton and Hutchings, 1982; Fowler and Boyd, 1998). Pilchard and anchovy juveniles first recruit to the fishery in March/April in the northern areas of the west coast, where the concentrations of plankton are greatest (Crawford et al., 1980). As the season progresses, there is a general southward movement, aided by inshore countercurrents, into newly productive areas, and eventually back to the spawning areas, completing the annual cycle. Pilchard are older at maturity, and have a longer lifespan, more protracted spawning season, and more extensive (than anchovy) migration patterns (including the midwinter "sardine run" along the coast of KwaZulu–Natal; Figure 2; Baird, 1971; Armstrong et al., 1991; Crawford, 1981a, b).
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Pilchard and anchovy shoal together during their first few months of life, when they are of similar size (Crawford et al., 1980; Crawford, 1981a), so directed fishing on anchovy as they migrate down the west coast on their way to spawning areas on the Agulhas Bank is inevitably accompanied by a bycatch of juvenile pilchard. This bycatch has a negative impact on the directed fishery for pilchard in subsequent years, because pilchard are more valuable as larger fish suitable for canning, and reach canning size only after they become mature. Juvenile pilchard are generally not targeted. Bycatches of pilchard are also made with targeted fishing for round herring, but those pilchard are mostly adult. Figure 3 provides an indication of the severity of the juvenile pilchard bycatch problem, particularly when anchovy abundance has been low (at a similar or lower level than pilchard). There exists, therefore, a fundamental trade-off in the pelagic fishery, between directed fishing for anchovy on the one hand (with its associated juvenile pilchard bycatch), and that for adult pilchard on the other. The concept of a joint MP provides a framework for quantifying this trade-off, subject to the constraint that acceptable levels of risk of resource "collapse" are not exceeded for either resource.
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Management
Management of pilchard and anchovy relies heavily on the results of two acoustic surveys held annually, one in November to survey the adult stocks, and one in May/June to survey recruitment for the year (Hampton, 1987, 1992). Prior to the implementation of OMP99, the typical management cycle for pilchard and anchovy would commence with TACs and TABs set at the start of the fishing season (January/February), on the basis of the results of the preceding November survey (provisional TAC/Bs were set before this, but they were minima, corresponding to fractions of the previous year's TACs and not based on any new data, and were over-ridden by the January/February TAC/Bs). The pilchard TAC remained in force (without alteration) for the remainder of the fishing season (officially ending in October, though usually extended to December), but the anchovy TAC was revised within the year for the following reasons:
- unlike the pilchard-directed TAC, which is intended to target adult pilchard (the next abundance estimate for which is provided by the following November survey, so there is no need for a within-season revision), the bulk of the anchovy TAC consists of juveniles, which start recruiting to the fishery along the west coast only from about April;
- a reliable estimate of the abundance of juvenile anchovy becomes available only once the recruit survey takes place in May/June;
- because it relates to fish yet to be assessed, the January/February anchovy TAC is based on the assumption that forthcoming anchovy recruitment will be average, an assumption that needs to be updated by the actual estimate when it becomes available;
- a scale-down factor is incorporated into the January/February anchovy TAC to safeguard against possible poor recruitment – this factor is no longer necessary once the recruit survey results become available;
- the additional flexibility offered by within-season revision of the anchovy TAC leads to better utilization of the anchovy resource – the alternative of a single TAC at the start of the year with no within-season revision would necessitate a more conservative approach to cater for the possibility of poor recruitment (Walters, 1989; Butterworth et al., 1993).
Calculation of the pilchard bycatch allowance (associated with the anchovy TAC) includes a component related to round herring (a fixed tonnage of pilchard is set aside for this), and another linked to the size of the anchovy TAC. The latter is a fixed proportion of this anchovy TAC, and is revised following the recruit survey because:
- the anchovy TAC is revised, so the bycatch allowance needs to reflect this;
- the pilchard bycatch taken when anchovy is targeted comprises juvenile fish, and must therefore depend on the size of pilchard recruitment – the fixed ratio (used to calculate the January/February pilchard bycatch allowance linked to anchovy) is adjusted to reflect this1.
One of the consequences of the introduction of the trade-off concept in OMP99 was that, if a viable pilchard fishery was to be guaranteed, limitations on juvenile pilchard bycatch, necessary to protect the directed pilchard fishery, would lead to smaller anchovy catches than that resource could actually sustain. In order to address this concern, the concept of a sub-season later in the year to target "clean" anchovy shoals was introduced. There are a few reasons why such an additional sub-season provides a practical basis to enhance anchovy catches.
- Juvenile pilchard and anchovy, which appear first in mixed shoals of fish of similar size when they recruit to the fishery, tend to separate later in the season, because the anchovy growth rate starts to slow before that of pilchard.
- This trend of increasing separation is evidenced by an examination of pilchard bycatch: anchovy ratios in the commercial catches, which show that, by August, these ratios have typically reduced to half their levels in May (De Oliveira, 2003).
- There is a narrow window between the times when the mixed shoals of juvenile fish separate (August/September) and when anchovy move offshore onto the wide Agulhas Bank to spawn (November), so becoming unavailable to the pelagic fleet, which operates close to the coast.
Even though the additional sub-season was predicated on the basis of near-pure anchovy catches, a modest pilchard TAB was nevertheless set for the additional sub-season (a fixed amount of 2000 t) in order to facilitate harvesting of the additional anchovy TAC. The anchovy TAC and associated pilchard TAB for the additional sub-season were clearly separated from the normal season, with observer coverage mandatory in the additional sub-season, to offset any incentive to discard catches with high levels of bycatch. The additional sub-season applied only to anchovy and any associated pilchard bycatch, whereas the pilchard-directed fishery and the pilchard bycatch associated with catches of round herring applied to the whole year. Figure 4 illustrates this typical annual cycle of events for the management of pilchard and anchovy, including this relatively recent modification of the additional sub-season for anchovy.
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Methods of developing management procedures |
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TopIntroduction and backgroundMethods of developing management...Results: comparing alternative...DiscussionReferences |
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The management features described in the previous section and summarized in Figure 4 necessarily dictate the structure and form of MPs for the South African pelagic fishery. The TAC/B equations and constraints given in Table 1 constitute the set of rules for OMP02. The simulation-testing framework (for details of this application, see De Oliveira, 2003) forms a key part of the development of a MP, and allows the performance of alternative MPs to be compared on the basis of summary performance statistics (described in Table 2).
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This framework essentially consists of an operating model to simulate the "true" dynamics of the resource, an assessment procedure used to estimate the parameters of this operating model, the MP rules (which include the TAC/B equations and constraints), and the summary performance statistics. In this case, 500 simulations of 20-year projection periods were carried out, each simulation representing a plausible "state of nature" (computationally, for each simulation, parameters of the operating model take on values from a single realization of the joint probability distribution given by the assessment procedure). Data typical of the type required by the MP rules in practice (and subject to the same error structure) were generated from the operating model and passed to the MP rules, which advised the TACs and passed them back to the operating model. At this stage, implementation error can be taken into account. For example, in this case the operating model generated future juvenile pilchard: anchovy catch ratios, to simulate the pilchard bycatch actually taken, which could turn out to be less than the TAB.
Each performance statistic provides a summary over all simulations of the performance of a particular MP over the projection period.
When comparing alternative MPs, performance of an MP is generally considered to be best when the risk of reducing abundance to a low level is small, the variations in TAC from year to year are low, and average catches are high. To consider how well these objectives are attained in quantitative terms, the following statistics (defined in Table 2) were considered:
- Depletion risk:
, 
, 
- TAC variability:
, 
- Average catch:
, 
, 
- TAC variability:
Naturally, these general objectives are in conflict, so trade-off choices are needed. In particular, it is not possible simultaneously to maximize the average directed pilchard and anchovy TACs to be expected, because of the juvenile pilchard bycatch with anchovy. A plot of average directed pilchard against average anchovy catches expected under a candidate MP is referenced below as a "trade-off" curve (see, for example, Figures 5–8).
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; (b) 
; (c) 
; (d) 
; (f) 
. The solid diamonds correspond to ß = 0.1, and the open squares to ß = 0.15.Another important aspect of MP development is to ensure robust performance of MPs across a range of alternative operating models, each reflecting a plausible representation of the fishery and resource dynamics compatible with available data. In other words, an OMP should allow reasonable attainment of objectives despite uncertainties about the fishery and resources. OMP02 was subjected to a number of such robustness tests, and detailed results can be found in De Oliveira (2003).
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Results: comparing alternative MPs |
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TopIntroduction and backgroundMethods of developing management...Results: comparing alternative...DiscussionReferences |
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Several candidate management procedures were investigated and the results presented to industry representatives, who helped narrow the number considered by advising on appropriate choices for constraint values. Nine of these candidate management procedures are considered here. For ease of presentation, the narrative focuses on the base-case procedure, M1, because during development this seemed the one most likely to be selected for implementation (in the form of a duly adopted OMP02), although such selection could be finalized only after due consideration of the results of all simulation tests.
For the purpose of this paper, management procedures can differ in the choice of constraint values and 
, and also in the choice of the control parameters 
ns, ads, and ß (Table 1). The former (constraints and ) reflect different pilchard–anchovy trade-off curves, whereas the latter correspond to different points on the same trade-off curve (see later discussion, and Figure 8). Therefore, one can speak of the M1 trade-off curve, which refers to the suite of management procedures with the same choice of constraints and as M1, or one can refer to M1 as the point on the M1 curve with the particular choice of control parameters associated with M1. The choice of constraint values and associated with the M1 curve are shown in Table 2. Where other candidate management procedures (or curves) are compared with M1 (or the M1 curve), only the constraint whose value has changed is shown, in Figure 8 and Table 3.
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, 
, and 
because ß > 0.1 (see Pilchard–anchovy (denoted P or A, respectively) trade-off curves were constructed by varying ß from 0 to 0.6 in steps of 0.01. For each value of ß, the procedure was tuned by alternately varying
ns and ads until 
and 
, so points on the trade-off curve are determined by either the pilchard or the anchovy (or both) depletion risk constraints being met. The specific choices of 0.1 and 0.3 duplicated levels considered appropriate in the formulation of previous OMPs. The associated abundance threshold for anchovy was, however, moved lower (from 0.2 K to 0.15 K) to allow for the fact that the extent of natural fluctuations in anchovy abundance had been estimated to be higher than previously believed (which meant in turn that the resource is robust to fluctuations down to lower levels of abundance than had previously been thought). The effect of this tuning is that, as ß is increased (moving from the bottom right to the top left of the trade-off curves in Figures 5–8), ns decreases (reflecting the trade-off between these two species), and ads increases (reflecting better utilization of the anchovy resource, which is possible because bycatch of juvenile pilchard is limited to a maximum of 2000 t in the additional sub-season). Therefore, even though ß, ns, and ads represent (apparently) three free parameters, their relationship above is such that only one free parameter (conveniently ß) remains, and serves as the parameter of the trade-off curve.
The value of ads was capped at 2, because the 
constraint (the maximum anchovy catch allowed during the additional sub-season) effectively ensures that there is nothing more to be gained from a choice exceeding this value. Furthermore, the constraint ads
ns was implemented to ensure consistency with the requirement that 
(Table 1). In Figures 5–8, the trade-off curves are mainly determined by the pilchard risk constraint coming into operation, except for the vertical segment on the right side, which is a reflection of the anchovy risk threshold coming into play.
Problems were encountered when constructing these trade-off curves (detailed in De Oliveira, 2003). One of these was that the 
constraints (minimum TACs) did not allow pilchard-directed catches to be zero when ß = 0, and the anchovy catches to likewise be zero when ns = 0. An additional problem was that, when ns = 0, ads = 2, which gave rise to the unrealistic situation that, even though the trade-off selection was to have no anchovy, anchovy would still be allocated in the additional sub-season. These problems were solved by replacing the minimum TACs 
with 
, shown in Table 1. These modifications essentially mean that, for ß choices reflecting a desired low pilchard catch to allow for high anchovy catches, the minimum pilchard TAC is reduced proportional to ß once ß drops below 0.1. A similar adjustment is made to ns for desired low anchovy catch situations. In addition, ads was reduced to zero as ß increased, in the manner detailed in Figure 5.2 of De Oliveira (2003).
The values for ß0 and 0 in Table 1 were selected on the basis of the results shown in Figure 5, which reveal the smoothest curves for ß0 = 0.1, with 0 = 0.4 a suitable intermediate value (too big a value would mean that 
would be reduced for most options for ns, while too small a value would start reducing the directed pilchard catch to guarantee the higher 
value).
Figure 6 is a plot of the M1 trade-off curve along with that associated with OMP99. The data updates and additional features now incorporated (M1) lead to a considerable improvement in the average catches possible from the fishery. The bars around the ß = 0.1 point on the M1 curve emphasize the considerable variation in annual catches associated with such MPs. Figure 7 illustrates the improvement in performance in terms of average catches over that of OMP99 as successive changes were introduced when developing the MPs presented in this paper. The additional sub-season allows further utilization of anchovy. It may lead to less anchovy, and hence less pilchard bycatch, being taken in the normal season, which allows for higher pilchard-directed catches, and thus improved utilization of the pilchard resource. A further general improvement in the utilization of both species is evident when account is taken of implementation error (allowing for the possibility that the pilchard TAB may not be fully utilized). The consequence of this is either to allow for more pilchard-directed catch (because in many years, not all the pilchard TAB will be used), or alternatively to take more anchovy catch (hence using a greater proportion of the pilchard TAB on average).
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for all curves, which is why curve (d) in this plot does not correspond exactly to M1 in Figure 8 contrasts the performance of M1 in terms of average catch with that for ten other MP candidates. For the same value of ß, increasing the maximum pilchard TAC constraint
(Panel a) increases pilchard catches, but reduces anchovy catch on average. However, reducing from 0.85 to 0.7 for a greater buffer against poor anchovy recruitment (Panel d) appears to have little effect on average catches, except for improving anchovy catches when an option reflecting low pilchard catches is selected. Decreasing the maximum downward adjustment constraint for pilchard 
(Panel b) is associated with a relatively large loss in anchovy average catch, but the trade-off curves appear to be relatively insensitive to changes in the equivalent constraint for anchovy 
(Panel e). Although decreases in the minimum TAC constraints 
do not appear to improve average catches by much (Panels c, f), catches are relatively sensitive to increases in these constraints, particularly for low values of ß in the case of anchovy. Table 3 repeats the results of Figure 8, showing the values for all summary performance statistics, but only for ß = 0.1375, which was the value of ß used for OMP99. These results are shown to provide some indication of the values of the summary statistics not shown in Figure 8. Of particular interest is that, under ß = 0.1375, smaller anchovy catches are obtained on average in the normal season (lasting roughly 8 months) than when there is also an additional season (lasting no longer than 4 months), for almost all MP variants. Decreasing the maximum percentage by which the pilchard TAC may drop from one year to the next (variant 3) also has a severe impact on anchovy catches and associated interannual variability in the normal season. However, all depletion statistics are fairly insensitive to the different MP variants considered. After joint consideration of such results by scientists and industry (including results from the robustness tests, which are not presented here), M1 was considered to reflect the best choice of operational constraints.
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Discussion |
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TopIntroduction and backgroundMethods of developing management...Results: comparing alternative...DiscussionReferences |
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Despite some initial difficulties related to delays in the rights allocation process for 2002, OMP02 was successfully implemented in the pelagic fishery, albeit in a slightly modified form from M1, in order to overcome these initial difficulties (see De Oliveira, 2003, for details). OMP02 represents a unique application of the MP approach. It tackles within a single framework the issues of:
- managing two highly dynamic resources whose associated fisheries are inter-dependent as a result of operational interaction and hence require an inter-species trade-off decision;
- taking due account of associated uncertainty in model hypotheses and data (through robustness tests not fully described in this paper, but reported in detail in De Oliveira, 2003).
A further feature that also formed part of OMP02, but was beyond the scope of this paper to consider, was a change in the way the trade-off decision (i.e. the point on the M1 trade-off curve eventually selected and implemented as OMP02) was made: from "externally" (as was done in the past for the fishery as a whole by the responsible government Minister) to "internally" (separately by each individual rights-holder, based on their own preferences). In a highly divergent industry, with some participants having sole interests in either canning (pilchard) or reduction (anchovy) operations, this was seen as a powerful tool to accommodate such differing interests in the two resources.
The MP approach, particularly in a multispecies context, has potential for application in fisheries under EU jurisdiction, and a number of EU projects have been based on such an approach (see, for example, Kell et al., 2002). More formal applications of this approach in the EU context may, however, prove to be more difficult than has been the case in South Africa for several reasons, including the political complexities implicit in the EU's Common Fishery Policy (the South African pelagic fishery operates entirely within South African waters, making it easier to manage). Another reason relates to a problem that has also surfaced in the South African pelagic fishery, namely that MPs have evolved into somewhat complex systems that few people (seldom including industry and managers) understand fully, despite their participation in the evaluation process. Although these complexities are necessary to maintain the flexibility needed for optimal utilization of resources (particularly so in the case of the South African pelagic fishery), they lead to the perception of MPs as mysterious "black boxes". Careful presentation and communication are required to offset consequent reservations that may arise about the approach.
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Acknowledgements |
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We thank South Africa's Department of Environmental Affairs and Tourism, Marine and Coastal Management, for their support of the first author while he was employed there, specifically including making freely available all the data on which this paper is based, and two anonymous reviewers for valued comments on an earlier draft.
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Footnotes |
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1 The earlier MPs used only the survey-based pilchard recruit estimate to adjust the fixed ratio, but later MPs incorporated the pilchard: anchovy ratio, as estimated from both the recruit survey and the industry's catches in May.
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References |
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