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Climate change (CC) can alter the configuration of marine ecosystems; however, ecosystem response and resilience to change are usually case‐specific. The effect of CC on the demersal resources of the Aegean Sea (east Mediterranean Sea) was investigated during the past six decades applying a combination of multivariate analysis, non‐additive modeling and the Integrated Resilience Assessment (IRA) framework. We focused on the study of: (i) the biological “system” complex, using proxies of biomass (landings per unit of capacity) for 12 demersal taxa, and (ii) the environmental “stressor” complex, described by 12 abiotic variables. Pronounced changes have occurred in both the environmental and biological system over the studied period. The majority of the environmental stressors exhibited strikingly increasing trends (temperature, salinity, primary production indices) with values started exceeding the global historical means during late 1980s‐early 1990s. It is suggested that the biological system exhibited a discontinuous response to CC, with two apparently climate‐induced regime shifts occurring in the past 25 years. There is evidence for two‐fold bifurcations and four tipping points in the system, forming a folded stability landscape with three basins of attraction. The shape of the stability landscape for the Aegean Sea's biological system suggests that while the initial state (1966–1991) was rather resilient to CC, absorbing two environmental step‐changes, this was not the case for the two subsequent ones (intermediate: 1992–2002; recent: 2003–2016). Given the current trajectory of environmental change, it is highly unlikely that the biological system will ever return to its pre‐1990s state, as it is entering areas of unprecedented climatic conditions and there is some evidence that the system may be even shifting toward a new state. Our approach and findings may be relevant to other marine areas of the Mediterranean and beyond, undergoing climate‐driven regime shifts, and can assist to their adaptive management., Applying a combination of multivariate analysis, non‐additive modelling and the Integrated Resilience Assessment (IRA) framework, we provide evidence that after the 1990s, the Aegean Sea has most likely entered areas of unprecedented climatic conditions, altering the biological system and making it highly unlikely to return to its pre‐1990s state.

Fisheries management typically aims at controlling exploitation rate (e.g., Fbar) to ensure sustainable levels of stock size in accordance with established reference points (e.g., FMSY, BMSY). Population selectivity (“selectivity” hereafter), that is the distribution of fishing mortality over the different demographic components of an exploited fish stock, is also important because it affects both Maximum Sustainable Yield (MSY) and FMSY, as well as stock resilience to overfishing. The development of an appropriate metric could make selectivity operational as an additional lever for fisheries managers to achieve desirable outcomes. Additionally, such a selectiv-ity metric could inform managers on the uptake by fleets and effects on stocks of various technical measures. Here, we introduce three criteria for selectivity metrics: (a) sensitivity to selectivity changes, (b) robustness to recruitment variability and (c) robustness to changes in Fbar. Subsequently, we test a range of different selectivity metrics against these three criteria to identify the optimal metric. First, we simulate changes in selectivity, recruitment and Fbar on a virtual fish stock to study the met-rics under controlled conditions. We then apply two shortlisted selectivity metrics to six European fish stocks with a known history of technical measures to explore the metrics’ response in real-world situations. This process identified the ratio of F of the first recruited age–class to Fbar (Frec/Fbar) as an informative selectivity metric for fisheries management and advice.

Ecological resilience has become a conceptual cornerstone bridging ecological processes to conservation needs. Global change is increasingly associated with local changes in environmental conditions that can cause abrupt ecosystem reorganizations attending to system-specific resilience fluctuations with time (i.e. resilience dynamics). Here we assess resilience dynamics associated with climate-driven ecosystems transitions, expressed as changes in the relevant contribution of species with different life-history strategies, in two benthopelagic systems. We analysed data from 1994 to 2019 coming from a scientific bottom trawl survey in two environmentally contrasting ecosystems in the Western Mediterranean Sea—Northern Spain and Alboran Sea. Benthopelagic species were categorized according to their life-history strategies (opportunistic, periodic and equilibrium), ecosystem functions and habitats. We implemented an Integrated Resilience Assessment (IRA) to elucidate the response mechanism of the studied ecosystems to several candidate environmental stressors and quantify the ecosystems’ resilience. We demonstrate that both ecosystems responded discontinuously to changes in chlorophyll-a concentration more than any other stressor. The response in Northern Spain indicated a more overarching regime shift than in the Alboran Sea. Opportunistic fish were unfavoured in both ecosystems in the recent periods, while invertebrate species of short life cycle were generally favoured, particularly benthic species in the Alboran Sea. The study illustrates that the resilience dynamics of the two ecosystems were mostly associated with fluctuating productivity, but subtle and long-term effects from sea warming and fishing reduction were also discernible. Such dynamics are typical of systems with wide environmental gradient such as the Northern Spain, as well as systems with highly hydrodynamic and of biogeographical complexity such as the Alboran Sea. We stress that management should become more adaptive by utilizing the knowledge on the systems’ productivity thresholds and underlying shifts to help anticipate both short-term/less predictable events and long-term/expected effects of climate change., SI

This study evaluates the relationship between both commercial and scientific spatial fisheries data and a new satellite-based estimate of potential fish production (Ocean Productivity available to Fish, OPFish) in the European Seas. To construct OPFish, we used productivity frontal features derived from chlorophyll-a horizontal gradients, which characterize 10%–20% of the global phytoplankton production that effectively fuels higher trophic levels. OPFish is relatively consistent with the spatial distribution of both pelagic and demersal fish landings and catches per unit of effort (LPUEs and CPUEs, respectively). An index of harvest relative to ocean productivity (HP index) is calculated by dividing these LPUEs or CPUEs with OPFish. The HP index reflects the intensity of fishing by gear type with regard to local fish production. Low HP levels indicate lower LPUEs or CPUEs than expected from oceanic production, suggesting over-exploitation, while high HP levels imply more sustainable fishing. HP allows comparing the production-dependent suitability of local fishing intensities. Our results from bottom trawl data highlight that over-exploitation of demersal species from the shelves is twice as high in the Mediterranean Sea than in the North-East Atlantic. The estimate of HP index by dominant pelagic and demersal gears suggests that midwater and bottom otter trawls are associated with the lowest and highest overfishing, respectively. The contrasts of fishing intensity at local scales captured by the HP index suggest that accounting for the local potential fish production can promote fisheries sustainability in the context of ecosystem-based fisheries management as required by international marine policies., With the institutional support of the ‘Severo OchoaCentre of Excellence’ accreditation (CEX2019-000928-S).

An increasing number of studies have been examining the functional configuration of biological communities or ecosystems using biological traits. Here, we investigated the temporal dynamics and resilience of the traits composition in Mediterranean fisheries landings over 31 years (1985-2015). We transcribed the FAO Mediterranean landings dataset for 101 marine species into a dataset of 23 traits related to the life cycle, distribution, ecology and behaviour. Mediterranean mean Sea Surface Temperature (SST) was evaluated as a potential driver of the traits composition. Trait dynamics were evaluated both individually and holistically by developing an Integrated Traits Resilience Assessment (ITRA). ITRA is a variation of the Integrated Resilience Assessment (IRA), a method to infer resilience dynamics and build stability landscapes of complex natural systems. Changes in landings trait dynamics were documented both for individual traits and for the entire traits 'system', and a relevant regime shift was detected in the second half of the 1990s. The traits system switched to higher optimal temperature, more summer spawning, shorter life span, smaller maximum size, shallower optimal depth and planktivorous diet. This shift was found to be a lagged discontinuous response to sea warming, which gradually eroded the resilience of the original state of the traits system, leading it into a new basin of attraction. The inclusion of ecological/response traits (related to environmental preferences) in our analyses indicates potential mechanisms that explain the observed shift, while changes in functional/effect traits indicate potential impacts on ecosystem functioning. Our findings suggest that changes in the Mediterranean ecosystems are evidently larger than previously thought, with profound implications for the management of this highly impacted sea. ​.

Marine biota are redistributing at a rapid pace in response to climate change and shifting seascapes. While changes in fish populations and community structure threaten the sustainability of fisheries, our capacity to adapt by tracking and projecting marine species remains a challenge due to data discontinuities in biological observations, lack of data availability, and mismatch between data and real species distributions. To assess the extent of this challenge, we review the global status and accessibility of ongoing scientific bottom trawl surveys. In total, we gathered metadata for 283,925 samples from 95 surveys conducted regularly from 2001 to 2019. We identified that 59% of the metadata collected are not publicly available, highlighting that the availability of data is the most important challenge to assess species redistributions under global climate change. Given that the primary purpose of surveys is to provide independent data to inform stock assessment of commercially important populations, we further highlight that single surveys do not cover the full range of the main commercial demersal fish species. An average of 18 surveys is needed to cover at least 50% of species ranges, demonstrating the importance of combining multiple surveys to evaluate species range shifts. We assess the potential for combining surveys to track transboundary species redistributions and show that differences in sampling schemes and inconsistency in sampling can be overcome with spatio‐temporal modeling to follow species density redistributions. In light of our global assessment, we establish a framework for improving the management and conservation of transboundary and migrating marine demersal species. We provide directions to improve data availability and encourage countries to share survey data, to assess species vulnerabilities, and to support management adaptation in a time of climate‐driven ocean changes., While many species are changing their spatial distributions rapidly with climate change, the global capacity to track these changes and then adapt management and policy has been limited. To build this capacity for demersal fishes, we compiled the largest worldwide collection of bottom trawl survey metadata and demonstrate how surveys can be combined to follow species across national and survey boundaries. Open data and transparent scientific assessment can be a key step towards improved management of redistributing transboundary species and stocks.

There is a growing number of methods to assess data-limited stocks. However, most of these methods require at least some basic data, such as commercial catches and life history information. Meanwhile, there are many commercial stocks with an even higher level of data limitation, for which the inference of stock status and the formulation of advice remain challenging. Here, we present a stepwise approach to achieve the best possible understanding of extremely data-limited stocks and facilitate their management. As a case study we use a stock of the shrimp Plesionika edwardsii (Decapoda, Pandalidae) from the eastern Mediterranean Sea, where the only available data was a sub-optimal sample of length frequencies coming from a small-scale trap fishery. We use a suite of different methods to explore and process the data, estimate the growth parameters, estimate the natural and fishing mortalities, and approximate the reference points, in order to provide a preliminary evaluation of stock status. We implement multiple methods for each step of this process, highlighting the strong and weak points of each one of them. Our approach illustrates the better insights that can be gained by applying ensembles of models, rather than a single ‘best’ model when working with limited data of poor quality. The stepwise approach we propose here is easily transferable to other extremely data-limited stocks to elucidate their status and inform their management.

Small-scale fisheries (SSFs) constitute a substantial component of European fisheries and have a high socioeconomic importance, especially for remote insular areas. Traps produce catches of high quality and value, associated with limited bycatch and low habitat impact. Long-standing trap SSFs in both the Mediterranean and the Atlantic showcase the potential of such SSFs to support remote fishing communities; however, trap SSFs remain relatively understudied. Here, we investigate the spatial and temporal dynamics of a Greek trap SSF targeting Plesionika narval (Fabricius, 1787) in the eastern Mediterranean, by means of Generalized Additive Models fitted on fishers’ logbook data from 2005 to 2014. The dynamics of both catch per unit effort (CPUE) and profits suggest a pronounced seasonality for this fishery, while there are also signs of local overexploitation in the traditional fishing grounds. Additionally, small vessels (

A systematic European Union (EU)-wide data framework for the collection of fisheries data in support of the EU Common Fisheries Policy (CFP) was first implemented in 2002. Since that time, EU data collection regulation has undergone 2 revisions in response to evolving policy needs. The European Commission’s Joint Research Centre (JRC) is responsible for conducting research and providing advice on fisheries management under the CFP, and since 2005 has worked closely with the Scientific, Technical and Economic Committee for Fisheries (STECF). JRC and STECF have an open data policy, and aggregated data submitted by EU member states in response to data calls issued under the provisions of the data collection regulation are published via the website of the STECF. This paper provides an overview of the fisheries data activities carried out by the JRC in support of and in collaboration with the STECF and discusses some of the benefits and drawbacks of such activities.

Discarding is a common practice in fisheries. Total discards are estimated to be about 30 million tons, representing around 23% of worldwide catches. Discarding is an undesirable practice, not only because of the waste of resources, but also because of its contribution to the overexploitation of fish stocks. Several countries have already established discard bans, to different extents (e.g., Norway, Iceland, Chile, New Zealand). The EU’s landing obligation (discard ban) is a major measure of the latest reform of the Common Fisheries Policy for EU fisheries. It aims to reduce unwanted catches in EU fisheries, by incentivizing improved selectivity and restoring fish stocks to levels that can sustain the maximum production over time without harming the biodiversity and the capacity of future generations to obtain fish. However, banning discards will inevitably induce diverse short- and long-term ecological, economic, and social impacts, which may determine whether the landing obligation’s objectives will be achieved.

Summary A survey-based assessment of an eastern Mediterranean data-limited black anglerfish (Lophius budegassa; Spinola, 1807) stock was carried out to elucidate its population and exploitation trends. A catch-based method was also applied to estimate its maximum sustainable yield (MSY). The effect on the long-term spawning stock biomass and yield of a wide range of exploitation regimes (combinations of F and selectivity) was investigated using an age-structured population model parameterised for Mediterranean anglerfish stocks. The analysis indicated an increasing trend of anglerfish fishing mortality (F) in the eastern Mediterranean from the mid-1990s onwards, and that recent catches were 41% higher than the median MSY estimate. Catching Mediterranean anglerfish at least three years after they mature at an F = 0.4–1 year−1 would ensure high yields at sustainable levels of stock depletion. Examination of the empirical exploitation regimes in five anglerfish stocks across the Mediterranean Sea illustrates their unfulfilled potential for higher sustainable yields, mainly due to overexploitation of juveniles.

Meta-analysis of marine biological resources can elucidate general trends and patterns to inform scientists and improve management. Crustacean stocks are indispensable for European and global fisheries; however, studies of their aggregate development have been rare and confined to smaller spatial and temporal scales compared to fish stocks. Here, we study the aggregate development of 63 NE Atlantic and Mediterranean crustacean stocks of six species (Nephrops norvegicus, Pandalus borealis, Parapenaeus longirostris, Aristeus antennatus, Aristaeomorpha foliacea and Squilla mantis) in 1990–2013 using biomass index data from official stock assessments. We implemented a dynamic factor analysis (DFA) to identify common underlying trends in biomass indices and investigate the correlation with the North Atlantic Oscillation (NAO) index. The analysis revealed increasing and decreasing trends in the northern and southern NE Atlantic, respectively, and stable or slowly increasing trends in the Mediterranean, which were not related to NAO. A separate meta-analysis of the fishing mortality (F) and biomass (B) of 39 analytically assessed crustacean stocks was also carried out to explore their development relative to MSY. NE Atlantic crustacean stocks have been exploited on average close to FMSY and remained well above BMSY in 1995–2013, while Mediterranean stocks have been exploited 2–4 times above FMSY in 2002–2012. Aggregate trends of European crustacean stocks are somewhat opposite to trends of fish stocks, suggesting possible cascading effects. This study highlights the two-speed fisheries management performance in the northern and southern European seas, despite most stocks being managed in the context of the European Union's Common Fisheries Policy.

The recent reform of the Common Fisheries Policy (CFP) in Europe highlights the need for improvements in both species and size selectivity. Regarding size selectivity, shifting selectivity towards older/larger fish avoids both growth and recruitment overfishing and reduces unwanted catches. However, the benefits to fish stocks and fishery yields from increasing age/size-at-selection are still being challenged and the relative importance of selectivity compared to that of exploitation rate remains unclear. Consequently, exploitation rate regulations continue to dominate management. Here, an age-structured population model parameterized for a wide range of stocks is used to investigate the effects of selectivity on spawning stock biomass (SSB) and yield. The generic effect of selectivity on SSB and yield over a wide range of stocks is compared to the respective relative effects of exploitation rate and several biological parameters. We show that yield is mainly driven by biological parameters, while SSB is mostly affected by the exploitation regime (i.e. exploitation rate and selectivity). Our analysis highlights the importance of selectivity for fisheries sustainability. Catching fish a year or more after they mature combined with an intermediate exploitation rate (F ≈ 0.3) promotes high sustainable yields at low levels of stock depletion. Examination of the empirical exploitation regimes of 31 NE Atlantic stocks illustrates the unfulfilled potential of most stocks for higher sustainable yields due to high juvenile selection, thus underscoring the importance of protecting juveniles. Explicitly incorporating selectivity scenarios in fisheries advice would allow the identification of optimal exploitation regimes and benefit results-based management.

Complex natural systems, spanning from individuals and populations to ecosystems and social-ecological systems, often exhibit abrupt reorganizations in response to changing stressors, known as regime shifts or critical transitions. Theory suggests that such systems feature folded stability landscapes with fluctuating resilience, fold-bifurcations, and alternate basins of attraction. However, the implementation of such features to elucidate response mechanisms in an empirical context is scarce, due to the lack of generic approaches to quantify resilience dynamics in individual natural systems. Here, we introduce an Integrated Resilience Assessment (IRA) framework: a three-step analytical process to assess resilience and construct stability landscapes of empirical systems. The proposed framework involves a multivariate analysis to estimate holistic system indicator variables, non-additive modelling to estimate alternate attractors, and a quantitative resilience assessment to scale stability landscapes. We implement this framework to investigate the temporal development of the Mediterranean marine communities in response to sea warming during 1985–2013, using fisheries landings data. Our analysis revealed a nonlinear tropicalisation of the Mediterranean Sea, expressed as abrupt shifts to regimes dominated by thermophilic species. The approach exemplified here for the Mediterranean Sea, revealing previously unknown resilience dynamics driven by climate forcing, can elucidate resilience and shifts in other complex systems.

Europe has a long tradition of exploiting marine fishes and is promoting marine economic activity through its Blue Growth strategy. This increase in anthropogenic pressure, along with climate change, threatens the biodiversity of fishes and food security. Here, we examine the conservation status of 1,020 species of European marine fishes and identify factors that contribute to their extinction risk. Large fish species (greater than 1.5 m total length) are most at risk; half of these are threatened with extinction, predominantly sharks, rays and sturgeons. This analysis was based on the latest International Union for Conservation of Nature (IUCN) European regional Red List of marine fishes, which was coherent with assessments of the status of fish stocks carried out independently by fisheries management agencies: no species classified by IUCN as threatened were considered sustainable by these agencies. A remarkable geographic divergence in stock status was also evident: in northern Europe, most stocks were not overfished, whereas in the Mediterranean Sea, almost all stocks were overfished. As Europe proceeds with its sustainable Blue Growth agenda, two main issues stand out as needing priority actions in relation to its marine fishes: the conservation of marine fish megafauna and the sustainability of Mediterranean fish stocks. Marine fishes exhibit high biodiversity 1,2 and have been culturally and nutritionally important throughout human history 3 . Europe, in particular, has a well-documented history of exploiting marine fish populations, written records of which commence in the classical works of ancient Greece. Although this historical exploitation has undoubtedly altered populations 4,5 and changed many seascapes 6 , marine defaunation in the region has not been as great as in terrestrial systems 7 . However, the use of ocean space and resources is increasing due to Europe’s Blue Growth strategy 8 , the nutritional requirements of an expanding human population are growing 9,10 and marine ecosystems will experience unusually rapid changes in future due to climate change 11,12 . Consequently there are imminent threats both to European marine biodiversity and fish resources 13 . It is important, therefore, to assess the threats of extinction to fish species and to ensure consistency in the management approach by the various agencies involved. We analysed data on the conservation status of 1,020 species of Europe’s marine fishes from the recent International Union for Conservation of Nature (IUCN) Red List assessments 14 to identify characteristics that make Europe’s fishes most susceptible to extinction risk. We then compared the Red List with 115 fish stock assessments (of 31 species) made by intergovernmental agencies charged with providing advice on the exploitation of commercial fishes. Previous comparisons of this sort applied criteria under various modelling assumptions 15,16, 17 or limited the comparison to biomass reference points 18 .

Nature Ecology & Evolution 1, 0170 (2017); published 26 May 2017; corrected 12 June 2017. In the original version of this Article, the European Commission was mistakenly included as an affiliation for Christos D. Maravelias. His contribution to this work was exclusively completed while at the Hellenic Centre for Marine Research.

International audience; Fisheries policy is increasingly influenced by civil society organizations. The newest example of this is the formulation of the landing obligation, a regulation that should reduce the contested practice of discarding unwanted fish. In this paper the implementation process of the landing obligation in four European countries is compared. From this comparison it becomes clear that fishers are working on diminishing discards. However it also shows that for the legitimacy, and the effectiveness of policy it is not only vital to increase the influence of civil society actors, but also the participation of resource users. Their views, knowledge, and cooperation are vital for a successful implementation of the regulation. Otherwise, resistance become too high, and regulation becomes more symbolic than a tool for change.

Exploitation rate, as measured by average fishing mortality, has been a major focus of fisheries management in the past half century in the NE Atlantic and its temporal development and negative impact on stock status are well-documented. This is not the case for juvenile exploitation, i.e. the proportional fishing mortality of juveniles, despite the expected benefits from allowing fish to spawn before capture. In this study, we describe the aggregate (cross-stock) temporal development of fishing mortality, juvenile exploitation and stock status for three ecologically distinct groups of ICES stocks (demersal roundfish, pelagic and flatfish stocks) and separately for cod stocks and NE Arctic (Barents Sea) stocks. Both the long- and short-term effects of the variation in fishing mortality and juvenile exploitation on the temporal development of stock status were explored within all five groups. The long-term aggregate temporal trends were represented for each group by calculating the average values of fishing mortality, juvenile exploitation and stock status over all stocks by year. On aggregate, time periods with high fishing mortalities, in conjunction with high juvenile exploitation, are associated with rapid declines in stock status. Stocks are better able to withstand higher fishing mortalities when juvenile exploitation is low. The short-term effects of fishing mortality and juvenile exploitation on aggregate stock status were investigated using multiple linear regressions. Significant negative effects of recent fishing mortality on stock status were found for all groups of stocks examined, whereas the effects of recent juvenile exploitation were mostly non-significant. Overall, the results indicate that when ICES stocks are considered on aggregate, exploitation rate is the main driver of stock status trends through time.

Vasilakopoulos, P., O'Neill, F. G., and Marshall, C. T. 2011. Misspent youth: does catching immature fish affect fisheries sustainability? – ICES Journal of Marine Science, 68: 1525–1534. The “spawn-at-least-once” principle suggests that sustainability is secured if fish become vulnerable to commercial gears only after they have spawned. However, some studies suggest that protecting immature fish is not essential to sustainability because extrinsic factors determine both recruitment and stock status. A meta-analysis was conducted to quantify the independent effects of exploitation pattern and exploitation rate on current stock status. The analysis used empirical data for 38 fish stocks of 13 species in the NE Atlantic. Two metrics of exploitation pattern were used and their sensitivity was compared. As expected, exploitation rate had a significant negative effect on current stock status. Exploitation patterns associated with high proportional fishing mortality of immature fish also had a significant negative effect on current stock status, providing empirical support for the “spawn-at-least-once” principle. When the fishing mortality of immature fish exceeds half that of mature fish, stock status falls below precautionary limits. Our results suggest that a sensitive metric of exploitation pattern could provide useful information about an aspect of exploitation that is currently overlooked by fisheries management regimes that focus primarily on exploitation rate.

The oilfish,Ruvettus pretiosus, is an incidental by-catch of the drifting surface longlines targeting swordfish and Thunnidae in the Mediterranean and elsewhere. Despite its global distribution and frequent occurrence in the catch of many fishing gears, little is known about its biology. In this study we examined the dietary preferences and reproductive biology of this species from specimens caught in the eastern Mediterranean. The most numerous and frequently occurring prey items were benthopelagic fish, followed by cephalopods. The sex-ratio was highly skewed in favour of females (1:8.4), while histological examination of the collected ovaries displayed six developmental stages (perinucleolar, early and late lipid stage; early, middle and late vitellogenesis). Oocyte diameter ranged from 23–69 μm at the perinucleolar stage to 224–366 μm at the late vitellogenesis stage. Spawning is expected to occur during mid and late summer; however there were no individuals available from this period. The findings are discussed in relation to the ecology of the species.

In this third Collective Article, with fisheries-related data from the Mediterranean Sea, we present the historical length distribution of Lophius budegassa in the catch of commercial trawlers in the Greek seas; length-weight and length-length relationships of five flatfish species ( Lepidorhombus boscii, L. whiffiagonis , Platichthys flesus , Pegusa lascaris and Solea solea ) from different coastal areas of Turkey (Black Sea and Eastern Mediterranean Sea); growth of settled Polyprion americanus and length-weight relationships of this species and of Deltentosteus quadrimaculatus , Capros aper and three commercially important groupers in the Eastern Mediterranean Sea; the age, growth and mortality of Zosterisessor ophiocephalus in the Eastern Adriatic Sea; the length-weight relationship and condition factor of Atherina boyeri in a Central Mediterranean semi-isolated lagoon, and also the length-weight and length-length relationships of three Alburnus species from different inland waters in Turkey.

Complex natural systems with eroded resilience, such as populations, ecosystems and socio-ecological systems, respond to small perturbations with abrupt, discontinuous state shifts, or critical transitions. Theory of critical transitions suggests that such systems exhibit fold bifurcations featuring folded response curves, tipping points and alternate attractors. However, there is little empirical evidence of fold bifurcations occurring in actual complex natural systems impacted by multiple stressors. Moreover, resilience of complex systems to change currently lacks clear operational measures with generic application. Here, we provide empirical evidence for the occurrence of a fold bifurcation in an exploited fish population and introduce a generic measure of ecological resilience based on the observed fold bifurcation attributes. We analyse the multivariate development of Barents Sea cod (Gadus morhua), which is currently the world's largest cod stock, over six decades (1949-2009), and identify a population state shift in 1981. By plotting a multivariate population index against a multivariate stressor index, the shift mechanism was revealed suggesting that the observed population shift was a nonlinear response to the combined effects of overfishing and climate change. Annual resilience values were estimated based on the position of each year in relation to the fitted attractors and assumed tipping points of the fold bifurcation. By interpolating the annual resilience values, a folded stability landscape was fit, which was shaped as predicted by theory. The resilience assessment suggested that the population may be close to another tipping point. This study illustrates how a multivariate analysis, supported by theory of critical transitions and accompanied by a quantitative resilience assessment, can clarify shift mechanisms in data-rich complex natural systems.

In this second Collective Article with fisheries-related data from the Mediterranean Sea we present the evaluation of bony structures in aging of Barbus tauricus, otolith dimensions-body length relationships for two species (Trachinus draco and Synchiropus phaeton), information on the growth of juvenile Thunnus thynnus and of Ruvettus pretiosus, weight-length relationships for three species (Aulopus fiamentosus, Thunnus thynnus and Tylosurus acus imperialis) and data on feeding habits and reproduction of Aulopus fiamentosus.

SummaryIn recent years, fisheries management has succeeded in stabilizing and even improving the state of many global fisheries resources [1–5]. This is particularly evident in areas where stocks are exploited in compliance with scientific advice and strong institutional structures are in place [1, 5]. In Europe, the well-managed northeast (NE) Atlantic fish stocks have been recovering in response to decreasing fishing pressure over the past decade [3–6], albeit with a long way to go for a universal stock rebuild [3, 7]. Meanwhile, little is known about the temporal development of the European Mediterranean stocks, whose management relies on input controls that are often poorly enforced. Here, we perform a meta-analysis of 42 European Mediterranean stocks of nine species in 1990–2010, showing that exploitation rate has been steadily increasing, selectivity (proportional exploitation of juveniles) has been deteriorating, and stocks have been shrinking. We implement species-specific simulation models to quantify changes in exploitation rate and selectivity that would maximize long-term yields and halt stock depletion. We show that stocks would be more resilient to fishing and produce higher long-term yields if harvested a few years after maturation because current selectivity is far from optimal, especially for demersal stocks. The European Common Fisheries Policy that has assisted in improving the state of NE Atlantic fish stocks in the past 10 years has failed to deliver similar results for Mediterranean stocks managed under the same policy. Limiting juvenile exploitation, advancing management plans, and strengthening compliance, control, and enforcement could promote fisheries sustainability in the Mediterranean.