Precautionary Reference Points Research Articles

Natural mortality estimations for beaked redfish (Sebastes mentella) – A long-lived ovoviviparous species of the Northeast Arctic

Beaked redfish (Sebastes mentella) is one of the few commercially important fish species producing living offspring. Like many other deep-water fishes, it is slow growing, late maturing and long-lived, getting as old as 65 years or even 75 years in some populations. The stock in the Norwegian and Barents Seas is analytically assessed since 2012, assuming a natural mortality (M) of 0.05 yr−1 across all ages, based on Hoenig’s longevity related estimator. Since then, several reviews and new studies have been published, affording a re-evaluation of the natural mortality in the assessment model. We estimated natural mortality of beaked redfish using 48 different estimators in two categories, either estimating M across the population or dependent on age, length or weight. The obtained estimates were highly variable, ranging from 0.01 to 0.32 yr−1 for estimates across the population, and 0.05–0.62 yr−1 for age or size dependent median-M. These wide ranges demonstrate the sensitivity of SSB to the input parameters as well as the pitfalls of using estimators developed for distant taxa. Of the 48 estimates, 20 were considered as potential candidates for updating the stock assessment model, yet not all of these were realistic. The frequency distribution of the estimators showed a peak around a value of 0.07 yr−1, lowering the estimated spawning stock biomass in the last year by about 300 kt but keeping it above the precautionary reference point for the stock. Estimators across the life-history of beaked redfish indicate a potential underestimation of natural mortality for early and overestimation for late age classes. Age and size related estimators are promising for the older ages but tend to extreme estimates for the early ages, which deserves further investigation.

Testing length-based reference points in a management strategy evaluation for cuckoo ray (Leucoraja naevus) and thornback ray (Raja clavata)

Abstract Elasmobranchs grow relatively slowly and mature at a relatively high age, leading to longer generation time. Due to low fecundity of these stocks, sufficient numbers of mature individuals are important to ensure a viable recruitment level and sustainable management. Length-based indicators (LBIs), such as the mean length and the mean length of the largest 5% in the catch, can be used to characterize the length distribution of exploited stocks and aid a data-limited assessment. Reference points for these indicators are calculated using basic life history parameters. Using cuckoo ray, Leucoraja naevus, and thornback ray, Raja clavata, as example species, we apply management strategy evaluations to test the performance of LBI-based harvest control rules (HCRs) in their ability to recover overexploited stocks. We illustrate the importance of the stock–recruitment relationship for the management outcome. If immature individuals are targeted by the fishery, HCRs perform better in terms of stock recovery when coupled with reference points, which account for the maturation schedule of the stock. The sensitivity of reference points to parameter misspecification means that elasmobranchs stocks in which immature individuals are exploited by the fishery may require more precautionary reference points, with consideration of the trade-off between biomass recovery and yield.

The role of uncertainty in the design of sustainable and precautionary management strategies for fisheries

AbstractEnvironmental variability has a strong influence on marine fish stocks. Thus, management and harvest policies based on deterministic indicators, such as maximum sustainable yield (MSY), may be inappropriate facing such uncertainties. In this study, we investigate the long‐term behavior of a single‐species fishery, whose stock is harvested by several fleets and affected by variability in the recruitment. The dynamics of this population is modeled by a discrete‐time stochastic age‐structured model. In this context, we introduce the concepts of maximum expected, log expected, and harmonic expected sustainable yield, as biological reference points. We illustrate these concepts with a case study of the Patagonian toothfish fishery in Chile and Argentina. Via Monte‐Carlo simulations, we verify that high levels of variability have a negative effect on all these maximum expected reference points, which suggests the need to be more cautious when large levels of variability on recruitment impact the fishery. Our simulations show that the deterministic MSY may not be attained in the presence of environmental noise, and therefore its use may lead to a failure of management strategies or rebuilding plans.Recommendations for Resource Managers For sustainable harvest, proper accounting of stochasticity in recruitment dynamics is necessary. For high levels of volatility, the use of deterministic reference points to develop regulations, such as maximum sustainable yield (MSY), may lead to overexploitation and even a possible extinction of the fishery. We extend the MSY to the stochastic age‐structured framework by means of maximum expected stationary yield, maximum expected log‐sustainable yield, and maximum expected harmonic sustainable yield, which can be used as precautionary reference points. These three maximum expected yields and their respective optimal fishing mortalities decrease when the variability of fish recruitment increases. This stresses the need to be more cautious in presence of volatility.

Fishing for MSY: using “pretty good yield” ranges without impairing recruitment

Pretty good yield (PGY) is a sustainable fish yield corresponding to obtaining no less than a specified large percentage of the maximum sustainable yield (MSY). We investigated 19 European fish stocks to test the hypothesis that the 95% PGY yield range is inherently precautionary with respect to impairing recruitment. An FMSY range was calculated for each stock as the range of fishing mortalities (F) that lead to an average catch of at least 95% of MSY in long-term simulations. Further, a precautionary reference point for each stock (FP.05) was defined as the F resulting in a 5% probability of the spawning-stock biomass falling below an agreed biomass limit below which recruitment is impaired (Blim) in long-term simulations. For the majority of the stocks analysed, the upper bound of the FMSY range exceeded the estimated FP.05. However, larger fish species had higher precautionary limits to fishing mortality, and species with larger asymptotic length were less likely to have FMSY ranges impairing recruitment. Our study shows that fishing at FMSY generally is precautionary with respect to impairing recruitment for highly exploited teleost species in northern European waters, whereas the upper part of the range providing 95% of MSY is not necessarily precautionary for small- and medium-sized teleosts.

Norway and Russia: Bargaining Precautionary Fisheries Management in the Barents Sea

The Barents Sea contains some of the most valuable fish resources in the world, including the world’s largest cod stock. Since the mid-1970s, Norway and the Soviet Union/Russia have managed the most important stocks in the area together, through the Joint Norwegian–Russian Fisheries Commission. During the 1990s, the precautionary approach was adopted as the leading device for global fisheries management, introducing a requirement for additional precaution when scientific evidence is uncertain, as well as a number of practical regulatory measures related to scientific research, regulation and enforcement. Since the late 1990s, the Joint Commission has gradually adopted a number of measures required by the precautionary approach. Russia has never formally introduced the principle in its own fisheries legislation, but by and large employed regulatory measures in line with it. The article presents the major precautionary regulatory measures adopted by the Commission, including precautionary reference points for spawning stocks and fish mortality, a harvest control rule for quota settlement and various enforcement initiatives. A particular focus is on Norwegian–Russian collaboration and how Norway has bargained with Russia for precautionary management measures.Keywords: Barents Sea, fisheries management, precautionary principleCitation: Arctic Review on Law and Politics, vol. 5, 1/2014 pp. 75–99. ISSN 1891-6252

Assessing the state of pelagic fish communities within an ecosystem approach and the European Marine Strategy Framework Directive

Abstract Pelagic fish are key elements in marine foodwebs and thus comprise an important part of overall ecosystem health. We develop a suite of ecological indicators that track pelagic fish community state and evaluate state of specific objectives against Good Environmental Status (GES) criteria. Indicator time-series are calculated for the EU Marine Strategy Framework Directive “Celtic Seas” (CS) and “Greater North Sea” subregions. Precautionary reference points are proposed for each indicator and a simple decision process is then used to aggregate indicators into a GES assessment for each subregion. The pelagic fish communities of both subregions currently appear to be close to GES, but each remains vulnerable. In the CS subregion, fishing mortality is close to the precautionary reference point, although the unknown dynamics of sandeel, sprat, and sardine in the subregion may reduce the robustness of this evaluation. In the North Sea, sandeel stocks have been in poor state until very recently. Pelagic fish community biomass is slightly below the precautionary reference point in both subregions.

Regional trade-offs from multi-species maximum sustainable yield (MMSY) management options

The maximum sustainable yield (MSY) is, theoretically, the largest yield that can be taken from a single species' stock over an indefinite period. Formulation of strategic MSY management goals is, however, complicated by the need to move beyond biological single-species considerations. Interactions among species necessitate multispecies (MMSY) definitions, incorporating ecological, economic and social considerations. We developed an ecological-economic model of the Baltic Sea, simulating stock dynamics of interacting populations of cod Gadus morhua, herring Clupea harengus and sprat Sprattus sprattus. We investigated a set of different strategic management options. These likely, yet non-formalized experiments evaluate and illuminate alternative regional trade-offs. We computed multi-species maximum economic yield (MMEY) under certain eco-logical constraints, with profits as a performance indicator. An unconstrained profit-maximizing management strategy would lead to a highly profitable cod fishery in a cod-dominated ecosystem. Concurrent sprat stock size (and profits) would be low, falling below ecological precautionary reference points. Consideration of ecological constraints on minimum stock sizes leaves a range of strategies, including the change from a cod-dominated to a more clupeid-dominated system. The regional distribution of profits depends on the management. Therefore, adjustment payments or other forms of compensation might be needed to achieve a concordant agreement on strategic multi-species management goals.

Modelling the spatio-temporal interplay between North Sea saithe (Pollachius virens) and multiple fleet segments for management evaluation

There is growing interest in bio-economic models as tools for understanding pathways of fishery behaviour, in order to assess the impact on natural resources. Based on ‘FishRent’, a modelling approach is presented that integrates economics of the fleet, the impact of fishing on stock development and their spatio-temporal interplay. The simulation of species seasonal movements in combination with both observed values and stochastic recruitment allowed analysing the economic response of fleet segments to changes in stock distribution and development. Optimisation of net profits determines the effort adjustment and spatial allocation of fleet segments, which in turn affects the level of catch rates. Effort tended to concentrate where fish abundance was high, but also where fishing costs were low. In simulations with the current management plan spawning stock of North Sea saithe (Pollachius virens) declined below its precautionary reference point. In response fishing far from home ports became expensive and 40% of the initial effort was shifted to areas closer to home ports, but as areas of high fish concentrations were located by the modelled fleet segments catch rates remained high. Changes in seasonal/annual stock distribution, the stock decline and costs influenced the change in fishing effort distributions leading to overestimated catch per unit of effort values that masked the decline of stock abundance.

Performance of Surplus Production Models with Time‐Varying Parameters for Assessing Multispecies Assemblages

AbstractSingle‐species surplus production models are often used to assess multispecies assemblages in data‐poor situations where catch and effort data are insufficient to perform individual species assessments. We examined the performance of single‐species surplus production models applied to aggregated multispecies assemblages and explored the incorporation of time‐varying parameters to improve model estimates. We simulated the dynamics of three species with different intrinsic growth rates and survey catchabilities over 50 years in the presence of fishing and a single fishery‐independent survey. Schaefer surplus production models with and without time‐varying growth rate and catchability were fitted to simulated data. We then compared the ability of each model to accurately estimate multispecies maximum sustainable yield and terminal year biomass and to accurately reflect overall trends in individual component stocks. All models produced biased estimates, but the accuracy of multispecies assemblage maximum sustainable yield was improved with the incorporation of time‐varying parameters. The terminal biomass of the assemblage was best estimated by a basic production model in two of three scenarios. Multispecies assemblage trends were not reflective of all individual component species, resulting in situations in which some species were overexploited and others underexploited. Although the incorporation of time‐varying parameters improved the accuracy of some estimates in this application, the direction and magnitude of bias may not be predictable unless the relative differences in growth rate and catchability among species in the assemblage are known. If single‐species surplus production models are the only viable option for modeling assemblages, precautionary reference points should be adopted. Scaling the level of precaution to the range of growth rates among species in the assemblage is recommended.Received February 19, 2012; accepted August 8, 2012

Assembly rules for aggregate-species production models: simulations in support of management strategy evaluation

Ecosystem-based fisheries management (EBFM) emphasizes sustainability at multiple levels of organization beyond single target species. Therefore, biological reference points (BRPs) for aggregated groups are required, which optimize yields while preventing overexploitation of in- dividual species. We evaluate the tradeoffs between yield and biodiversity objectives for a wide range of aggregation strategies using multispecies surplus production models and comparing 2 simulated fish communities. We simulated population trajectories with an operating model de - tailing predation and competitive interactions for all individual species within each community, and with additional stochastic environmental variability for one community. Species trajectories were then aggregated by functional feeding guild, taxonomy, habitat association, size class, and at the entire community level. We estimated production parameters and BRPs (e.g. maximum sustainable yield, MSY) using a simple assessment model applied to each aggregated time series, then we ap- plied the MSY fishing rates to each simulated community as alternative fishing strategies and com- pared equilibrium biomass and yield under each strategy. We were able to define multi-species ref- erence points to meet both yield and biodiversity objectives across full system, taxonomic, habitat, feeding, and size-based aggregations. Species complexes were best able to meet both objectives when species with broadly similar productivity, environmental sensitivity and species interactions were aggregated into the complex. The impacts of simulated environmental variability on BRPs were substantial for certain species and aggregates, so including the combined impacts of environ- mental variation and species interactions in precautionary reference points appears critical to EBFM.

Assessment and management of Cape horse mackerel Trachurus capensis off Namibia based on a fleet-disaggregated age-structured production model

The Cape horse mackerel stock off Namibia is assessed using a fleet-disaggregated age-structured production model including historical International Commission for the Southeast Atlantic Fisheries (ICSEAF) and current data. Data from acoustic biomass surveys, on commercial catch per unit effort and on commercial catch-at-age, were used to estimate current stock status over a range of model specifications. A management tool, the so-called management monitor graph, was introduced in order to track past management relative to stock status. Target, limit and precautionary reference points, decision rules and harvesting strategies, according to which the stock should be managed, are described and tested. The target reference point was set at maximum sustainable yield (MSY), the precautionary reference point at 80% of MSY and the limit reference point at 30% of MSY. Owing to some inconsistencies in the dataseries, evaluation of the current state of the resource is challenging, but estimates are that the resource is around the MSY level, somewhere between 250 000 and 300 000 t.

A generalization of the three-stage model for advice using the precautionary approach in fisheries, to apply broadly to ecosystem properties and pressures

AbstractRice, J. C. 2009. A generalization of the three-stage model for advice using the precautionary approach in fisheries, to apply broadly to ecosystem properties and pressures. – ICES Journal of Marine Science, 66: 433–444. The six assumptions of the three-stage model for fisheries advice using a precautionary approach are itemized. The general applicability of each is considered for use with any indicator of ecosystem status, or human pressure on the ecosystem indicator, rather than just spawning-stock biomass (SSB) and fishing mortality. The framework is fully generalizable, at least conceptually, without requiring additional assumptions or extensions that are less plausible than the assumptions already made in fisheries applications. However, application of the three-stage framework in fisheries hinges on the existence of some relationship between stock productivity and SSB as the basis for selecting a limit reference point and positioning a precautionary reference point. Three types of relationship can exist in fisheries data, and the framework has strategies for dealing with each. In an ecosystem application, the notion of a relationship between productivity and the amount of an ecosystem feature is sometimes appropriate, but sometimes the response variable may be resilience of the feature to perturbation or its ability to serve some ecosystem function as a function of the extent of the feature. The generalized framework accommodates all three types of response in five functional relationships, each of which can allow locating a candidate limit reference point.

Limits to transparency—exploring conceptual and operational aspects of the ICES framework for providing precautionary fisheries management advice

Abstract Hauge, K. H., Nielsen, K. N., and Korsbrekke, K. 2007. Limits to transparency—exploring conceptual and operational aspects of the ICES framework for providing precautionary fisheries management advice. – ICES Journal of Marine Science, 64: 738–743. ICES precautionary approach to fisheries management advice is based on limit reference points (LRPs) reflecting stock status and precautionary reference points (PRPs) reflecting risk levels. As LRPs are exclusively science-based, while PRPs are management-based, this framework is deployed towards satisfying the ideal of a clear division of science and management's responsibilities. We discuss the variety of technical definitions of reference points and their use in the advisory process. There are inconsistencies in the use of reference points and a tendency to downplay uncertainty. Although the framework can be improved, we argue that some dilemmas will remain. First, transparency of uncertainty presupposes a simple and understandable framework. However, translation of the complexity of natural and human interactions into simple concepts leads to problematic standardization. Second, a clear-cut division of responsibility between science and management is not feasible because LRPs cannot be purely science-based and PRPs cannot be purely management-based. Such dilemmas set fundamental limits to what can be expected from the framework in terms of handling and communicating uncertainty. We suggest that comprehensive dialogue between science and management and explicit reflection on their respective roles will prove more effective at enhancing precautionary and transparent advice on fisheries than adhering to the ideal of strict separation.

Consequences of bias in age estimation on assessment of the northern stock of European hake (Merluccius merluccius) and on management advice

Abstract Bertignac, M., and de Pontual, H. 2007. Consequences of bias in age estimation on assessment of the northern stock of European hake (Merluccius merluccius) and on management advice. – ICES Journal of Marine Science, 64: 981–988. The results of a pilot tagging study on hake (Merluccius merluccius), conducted in the northern part of the Bay of Biscay in 2002, indicate that growth rates for this stock may be currently underestimated because of biased estimates of age. The impact that such a bias may have on the stock dynamics and the trends of the key population parameters, recruitment, spawning-stock biomass (SSB), and mortality are investigated. Assuming new growth parameters, a new age–length key is derived and used to produce and catch-at-age data and abundance indices, which are then used to assess the stock. Bias in estimating age affects the absolute levels of fishing mortality and stock biomass estimates, and also impacts the trend in SSB. However, trends in fishing mortality and recruitment are comparable, and the stock status with respect to precautionary reference points is broadly the same. As expected, the simulation also shows that the stock may be more reactive to changes in fishing levels, which affect medium-term forecasts. Long-term sustainable yields may also be impacted.

Reference points and management strategies: lessons from quantum mechanics

Abstract Fisheries management often relies heavily on precautionary reference points estimated from complex statistical models. An alternative approach uses management strategies defined by mathematical algorithms that calculate controls, like catch quotas, directly from the observed data. We combine these two distinct paradigms into a common framework using arguments from the historical development of quantum mechanics. In fisheries, as in physics, the core of the argument lies in the technical details. We illustrate the process of designing a management algorithm similar to one actually used by the International Whaling Commission. Reference points and surplus production models play a conceptual role in defining management strategies, even if marine populations do not obey such simplistic rules. Physicists have encountered similar problems in formulating quantum theory, where mathematical objects with seemingly unrealistic properties generate results of great practical importance.

Evolution of the state of fish stocks in the Northeast Atlantic within a precautionary framework, 1970–2003: a synoptic evaluation

AbstractThe state and trajectory of some of the stocks assessed by ICES in the North Atlantic in the period 1970–2003 are synoptically represented on a single system of representation of fishing mortality and biomass with precautionary reference points used as limits and thresholds. The results indicate that for nearly 30 years, the status of the stocks in relation to the precautionary reference points has been degrading in terms of spawning biomass and excess fishing mortality, driving most resources down close to and often beyond those reference points. The situation seems to have improved during the past decade, with some exceptions, as shown by progressive shift of the mean position of the stocks away from excessive mortality (since the early 1990s) and, after a time-lag, away from low biomass (since the early 2000s). The proposed representation system sticks to the reference points and value judgements used in the ICES context, but could be used with any equivalent precautionary system of representation.

Testing the MULTIFAN-CL assessment model using simulated tuna fisheries data

Data sets similar to those available on yellowfin tuna (Thunnus albacares) fisheries of the western and central Pacific ocean (WCPO) were generated by numerical simulations, and then analyzed with a recently developed statistical catch-at-age model (MULTIFAN-CL) to assess its performance under different conditions concerning data availability, observation errors, and fishery complexity. Given a 37-year time series of catch, standardized fishing effort, catch length frequencies, all stratified by period, region and fishery, MULTICAN-CL provided estimates of several population and fishery parameters that were relatively close to the simulated values. The least biased estimates were obtained with more informative data sets obtained from more complex fishery scenarios with greater spatial stratification. For such cases, estimates of some precautionary reference points were within ±12% of the simulated values. Additional tests are proposed assess the effects of alternative sources of information and different errors on the accuracy of various estimates and reference points computed with this model.

Performance of precautionary reference points in providing management advice on North Sea fish stocks

Abstract For 17 stocks in the North Sea, the performance and effectiveness of management advice using precautionary reference points was evaluated. Three criteria were used to identify whether a stock was within safe biological limits: SSB < Bpa, F > Fpa, or SSB < Bpa and F > Fpa. Four scenarios were considered, comparing the advice in the assessment year with what is retrospectively (2002 assessment) known to be the status of the stock at that time: (1) stock outside safe biological limits, advice to reduce fishing; (2) stock outside safe biological limits, advice for status quo harvesting; (3) stock within safe biological limits, advice to reduce fishing; and (4) stock within safe biological limits, advice for status quo (or increased) harvesting. Signal Detection Theory was applied to these scenarios, and the proportion of Hits (1 and 4), Misses (2), and False Alarms (3) were determined for each year as the proportion of the stocks for which the respective scenarios applied. Using both Bpa and Fpa was deemed the approach with the lowest error rate, and it resulted in about the same proportion of Hits in management advice as when Bpa alone was used (62%), but the proportion of Misses was slightly lower (24% vs. 26%). Therefore, the suggested EcoQ element would be the proportion of commercial fish stocks within safe biological limits (i.e. SSB > Bpa, F < Fpa), and the Ecological Quality Objective (EcoQO) should be that this EcoQ should be at or above a desired level. This desired level is a societal/political decision relative to the EcoQ reference level (i.e. where the anthropogenic influence on the ecological system is minimal), which by definition is 100%. At present, probably <10% of North Sea fish stocks are within safe biological limits, despite the relatively high Hit rate of >60%. A possible explanation is that most of these stocks (e.g. flatfish and roundfish) are caught in a mixed fishery, for which TAC management is less effective.

Application of a stochastic spawning stock biomass per recruit model for the horse clam fishery in British Columbia

A directed commercial fishery on horse (gaper) clams, Tresus capax and Tresus nuttallii (Bivalvia: Mactridae) is being developed in BC, Canada. We adapted a spawning stock biomass per recruit (SPR) analysis to evaluate the effect of different multi-year rotation fisheries and alternative exploitation rates on the stock reproduction potential. Our analysis also incorporated variation in the estimates of natural mortality rate and growth, converting uncertainties inherent in scientific knowledge into estimates of biological risk. The information produced will enable fishery managers to choose a fishing scheme based on the degree of precaution required. At the initial phase of developing this fishery, a highly precautionary biological reference point is recommended.

Sustainable yield indicators from biomass: are there appropriate reference points for use in tropical fisheries?

Various methods have been proposed to calculate maximum sustainable yield, MSY, from biomass estimates, but the classical approach of Gulland, MSY = 0.5 M B 0 is still widely used, despite overwhelming theoretical and practical evidence pointing to its limited value, probably due to confusion as to the alternative methods available. A review of alternative methods is presented and their applicability to species with high values of M discussed. An extreme-value strategy is proposed for introducing considerations of risk and precaution into a management system based on precautionary reference points. We also focus on problems of estimating MSY and other reference points, review alternative estimators and discuss some of the ecological and life history criteria that affect how these estimators should be used: as targets or limits for exploitation, as indicators of conformity under sustainable harvesting conditions, or even for ecocertification of responsible or sustainable fisheries.