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APPENDIX I - Fishery checklist

The Marine Stewardship Council ( has developed a series of principles and criteria which allow the fishery management to be measured against the FAO Code of Conduct for Responsible Fisheries.

Many of the criteria can be directly related to CITES requirements. However, the MSC and FAO Code of Conduct go well beyond CITES minimum requirements in their definition of good management.

By applying good management defined by the Code of Conduct, not only will CITES requirements be met, but various pressures leading to overfishing will be removed.

The principles, criteria and guidelines are provided herewith a commentary for conch and can be used to assess a fishery to see how well management is being applied. All the issues raised should be considered by the fishery managers in developing a sound management system. The priority of requirements (first and second) is also listed. (The guidelines have been adapted from Moody Marine Ltd. Scoring guidelines are available, with other documentation, from the Marine Stewardship Council website Those components considered to be most relevant to the CITES regulations and requirements are Principle 1 and all its sub-components, 2C, 3A, 3B1 and 3G.

Principle 1:

A fishery must be conducted in a manner that does not lead to over-fishing or depletion of the exploited populations and, for those populations that are depleted; the fishery must be conducted in a manner that demonstrably leads to their recovery.

Scoring Guideline




There should be sufficient information on the target species and stock to allow the effects of the fishery on the stock to be evaluated.


Can the species be readily identified?




Is the life history of the species understood?


Yes, although where larvae may come from in each case is not necessarily known. (i.e. a stock may be shared with neighbouring fisheries).


Is the geographical range of the target stock known?


In all cases a management unit can be defined relatively easily using depth contours. Adult stocks are not thought to migrate through deep water.


Is there information on fecundity/recruitment and factors causing natural mortality?


There is considerable general biological information available on conch.


Is information collected on the abundance/density of the stock?


This is necessary either through CPUE or surveys.


Are there other fisheries identified in the area that are not subject to certification?


Shared stocks and illegal, unrecorded fishing need to be taken into account when setting controls and managing the fishery.


There should be sufficient information on the fishery to allow its effects on the target stock to be evaluated


Is fishery related mortality recorded/estimated (including landings, discards and incidental mortality)?


All catches need to be recorded or well estimated


Is fishing effort recorded/estimated?


A high proportion of effort and its associated catch needs to be recorded


Are fishing methods known throughout the fishery?


The different vessels and their fishing techniques need to be registered.


Are gear types and selectivity known for the fishery?



Is information available on the variations in gear selectivity and catchability over time?


The main issue for selectivity is water depth and fishing location.


Have appropriate reference levels been developed for the stock?


Are there appropriate target reference points?


Appropriate optimal socio-economic levels of exploitation need to be identified.


Are there appropriate limit and precautionary reference points or decision rules?


Limit reference points and decision rules need to be related to management actions, such as rebuilding programs.


Do reference points meet acceptable international standards?


Any reference points and rules need scientific justification.


Is there a well-defined and effective harvest strategy to manage the target?


Is there a mechanism in place to contain fishing effort as required?


The capability of management to control effort and fishing capacity needs to be in place and demonstrated.


Are clear, tested decision rules set out?


Decision rules need to be agreed with all parties and clearly documented in the management plan.


Are appropriate management tools specified to implement decisions in terms of input and/or output controls?


The prospective fishery controls need to be specified. These controls should apply a limit to the total catch.


Is there a robust assessment of stocks?


Are assessment models used?


One or more operational model should be developed. The same or different models may be used to estimate parameters, and therefore indicators and reference points.


Does the assessment take into account major uncertainties in data and have assumptions been evaluated?


Models fitted to data should at the very least indicate confidence intervals on results.


Are uncertainties and assumptions reflected in management advice?


Uncertainties and assumptions need to be documented and where possible their implications assessed. Management controls need to be robust to the main uncertainties.


Does the assessment evaluate current stock status relative to reference points?


The main task of each assessment should be to define stock status and offer management advice to achieve the various objectives.


Does the assessment include the consequences of current harvest strategies?



Is the stock(s) at appropriate reference level(s)?


Is the stock(s) at or above reference levels?


The status of the stock needs to be defined where this has not been done. This should lead automatically to pre-planned actions if the stock is found to be below limit or precautionary reference points. Actions should be specified in the management plan.


If the stock is below the limit reference, is rebuilding specified in the decision rule being implemented?


Principle 2:

Fishing operations should allow for the maintenance of the structure, productivity, function and diversity of the ecosystem (including habitat and associated dependent and ecologically related species) on which the fishery depends

Scoring Guideline




Is there adequate determination of ecosystem factors relevant to the geographical scale and life-history strategy of the target species?


Are the nature and distribution of habitats relevant to the fishing operations known?


Generally mapping of relevant habitats for this species is straightforward. If density surveys are to be used, some sort of map is necessary.


Is information available on non-target species affected by the fishery?


Fishers will probably take by-catch opportunistically. Such by-catch needs to be monitored. It may be necessary to consider conch as part of a multispecies fishery.


Is information available on the position and importance of the target species within the food web?


There is predation information, but not enough for ecosystem models.


Is there information on the potential for the ecosystem to recover from fishery related impacts?


Unless there is monitoring of several key species, this will be difficult to assess. Even where such monitoring takes place, relating changes specifically to conch fishing will be difficult. In general, the ecosystem may be considered not to be sensitive to conch abundance if overfishing is not occurring.


Are general risk factors adequately determined?


Is information available on the nature and extent of the by-catch (capture of non-target species)?


This would need to be monitored. Divers sometimes catch other species opportunistically.


Is the fishery conducted in a manner which does not have unacceptable impacts on recognized protected, endangered or threatened species?


Is there information on the presence and populations of protected species?


CITES Appendix II is relevant here. Any potential impacts on hard corals and seagrass should also be considered (e.g. from shell discards). It is unlikely that there will be significant impact on other species.


Are interactions of the fishery with such species adequately determined?


Impacts will have to be reviewed. If there are any impacts they will have to be quantitatively assessed. This would involve an infrequent mini-assessment of the species involved.


Is information available on the extent and significance of such interactions?



Is there adequate knowledge of the effects of gear-use on the receiving ecosystem and extent and type of gear losses?


Is there adequate knowledge of the physical impacts on the habitat due to use of gear?


This should be negligible unless fishers are anchoring on coral reefs or discarding shells in inappropriate places.


Is any gear lost during fishing operations (ghost fishing)?


Unless gears are set nets or traps, this will not apply.


Do assessments of impacts associated with the fishery including the significance and risk of each impact, show no unacceptable impacts on the ecosystem structure and/or function, on habitats or on the populations of associated species?


Have all the significant effects of the fishery on the ecosystem been identified?


Main impacts are likely to be discard of shells, discard of tissue after processing and by-catch or multispecies effects.


Does the removal of target stocks have unacceptable impacts on ecosystem structure and function?


If recruitment is relatively unaffected, it is unlikely the fishery will be having a significant impact.


Does the removal of non-target stocks have unacceptable impacts on ecosystem structure and function?


By-catch is unlikely to be important. If conch forms part of a multispecies fishery, all the main species will have to be assessed.


Does the fishery have unacceptable impacts on habitat structure?


Discards of shells may cause problems or may enhance habitat as artificial reefs.


Is associated species diversity and productivity affected to unacceptable levels?


If any potential impacts are identified they will need to be addressed by a research programme.


Are strategies developed within the fisheries management system to address and restrain any significant impacts of the fishery on the ecosystem?


Are levels of acceptable impact determined and reviewed?


This would require some scientific assessment of acceptable impact. This would follow standard environmental impact procedures.


Are management objectives set in terms of impact identification and avoidance/reduction?



Are management measures in place to modify fishery practices in light of the identification of unacceptable impacts?


Principle 3:

The fishery is subject to an effective management system that respects local, national and international laws and standards and incorporates institutional and operational frameworks that require use of the resource to be responsible and sustainable

Scoring Guideline




Does a management system with clear lines of responsibility exist?


Are organisations with management responsibility clearly defined including areas of responsibility and interactions?


Setting up the authorities may require legislation. An independent scientific authority needs to be designated with the necessary resources to conduct assessments. The management authority should include a transparent decision making mechanism.


Does the management system contain clear short and long-term objectives?


These should be clearly stated in the management plan. Objectives should be compatible with CITES Appendix II.


Do operational procedures exist for meeting objectives?


Controls need to be specified which limit the amount of fishing which can be conducted. There needs to be an enforceable method for applying controls, such as vessel register and catch monitoring.


Are there procedures for measuring performance relative to the objectives?


Controls must demonstrably reduce catches where necessary. Catches therefore must be monitored.


Do measures exist for implementing a precautionary approach in the absence of sufficient information?


Precautionary limits must be applied based on rapid information gathered immediately. Length frequency, fisher interviews and density surveys will provide information rapidly enough for an initial assessment. These assessments can be updated as more information becomes available.


Does the system include a consultative process including affected parties?


Some formal system whereby the fishers and the fishing industry can raise issues must exist.


Is there an appropriate mechanism for the resolution of disputes within the system?


A mechanism needs to be defined where by interested parties can make formal and transparent representation on issues in the fishery.


Does the management system have a clear legal basis?


Is the fishery consistent with International Conventions and Agreements?


Legislation may eventually need to be updated. However, policy statements in line with regulations set according to scientific advice should be initially sufficient. Clearly, CITES figures largely in this.


Is the fishery consistent with national legislation?


The fishery activities should be compared against legislation. Any conflicts need to be assessed through recorded meetings with fishers and industry.


Does the system observe the legal and customary rights of people dependent upon fishing?



Are fishers aware of legal requirements?



Does the management system operate in a manner appropriate to the objectives of the fishery?


Does the system include subsidies that contribute to unsustainable fishing?


Any subsidies for fishing may severely undermine sustainable fisheries. In general, it needs to be proved that such subsidies do not exist.


Does the system include economic/social incentives that contribute to sustainable fishing?



Is the system consistent with the cultural context, scale and intensity of the fishery?


In general this will not be a problem unless there is a significant number of commercial foreign vessels.


Does the management system include measures to achieve objectives for the target stock?


Are the resource and effects of the fishery monitored?


Catch, effort, mean meat weight, size frequency and density surveys should allow the scientific authority to monitor most of the changes in the fishery.


Are results evaluated against target and limit reference points?


This will require the regular evaluation of relevant indicators


Do procedures exist for reductions in harvest in light of monitoring results.


There should be a demonstrable ability to control fishery harvest levels.


Does the management system include measures to achieve objectives for the affected ecosystem?


Are measures in place to address (avoid or minimize) significant environmental impacts?


The management will need to review how and where shells and tissue are discarded.


Do fishing operations implement appropriate fishing methods designed to minimize adverse impacts on habitat, especially in critical or sensitive zones such as spawning or nursery areas?


It is unlikely that fishing practices have a significant impact on the habitat.


Are no take zones appropriate and, if so, are these established?


This is a decision for management whether to use no take zones or not. Where used, they need to be enforced and their effectiveness monitored.


Do measures include impacts on non-target species and inadvertent impacts upon target species?


Measures to avoid by-catch if necessary should be straightforward in the commercial fishery.


Do measures include operational waste (gear, fuel, and waste?)


It may prove appropriate to control shell and tissue discarding by processors and fishers.


Does the fishery employ destructive fishing practices?


Destructive fishing practices are most likely not an issue for conch. There are various issues with running a vessel.


Does a research plan exist in line with the management system to address information needs?


Have key research areas requiring further information been identified?


Potential yields and hence initial reference points will have to be established.


Is research planned/undertaken to meet the specific requirements of the management plan?


Scientific research will be required to assess the unexploited state of the fishery. Various biological models of the species, such as growth and natural mortality rates, will be useful in refining management.


Is relevant research carried out by other organisations and is this taken into consideration?


There has been considerable research on conch. How and when it may be used once a basic system is in place should be reviewed.


Are control measures in place to ensure the management system is effectively implemented?


Are information, instruction and/or training provided to fishery operatives in the aims and methods of the management system?


Fishers and fishing industry employees should be involved in and aware of the management system as much as possible. This will help with compliance. Where fishers contravene the system, management needs to be able to show effective corrective actions, such as prosecutions, have been applied.


Is surveillance and monitoring in place to ensure that requirements of the management system are complied with?



Can corrective actions be applied in the event of non-compliance?



Do fishery operatives assist in the collection of catch, discard and other relevant data?



Is the management system subject to internal review?


Independent reviews of the management plan and scientific assessments are highly desirable.


Is the management system subject to external review?


APPENDIX II - Interpreting mean meat weight

1. Factors controlling meat weight

Mean weight of conch meat pieces may change in a fishery due to three causes:

Controlling mean size by itself will be inadequate in protecting the stock. In observing any particular catch composition, it may be difficult to interpret the meaning with respect to the underlying population from which the catch is drawn. For example, a high proportion of mature conch in the catches may indicate that the stock is healthy with a large spawning stock. It may also indicate that recruitment has failed and fishers are switching to depleting the spawning stock in deeper waters.

2. Reference points

Mean size could be used for two purposes. If mean size can be linked to the proportion of the catch which is mature, some minimum size can be set to ensure that this proportion remains high. Conceptually, this will help to ensure that animals are only exploited once they have had a chance to spawn and that the spawning stock will be maintained.

Interpreting such a policy in terms of fishing mortality will depend on selectivity, but in general the implication would be that the fishery is directed at the mature stock and that spawning would be less likely to be affected. Even a high fishing mortality should allow a significant proportion to spawn before being caught if the maximum size is set high enough. Ensuring that some minimum proportion of animals reach maturity is usually managed by spawners-per-recruit analyses.

Given the variability in size at age, size at maturity and so on, it is not possible to specify a meat weight where all conches will be mature. A reasonable limit reference point would be the mean weight where 50 percent (or some other percentage) are mature. Maturity is relatively easy to measure from the shell (flared lip) as well as the body prior to processing. Size composition data would have to be collected on individuals before and immediately after processing to enable appropriate estimates to be made. Such conversion models do not have to rely on random samples. Specifically larger and smaller individuals can be selected to get a good range. The analysis is straightforward using generalized linear models.

A more specific proposal can be made in the case of avoiding growth overfishing. For any animal which is caught, a choice could be made between leaving it in the sea, allowing it to grow at the risk of dying from natural causes or catching it now. Balancing the losses from mortality against gains from growth is usually managed by yield-per-recruit analyses (See Section 11.3).

Per-recruit analyses can be carried out without data as long as a reasonable growth and mortality model is available (Figure 4). The following yield-per-recruit analysis uses the Gompertz growth and maturity models, and parameters used in the Belize conch stock assessment workshop 1999 (CRFM, 1999). The model and parameters are presented as an example and would need to be reviewed and, ideally, estimated for each fishery.

Although meat weight is shown to be approximately linearly related to fishing mortality, the change is relatively small (Figure 4). It is possible that measurement errors will give a wide range of possible fishing mortality estimates for any given meat weights. Nevertheless the mean weight can be interpreted as long as the fundamental assumptions are not violated.

Table 7: Parameters used in the yield-per-recruit model. Parameters and models are taken from CRFM (1999), but are not the only parameters and models which could be proposed. Alternatives should be considered before applying this approach.

Gompertz Growth Model

Wt = a1 exp(a2(1-exp(-a3t)))





Age at first capture






A mean weight based on yield-per-recruit assumes a particular selectivity and fixed recruitment. If these assumptions are incorrect, the SPR and YPR based reference points may be poor estimates. Size frequency data in many cases will show such assumptions are false and hence interpretation of mean meat weight invalid. An alternative more robust approach is desirable.

Figure 4: Spawning biomass per-recruit and yield per-recruit indicating the SPR40%, F0.1 and FMSY for conch using the growth and mortality parameters indicated. SPR40% is the fishing mortality where the spawning biomass has been reduced to 40 percent of its unexploited state. F0.1 and FMSY are the fishing mortality where the YPR slope is 10 percent of the initial slope and the YPR maximum respectively. Each fishing mortality reference maps directly to an equivalent mean weight. Hence, given a per-recruit analysis, mean weight might be used as a proxy for fishing mortality. However, the method assumes constant recruitment and knife edge selectivity.

3. Example decision rule

The following example illustrates an approach where data can be immediately used to make a decision. The method focuses on growth, but a similar method should be developed for maturity, looking to maintain a desirable ratio of mature to immature conch in the catches. Such an approach will require the expected ratio in a lightly exploited fishery, which was not available for this analysis.

An alternative but closely related approach to yield-per-recruit would look at actual size compositions in the catches and decide whether overall it would have been better to leave the animals in the sea longer to grow rather than catch them now. Such a system would be independent of selectivity and recruitment, but would reflect current catch composition and would change in relation to these effects. Hence, a strong recruitment might well lead to advice to reduce fishing mortality. The approaches are best encapsulated as decision rules, whereby actions taken on an indicator’s values in relation to reference points.

For any particular size composition, the net gain in leaving the animals in the sea can be derived from the growth model:

where C is the catch weight, Y1 is the yield of the ith conch in the catch and Wit is the weight of the ith conch in the catch (sample) given that its age is t and natural mortality is M. Where discounting is used, M becomes natural mortality plus the discount rate. The calculation for the marginal yield (dYi/dt) can be summed over the sample. A positive number will indicate that overall greater gains would have been made by leaving these conches in the sea and catching them later.

For the Gompertz growth model, the marginal yield equation for the catch composition becomes:

The critical point will be where the marginal yield is zero, where it switches from being positive to negative. This represents the optimal point for the yield. Through simplification and substitution this point can be defined as:

For a particular sample, where the score S is negative, the implication is yield would be improved by increasing the fishing mortality. Conversely, when S is positive, yield would be increased by reducing fishing mortality. The score itself might therefore be used as an indicator determining the performance of catches in relation to growth. The absolute sum of the score measuring the difference of each size from the optimal size can also be used to indicate the efficiency of the current selectivity. These indicators might be used to measure and quantify various management controls which could improve selectivity as well as advice on fishing mortality levels.

This analysis was conducted on Belize data (from CRFM, 1999) for illustration purposes using the previous growth and mortality parameters (Table 7). The data show a large change in catch composition due to different sampling activities (Figure 5). This change is clearly picked up both by the score and the mean weight indicator, both implying rightly that the 1998 size composition would represent growth overfishing.

Where only a mean meat weight is available, the score can be applied to the single value. This point would be the size where, for example, an aquaculturist or farmer would harvest the resource. For the Belize parameters, the optimum would be 190g mean meat weight. This ignores the variation in size in the catches, but nevertheless gives some indication of whether meat weights are too small.

Figure 5: Catch size composition reported for Belize 1996-1998 (CRFM, 1999). The compositions show a significant change from 1996/97 to 1998 due to a change in sampling practice and does not represent catches. The data are used for illustration purposes only.

Table 8: Mean weight and scores for Belize weight frequency sample data. The mean weight fell in 1998. The score indicates that if 1998 composition represented the catch, growth overfishing would occur. Conversely 1996-97 suggests fishing mortality could increase. The absolute score measures the inefficiency of the gear selectivity. The lower this score, the closer the sizes will be to the optimum size. Controls which reduce this score could increase yield without increasing fishing mortality.








Mean Weight (g)




Mean Abs Score




4. Growth model

The decision rule is sensitive to the choice of growth model and parameters. It is important that a growth model is used that is as reliable as possible.

The size frequency data from Belize suggests the asymptotic size of 240 g is probably too small. Carrying out the procedure for a more realistic 300 g asymptotic size suggests an optimal mean meat weight of 236 g, and that 1996/97 is very close to this optimum (i.e. fully exploited).

The growth model is deterministic in this analysis. A slightly more sophisticated approach would allow the model to describe the mean growth and allow for growth variability. Further work would allow uncertainty in parameter values to be represented. Decision rules are particularly good at coping with uncertainty as they allow the costs of making the wrong decision to be explicitly taken into account.

APPENDIX III - Participatory fisheries stock assessment (ParFish)

ParFish implements a multi-criterion decision-making methodology to provide management advice for data-poor, artisanal fisheries in developing countries. The method applies Bayesian decision analysis by identifying the "Bayes action" (see Lindgren, 1976 p.374, for example). All analyses have explicit risks with the optimum action maximizing the expected utility. The method focuses on rapid inexpensive assessment methods to initiate adaptive management.

The standard stock assessment models still form the basis of the method. The software allows the method to be applied without knowledge of the numerical routines. Robust statistical techniques have been chosen where ever possible to improve results.

The method works by specifying a simulation model representing the behaviour of the fishery. Simulation model parameter sets are drawn at random from a probability distribution constructed from the available information to run simulations. These are used to simulate the possible behaviour of the fishery in response to a fishery control. The fishery controls supported are effort, catch and closed area controls. During the simulation, the state of the stock and the preference score as indicated by the fishers is recorded. These are used to calculate the state of the stock and the fishery in relation to the relevant reference points.

The probability modelling is based on parameter frequencies. This allows complex models to be broken down into simpler components. Modelling frequencies, as opposed to modelling data directly, allows a wide range of information sources to be used. Probabilities are modelled using multi-dimensional non-parametric kernel smoothers. Smoothing is carried over all dimensions and random draws (selections) from the posterior are very fast.

Kernel smoothing functions are a non-parametric way to estimate probability densities from frequency data. They spread individual points in smooth functions around the point. They work on the same principle as histograms, but have better statistical properties. The smoothing, and hence weighting amongst the different data sources, is estimated directly from the data themselves using a least squares cross-validation technique (see Silverman, 1986).

Fisher interviews form an important component of the method. Interviews are used to:

The method supports fishing experiments as well as standard catch-effort data models. Fishing experiments allow catchability (fishing mortality) to be estimated rapidly.

Field testing in the Turks and Caicos Islands was used to test whether interviews can be relied upon to provide sensible management advice. It was shown in the Turks and Caicos case that interviews provided advice which, if applied in 1974, would be expected to have obtained much greater benefits from the fishery than that which was obtained under no catch control.

1. Turks and Caicos Islands Retrospective Analysis

The example illustrates an important tenet of the precautionary approach, that a lack of information should not be used as a reason to delay action. Methods exist, such as ParFish, for which data can be both rapidly collected and inexpensive. These can lead to making decisions in the short term which will be a very great improvement over taking no action.

Using interview data in the assessment, it was tested against standard catch and effort stock assessment using decision analysis (see PFSA, 2003). Interviews were conducted in July 2003 to obtain stock assessment information from fishers. The Turks and Caicos Islands has a 30-year catch and effort time series which can generate not only an assessment for comparison with the interview decision analysis but also can indicate what would have happened had a quota based on the interviews been applied. It was of interest to see how well management would do if actions were based only on the interview data.

The fishery is managed through a quota, so this is the appropriate control. A standard stock assessment using the logistic model fitted to the catch-effort time series indicated the current quota of 1.675 million pounds as too high; and recommended lowering it to 1.6 million pounds landed weight. Using the preference information, the stock assessment based upon both the interview and catch-effort model combined and the catch-effort model alone suggest a lower quota around 1.53 and 1.38 million pounds respectively. Interviews by themselves are much less accurate (as indicated by the much lower limit control), but nevertheless recommends a target of 1.68 million pounds, reasonably close but above the other targets.

Table 9: Target and limit controls for the Turks and Caicos Islands conch fishery based on catch-effort and interview data.


Target control

Limit control

Interviews and catch-effort model combined



Interviews data only



Catch-effort model only



If it is assumed that fishers knew as much in 1974 as they do now, we can use the interview data as representative of what would have been obtained had the interviews been conducted at the beginning of the time series. Hence, the interview-only target quota can be applied at that point to see what might have happened to the fishery had this stock assessment method been applied, assuming that the logistic and maximum likelihood parameter estimates are correct.

The actual total catch over the period 1975-2002 was 45.47 million pounds. Had the 1.68 million pound quota been applied, the results suggest a total catch of 47.00 million pounds. This quota would realize higher catches in the longer term by foregoing higher catches in the late 1970s. A discount rate of around 5 percent yields approximately the same net present value between the two options.

The real gain, however, would have been the rise in catch rate (Figure 6). The catch-effort model suggests the stock was in an overfished state in 1974 and an enforced quota would have led to stock recovery. In other words, the catch would be met with much less work and costs than is now applied (from 3 300 boat days down to 2 500 boat days to realize the same catch). It indicates considerable benefits to using just interviews in this case, but would need more testing to make the case as a general statement. In particular, in cases where it turns out the logistic is not the best model, it needs to be shown that interviews may still have value in setting initial targets.

Figure 6: Expected catch per boat day (CPUE) from the fitted logistic model and the projected CPUE with 1.68 million pound quota.

The cost of applying the quota is that, without the depletion in the mid 1980s, less information would now be available on the behaviour of the stock, so that the current stock assessment would be less reliable. This problem would have to have been addressed through increased research activities.

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