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Fisheries management is largely based on the principle of achieving the maximum sustainable yield (MSY) with little regard for nutritional value. Management strategies maximizing nutrients rather than yield, however, may provide a smarter contribution to global food and nutrition security. Here, we present a novel fisheries management strategy: fishing at maximum nutritional yield (F MNY), the exploitation rate at which essential nutrients are maximized. Combining top-down population modelling approaches with bottom-up nutrient compositional analysis, we compared nutrient yields across seasons for Europe's most valuable fishery (Atlantic mackerel, Scomber scombrus). F MNY estimates differed between nutrients, but were equal to, or lower than, F MSY. An autumn fishery provided higher amounts of lipids, omega-3 fatty acids, and protein, whereas vitamin D3, and calcium were maximized in winter. Aligning national fisheries policies and nutrition objectives is paramount to realising the potential of seafood in building healthier food systems. Developing novel fisheries management strategies, such as F MNY, where fisheries are optimised for human nutrition will, therefore, contribute to nutrient sustainability and help improve human health and diets. [ABSTRACT FROM AUTHOR]

Sprat are commercially valuable and are an important component of the North-East Atlantic ecosystem as major predators of zooplankton, competitors with herring, and prey for piscivorous fish, marine mammals, and seabirds. Despite this, insufficient information exists for Celtic Seas sprat, one of five North-East Atlantic stocks, to estimate stock status. To ensure the sustainable exploitation of sprat, the health of the Celtic Seas ecosystem, and the wider fisheries sector, we conduct a management strategy evaluation to stress test the current single-species advice framework. The aim is to evaluate whether ecosystem objectives can be achieved under single-species maximum sustainable yield and precautionary advice frameworks. An operating model was conditioned on life history theory and strategic information from ecosystem models. We showed that in-year advice using an empirical rule could achieve management objectives and help balance the trade-offs between fishing activities and ecosystem health. The approach allows ecosystem understanding to be incorporated within existing precautionary and maximum sustainable yield frameworks to provide a robust management framework that can meet multiple objectives despite uncertainty. [ABSTRACT FROM AUTHOR]

The Precautionary Approach to Fisheries Management requires an assessment of the impact of uncertainty on the risk of achieving management objectives. However, the main quantities, such as spawning stock biomass (SSB) and fish mortality (F), used in management metrics cannot be directly observed. This requires the use of models to provide guidance, for which there are three paradigms: the best assessment, model ensemble, and Management Strategy Evaluation (MSE). It is important to validate the models used to provide advice. In this study, we demonstrate how stock assessment models can be validated using a diagnostic toolbox, with a specific focus on prediction skill. Prediction skill measures the precision of a predicted value, which is unknown to the model, in relation to its observed value. By evaluating the accuracy of model predictions against observed data, prediction skill establishes an objective framework for accepting or rejecting model hypotheses, as well as for assigning weights to models within an ensemble. Our analysis uncovers the limitations of traditional stock assessment methods. Through the quantification of uncertainties and the integration of multiple models, our objective is to improve the reliability of management advice considering the complex interplay of factors that influence the dynamics of fish stocks. [ABSTRACT FROM AUTHOR]

Fisheries management needs to ensure that resources are exploited sustainably, and the risk of depletion is at an acceptable level. However, often uncertainty about resource dynamics exists, and data availability may differ substantially between fish stocks. This situation can be addressed through tiered systems, where tiers represent different data limitations, and tier‐specific stock assessment methods are defined, aiming for risk equivalence across tiers. As case studies, we selected stocks of European plaice, Atlantic cod and Atlantic herring, where advice is provided by the International Council for the Exploration of the Sea (ICES). We conducted a closed‐loop simulation to compare risk equivalence between the data‐rich ICES MSY rule, based on a quantitative stock assessment, and the revised data‐limited empirical management procedures of the ICES advice framework. The simulations indicated that the data‐limited approaches were precautionary and did not lead to a higher risk of depletion than the data‐rich approach. Although the catch based on generic data‐limited approaches was lower, stock‐specific optimisation improved management performance with catch levels comparable with the data‐rich approach. Furthermore, the simulation indicated the ICES MSY rule can fail to meet management objectives due to increased depletion risk when management reference points are set suboptimally. We conclude that the recent revisions of the ICES system explicitly account for risk equivalence for data‐limited fisheries management and are a major step forward. Finally, we advocate further consideration of simple empirical management procedures irrespective of data limitations due to their ability to meet fisheries management objectives with greater simplicity. [ABSTRACT FROM AUTHOR]

In data-poor situations, length-based indicators (LBIs) and reference points based on life history parameters have been proposed to classify stocks according to conservation status and yield optimization. Given the variety of potential LBIs, life history traits, and fisheries, it is necessary to evaluate the robustness of length-based advice to ensure that despite uncertainty that management objectives will still be met. Therefore, a simulation procedure was employed where an Operating Model conditioned on life history parameters was used to generate pseudo data. Receiver operator characteristics and the true skill score were then used to screen LBIs based on their ability to identify overfishing and recovery. It was found that LBIs performed better for long-lived species with low individual growth rates, those aimed at ensuring the conservation of mature fish performed better than those aimed at the conservation of immature fish, are better at indicating trends than at quantifying exploitation level, and in general were robust to uncertainty about dynamic processes. [ABSTRACT FROM AUTHOR]

Many management bodies require applying the precautionary approach when managing marine fisheries resources to achieve sustainability and avoid exceeding limits. For data-limited stocks, however, defining and achieving management objectives can be difficult. Management procedures can be optimized towards specific management objectives with genetic algorithms. We explored the feasibility of including an objective that limited the risk of a stock falling below various limit reference points in the optimization routine for an empirical data-limited control rule that uses a biomass index, mean catch length, and includes constraints (the "rfb-rule"). This was tested through management strategy evaluation on several fish stocks representing various life-history traits. We show that risk objectives could be met, but more restrictive risk limits can lead to a potential loss of yield. Outcomes were sensitive to simulation conditions such as observation uncertainty, which can be highly uncertain in data-limited situations. The rfb-rule outperforms the method currently applied by ICES, particularly when risk limitation objectives are considered. We conclude that the application of explicit precautionary levels is useful to avoid overfishing. However, we caution against the indiscriminate use of arbitrary risk limits without scientific evaluation to analyse their impact on stock yields and sustainability. [ABSTRACT FROM AUTHOR]

The adoption of the Precautionary Approach requires providing advice that is robust to uncertainty. Therefore, when conducting stock assessment alternative, model structures and data sets are commonly considered. The primary diagnostics used to compare models are to examine residuals patterns to check goodness-of-fit and to conduct retrospective analysis to check the stability of estimates. However, residual patterns can be removed by adding more parameters than justified by the data, and retrospective patterns removed by ignoring the data. Therefore, neither alone can be used for validation, which requires assessing whether it is plausible that a system identical to the model generated the data. Therefore, we use hindcasting to estimate prediction skill, a measure of the accuracy of a predicted value unknown by the model relative to its observed value, to explore model misspecification and data conflicts. We compare alternative model structures based on integrated statistical and Bayesian state-space biomass dynamic models using, as an example, Indian Ocean yellowfin tuna. Validation is not a binary process (i.e. pass or fail) but a continuum; therefore, we discuss the use of prediction skill to identify alternative hypotheses, weight ensemble models and agree on reference sets of operating models when conducting Management Strategy Evaluation. [ABSTRACT FROM AUTHOR]

Many data-limited fish stocks worldwide require management advice. Simple empirical management procedures have been used to manage data-limited fisheries but do not necessarily ensure compliance with maximum sustainable yield objectives and precautionary principles. Genetic algorithms are efficient optimization procedures for which the objectives are formalized as a fitness function. This optimization can be included when testing management procedures in a management strategy evaluation. This study explored the application of a genetic algorithm to an empirical catch rule and found that this approach could substantially improve the performance of the catch rule. The optimized parameterization and the magnitude of the improvement were dependent on the specific stock, stock status, and definition of the fitness function. The genetic algorithm proved to be an efficient and automated method for tuning the catch rule and removed the need for manual intervention during the optimization process. Therefore, we conclude that the approach could also be applied to other management procedures, case-specific tuning, and even data-rich stocks. Finally, we recommend the phasing out of the current generic ICES "2 over 3" advice rule in favour of case-specific catch rules of the form tested here, although we caution that neither works well for fast-growing stocks. [ABSTRACT FROM AUTHOR]

Worldwide, the majorities of fish stocks are data-limited and lack fully quantitative stock assessments. Within ICES, such data-limited stocks are currently managed by setting total allowable catch without the use of target reference points. To ensure that such advice is precautionary, we used management strategy evaluation to evaluate an empirical rule that bases catch advice on recent catches, information from a biomass survey index, catch length frequencies, and MSY reference point proxies. Twenty-nine fish stocks were simulated covering a wide range of life histories. The performance of the rule varied substantially between stocks, and the risk of breaching limit reference points was inversely correlated to the von Bertalanffy growth parameter k ⁠. Stocks with k > 0.32   year−1 had a high probability of stock collapse. A time series cluster analysis revealed four types of dynamics, i.e. groups with similar terminal spawning stock biomass (collapsed, B MSY, 2 B MSY, 3 B MSY). It was shown that a single generic catch rule cannot be applied across all life histories, and management should instead be linked to life-history traits, and in particular, the nature of the time series of stock metrics. The lessons learnt can help future work to shape scientific research into data-limited fisheries management and to ensure that fisheries are MSY compliant and precautionary. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Fisheries & Aquatic Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Reference points based on fishing mortality ( F) and spawning stock biomass ( SSB) are a requirement of many fisheries management frameworks. SSB is assumed to be a proxy for stock reproductive potential ( SRP). Limit reference points based on SSB are used to indicate the level of biomass below which productivity is affected. SSB fails to account for changes in fecundity, egg viability and sex ratio, and it has been argued that total egg production ( TEP) provides a better reflection of SRP. We explore how accounting for TEP impacts limit reference points and evidence for a relationship between stock and recruit. Time series of SSB and TEP are compared for three North Sea stocks: cod ( Gadus morhua), herring ( Clupea harengus) and plaice ( Pleuronectes platessa). Dynamics based on TEP are different from those based on SSB for cod and plaice, but the stock-recruit relationships were not 'improved' using TEP. Shifts in productivity (spawner per recruit) occur in all three time series and SSB underestimated uncertainty. Yet again, it was shown that assumptions of stationarity about fish population productivity are incorrect. We argue that the use of TEP does improve the realism in our understanding of stock dynamics, and demographically, more complex management strategy evaluation is required to develop management procedures that are robust to uncertainty and integrate F and the demographic health of a stock. Empirical feedback control systems based on fisheries independent indices including surveys of eggs, larvae, recruits, juveniles or spawning adults should be evaluated and compared to traditional approaches. [ABSTRACT FROM AUTHOR]

Using a management strategy evaluation approach, we compare a range of new and established management procedures (MPs) for setting catch-limits in fisheries. Performance is evaluated with respect to fish life history type, level of stock depletion, data quality, and autocorrelation in recruitment strength. We quantify the robustness of each MP with respect to the various observation processes. Methods using observations of absolute biomass or stock depletion offer the best overall performance and this is consistent across life history types, data qualities, and stock depletion levels. Simple MPs can outperform conventional data-limited methods and data-rich assessments that use time-series of catch and effort data. MP performance is most sensitive to biases in catch data. Our results indicate that often tuning MPs for specific stocks is important, though this may not be viable in data-poor assessment scenarios because of insufficient data and analysis resources. [ABSTRACT FROM AUTHOR]

Engelhard, G. H., Pinnegar, J. K., Kell, L. T., and Rijnsdorp, A. D. 2011. Nine decades of North Sea sole and plaice distribution. – ICES Journal of Marine Science, 68: 1090–1104.Recent studies based mainly on research survey data suggest that within the North Sea, sole Solea solea and plaice Pleuronectes platessa have exhibited distribution shifts in recent decades—on average southward for sole and northward to deeper waters for plaice. Various hypotheses may account for such shifts, including climate change effects and more intensive fishing in southern and shallower waters; but the relatively short time-span of datasets analysed so far (∼3 decades) has complicated the separation of these two effects. We have made use of a unique dataset of catch and effort data for British North Sea trawlers; these cover nine decades (spanning the period 1913–2007) and are spatially detailed by ICES rectangle (0.5° latitude by 1° longitude). We quantify, for the first time, long-term distribution changes of North Sea sole and plaice over a period approaching a century, and demonstrate that the distribution shift in plaice was attributable to climate change rather than to fishing, but that both climate and fishing played a role in the distribution shift of sole. The discussion also highlights the potential impact of additional factors, including eutrophication, prey availability, and habitat modification. [ABSTRACT FROM PUBLISHER]

Tidd, A. N., Hutton, T., Kell, L. T., and Padda, G. 2011. Exit and entry of fishing vessels: an evaluation of factors affecting investment decisions in the North Sea English beam trawl fleet. – ICES Journal of Marine Science, 68: 961–971.A profitable fishery attracts additional effort (vessels enter), eventually leading to overcapacity and less profit. Similarly, fishing vessels exit depending on their economic viability (or reduced expectations of future benefits) or encouraged by schemes such as decommissioning grants and/or when there is consolidation of fishing effort within a tradable rights-based quota system (e.g. individual transferable quotas). The strategic decision-making behaviour of fishers in entering or exiting the English North Sea beam trawl fishery is analysed using a discrete choice model by integrating data on vessel characteristics with available cost data, decommissioning grant information, and other factors that potentially influence anticipated benefits or future risks. It is then possible to predict whether operators choose to enter, stay, exit, or decommission. Important factors affecting investment include vessel age and size, future revenues, operating costs (e.g. fuel), stock status of the main target species, and the impact of management measures (e.g. total allowable catches) and total fleet size (a proxy for congestion). Based on the results, the predicted marginal effects of each factor are presented and the impact of each is discussed in the context of policies developed to align fleet capacity with fishing opportunities. [ABSTRACT FROM PUBLISHER]

Ecological risk assessment is a useful methodology for assisting the management of fisheries from an ecosystem perspective. Atlantic tuna fisheries, managed by the International Commission for the Conservation of Atlantic Tunas (ICCAT), are economically important and interact with several bycatch species. In spite of these interactions, no comprehensive ecological risk assessment has been conducted for bycatch species caught in ICCAT fisheries. In this paper, we followed a two stage approach with the objective of assessing the relative risk of species being negatively impacted by Atlantic tuna fisheries. An analysis of the ICCAT bycatch species list (which includes all species reported to have interacted with different tuna fishing gears operating in the Atlantic) revealed that most of these species are caught in longline fisheries, followed by gillnets and purse seines. According to the IUCN red list, 7 species of the ICCAT bycatch list (3 coastal sharks, 3 sea turtles and one seabird) are categorized as critically endangered. In our study, and based on their life history characteristics, marine mammals and coastal sharks caught in ICCAT fisheries showed the highest intrinsic vulnerability values. A productivity susceptibility analysis for the European Union (EU) tropical tuna purse seine fleet and the United States (US) pelagic longline fleet revealed two groups with high relative risk scores. The first one included pelagic and coastal sharks, characterized by relatively low productivities, and the second one included teleosts, characterized by higher productivities but high susceptibility to purse seine and longline gears. Some alternative approaches to conduct productivity susceptibility analyses in the context of ecological risk assessments are discussed. [ABSTRACT FROM PUBLISHER]

Dickey-Collas, M., Nash, R. D. M., Brunel, T., van Damme, C. J. G., Marshall, C. T., Payne, M. R., Corten, A., Geffen, A. J., Peck, M. A., Hatfield, E. M. C., Hintzen, N. T., Enberg, K., Kell, L. T., and Simmonds, E. J. 2010. Lessons learned from stock collapse and recovery of North Sea herring: a review. – ICES Journal of Marine Science, 67: 1875–1886. The collapse and recovery of North Sea herring in the latter half of the 20th century had both ecological and economic consequences. We review the effect of the collapse and investigate whether the increased understanding about the biology, ecology, and stock dynamics gained in the past three decades can aid management to prevent further collapses and improve projections of recovery. Recruitment adds the most uncertainty to estimates of future yield and the potential to reach biomass reference points within a specified time-frame. Stock–recruitment relationships must be viewed as being fluid and dependent on ecosystem change. Likewise, predation mortality changes over time. Management aimed at maximum sustainable yield (MSY) fishing mortality targets implies interannual variation in TACs, and variability in supply is therefore unavoidable. Harvest control rules, when adhered to, aid management greatly. We advocate that well-founded science can substantially contribute to management through improved confidence and increased transparency. At present, we cannot predict the effects of collapse or recovery of a single stock on the ecosystem as a whole. Moreover, as managers try to reconcile commitments to single-species MSY targets with the ecosystem-based approach, they must consider the appropriate management objectives for the North Sea ecosystem as a whole. [ABSTRACT FROM PUBLISHER]

Butterworth, D. S., Bentley, N., De Oliveira, J. A. A., Donovan, G. P., Kell, L. T., Parma, A. M., Punt, A. E., Sainsbury, K. J., Smith, A. D. M., and Stokes, T. K. 2010. Purported flaws in management strategy evaluation: basic problems or misinterpretations? – ICES Journal of Marine Science, 67: 567–574.Rochet and Rice, while recognizing management strategy evaluation (MSE) as an important step forward in fisheries management, level a number of criticisms at its implementation. Some of their points are sound, such as the need for care in representing uncertainties and for thorough documentation of the process. However, others evidence important misunderstandings. Although the difficulties in estimating tail probabilities and risks, as discussed by Rochet and Rice, are well known, their arguments that Efron's non-parametric bootstrap re-sampling method underestimates the probabilities of low values are flawed. In any case, though, the focus of MSEs is primarily on comparing performance and robustness across alternative management procedures (MPs), rather than on estimating absolute levels of risk. Qualitative methods can augment MSE, but their limitations also need to be recognized. Intelligence certainly needs to play a role in fisheries management, but not at the level of tinkering in the provision of annual advice, which Rochet and Rice apparently advocate, inter alia because this runs the risk of advice following noise rather than signal. Instead, intelligence should come into play in the exercise of oversight through the process of multiannual reviews of MSE and associated MPs. A number of examples are given of the process of interaction with stakeholders which should characterize MSE. [ABSTRACT FROM PUBLISHER]

Mäntyniemi, S., Kuikka, S., Rahikainen, M., Kell, L. T., and Kaitala, V. 2009. The value of information in fisheries management: North Sea herring as an example. – ICES Journal of Marine Science, 66: 2278–2283.We take a decision theoretical approach to fisheries management, using a Bayesian approach to integrate the uncertainty about stock dynamics and current stock status, and express management objectives in the form of a utility function. The value of new information, potentially resulting in new control measures, is high if the information is expected to help in differentiating between the expected consequences of alternative management actions. Conversely, the value of new information is low if there is already great certainty about the state and dynamics of the stock and/or if there is only a small difference between the utility attached to different potential outcomes of the alternative management action. The approach can, therefore, help when deciding on the allocation of resources between obtaining new information and improving management actions. In our example, we evaluate the value of obtaining hypothetically perfect knowledge of the type of stock–recruitment function of the North Sea herring (Clupea harengus) population. [ABSTRACT FROM PUBLISHER]

Kell, L. T., Dickey-Collas, M., Hintzen, N. T., Nash, R. D. M., Pilling, G. M., and Roel, B. A. 2009. Lumpers or splitters? Evaluating recovery and management plans for metapopulations of herring. – ICES Journal of Marine Science, 66: 1776–1783.The long-term management of a stock representing a metapopulation has been simulated in a case study loosely based upon herring to the west of the British isles, where stocks are currently assessed and managed by management area, although there is evidence of mixing between stocks (in terms of connectivity, migrations, and exploitation). The simulations evaluate scientific advice (based on virtual population analysis, VPA) and the sustainability of fishing under two population-structure scenarios, corresponding either to discrete stocks, which only mix on the feeding grounds, or where diffusion between stocks takes place. The ability of stock assessment to monitor stock status and exploitation levels was evaluated for defining stocks based on fishing areas and for stocks that combined fishing areas. The study showed that assessment based on VPA of the metapopulation could fail to detect overexploitation of stocks and fail to detect and distinguish between the effects of exploitation and regime shifts. [ABSTRACT FROM PUBLISHER]

Pilling, G. M., Kell, L. T., Hutton, T., Bromley, P. J., Tidd, A. N., and Bolle, L. J. 2008. Can economic and biological management objectives be achieved by the use of MSY-based reference points? A North Sea plaice (Pleuronectes platessa) and sole (Solea solea) case study. – ICES Journal of Marine Science, 65: 1069–1080.We examined the biological and economic impact of changing from management based on single-species limit reference points to one based on alternative targets, using the multispecies multifleet North Sea flatfish fishery. The robustness of reference points was tested against identified changes in plaice and sole biology. Current ICES single-species limit and precautionary biomass and fishing mortality reference points were seldom consistent with each other. Although they were generally robust to biological uncertainty, fishing at Fpa for sole could lead to stock collapse under one biological scenario. Adoption of alternative targets would reduce reliance on current reference points as stocks moved to a more sustainable state. Maximum sustainable yield (MSY), maximum economic yield (MEY), and maximum employment conditions implied different effort levels in the two fleets modelled, and different profits. Ftarget could be achieved with equal effort reductions in both fleets. Changes in stock biology affected the fishing effort required to maximize employment within the fishery, whereas MSY, Fmax, and MEY targets were robust to this uncertainty. Resulting profits and yields did vary widely, however. The selection of target reference points therefore requires stakeholders to define fishery objectives explicitly, against which targets can be evaluated for the resulting trade-offs between risk to stocks, yield, employment, and other social objectives. [ABSTRACT FROM PUBLISHER]

Aps, R., Kell, L.T., Lassen, H., and Liiv, I. 2007. Negotiation framework for Baltic fisheries management: striking the balance of interest. – ICES Journal of Marine Science, 64: 858–861. We explore the issue of balancing stakeholder interests in the translation of science-based advice into agreed management measures. We also analyse the outcome of negotiations within the International Baltic Sea Fishery Commission (IBSFC) for setting the total allowable catch (TAC) for Baltic herring, sprat, cod, and salmon between 1977 and 2004. Given the political and economic pressure inherent in fishery management, IBSFC Contracting Parties, as maximizers of economic value, often set the TAC by unit stock in excess of what was considered sustainable. TACs set in excess of sustainable levels of exploitation (decision-overfishing) reflect the relative importance that negotiating parties attribute to the interests of multiple groups participating in the fishing industry. Such decision-overfishing can be seen as management failure to secure public interest in the long-term health of fish populations. The potential political and social causes of overfishing have to be addressed and removed before measures can be implemented that might reach the goal of sustainable development. [ABSTRACT FROM PUBLISHER]

Copyright of Canadian Journal of Fisheries & Aquatic Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Fisheries & Aquatic Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Robustness of both short-term stock biomass recovery and longer-term sustainable management strategies to different plausible climatic change scenarios were evaluated for North Sea cod (Gadus morhua), where climate was assumed to impact growth and recruitment. In the short term, climate change had little effect on stock recovery, which depends instead upon reducing fishing effort to allow existing year classes to survive to maturity. In the longer term, climate change has greater effects on stock status, but higher yields and biomass can be expected if fishing mortality is reduced. Incorporating environmental covariates in stock assessment predictions will not achieve sustainable resource use. The implications of climate change for biological reference points depend upon the mechanism through which temperature acts on recruitment, i.e. on juvenile survival or carrying capacity. It is not possible to distinguish between these processes with stock assessment data sets alone. However, this study indicates that reference points based on fishing mortality appear more robust to uncertainty than those based on biomass. Ideally, simpler management procedures are required that meet pre-agreed management objectives and are robust to uncertainty about the true dynamics. [Copyright &y& Elsevier]

Ecosystem-based management requires the development of indicators that allow anthropogenic impacts to be detected against the background of natural variation. Size-based community metrics are potentially useful indicators because of their theoretical foundation and practical utility. Temporal and spatial patterns in size-based community metrics for Celtic Sea fish are described and calculated using data from the English groundfish survey of the area (1987–2003). The results reveal that the size structure of the community has changed over time, and that a decrease in the relative abundance of larger fish was accompanied by an increase in smaller fish (4–25g). Temporal analyses of the effects of fishing and climate variation suggest that fishing generally has had a stronger effect on size structure than changes in temperature. Therefore, size-based metrics respond clearly to the effects of fishing even in variable environments, reflecting the ubiquity of size-based processes in defining community structure and responses to mortality. Spatial analyses were inconclusive, probably owing to the limited area for which fishing effort, temperature, and survey data were all available. [Copyright &y& Elsevier]