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Abstract

Managing fisheries presents trade-offs between objectives, for example yields, profits, minimizing ecosystem impact, that have to be weighed against one another. These trade-offs are compounded by interacting species and fisheries at the ecosystem level. Weighing objectives becomes increasingly challenging when managers have to consider opposing objectives from different stakeholders. An alternative to weighing incomparable and conflicting objectives is to focus on win–wins until Pareto efficiency is achieved: a state from which it is impossible to improve with respect to any objective without regressing at least one other. We investigate the ecosystem-level efficiency of fisheries in five large marine ecosystems (LMEs) with respect to yield and an aggregate measure of ecosystem impact using a novel calibration of size-based ecosystem models. We estimate that fishing patterns in three LMEs (North Sea, Barents Sea and Benguela Current) are nearly efficient with respect to long-term yield and ecosystem impact and that efficiency has improved over the last 30 years. In two LMEs (Baltic Sea and North East US Continental Shelf), fishing is inefficient and win–wins remain available. We additionally examine the efficiency of North Sea and Baltic Sea fisheries with respect to economic rent and ecosystem impact, finding both to be inefficient but steadily improving. Our results suggest the following: (i) a broad and encouraging trend towards ecosystem-level efficiency of fisheries; (ii) that ecosystem-scale win–wins, especially with respect to conservation and profits, may still be common; and (iii) single-species assessment approaches may overestimate the availability of win–wins by failing to account for trade-offs across interacting species.

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... One critical challenge for the theory underlying EBFM is predicting which harvest policies are most efficient at the ecosystem level, that is those that best satisfy a trade-off between maximizing fishery yield or profit and producing a desired community state (e.g. a sustainable biomass level) (Andersen, Brander, & Ravn-Jonsen, 2015;Jacobsen, Burgess, & Andersen, 2017). For example, traditional population-based perspectives on optimal multispecies fishery management typically indicated that the pathway to efficiency was selective targeting of only the most productive and marketable species at mature sizes; however, contradictory results from modern ecosystem models have led some researchers to the conclusion that unselective fishing, or harvesting all species and sizes in proportion to their productivity would produce better outcomes (Garcia et al., 2012). ...
... Fish vital rates are most affected by size, and body size also determines the distribution of abundance among marine species (Sheldon & Parsons, 1967;Sheldon, Prakash, & Sutcliffe, 1972) through basic physiological constraints of predator-prey interactions (Andersen & Beyer, 2006). Recently developed community models using individual size as a functional trait are providing general insights for multispecies harvest strategies (Andersen, Brander, et al., 2015;Jacobsen et al., 2017;Jacobsen, Gislason, & Andersen, 2014), and we expect that development and use of similar trait-based models will be critical for designing specific policy actions and evaluating their performance towards the implementation of EBFM. ...
... Furthermore, the models have been applied to several large marine ecosystems to predict efficient ecosystem level fishing patterns. These applications inform strategic EBFM by quantifying the trade-off between yield and ecosystem state, through incorporating biotic interactions between different sized individuals and how they are affected by fishing (Jacobsen et al., 2017). ...
Article
Analysing how fish populations and their ecological communities respond to perturbations such as fishing and environmental variation is crucial to fisheries science. Researchers often predict fish population dynamics using species‐level life‐history parameters that are treated as fixed over time, while ignoring the impact of intraspecific variation on ecosystem dynamics. However, there is increasing recognition of the need to include processes operating at ecosystem levels (changes in drivers of productivity) while also accounting for variation over space, time and among individuals. To address similar challenges, community ecologists studying plants, insects and other taxa increasingly measure phenotypic characteristics of individual animals that affect fitness or ecological function (termed “functional traits”). Here, we review the history of trait‐based methods in fish and other taxa, and argue that fisheries science could see benefits by integrating trait‐based approaches within existing fisheries analyses. We argue that measuring and modelling functional traits can improve estimates of population and community dynamics, and rapidly detect responses to fishing and environmental drivers. We support this claim using three concrete examples: how trait‐based approaches could account for time‐varying parameters in population models; improve fisheries management and harvest control rules; and inform size‐based models of marine communities. We then present a step‐by‐step primer for how trait‐based methods could be adapted to complement existing models and analyses in fisheries science. Finally, we call for the creation and expansion of publicly available trait databases to facilitate adapting trait‐based methods in fisheries science, to complement existing public databases of life‐history parameters for marine organisms.
... Ideally, the period for calibration should exhibit relative stability, but such periods do not exist in the Baltic Sea, which is greatly influenced by anthropogenic activities and has undergone dramatic structural changes over the last four decades (Möllmann et al. 2009). We chose to calibrate our model to the time period of 1992-2002 as in Jacobsen et al. (2017), which is a period after an ecological regime shift, characterized by high fishing mortality on cod, low cod and herring abundance and high sprat abundance (Gårdmark et al. 2015) (Fig. S4). The cut-off at 2002 also ensured that we did not calibrate the model to the period starting from mid 2000's when the growth capacity, condition, ...
... , determines the maximum number of offspring that can be produced by a population in a given time step and serves as a density independent cap on reproduction. This parameter determines how species will respond to exploitation and perturbations, and is one of the main parameters that is calibrated in multispecies models (e.g., Blanchard et al. 2014;Jacobsen et al. 2017). We used the "L-BFGS-B" ...
... Growth curves emerging from the model were in close agreement with von Bertalanffy curves fitted to length-at-age data from trawl surveys (Fig. S6), after a stepwise manual increase of the constant in the allometric maximum-consumption rate (ℎ ) (Supporting Information). The level of density dependence imposed by the stock-recruitment function (see Eq. 14-15) was also evaluated by assessing the ratio of the physiological recruitment, ℎ , , to the recruitment (Jacobsen et al. 2017) (Supporting Information). These final values mean that stock recruitment is sensitive to the stock biomass, but there is some density dependence limiting recruitment (i.e., not all spawn produced become recruits). ...
Article
Full-text available
Resolving the combined effect of climate warming and exploitation in a food web context is key for predicting future biomass production, size‐structure, and potential yields of marine fishes. Previous studies based on mechanistic size‐based food web models have found that bottom‐up processes are important drivers of size‐structure and fisheries yield in changing climates. However, we know less about the joint effects of ‘bottom‐up’ and physiological effects of temperature; how do temperature effects propagate from individual‐level physiology through food webs and alter the size‐structure of exploited species in a community? Here we assess how a species‐resolved size‐based food web is affected by warming through both these pathways, and by exploitation. We parameterize a dynamic size spectrum food web model inspired by the offshore Baltic Sea food web, and investigate how individual growth rates, size‐structure, relative abundances of species and yields are affected by warming. The magnitude of warming is based on projections by the regional coupled model system RCA4‐NEMO and the RCP 8.5 emission scenario, and we evaluate different scenarios of temperature dependence on fish physiology and resource productivity. When accounting for temperature‐effects on physiology in addition to on basal productivity, projected size‐at‐age in 2050 increases on average for all fish species, mainly for young fish, compared to scenarios without warming. In contrast, size‐at‐age decreases when temperature affects resource dynamics only, and the decline is largest for young fish. Faster growth rates due to warming, however, do not always translate to larger yields, as lower resource carrying capacities with increasing temperature tend to result in declines in the abundance of larger fish and hence spawning stock biomass. These results suggest that to understand how global warming affects the size structure of fish communities, both direct metabolic effects and indirect effects of temperature via basal resources must be accounted for.
... The interaction matrix parameters were further explored 367 in uncertainty analyses. 368 369 One of the key parts of model parametrisation and calibration is finding parameters for reproduction and 370 recruitment that enable species co-existence, reasonable biomass values, and expected resilience to 371 exploitation (Jacobsen et al. 2017). To this end, we iteratively tuned two species-specific reproduction 372 parameters -the maximum recruitment parameter Rmax and the reproductive efficiency parameter (Eq10, 373 11 in Table S1). ...
... Most multi-species food web and complex models with large numbers of parameter apply a 389 similar procedure (e.g. (Smith et al. 2015, Jacobsen et al. 2017, Ayllón et al. 2021), with 390 more rigorous parameter uncertainty evaluation limited to specific cases (e.g. (Thorpe et al. 2015, Spence 391 et al. 2016) and mostly focusing on species recruitment parameters (Rmax) evaluated against time series of 392 catches. ...
... Assumptions about the stock-recruitment relationship in each species is likely to have large effects on the emergent species response to fishing. This response will be determined by species reproduction parameters, such as maturation size, reproduction allocation curve, as well as reproduction efficiency and maximum recruitment parameters (ε and Rmax) (see , chapter 4, (Jacobsen et al. 2017) for further details). Therefore, in order to achieve reasonable species dynamics in response to fishing it is important to ensure that linear and non-linear terms of recruitment dynamics (defined by ε and Rmax) are in a reasonable range. ...
... First, when different parts of a system interact (e.g., shipping impacts the fishing industry), managing each component separately tends to produce sub-optimal outcomes at the system level, even if all components are managed for the same objectives. For example, managing several interacting fish stocks individually to maximum sustainable yield (MSY) will almost never result in ecosystem-wide MSY [4,5]. Second, models and projections of individual components of the system are often biased by failing to account for interactions with other components. ...
... Studies have evaluated the efficiency of resource management in a wide variety of contexts. Often, they have found the current management or state to be inefficient (e.g., Polasky et al. [15] in the context of land use; Mueller et al. [16] in the context of fertilizer use; Jacobsen et al. [5] in the context of fishing within an ecosystem). No study can evaluate every possible objective, so some management systems may seem inefficient in lower dimensions when they are actually efficient once other important objectives are accounted for (illustrated in Fig. 1B; e.g., see [17,18] for discussion in the context of incorporating often unaccounted-for equity objectives). ...
... [48,49]), size-or niche-based species-interaction rules (e.g. [50], and others deriving from it [5]). For a simple example (Fig. 2E), bioenergetic accounting allows measurements of trophic transfer efficiencies and primary production to translate into available production estimates for all trophic levels (see [51] for review), which can be compared with catches-even if biomass is not known-to assess ecosystem-wide fishery sustainability [52]. ...
... Multi-species size spectrum models (MSSMs) include a more detailed physiological description of individual life histories than other modeling approaches that permit size and stage-structured diet shifts (e.g. Atlantis, Ecopath with Ecosim, Gadget; Persson et al. 2014) and their ability to represent species and their fisheries, which are inherently size-selective, make them useful tools for evaluating harvest tradeoffs and management strategies (Houle et al. 2012, Blanchard et al. 2014, Kolding et al. 2015, Zhang et al. 2016, Jacobsen et al. 2017). In previous MSSM simulation studies, removal of large individuals through fishing triggered damped oscillations down the size spectrum, analogous to the alternating changes in abundance with trophic level that typify top-down cascades in conventional food chain models (Andersen and Pedersen 2010, Houle et al. 2012, Rossberg 2012, Szuwalski et al. 2017. ...
... to scale prey encounter rates according to relative predation risk (Jacobsen et al. 2017). ...
... We do this by developing two sets of alternative MSSMs. The first model set consists of size-invariant prey species preferences that are derived from different assumptions about the processes influencing prey preference (Blanchard et al. 2014, Jacobsen et al. 2017, Szuwalski et al. 2017. Following the approach of previous studies, the models were calibrated to the EBS using biomass and catch data. ...
Article
Ontogenetic diet shifts are pervasive in food webs, but rules governing their emergence and the implications for trophic cascades are only partly understood. Recent theoretical advances in multispecies size spectrum models (MSSMs) predict that the emergence of ontogenetic diet shifts are driven primarily by size‐selective predation and changes in the relative abundances of suitably sized prey. However, these assumptions have not yet been tested with data. Here, we developed alternative MSSMs based on different assumptions about the nature of species and size‐based preferences and tested them using an extensive dietary database for the Eastern Bering Sea (EBS). MSSMs with both size and species‐specific prey preferences correctly predicted approximately three‐fold more of the diet links than those that assumed fixed species preferences. Importantly, these model assumptions also had a profound effect on the strength of fishing‐induced trophic cascades and the emergent trophic structure of the community with and without fishing. The diet‐informed models exhibited lower predation mortality rates, particularly for small individuals (less than 1 g) which, in turn, reduced the intensity and reach of fishing‐induced trophic cascades up the size spectrum. If the level and size dependency of piscivory observed in EBS predators is typical of other systems, the potential for fishing‐induced trophic cascades may be over‐stated in MSSMs as they are currently formulated and parameterized. Representation of species‐specific ontogenetic shifts in diet can strongly influence system responses to perturbations, and the extensions we propose should accelerate adoption of MSSMs as frameworks for exploring size‐based food web theory and developing modeling tools to support strategic management decisions. This article is protected by copyright. All rights reserved.
... Contemporary fisheries management is founded on catch-based reference points that quantify the maximum sustainable yield (MSY) available from single-species stocks (Costello et al., 2016;Hilborn et al., 2020) and occasionally as the multispecies maximum sustainable yield (mMSY) (Briton et al., 2019). MSY has been pivotal in rebuilding fish catches in multiple locations (Hilborn et al., 2020) but can conflict with management objectives when species or stocks have ecological or social values that are compromised by fishing at maximum sustainable catch limits, such as conservation status or economic profitability (Andersen et al., 2015;Jacobsen et al., 2017;Matsuda & Abrams, 2006). As a result, maximum economic yield (Dichmont et al., 2010) and ecosystem indicators (Jennings, 2005;Shin et al., 2005) have been developed to understand synergies and trade-offs between MSY and distinct management objectives. ...
... We develop a conceptual framework to estimate multispecies Maximum Nutrient Yield (mMNY) for fisheries and examine potential trade-offs with mMSY. Next, we combine nutrient content data (Hicks et al., 2019) with two empirically validated multispecies models that have been used to explore fisheries policy objectives for the North Sea and Baltic Sea (Jacobsen et al., 2017). Following previous use of these models, our analysis is designed for strategic use in evaluating management approaches, here to demonstrate a proof-of-concept for mMNY, rather than tactical use in setting catch limits and evaluating uncertainty in parameter estimation Plagányi et al., 2014). ...
... Data Availability Statement 10 et al., 2014) and a Baltic Sea fish assemblage of 3 interacting pelagic and demersal species (Jacobsen et al., 2017). Species are defined by species-specific life-history parameters, and allometric scaling rules are used to scale individual processes (growth and mortality) to population-and community-level size structure (Andersen et al., 2016;Jacobsen et al., 2014). ...
Article
Full-text available
Wild-caught fish are a bioavailable source of nutritious food that, if managed strategically , could enhance diet quality for billions of people. However, optimising nutrient production from the sea has not been a priority, hindering development of nutrition-sensitive policies. With fisheries management increasingly effective at rebuilding stocks and regulating sustainable fishing, we can now begin to integrate nutritional outcomes within existing management frameworks. Here, we develop a conceptual foundation for managing fisheries for multispecies Maximum Nutrient Yield (mMNY). We empirically test our approach using size-based models of North Sea and Baltic Sea fisheries and show that mMNY is predicted by the relative contribution of nutritious species to total catch and their vulnerability to fishing, leading to trade-offs between catch and specific nutrients. Simulated nutrient yield curves suggest that vitamin D, which is deficient in Northern European diets, was underfished at fishing levels that returned maximum catch weights. Analysis of global catch data shows there is scope for nutrient yields from most of the world's marine fisheries to be enhanced through nutrient-sensitive fisheries management. With nutrient composition data now widely available, we expect our mMNY framework to motivate development of nutrient-based reference points in specific contexts, such as data-limited fisheries. Managing for mMNY alongside policies that promote access to fish could help close nutrient gaps for coastal populations, maximising the contribution of wild-caught fish to global food and nutrition security. K E Y W O R D S fisheries management, food security, nutrition, overfishing, seafood, sustainable fisheries 2 | ROBINSON et al.
... To make the idea of EBFM operational, ecosystem models are necessary to predict future changes in fisheries yields and ecosystem dynamics with respect to different fishing patterns and management regimes. Recent decades have witnessed growing interest and a bloom of ecosystem models (Blanchard et al., 2012;Jacobsen et al., 2013Jacobsen et al., , 2017. However, ecosystem models usually include a multitude of parameters and require intense efforts in data collection and model validation (Garcia, 2003). ...
... Toward sustainable fishery and health ecosystem, it is important to avoid unintended community consequences, including habitat destruction, decline in non-target species, and changes in the function and structure of ecosystems (Pikitch et al., 2004). Ecosystem models could be used to address the knowledge gaps, e.g., assessing the current state and changes of the ecosystem, examining the effects of human-induced and environmental changes (Blanchard et al., 2012;Jacobsen et al., 2013Jacobsen et al., , 2017, clarifying species interactions , diversitystability links (Zhang et al., 2013), and eco-evolutionary processes (Zhang, L. et al., 2015). Therefore, we highlight that the MSSM can contribute to the management of mixed fisheries because it could account for the species interactions and external disturbances and capture temporal changes across the community. ...
Article
Full-text available
Ecosystem models have been developed for detecting community responses to fishing pressure and have been widely applied to predict the ecological effects of fisheries management. Key challenges of ecosystem modeling lie in the insufficient quantity and quality of data, which is unfortunately common in the marine ecosystems of many developing countries. In this study, we aim to model the dynamics of multispecies fisheries under data-limited circumstances, using a multispecies size-spectrum model (MSSM) implemented in the coastal ecosystem of North Yellow Sea, China. To make most of available data, we incorporated a range of data-limited methods for estimating the life-history parameters and conducted model validation according to empirical data. Additionally, sensitivity analyses were conducted to evaluate the impacts of input parameters on model predictions regarding the uncertainty of data and estimating methods. Our results showed that MSSM could provide reasonable predictions of community size spectra and appropriately reflect the community composition in the studied area, whereas the predictions of fisheries yields were biased for certain species. Errors in recruitment parameters were most influential on the prediction of species abundance, and errors in fishing efforts substantially affected community-level indicators. This study built a framework to integrate parameter estimation, model validation, and sensitivity analyses altogether, which could guide model development in similar mixed and data-limited fisheries and promote the use of size-spectrum model for ecosystem-based fisheries management.
... In some ecoregions, fishing mortality values from SSMs either do not exist for all species or only qualitative patterns are reported. In studies with MSMs, fishing dynamics for species without fishing mortality values from SSMs are added using ad hoc methods (Jacobsen et al., 2017). Further, as models are simplifications of reality and often the fishing mortality is treated as a "tuning parameter," the fishing mortality values lose their interpretation outside of the fitted model (Rougier & Beven, 2013). ...
... Before this study, fitting size-based MSMs to species that did not have full assessments with absolute values of the fishing mortality was not possible without making strong assumptions about their fishing mortality values (Jacobsen et al., 2017). This would be particularly the case for species with limited data (Quárou & Tomini, 2013). ...
Article
In marine management, fish stocks are often managed on a stock‐by‐stock basis using single‐species models. Many of these models are based upon statistical techniques and are good at assessing the current state and making short‐term predictions; however, as they do not model interactions between stocks, they lack predictive power on longer timescales. Additionally, there are size‐based multi‐species models that represent key biological processes and consider interactions between stocks such as predation and competition for resources. Due to the complexity of these models, they are difficult to fit to data, and so many size‐based multi‐species models depend upon single‐species models where they exist, or ad hoc assumptions when they do not, for parameters such as annual fishing mortality. In this paper, we demonstrate that by taking a state‐space approach, many of the uncertain parameters can be treated dynamically, allowing us to fit, with quantifiable uncertainty, size‐based multi‐species models directly to data. We demonstrate this by fitting uncertain parameters, including annual fishing mortality, of a size‐based multi‐species model of the Celtic Sea, for species with and without single‐species stock assessments. Consequently, errors in the single‐species models no longer propagate through the multi‐species model and underlying assumptions are more transparent. Building size‐based multi‐species models that are internally consistent, with quantifiable uncertainty, will improve their credibility and utility for management. This may lead to their uptake by being either used to corroborate single‐species models; directly in the advice process to make predictions into the future; or used to provide a new way of managing data‐limited stocks.
... Multispecies and ecosystem models are often complex and still mostly used for strategic advice (e.g. Jacobsen et al. 2016;Skern-Mauritzen et al. 2016), but there has recently been considerable attention paid to building MICE (i.e. models of a small subset of ecosystem components chosen based on the management question and data availability) that can be fit to data (rather than parameterized) and have an explicit tactical focus (Plag anyi et al. 2014). ...
... Of course, avoiding potential statistical biasthe focus of this studyis but one of many important considerations in prioritizing transitions from single-species to ecosystem-based management approaches (see Dickey-Collas et al. 2014;Plag anyi et al. 2014 for a more detailed discussion of some of the other considerations designing models and their scope). For example, one of most important functions of ecosystem modelling approaches is to quantify trade-offs between multiple competing objectives, which are often created in large part by the interactions between different ecosystem components (see Jacobsen et al. 2016;Rindorf et al. 2016;Weijerman et al. 2016, for recent examples from diverse ecosystems). Getting the most value from limited data collection and management budgets is another important consideration. ...
Article
Full-text available
Fished populations exist within complex ecosystems but are typically assessed using single species models. It is often lamented that stock assessments rarely account for other ecosystem components explicitly, but in most fisheries there are clear difficulties in implementing data-intensive ecosystem-based assessment approaches. Addressing these competing challenges requires prioritizing investments in expanded assessment frameworks. To provide high-level conceptual guidance to such prioritization, here we use general analytical theory to identify (i) characteristics of fish stocks that tend to facilitate or inhibit the precision and accuracy of reference points from single-species assessments , (ii) characteristics of ecosystem components that introduce the greatest bias/ imprecision into single-species reference points and (iii) warning signs within single-species frameworks that important ecosystem components may not be adequately accounted for. We synthesize and expand on theories from various branches of applied mathematics addressing analogous questions. Our theory suggests that (i) slow population dynamics (relative to the dynamics of other ecosystem components) and a wide range of abundance observations promote precision and accuracy of single-species reference points; (ii) ecosystem components that strongly influence the focal stock's growth, and change on similar timescales as the focal stock's abundance, introduce the greatest bias/imprecision to single-species reference points; and (iii) signs of potential challenges for single-species assessment include fast population dynamics, 'hydra effects' (i.e. abundance and fishing pressure simultaneously increase), and recently detected extinctions, invasions or regime shifts in closely connected ecosystem components. Our results generalize to other levels of abstraction and provide strategic insights complementing tactical simulation approaches such as management strategy evaluation.
... Here, we ask how large the contribution of predation mortality is as a driver of forage fish dynamics, to understand the role of top-down control on forage fish variability. Top-down control has previously been shown to influence marine prey populations (Worm & Myers, 2003), and models predict that decreasing predation mortality by fishing predators can lead to an increase in forage fish catches (Andersen, Brander, & Ravn-Jonsen, 2015;Jacobsen, Burgess, & Andersen, 2017;Szuwalski, Burgess, Costello, & Gaines, 2017). We specifically asked whether changes in predation mortality are depensatory (increasing with decreasing abundance and vice versa), as is expected from standard functional response models, or whether they are compensatory (increasing with increasing abundance) as is expected if predators shift feeding towards abundant prey (Anderson, 2001). ...
... is still an open question with conflicting proposals: a decrease in forage fish exploitation to accommodate food for predators (Pikitch et al., 2014), an increase in catches of smaller fish due to their high productivity (Garcia et al., 2012;Jacobsen, Gislason, & Andersen, 2014) or the more pragmatic "efficiency frontiers" that choose the best strategy in an ecosystem based on economic or yield efficiency (Jacobsen et al., 2017). We recommend combining strategic and tactical approaches to obtain a better understanding of mechanisms underlying forage fish dynamics to guide management on long and short time scales. ...
Article
Forage fish are a vital part of marine ecosystems, partly by supporting some of the largest fisheries worldwide, but also due to their role in food webs as prey for larger fish and other predators. One of the unresolved questions about forage fish dynamics is the causes of their significant temporal fluctuations. These fluctuations are often attributed to changes in environmental conditions, but direct correlations have proven hard to find. Here, we show how time‐varying predation mortality additionally plays a substantial role in forage fish population fluctuations. By analysing 10 stocks that have estimates of natural mortality changes through time, we find that natural mortality on average increases as population biomass declines towards a trough, and to a lesser degree decreases, when their biomass is growing towards a peak. While depensatory mortality was dominant on average in biomass dynamics leading up to peaks or troughs, some of the stocks exhibited compensatory mortality emphasizing variation between stocks. Furthermore, we show that the magnitude of natural mortality and productivity is generally higher than fishing mortality. The results underscore the importance of top‐down control on the dynamics of forage fish. We conclude that a holistic ecosystem analysis is required for a better ecological understanding of forage fish dynamics.
... Second, when ontogenetic variation in body size is small (e.g., in seabirds [65]) simpler unstructured, stage-structured, or allometric models (that use a mean body size) are likely to be more appropriate than SSMs [4,66]. Third, SSMs have generally been applied at regional and larger spatial [57,67,68] scales, and might not be as appropriate at finer scales [33]. Many management-related questions need to be addressed on a local scale where the community dynamics might be well understood in terms of species and habitat interactions [69], and the size-dependent nature of these interactions are nuances rather than key drivers of the dynamics. ...
... Despite SSMs not having been fully developed all the way from bacteria to whales, in many respects, the recent achievements of size-based models extend beyond Sheldon[ 3 1 _ T D $ D I F F ] 's initial vision for describing the size spectrum (Box 2). SSMs are being used to examine: spatial distributions of abundance [6], species interactions [57], diversity-stability links [55], eco-evolutionary processes [70], and consequences of human-induced and environmental change [68,71,72]. Here, we highlight four promising research innovations that will help us realize the full potential and wider generality of this approach for modeling whole ecosystems. ...
Article
Size-based ecosystem modeling is emerging as a powerful way to assess ecosystem-level impacts of human- and environment-driven changes from individual-level processes. These models have evolved as mechanistic explanations for observed regular patterns of abundance across the marine size spectrum hypothesized to hold from bacteria to whales. Fifty years since the first size spectrum measurements, we ask how far have we come? Although recent modeling studies capture an impressive range of sizes, complexity, and real-world applications, ecosystem coverage is still only partial. We describe how this can be overcome by unifying functional traits with size spectra (which we call functional size spectra) and highlight the key knowledge gaps that need to be filled to model ecosystems from bacteria to whales.
... An alternative is to assign multiple objectives and present a set of policies that represents the best possible trade-offs between them. This is multi-objective optimisation (Deb 2001;Luke 2009) the output of which is a Pareto front: the set of efficient (highest scoring) choices over the full range of policy variable combinations (see Jacobsen et al. 2017, for a fisheries example). One way to understand the Pareto front is to consider it as the 'budget constraint' for the policy maker, in that it expresses what must be given up in one objective to improve another. ...
Article
Full-text available
Sustainable management of complex human–environment systems, and the essential services they provide, remains a major challenge, felt from local to global scales. These systems are typically highly dynamic and hard to predict, particularly in the context of rapid environmental change, where novel sets of conditions drive coupled socio-economic-environmental responses. Faced with these challenges, our tools for policy development, while informed by the past experience, must not be unduly constrained; they must allow equally for both the fine-tuning of successful existing approaches and the generation of novel ones in unbiased ways. We study ocean fisheries as an example class of complex human–environmental systems, and present a new model (POSEIDON) and computational approach to policy design. The model includes an adaptive agent-based representation of a fishing fleet, coupled to a simplified ocean ecology model. The agents (fishing boats) do not have programmed responses based on empirical data, but respond adaptively, as a group, to their environment (including policy constraints). This conceptual model captures qualitatively a wide range of empirically observed fleet behaviour, in response to a broad set of policies. Within this framework, we define policy objectives (of arbitrary complexity) and use Bayesian optimization over multiple model runs to find policy parameters that best meet the goals. The trade-offs inherent in this approach are explored explicitly. Taking this further, optimization is used to generate novel hybrid policies. We illustrate this approach using simulated examples, in which policy prescriptions generated by our computational methods are counterintuitive and thus unlikely to be identified by conventional frameworks.
... Size spectra describe the abundance of individuals in a food web as a function of body size (Sheldon, Prakash, & Sutcliffe, 1972). The first size spectrum models were developed to explain remarkably consistent size spectra slopes in pelagic food webs (Sheldon et al., 1972;Sprules & Barth, 2015), with recent extensions developed to investigate human and environmental impacts on marine ecosystems (e.g., Blanchard et al., 2014;Jacobsen, Burgess, & Andersen, 2017;Jennings & Blanchard, 2004;Jennings & Collingridge, 2015;Rochet & Benoît, 2012). Broadly, size spectrum models can be divided according to whether they provide equilibrium (static) predictions of size spectra or model system processes and size distributions dynamically (Blanchard, Heneghan, Everett, Trebilco, & Richardson, 2017). ...
Article
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Food web structure and dynamics depend on relationships between body sizes of predators and their prey. Species‐based and community‐wide estimates of preferred and realized predator–prey mass ratios (PPMR) are required inputs to size‐based size spectrum models of marine communities, food webs, and ecosystems. Here, we clarify differences between PPMR definitions in different size spectrum models, in particular differences between PPMR measurements weighting prey abundance in individual predators by biomass (rbio) and numbers (rnum). We argue that the former weighting generates PPMR as usually conceptualized in equilibrium (static) size spectrum models while the latter usually applies to dynamic models. We use diet information from 170,689 individuals of 34 species of fish in Alaskan marine ecosystems to calculate both PPMR metrics. Using hierarchical models, we examine how explained variance in these metrics changed with predator body size, predator taxonomic resolution, and spatial resolution. In the hierarchical analysis, variance in both metrics emerged primarily at the species level and substantially less variance was associated with other (higher) taxonomic levels or with spatial resolution. This suggests that changes in species composition are the main drivers of community‐wide mean PPMR. At all levels of analysis, relationships between weighted mean rbio or weighted mean rnum and predator mass tended to be dome‐shaped. Weighted mean rnum values, for species and community‐wide, were approximately an order of magnitude higher than weighted mean rbio, reflecting the consistent numeric dominance of small prey in predator diets. As well as increasing understanding of the drivers of variation in PPMR and providing estimates of PPMR in the north Pacific Ocean, our results demonstrate that that rbio or rnum, as well as their corresponding weighted means for any defined group of predators, are not directly substitutable. When developing equilibrium size‐based models based on bulk energy flux or comparing PPMR estimates derived from the relationship between body mass and trophic level with those based on diet analysis, weighted mean rbio is a more appropriate measure of PPMR. When calibrating preference PPMR in dynamic size spectrum models then weighted mean rnum will be a more appropriate measure of PPMR. Predator‐to‐prey body mass ratios (PPMRs) are key parameters in size spectrum models, but are conceptualized differently depending on the type of model. We clarify the definitions which differ according to whether individual prey are weighted numerically or by biomass. Using diet data from 170,689 individual fish predators, we show that that the two metrics are not substitutable and evaluate how variance in PPMR metrics emerge across taxonomic levels and spatial scales.
... Managing fisheries is complex due to the multiple objectives encompassing economic, ecological and social goals [22] that can result in trade-offs; where an improvement in one objective may be at the detriment of another [39]. A more holistic framework of ecosystem-based management and ecosystem services is proposed as a way of dealing with the resultant trade-offs between objectives [76]. ...
Article
In July 2015, Scotland became one of the first countries to sign up to the UN Sustainable Development Goals (SDGs) which, unlike their forerunner the Millennium Development Goals, are not restricted to developing nations. Their respective targets should drive policy decisions for Scottish fisheries, in keeping with the universal intent of the new goals. This paper explores the relevance of SDG 14 to the Scottish fishing industry, noting that there are a number of linkages with other goals and targets that should be considered within management frameworks. Scottish fishing has a long history, but the size of the inshore fleet has seen decline in recent decades, particularly of small-scale fishers in rural communities. Available literature was reviewed and a survey of active Scottish fishers conducted to explore the current availability and equality of distribution of benefits from ecosystem services to Scottish fisheries, and the factors that affect them. The findings suggest that benefits may not currently be equally distributed across Scottish fisheries; this is largely sector dependent and driven by market forces, but also relates to gaps in current management and monitoring systems. Furthermore, the potential benefits to fisheries of marine protected areas (MPAs) established for conservation purposes are not adequately assessed as part of their design, which may result in less support from fisheries stakeholders and reduce the benefit to ecosystem services. It concludes with some recommendations for consideration by decision-makers to improve how fishing businesses and communities could benefit more from ecosystem services whilst operating within environmental limits.
... This trend may evolve toward multiobjective approaches using multispecies population models, that is, toward ecosystem management. Studies in this direction already exist-see, for example, White et al. (2012), Tromeur and Loeuille (2017), and Jacobsen et al. (2017). Our four measures of conservation can be extended to more general multispecies settings, and the present method using Pareto fronts to find sustainable harvesting strategies can then be applied in such general settings as well. ...
Article
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Sustainable yields that are at least $80\%$ of the maximum sustainable yield are sometimes referred to as pretty good yield (PGY). The range of PGY harvesting strategies is generally broad and thus leaves room to account for additional objectives besides high yield. Here, we analyze stage-dependent harvesting strategies that realize PGY with conservation as a second objective. We show that (1) PGY harvesting strategies can give large conservation benefits and (2) equal harvesting rates of juveniles and adults is often a good strategy. These conclusions are based on trade-off curves between yield and four measures of conservation that form in two established population models, one age-structured and one stage-structured model, when considering different harvesting rates of juveniles and adults. These conclusions hold for a broad range of parameter settings, though our investigation of robustness also reveals that (3) predictions of the age-structured model are more sensitive to variations in parameter values than those of the stage-structured model. Finally, we find that (4) measures of stability that are often quite difficult to assess in the field (e.g.~basic reproduction ratio and resilience) are systematically negatively correlated with impacts on biomass and impact on size structure, so that these later quantities can provide integrative signals to detect possible collapses.
... This trend may evolve toward multiobjective approaches using multispecies population models, that is, toward ecosystem management. Studies in this direction already exist-see, for example, White et al. (2012), Tromeur andLoeuille (2017), andJacobsen et al. (2017). Our four measures of conservation can be extended to more general multispecies settings, and the present method using Pareto fronts to find sustainable harvesting strategies can then be applied in such general settings as well. ...
... Ecosystem-based fisheries management involves a range of trade-offs among competing objectives, including maximising yields, maximising economic profits, and minimising environmental impact and biodiversity loss ( Zhou et al., 2010, Burgess et al., 2015, Jacobsen et al., 2016). How these objectives should be weighted is more of a sociopolitical question than a scientific one, and will clearly involve compromises. ...
Article
Zhou & Smith (2017) investigate different multi-species harvesting scenarios in a simple Holling-Tanner model. Among these scenarios are two methods for implementing balanced harvesting, where fishing is distributed across trophic levels in accordance with their productivity. This note examines the effects of a different quantitative implementation of balanced harvesting, where the fishing mortality rate is proportional to the total production rate of each trophic level. The results show that setting fishing mortality rate to be proportional to total production rate, rather than to productivity per unit biomass, better preserves trophic structure and provides a crucial safeguard for rare and threatened ecological groups. This is a key ingredient of balanced harvesting if it is to meet its objective of preserving biodiversity.
... In this regard, taking out insurance policies is an effective way to transfer risk [3]. Thus, as a result, Pareto efficiency occurs, whereby risks are transferred to another party, who can manage and bear them more effectively [103]. Furthermore, the insurance premium is also paid to the second party for its risk-bearing capability [3]. ...
Article
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In Pakistan, the fisheries sector is capable of making a significant contribution to the national economy. However, the proper and sustainable development of this sector is essential to its success, and we need to be aware of all the risks that it faces. At present, there is a dearth of comprehensive research that details, compares, and proposes applied measures to mitigate the risks facing the fisheries sector. Thus, this study is the first novel attempt to fill this gap. The data were collected through a survey and analyzed by multi-criteria decision analysis (MCDA). The study postulates that Sindh fisheries are affected by five main risk factors, namely technical, market, ecological, natural, and management. These risk factors are arranged from least to most significant. With regard to the performances of the main risk factors, management risk was ranked as the greatest risk, followed by ecological risk, natural risk, and technical risk. The findings of this study provide a road map for managerial decisions. Furthermore, this study also presents some potential limitations related to the scale of the data and analysis methods. Future studies may therefore use data collected on a large scale and alternative quantitative approaches.
... The alternative perspective equally applies: an impact on the ecosystem leads to an impact on the target species. In the past, neglecting this interaction between target species and ecosystems has led to unsustainable fisheries management and collapse of fish stocks (Hilborn 2011;Jacobsen et al. 2017;Skern-Mauritzen et al. 2016). ...
... Because depredation can induce complex changes in marine socio-ecosystem dynamics, it is essential for ecosystem-based fisheries management to account for this behaviour. While ecosystem-based fisheries management is increasingly supported by a suite of modelling approaches, especially trophic modelling (Hollowed, 2000) using Ecopath (Plagányi and Butterworth, 2004), Atlantis (Fulton et al., 2011), or diverse size- (Blanchard et al., 2014) or traits-based models (Jacobsen et al., 2017;Trenkel, 2018), to date, none have incorporated depredation on fishery catches. In fact, very few studies have examined the effects of depredation through holistic approaches. ...
Article
Ecosystem-based approaches are increasingly used in fisheries management to account for the direct trophic impacts of fish population harvesting. However, fisheries can also indirectly alter ecosystem structure and functioning, for instance via the provision of new feeding opportunities to marine predators. For instance, marine depredation, where predators feed on fishery catches on fishing gear, is a behaviour developed by many marine species globally. This behaviour can modify both the ecological role of predators and fisheries performance. Yet, these ecosystem-wide effects of depredation are rarely considered holistically. In this study, we explored different ways of incorporating depredation into an Ecopath trophic model. We assessed, through a subantarctic case study, how three alternative model structures can account for depredation effects on fishery catches, predator and non-commercial prey populations, as well as target fish stocks. While none adequately addresses all facets of depredation, the alternative models can to some extent capture how depredation can lead to increased fishing pressure on stocks. As structural specificities of Ecopath prevented us from representing other depredation effects such as provisioning effects for predator populations, we conclude this study with a set of guidance to effectively capture the complex effects of depredation in marine ecosystems and fisheries models.
... The models link all physiological processes and patterns of predation and mortality, that is, big fish eat small fish, to individual body weight, which is a simplification that enables characterization of fish communities with few parameters. As a result, size-based models have been used across marine regions to describe fish communities and implemented in a global context, for example, Jacobsen et al. (2017) and Jennings and Collingridge (2015). ...
Article
Aim Understanding how fish food webs emerge from planktonic and benthic energy pathways that sustain them is an important challenge for predicting fisheries production under climate change and quantifying the role of fish in carbon and nutrient cycling. We examine if a trait-based fish community model using the fish traits of maximum body weight and vertical habitat strategy can meet this challenge by globally representing fish food web diversity. Location Global oceans. Time period Predictions are representative of the early 1990s. Major taxa studied Marine teleost fish. Methods We present a size- and trait-based fish community model that explicitly resolves the dependence of fish on pelagic and benthic energy pathways to globally predict fish food web biogeography. The emergent food web structures are compared with regionally calibrated models in three different ecosystem types and used to estimate two fish ecosystem functions: potential fisheries production and benthic–pelagic coupling. Results Variations in pelagic–benthic energy pathways and seafloor depth drive the emergent biogeography of fish food webs from shelf systems to the open ocean, and across the global ocean. Most shelf regions have high benthic production, which favours demersal fish that feed on pelagic and benthic pathways. Continental slopes also show a coupling of benthic and pelagic pathways, sustained through vertically migrating and interacting mesopelagic and deep-sea demersal fish. Open ocean fish communities are primarily structured around the pelagic pathway. Global model results compare favourably with data-driven regional food web models, suggesting that maximum weight and vertical behaviour can capture large-scale variations in food web structure. Main conclusions Mechanistically linking ocean productivity with upper trophic levels using a size- and trait-based fish community model results in spatial variations in food web structure. Energy pathways vary with ocean productivity and seabed depth, thereby shaping the dominant traits and fish communities across ocean biomes.
... Single-species approaches may perform inefficiently for ecosystem-level management because of ignoring comprehensive fishing impacts on the ecosystem (Jacobsen et al., 2017). End-to-end modeling approaches like the one used in this study can be used to investigate the impact of changed trophic interactions. ...
Article
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Single-species fisheries management (SSFM) is applied to many fisheries ecosystems around the world. The associated ecological impacts are usually not well understood due to the lack of considering trophic interactions among species in the ecosystem. This impedes the implementation of SSFM in an ecosystem context and reduces our ability to understand the possible ecological impacts of fishing activities. This study focuses on two economically important species in the Jiaozhou Bay, China: the short-lived, fast-growing, and relatively abundant Japanese mantis shrimp (Oratosquilla oratoria) and the long-lived, slow-growing, and less abundant Korean rockfish (Sebastes schlegelii). We evaluated how varying trophic interactions influenced O. oratoria and S. schlegelii (i.e., target-species) who were managed under constant fishing pressure. The increase of fishing pressure to other species (i.e., non-target species) was beneficial to O. oratoria and S. schlegelii. O. oratoria was more sensitive to the decrease of fishing pressure to other species. The predation mortality of age-0 O. oratoria increased with the increased fishing pressure to other species. The predation mortality of age-1 O. oratoria and age-0 S. schlegelii had negative relationships with the fishing pressure to other species. Age-1 S. schlegelii seemed not to be sensitive to the changes in trophic interactions. The predation mortality of O. oratoria and S. schlegelii had bigger changes than the starvation mortality after fishing changed. It suggested the prey-predator relationship had a bigger impact than the food competition. The increase of high-trophic-level fish Johnius belangerii fishery positively impacted O. oratoria, but negatively impacted S. schlegelii. S. schlegelii was more sensitive to the changes of the low-trophic-level fish Pholis fangi fishery. Given the complex dynamics of ecosystems, this study highlights the importance of species-specific responses of fishes to shifting trophic interactions in fisheries management.
... In this study, we parameterized a multi-species size spectrum model for a typical north temperate lake. We believe this is one of the first applications of this model to a freshwater system (for marine examples, see Blanchard et al., 2014;Jacobsen et al., 2016;Zhang et al., 2016b;Szuwalski et al., 2017;Reum et al., 2019). To streamline future applications of the model and identify data needs in the context of freshwater fisheries management, we sought to identify which life-history parameters would have the greatest influence on model output. ...
Article
Ecosystem-based approaches that take species interactions into account have shifted to the forefront of fisheries modelling and management in recent years. As a result, multispecies size spectrum models have been increasingly used to explore impacts of fishing on marine community dynamics. The use of these models, which has been facilitated by the development of the R package mizer, requires the estimation of species-specific parameters related to growth, reproduction, and feeding. These parameters, which may be estimated from imperfect information, may contribute to model uncertainty and thus reduce the value of information available for management purposes. In this study of a freshwater fishery, we conduct a comprehensive global sensitivity analysis pairing the Morris and Sobol methods to identify life-history parameters having the largest influence on model outputs. Here, we focus on (i) the size spectrum slope, (ii) the scatter around the linear relationship of the size spectrum, (iii) total biomass, and (iv) species diversity. We found that parameters relating to growth, namely the von Bertalanffy growth coefficient and asymptotic mass, had the greatest influence on our size spectrum model results. This was particularly true for top predators and the most abundant species. Our results suggest that estimation of growth parameters of top predators be given priority to reduce uncertainty in model output, and ultimately, fisheries management.
... R-squared (R 2 ) ranging from 0 to 1 was used to indicate the statistical measure of fit between two sets of data. The changing trend between predictions and observations can better demonstrate the goodness of fit than a specific value matched in a given time period (Jacobsen et al., 2017). Most species in the size-spectrum model began to be exploited in the 1950s. ...
Article
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The size-spectrum model has been considered a useful tool for understanding the structures of marine ecosystems and examining management implications for fisheries. Based on Chinese tuna longline observer data from the central and eastern tropical Pacific Ocean and published data, we developed and calibrated a multispecies size-spectrum model of twenty common and commercially important species in this area. We then use the model to project the status of the species from 2016 to 2050 under five constant-fishing-mortality management scenarios: (1) F=0; (2) F=Frecent, the average fishing mortality from 2013 to 2015; (3) F=0.5Frecent; (4) F=2Frecent and (5) F=3Frecent. Several ecological indicators were used to track the dynamics of the community structure under different levels of fishing, including the mean body weight, slope of community size spectra (Slope), and total biomass. The validation demonstrated that size-at-age data of nine main catch species between our model predictions and those empirical data from assessments by the Western and Central Pacific Fisheries Commission matched well, with the R2>0.9. The direct effect of fishing was the decreasing abundance of large-sized individuals. The mean body weight in the community decreased by ∼1 500 g (21%) by 2050 when F doubled from Frecent to 2Frecent. The higher the fishing mortality, the steeper the Slope was. The projection also indicated that fishing impacts reflected by the total biomass did not increase proportionally with the increasing fishing mortality. The biomass of the main target tuna species was still abundant over the projection period under the recent fishing mortality, except Albacore tuna (Thunnus alalunga). For sharks and billfishes, their biomass remained at relatively higher levels only under the F=0 scenario. The results can serve as a scientific reference for alternative management strategies in the tropical Pacific Ocean.
... Because depredation can induce complex changes in marine socio-ecosystem dynamics, it is essential for ecosystem-based fisheries management to account for this behaviour. While ecosystembased fisheries management is increasingly supported by a suite of modelling approaches, especially trophic modelling (Hollowed, 2000) using Ecopath (Plagányi & Butterworth, 2004), Atlantis (Fulton et al., 2011), or diverse size- (Blanchard et al., 2014) or traits-based models (Jacobsen et al., 2017;Trenkel, 2018), to date, none have incorporated depredation on fishery catches. In fact, very few studies have examined the effects of depredation through holistic approaches. ...
Thesis
Les espèces qui se nourrissent de plantes ou d’animaux élevés ou capturés par l’homme, un comportement appelé « déprédation », entraînent souvent de graves Conflits Homme-Faune sauvage (CHF). La déprédation a été signalée dans le monde entier et, dans les écosystèmes marins, elle a été développée par de nombreux grands prédateurs se nourrissant des prises de pêche, ce qui a un impact à la fois sur les activités de pêche et les interactions écologiques. Cependant, bien que les approches écosystémiques soient de plus en plus utilisées dans la gestion des pêches, les effets de la déprédation sur l’ensemble de l’écosystème sont encore rarement considérés de manière holistique. Par conséquent, cette thèse a (i) identifié les limites, manques et priorités pour le développement d’approches de modélisation intégrant la déprédation et (ii) évalué la capacité de deux approches de modélisation existantes pour caractériser les conséquences de la déprédation marine et, plus spécifiquement, comprendre les enjeux et conditions requises pour que les activités d’exploitation halieutique et les déprédateurs marins puissent co-exister. Cette thèse est composée de cinq chapitres. Le chapitre 1 présente le contexte dans lequel s’inscrit ces travaux. Le chapitre 2 identifie les principales lacunes dans les connaissances et met en évidence les principales orientations futures pour parvenir à une inclusion efficace de la déprédation dans les études de modélisation en réalisant une revue systématique. Le chapitre 3 utilise le cadre Ecopath pour évaluer les effets de la déprédation sur l'écosystème dans une étude de cas bien documentée impliquant des mammifères marins et une pêcherie commerciale. Le chapitre 4 s'appuie sur une modélisation qualitative pour évaluer les conditions de persistance d'une ressource exploitée, d'une pêcherie et d'une espèce déprédatrice dans les systèmes marins touchés par la déprédation, et la façon dont la déprédation marine affecte les réponses à long terme à des scénarios alternatifs. Enfin, la discussion générale présentée dans le chapitre 5, fournit des recommandations qui vise à mieux comprendre et prévoir les effets de la déprédation au niveau du socio-écosystème.
... R-squared (R 2 ) ranging from 0 to 1 was used to indicate the statistical measure of fit between two sets of data. The changing trend between predictions and observations can better demonstrate the goodness of fit than a specific value matched in a given time period (Jacobsen et al., 2017). Most species in the size-spectrum model began to be exploited in the 1950s. ...
Article
Catch, bycatch and discard information is important for the assessment and management of fisheries. Using Chinese pelagic tuna longline observer data from 2010 to 2018, we studied the catch composition in the Chinese pelagic tuna longline fisheries in Atlantic targeting bigeye tuna (Thunnus obesus) and bluefin tuna (Thunnus thynnus), and analyzed the survival status and discard rates of common bycatch species. A total of 55 species, including tunas, billfishes, sharks, sea turtles, cetaceans, seabirds, and other pelagic species, were observed. The results indicated that the catch composition of the Chinese pelagic tuna longline fishery targeting bigeye tuna was significantly different from that targeting bluefin tuna. The annual discard rates of common species decreased over this period. Discard rate by length and discard mortality for common species were varied among species. This is the first study to estimate catch, bycatch, and discard using Chinese pelagic tuna longline observer data in the Atlantic Ocean, which is important for the management of Chinese tuna longline fisheries in Atlantic Ocean.
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Balanced harvest has been proposed to reduce fishing impact on ecosystems while simultaneously maintaining or even increasing fishery yield. The concept has attracted broad interest, but also received criticisms. In this paper, we examine the theory, modelling studies, empirical evidence, the legal and policy frameworks, and management implications of balanced harvest. The examination reveals unresolved issues and challenges from both scientific and management perspectives. We summarize current knowledge and address common questions relevant to the idea. Major conclusions include: balanced harvest can be expressed in several ways and implemented on multiple levels, and with different approaches e.g. métier based management; it explicitly bridges fisheries and conservation goals in accordance with international legal and policy frameworks; modelling studies and limited empirical evidence reveal that balanced harvest can reduce fishing impact on ecosystem structure and increase the aggregate yield; the extent of balanced harvest is not purely a scientific question, but also a legal and social choice; a transition to balanced harvest may incur short-term economic costs, while in the long-term, economic results will vary across individual fisheries and for society overall; for its application, balanced harvest can be adopted at both strategic and tactical levels and need not be a full implementation, but could aim for a “partially-balanced” harvest. Further objective discussions and research on this subject are needed to move balanced harvest toward supporting a practical ecosystem approach to fisheries.
Article
Balanced harvesting has been proposed as a fisheries management strategy to mitigate the impacts of fisheries removal on ecosystem structure. One definition of balanced harvest is that all species should be harvested in proportion to their annual production. However, most marine ecosystems lack comprehensive production estimates necessary to empirically measure the degree of balance. We developed and tested 2 new methods for estimating fish biomass production at the species level with limited data requirements. Application of our techniques to 4 ecological production units in the northwest Atlantic (Mid-Atlantic Bight, Georges Bank, Gulf of Maine, and western Scotian Shelf) from 1991-2013 provided a direct estimate of 1.9 million t yr ⁻¹ of total fish production. The degree of balance between catch and production distributions at the species level, assessed using the proportional similarity index, ranged from 0.34 to 0.83 on a scale from near 0 to 1. Increased balance was positively associated with yield in the Gulf of Maine (Spearman’s, p = 0.04). Increased balance was negatively associated with an ecosystem impact indicator in the Gulf of Maine (Spearman’s, p = 0.03) and Mid-Atlantic Bight (Spearman’s, p = 0.02). These case studies provide some evidence of benefit to humans and reduced ecosystem harm from more balanced harvest. More importantly, we provide a unique empirical metric of balanced harvest at the species level, and develop potential indicators and methods for ecosystem-based fisheries management.
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Over the last decades, the fishery production has increased remarkably as the global demand expands. As a result, fisheries resources in many areas are now shows a downward trend. To cope with this situation, the methods of fishery resource management have made great progress both in system and technology under the policy of how to catch fish maintaining reproduction. However, in recent years the enlargement of processing volume and distribution range has increased the necessity of considering the environmental impact of fishery such as energy consumption and waste on sea as well as land. With this situation, the updating of management concept has been discussed and the research on aquaculture and fishery using LCA is gradually increasing after 2000. Furthermore, in recent years, the possibility of evaluation of comprehensive environmental impact to marine ecosystem including fishery resources are mentioned. This article presents various problems of fishery and shows discussion on the status of fishery LCA studies.
Article
In this paper, I argue that we have at hand what is needed to provide scientific advice for ecosystem-based management of small pelagics and other species groups now. The ingredients for this advice are (i) large marine ecosystems as spatial management units; (ii) maintaining ecosystem productivity and exploiting at multispecies maximum yield as overarching management objectives; (iii) assessment of ecosystems by evaluating changes in primary productivity; (iv) an operational management procedure in which single-species catch proposals are adjusted to ecosystem productivity using a set of control rules. Inspection of historic landings for small pelagics and other small species in the Northeast Atlantic (ICES area) reveals that most likely fisheries exploitation does not, and never did, exceed system productivity in most LMEs and is therefore overall sustainable, although not necessarily for individual stocks.
Article
The discipline and practice of fisheries science and management have had an useful, successful, and interesting history. The discipline has developed over the past century and a half into a very reductionist, highly quantitative, socially impactful endeavor. Yet given our collective successes in this field, some notable challenges remain. To address these challenges, many have proposed ecosystem-based fisheries management that takes a more systematic approach to the management of these living marine resources. Here I describe systems theory and associated constructs underlying system dynamics, elucidate how aggregate properties of systems can and have been used, contextualize these aggregate features relative to optimal yield, and note how this approach can produce useful estimates and outcomes for fisheries management. I explore two contrasting examples where this approach has and has not been considered, highlighting the benefits of applying such an approach. I conclude by discussing ways in which we might move forward with a portfolio approach for both the discipline and practice of fisheries science and management.
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Resolving the combined effect of climate warming and exploitation in a food web context is key for predicting future biomass production, size-structure, and potential yields of marine fishes. Previous studies based on mechanistic size-based food web models have found that bottom-up processes are important drivers of size-structure and fisheries yield in changing climates. However, we know less about the joint effects of "bottom-up" and "top-down" effects of temperature: how do temperature effects propagate from individual-level physiology through food webs and alter the size-structure of exploited species in a community? Here we assess how a species-resolved size-based food web is affected by warming through both these pathways, and by exploitation. We parameterize a dynamic size spectrum food web model inspired by the offshore Baltic Sea food web, and investigate how individual growth rates, size-structure, relative abundances of species and yields are affected by warming. The magnitude of warming is based on projections by the regional coupled model system RCA4-NEMO and the RCP 8.5 emission scenario, and we evaluate different scenarios of temperature dependence on fish physiology and resource productivity. When accounting for temperature-effects on physiology in addition to on basal productivity, projected size-at-age in 2050 increases on average for all fish species, mainly for young fish, compared to scenarios without warming. In contrast, size-at-age decreases when temperature affects resource dynamics only, and the decline is largest for young fish. Faster growth rates due to warming, however, do not always translate to larger yields, as lower resource carrying capacities with increasing temperature tend to result in declines in the abundance of larger fish and hence spawning stock biomass (the part of the population exposed to fishing). These results show that to understand how global warming impacts the size structure of fish communities, both direct metabolic effects and indirect effects of temperature via basal resources must be accounted for.
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Indiscriminate and intense fishing has occurred in many marine ecosystems around the world. Although this practice may have negative effects on biodiversity and populations of individual species, it may also increase total fishery productivity by removing predatory fish. We examine the potential for this phenomenon to explain the high reported wild catches in the East China Sea-one of the most productive ecosystems in the world that has also had its catch reporting accuracy and fishery management questioned. We show that reported catches can be approximated using an ecosystem model that allows for trophic cascades (i.e., the depletion of predators and consequent increases in production of their prey). This would be the world's largest known example of marine ecosystem "engineering" and suggests that trade-offs between conservation and food production exist. We project that fishing practices could be modified to increase total catches, revenue, and biomass in the East China Sea, but single-species management would decrease both catches and revenue by reversing the trophic cascades. Our results suggest that implementing single-species management in currently lightly managed and highly exploited multispecies fisheries (which account for a large fraction of global fish catch) may result in decreases in global catch. Efforts to reform management in these fisheries will need to consider system wide impacts of changes in management, rather than focusing only on individual species.
Thesis
La surpêche affecte les structures et dynamiques de nombreux écosystèmes marins, ainsi que les services écosystémiques qui en dépendent. En réponse, scientifiques et gestionnaires plaident pour une gestion écosystémique des pêches, intégrant la complexité des écosystèmes exploités, et fondée sur des objectifs de durabilité écologiques comme économiques. Dans ce cadre, l'objectif de cette thèse est d'élaborer une approche écosystémique de la gestion des pêches, conciliant la préservation de la biodiversité et de la résilience des écosystèmes exploités avec le maintien d'une production et de profits élevés. Pour cela, nous développons des modèles bio-économiques de pêcheries mixtes, constituées d'espèces indépendantes ou en interaction trophique. Nous montrons que maximiser l'ensemble des captures ou des profits d'une pêcherie mixte peut menacer la biodiversité et la résilience des écosystèmes exploités, mais que des instruments économiques peuvent y remédier. L'aversion au risque en présence d'incertitude favorise aussi une réconciliation entre différents enjeux de gestion. Nous déployons ensuite des approches de gestion multi-critères, afin d'identifier les meilleures stratégies en termes écologiques et économiques. Les stratégies choisies dépendent des préférences des gestionnaires : favoriser la production suppose d'orienter la pêche vers les faibles niveaux trophiques, tandis que favoriser la biodiversité ou la résilience suppose d'orienter la pêche vers des niveaux trophiques plus élevés. Nous suggérons ainsi qu'une diversification du profil de pêche permettrait de concilier enjeux écologiques et économiques pour une gestion écosystémique et durable des pêches.
Article
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The advent of an ecosystem-based approach dramatically expanded the scope of fisheries management, creating a critical need for new kinds of data and quantitative approaches that could be integrated into the management system. Ecosystem models are needed to codify the relationships among drivers, pressures and resulting states, and to quantify the trade-offs between conflicting objectives. Incorporating ecosystem considerations requires moving from the single-species models used in stock assessments, to more complex models that include species interactions, environmental drivers and human consequences. With this increasing model complexity, model fit can improve, but parameter uncertainty increases. At intermediate levels of complexity, there is a ‘sweet spot’ at which the uncertainty in policy indicators is at a minimum. Finding the sweet spot in models requires compromises: for example, to include additional component species, the models of each species have in some cases been simplified from age-structured to logistic or bioenergetic models. In this paper, we illuminate the characteristics, capabilities and short-comings of the various modelling approaches being proposed for ecosystem-based fisheries management. We identify key ecosystem needs in fisheries management and indicate which types of models can meet these needs. Ecosystem models have been playing strategic roles by providing an ecosystem context for single-species management decisions. However, conventional stock assessments are being increasingly challenged by changing natural mortality rates and environmentally driven changes in productivity that are observed in many fish stocks. Thus, there is a need for more tactical ecosystem models that can respond dynamically to changing ecological and environmental conditions.
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Balanced harvesting (BH) has been proposed as an alternative to the paradigm of more selective fishing as practiced in most European and North American fisheries management. We examine options for the implementation of BH and evaluate the issues raised in such an implementation. Implementation is considered at the whole ecosystem level, in terms of the patterns of removal for all species, both commercial and bycatch. We suggest that a “laissez-faire” approach analogous to the African lakes where BH was first observed is inappropriate in managed developed world fisheries. We consider two further approaches: focusing on either the species caught or on the sizes of animal alone. We find that aiming to harvest all species with an exploitation rate appropriate to their productivity would require a degree of micro-management that is probably unachievable, with all captured species “choking” the fishery in sequence. The size-based approach works with an exploitation rate appropriate to the productivity at size, with no consideration of the species involved. This might superficially be easier to implement, as management would involve a limited number of size classes only. However, problems may arise due to the likely faster capture of the more easily catchable fish, and also likely targeting of the more valuable species within a size class. We identify a possible third option of “broad brush” métier-based management that may resolve some of these problems. Other issues include the management of protected, endangered, and threatened species (including mammals, reptiles, and birds), the management of already severely depleted stocks, and the capture of benthic invertebrates.
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Size spectrum models have emerged from 40 years of basic research on how body size determines individual physiology and structures marine communities. They are based on commonly accepted assumptions and have a low parameter set, making them easy to deploy for strategic ecosystem-oriented impact assessment of fisheries. We describe the fundamental concepts in size-based models about food encounter and the bioenergetics budget of individuals. Within the general framework, three model types have emerged that differ in their degree of complexity: the food-web, the trait-based, and the community models. We demonstrate the differences between the models through examples of their response to fishing and their dynamic behavior. We review implementations of size spectrum models and describe important variations concerning the functional response, whether growth is food-dependent or fixed, and the density dependence imposed on the system. Finally, we discuss challenges and promising directions.
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An often-cited impediment to the operationalization of ecosystem-based fisheries management is the lack of a governance structure that explicitly provides the authority and framework for implementing this holistic approach to fisheries management. However within the United States and elsewhere in the world, the concept of optimum yield appears to be an explicit mandate and framework that can and should be used to operationalize ecosystem-based fisheries management. This optimum yield policy has been hidden in plain sight for close to 40 years, largely due to happenstance, as other factors facing society-at-large have masked the original intent behind this concept. This paper describes the similarities between optimum yield and ecosystem-based fisheries management, how it has been overlooked in the past, and how the concept can be used to operationalize ecosystem-based fisheries management.
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Ecosystem modeling is becoming an integral part of fisheries management, but there is a need to identify differences between predictions derived from models employed for scientific and management purposes. Here, we compared two models: a biomass-based food-web model (Ecopath with Ecosim) and a size structured fish community model. The models were compared with respect to predicted ecological consequences of fishing to identify commonalities and differences in model predictions for the California Current fish community. We compared the models regarding direct and indirect responses to fishing on one or more species. The size based model predicted a higher fishing mortality needed to reach maximum sustainable yield than EwE for most species. The size based model also predicted stronger top-down effects of predator removals than EwE. In contrast, EwE predicted stronger bottom-up effects of forage fisheries removal. In both cases the differences are due to the presumed degree of trophic overlap between juveniles of large-bodied fish and adult stages of forage fish. These differences highlight how each models emphasis on distinct details of ecological processes affect their predictions, underscoring the importance of incorporating knowledge of model assumptions and limitation, possibly through using model ensembles, when providing model-based scientific advice to policy makers.
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Rice, J., and Duplisea, D. 2013. Management of fisheries on forage species: the test-bed for ecosystem approaches to fisheries. – ICES Journal of Marine Science, 71: . In the 1970s and 1980s, core ideas about management of fisheries on forage species emerged from work on the dynamics of foodweb models and multispecies assessments, leading to proposals for management that took some account of the role of forage species in marine ecosystems. Key developments in those years are summarized in the first part of this paper. From the 1980s to the 2000s, studies of the response of forage species to environmental variation brought into question the robustness of management strategies for forage species. As a result, additional management strategies were proposed to accommodate environmental drivers as well as dependent predators. The paper reviews these developments. This paper brings these separate lines together in a systematic framework for evaluating the performance of six different management strategies for forage species, relative to four different ecosystem considerations, as well as relative to the contribution of forage fisheries to economic prosperity and food security. The tabulated outcomes synthesize primary and secondary literature and meeting deliberations as the application of an ecosystem approach to management has evolved. No strategy is optional for all forage fisheries. As experience accumulates, the guidance in the tables comprising the framework will improve.
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Despite the many scientific and public discussions on the sustainability of fisheries, there are still great differences in both perception and definition of the concept. Most authors now suggest that sustainability is best defined as the ability to sustain goods and services to human society, with social and economic factors to be considered along with environmental impacts. The result has been that each group (scientists, economists, NGOs etc.) defines “sustainable seafood” using whatever criteria it considers most important, and the same fish product may be deemed sustainable by one group and totally unsustainable by another one. We contend, however, that there is now extensive evidence that an ecological focus alone does not guarantee long-term sustainability of any form and that seafood sustainability must consistently take on a socio-ecological perspective if it is to be effective across cultures and in the future. The sustainability of seafood production depends not on the abundance of a fish stock, but on the ability of the fishery management system to adjust fishing pressure to appropriate levels. While there are scientific standards to judge the sustainability of food production, once we examine ecological, social and economic aspects of sustainability there is no unique scientific standard.
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Fish stock productivity, and thereby sensitivity to harvesting, depends on physical (e.g. ocean climate) and biological (e.g. prey availability, competition and preda-tion) processes in the ecosystem. The combined impacts of such ecosystem pro-cesses and fisheries have lead to stock collapses across the world. While traditional fisheries management focuses on harvest rates and stock biomass, incorporating the impacts of such ecosystem processes are one of the main pillars of the ecosys-tem approach to fisheries management (EAFM). Although EAFM has been formally adopted widely since the 1990s, little is currently known to what extent ecosystem drivers of fish stock productivity are actually implemented in fisheries management. Based on worldwide review of more than 1200 marine fish stocks, we found that such ecosystem drivers were implemented in the tactical management of only 24 stocks. Most of these cases were in the North Atlantic and north-east Pacific, where the scientific support is strong. However, the diversity of ecosystem drivers imple-mented, and in the approaches taken, suggests that implementation is largely a bottom-up process driven by a few dedicated experts. Our results demonstrate that tactical fisheries management is still predominantly single-species oriented taking little account of ecosystem processes, implicitly ignoring that fish stock production is dependent on the physical and biological conditions of the ecosystem. Thus, while the ecosystem approach is highlighted in policy, key aspects of it tend yet not to be implemented in actual fisheries management.
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The advent of an ecosystem-based approach dramatically expanded the scope of fisheries management, creating a critical need for new kinds of data and quantitative approaches that could be integrated into the management system. Ecosystem models are needed to codify the relationships among drivers, pressures and resulting states, and to quantify the trade-offs between conflicting objectives. Incorporating ecosystem considerations requires moving from the single-species models used in stock assessments, to more complex models that include species interactions, environmental drivers and human consequences. With this increasing model complexity, model fit can improve, but parameter uncertainty increases. At intermediate levels of complexity, there is a ‘sweet spot’ at which the uncertainty in policy indicators is at a minimum. Finding the sweet spot in models requires compromises: for example, to include additional component species, the models of each species have in some cases been simplified from age-structured to logistic or bioenergetic models. In this paper, we illuminate the characteristics, capabilities and short-comings of the various modelling approaches being proposed for ecosystem-based fisheries management. We identify key ecosystem needs in fisheries management and indicate which types of models can meet these needs. Ecosystem models have been playing strategic roles by providing an ecosystem context for single-species management decisions. However, conventional stock assessments are being increasingly challenged by changing natural mortality rates and environmentally driven changes in productivity that are observed in many fish stocks. Thus, there is a need for more tactical ecosystem models that can respond dynamically to changing ecological and environmental conditions.
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Marine spatial planning (MSP), whereby areas of the ocean are zoned for different uses, has great potential to reduce or eliminate conflicts between competing management goals, but only if strategically applied. The recent literature overwhelmingly agrees that including stakeholders in these planning processes is critical to success; but, given the countless alternative ways even simple spatial regulations can be configured, how likely is it that a stakeholder-driven process will generate plans that deliver on the promise of MSP? Here, we use a spatially explicit, dynamic bioeconomic model to show that stakeholder-generated plans are doomed to fail in the absence of strong scientific guidance. While strategically placed spatial regulations can improve outcomes remarkably, the vast majority of possible plans fail to achieve this potential. Surprisingly, existing scientific rules of thumb do little to improve outcomes. Here, we develop an alternative approach in which models are used to identify efficient plans, which are then modified by stakeholders. Even if stakeholders alter these initial proposals considerably, results hugely outperform plans guided by scientific rules of thumb. Our results underscore the importance of spatially explicit dynamic models for the management of marine resources and illustrate how such models can be harmoniously integrated into a stakeholder-driven MSP process.
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Balanced harvesting, where species or individuals are exploited in accordance with their productivity, has been proposed as a way to minimize the effects of fishing on marine fish communities and ecosystems. This calls for a thorough examination of the consequences balanced harvesting has on fish community structure and yield. We use a size- and trait-based model that resolves individual interactions through competition and predation to compare balanced harvesting with traditional selective harvesting, which protects juvenile fish from fishing. Four different exploitation patterns, generated by combining selective or unselective harvesting with balanced or unbalanced fishing, are compared. We find that unselective balanced fishing, where individuals are exploited in proportion to their productivity, produces a slightly larger total maximum sustainable yield than the other exploitation patterns and, for a given yield, the least change in the relative biomass composition of the fish community. Because fishing reduces competition, predation and cannibalism within the community, the total maximum sustainable yield is achieved at high exploitation rates. The yield from unselective balanced fishing is dominated by small individuals, whereas selective fishing produces a much higher proportion of large individuals in the yield. Although unselective balanced fishing is predicted to produce the highest total maximum sustainable yield and the lowest impact on trophic structure, it is effectively a fishery predominantly targeting small forage fish.
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The impact of fishing on chondrichthyan stocks around the world is currently the focus of considerable international concern. Most chondrichthyan populations are of low productivity relative to teleost fishes, a consequence of their different life-history strategies. This is reflected in the poor record of sustainability of target shark fisheries. Most sharks and some batoids are predators at, or near, the top of marine food webs. The effects of fishing are examined at the single-species level and through trophic interactions. We summarize the status of chondrichthyan fisheries from around the world. Some 50% of the estimated global catch of chondrichthyans is taken as by-catch, does not appear in official fishery statistics, and is almost totally unmanaged. When taken as by-catch, they are often subjected to high fishing mortality directed at teleost target species. Consequently, some skates, sawfish, and deep-water dogfish have been virtually extirpated From large regions. Some chondrichthyans are more resilient to fishing and we examine predictions on the vulnerability of different species based on their life-history and population parameters. At the species level, fishing may alter size structure and population parameters in response to changes in species abundance. We review the evidence for such density-dependent change. Fishing can affect trophic interactions and we examine cases of apparent species replacement and shifts in community composition. Sharks and rays learn to associate trawlers with food and feeding on discards may increase their populations. Using ECOSIM, we make some predictions about the long-term response of ecosystems to fishing on sharks. Three different environments are analysed: a tropical shelf ecosystem in Venezuela, a Hawaiian coral reef ecosystem, and a North Pacific oceanic ecosystem. (C) 2000 International Council for the Exploration of the Sea.
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Forage fish play a pivotal role in marine ecosystems and economies worldwide by sustaining many predators and fisheries directly and indirectly. We estimate global forage fish contributions to marine ecosystems through a synthesis of 72 published Ecopath models from around the world. Three distinct contributions of forage fish were examined: (i) the ecological support service of forage fish to predators in marine ecosystems, (ii) the total catch and value of forage fisheries and (iii) the support service of forage fish to the catch and value of other commercially targeted predators. Forage fish use and value varied and exhibited patterns across latitudes and ecosystem types. Forage fish supported many kinds of predators, including fish, seabirds, marine mammals and squid. Overall, forage fish contribute a total of about $16.9 billion USD to global fisheries values annually, i.e. 20% of the global ex-vessel catch values of all marine fisheries combined. While the global catch value of forage fisheries was $5.6 billion, fisheries supported by forage fish were more than twice as valuable ($11.3 billion). These estimates provide important information for evaluating the trade-offs of various uses of forage fish across ecosystem types, latitudes and globally. We did not estimate a monetary value for supportive contributions of forage fish to recreational fisheries or to uses unrelated to fisheries, and thus the estimates of economic value reported herein understate the global value of forage fishes.
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The decline of the Eastern Baltic cod (Gadus morhua) stock from highest to lowest stock levels on record throughout the 1980s and early 1990s was caused by a combination of recruitment failure and increasing fishing pressure at declining stock sizes. The processes driving the reproductive success are largely understood, but the consequences of these changes for fisheries management are far less evident. This includes doubts about the adequacy of the biological reference points presently used to advise on the stock status, and the need of their revision given that environmental changes have affected stock productivity. Long-term projections suggest that under adverse environmental conditions for reproduction, harvesting at fishing mortality determined as precautionary may not lead to a recovery of the stock to a biomass level considered precautionary. Thus, a revision of either the limit fishing mortality or the limit biomass reference point is indicated. However, an accepted methodology to de-termine these reference points in situations of changing stock productivity or system carrying capacity does not exist. Environmental conditions affecting recruitment matter not only for the determination of limit reference points, but according to long-term simulations also for target fishing mortalities, being central parts of harvest control rules in several management plans.
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Cod stocks in the North West Atlantic and the Baltic Sea have shown similar dynamics in recent decades with a rapid decline in abundance and a lack of stock recovery following a period of large biomass. We explore whether the lack of recovery can be ascribed to an emergent Allee effect, which is a mechanism intrinsic to the community in contrast to explanations involving environmental factors. We formulate a stage-structured biomass model for the cod–sprat interaction in the Baltic Sea, paying special attention to the size-dependent prey preference of differently sized cod. The model predicts that alternative community states can occur under the same environmental conditions, in which cod is either present or absent. In a stable equilibrium with its main prey cod has a strong effect on the prey size distribution, resulting in larger densities of preferred prey sizes for cod than in the absence of any predation. Cod thus shapes its food environment to its own benefit. Furthermore, in response to increased exploitation cod biomass and yield tend to increase unless a stock collapse is imminent. After a cod stock collapse and the consequent drop in predation the prey size distribution becomes stunted and offers insufficient food for cod to grow and recover. These results are consequences of the indirect effects of predation and harvesting, whereby increased mortality relaxes competition among surviving individuals, leading to an increase in food intake and hence increased somatic growth and reproduction. We review observed community changes following the collapse of the cod stocks in the North West Atlantic and the Baltic Sea in the light of model predictions. In line with our model predictions growth in body size of cod has slowed down after the collapse, despite high densities of prey biomass. Furthermore, estimates of total prey population fecundity in the Baltic Sea identify the emergent Allee effect as a potentially important mechanism contributing to the lack of cod recovery.
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Marine spatial planning (MSP) is an emerging responsibility of resource managers around the United States and elsewhere. A key proposed advantage of MSP is that it makes tradeoffs in resource use and sector (stakeholder group) values explicit, but doing so requires tools to assess tradeoffs. We extended tradeoff analyses from economics to simultaneously assess multiple ecosystem services and the values they provide to sectors using a robust, quantitative, and transparent framework. We used the framework to assess potential conflicts among offshore wind energy, commercial fishing, and whale-watching sectors in Massachusetts and identify and quantify the value from choosing optimal wind farm designs that minimize conflicts among these sectors. Most notably, we show that using MSP over conventional planning could prevent >$1 million dollars in losses to the incumbent fishery and whale-watching sectors and could generate >$10 billion in extra value to the energy sector. The value of MSP increased with the greater the number of sectors considered and the larger the area under management. Importantly, the framework can be applied even when sectors are not measured in dollars (e.g., conservation). Making tradeoffs explicit improves transparency in decision-making, helps avoid unnecessary conflicts attributable to perceived but weak tradeoffs, and focuses debate on finding the most efficient solutions to mitigate real tradeoffs and maximize sector values. Our analysis demonstrates the utility, feasibility, and value of MSP and provides timely support for the management transitions needed for society to address the challenges of an increasingly crowded ocean environment.
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Concern about the impact of fishing on ecosystems and fisheries production is increasing (1, 2). Strategies to reduce these impacts while addressing the growing need for food security (3) include increasing selectivity (1, 2): capturing species, sexes, and sizes in proportions that differ from their occurrence in the ecosystem. Increasing evidence suggests that more selective fishing neither maximizes production nor minimizes impacts (4–7). Balanced harvesting would more effectively mitigate adverse ecological effects of fishing while supporting sustainable fisheries. This strategy, which challenges present management paradigms, distributes a moderate mortality from fishing across the widest possible range of species, stocks, and sizes in an ecosystem, in proportion to their natural productivity (8), so that the relative size and species composition is maintained
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Low–trophic level species account for more than 30% of global fisheries production and contribute substantially to global food security. We used a range of ecosystem models to explore the effects of fishing low–trophic level species on marine ecosystems, including marine mammals and seabirds, and on other commercially important species. In five well-studied ecosystems, we found that fishing these species at conventional maximum sustainable yield (MSY) levels can have large impacts on other parts of the ecosystem, particularly when they constitute a high proportion of the biomass in the ecosystem or are highly connected in the food web. Halving exploitation rates would result in much lower impacts on marine ecosystems while still achieving 80% of MSY.
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Globally, many fish species are overexploited, and many stocks have collapsed. This crisis, along with increasing concerns over flow-on effects on ecosystems, has caused a reevaluation of traditional fisheries management practices, and a new ecosystem-based fisheries management (EBFM) paradigm has emerged. As part of this approach, selective fishing is widely encouraged in the belief that nonselective fishing has many adverse impacts. In particular, incidental bycatch is seen as wasteful and a negative feature of fishing, and methods to reduce bycatch are implemented in many fisheries. However, recent advances in fishery science and ecology suggest that a selective approach may also result in undesirable impacts both to fisheries and marine ecosystems. Selective fishing applies one or more of the "6-S" selections: species, stock, size, sex, season, and space. However, selective fishing alters biodiversity, which in turn changes ecosystem functioning and may affect fisheries production, hindering rather than helping achieve the goals of EBFM. We argue here that a "balanced exploitation" approach might alleviate many of the ecological effects of fishing by avoiding intensive removal of particular components of the ecosystem, while still supporting sustainable fisheries. This concept may require reducing exploitation rates on certain target species or groups to protect vulnerable components of the ecosystem. Benefits to society could be maintained or even increased because a greater proportion of the entire suite of harvested species is used.
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The Millennium Ecosystem Assessment (MA) introduced a new framework for analyzing social-ecological systems that has had wide influence in the policy and scientific communities. Studies after the MA are taking up new challenges in the basic science needed to assess, project, and manage flows of ecosystem services and effects on human well-being. Yet, our ability to draw general conclusions remains limited by focus on discipline-bound sectors of the full social-ecological system. At the same time, some polices and practices intended to improve ecosystem services and human well-being are based on untested assumptions and sparse information. The people who are affected and those who provide resources are increasingly asking for evidence that interventions improve ecosystem services and human well-being. New research is needed that considers the full ensemble of processes and feedbacks, for a range of biophysical and social systems, to better understand and manage the dynamics of the relationship between humans and the ecosystems on which they rely. Such research will expand the capacity to address fundamental questions about complex social-ecological systems while evaluating assumptions of policies and practices intended to advance human well-being through improved ecosystem services.
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Removal of top predators from ecosystems can result in cascading effects through the trophic levels below, completely restructuring the food web. Cascades have been observed in small-scale or simple food webs, but not in large, complex, open-ocean ecosystems. Using data spanning many decades from a once cod-dominated northwest Atlantic ecosystem, we demonstrate a trophic cascade in a large marine ecosystem. Several cod stocks in other geographic areas have also collapsed without recovery, suggesting the existence of trophic cascades in these systems.
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The strategic objectives for fisheries, which are enshrined in international conventions, are to maintain or restore stocks to produce maximum sustainable yield (MSY) and to implement the ecosystem approach, requiring that interactions between species be taken into account and conservation constraints be respected. While the yield and conservation aims are, to some extent, compatible when a fishery for a single species is considered, species interactions entail that MSY for a species depends on the species with which it interacts, and the yield and conservation objectives therefore conflict when an ecosystem approach to fisheries management is required. We applied a conceptual size- and trait-based model to clarify and resolve these issues by determining the fishing pattern that maximizes the total yield of an entire fish community in terms of catch biomass or economic rent under acceptable conservation constraints. Our results indicate that the eradication of large, predatory fish species results in a potential maximum catch at least twice as high as if conservation constraints are imposed. However, such a large catch could only be achieved at a cost of forgone rent; maximum rent extracts less than half of the potential maximum catch mass. When a conservation constraint is applied, catch can be maximized at negligible cost in forgone rent, compared with maximizing rent. Maximization of rent is the objective that comes closest to respecting conservation concerns.
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Balanced harvesting – harvesting all species and sizes in an ecosystem in proportion to their productivity – is a fisheries management strategy that has been suggested recently to increase yields, while reducing overall ecosystem impact. However, some aspects of balanced harvesting are controversial, including its call for extensive harvesting of juveniles and forage fish. Balanced harvesting also calls for targeting species and size-classes that are not currently marketable, possibly at a significant economic cost. Some have argued that this cost is outweighed by the ecological benefits of maintaining the ecosystem size and trophic structures and by the benefits of extra yield for food security. There is broad consensus that balanced harvesting would require major changes to fishery management institutions and consumer behaviour, and it is unclear to what extent it is physically possible with current technologies. For this reason, we argue that steps to implement balanced harvesting are difficult to justify until the case for it is more clearly resolved. We outline some of the pivotal questions that must be answered to make a convincing case for or against balanced harvesting, many of which can be answered empirically. In identifying these questions, we hope to offer a constructive path forward in resolving some of the key issues in the balanced harvesting debate.
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A novel method for identifying “key” prey species such as forage fish, upon which upper trophic level predators depend, is proposed. Forage fish fisheries collectively constitute 30% of global fishery landings and are important prey for other fished species as well as marine mammals and seabirds. The SURF index (SUpportive Role to Fishery ecosystems) for each prey species weights food web connectance by the importance of trophic connections, so that higher scores indicate a greater potential for indirect food web effects of forage fish fisheries. We show that the SURF index is less sensitive to choices on degree of taxonomic aggregation of analysis than typical connectance measures. Moreover, we show that SURF provides more robust predictions of which species have greatest effects on other food web components. This rapid and empirically based method has utility in ensuring that management plans for these species take into account the broader ecosystem impacts of different harvest levels.
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The world's seas and oceans are a vital source of animal protein from fishing and a major contributor to global food security. It has been argued that global wild-catch production has reached its limit, and there is concern that many species are overfished. Concerns are also mounting about the state of marine ecosystems and the ecological impacts of fishing on them, with increasing efforts to protect marine biodiversity. Fisheries appear to be at an impasse – demand for seafood is rising but so is concern about the impacts of fishing. However, through a simple analysis, we show that global exploitation rates are well below long-term sustainable levels at a whole ecosystem level. The oceans can support considerably higher sustainable catch than currently harvested. Overfishing has happened but only to a small fraction of species as a result of intensive and selective fishing. Shifting fishing effort away from highly targeted stocks towards currently underutilized species would reduce pressure on overfished species, result in fewer adverse ecosystem effects of fishing and increase overall fisheries production. This shift requires significant changes to our views about seafood, particularly in the developed world. We suggest ways in which this paradigm shift could happen and the range of expertise that would be required to achieve higher global yields with less ecological impact.
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Ecosim models have been fitted to time-series data for a wide variety of ecosystems for which there are long-term data that confirm the models' ability to reproduce past responses of many species to harvesting. We subject these model ecosystems to a variety of harvest policies, including options based on harvesting each species at its maximum sustainable yield (MSY) fishing rate. We show that widespread application of single-species MSY policies would in general cause severe deterioration in ecosystem structure, in particular the loss of top predator species. This supports the long-established practice in fisheries management of protecting at least some smaller “forage” species specifically for their value in supporting larger piscivores.
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Triple-bottom-line outcomes from resource management and conservation, where conservation goals and equity in social outcomes are maximized while overall costs are minimized, remain a highly sought-after ideal. However, despite widespread recognition of the importance that equitable distribution of benefits or costs across society can play in conservation success, little formal theory exists for how to explicitly incorporate equity into conservation planning and prioritization. Here, we develop that theory and implement it for three very different case studies in California (United States), Raja Ampat (Indonesia), and the wider Coral Triangle region (Southeast Asia). We show that equity tends to trade off nonlinearly with the potential to achieve conservation objectives, such that similar conservation outcomes can be possible with greater equity, to a point. However, these case studies also produce a range of trade-off typologies between equity and conservation, depending on how one defines and measures social equity, including direct (linear) and no trade-off. Important gaps remain in our understanding, most notably how equity influences probability of conservation success, in turn affecting the actual ability to achieve conservation objectives. Results here provide an important foundation for moving the science and practice of conservation planning-and broader spatial planning in general-toward more consistently achieving efficient, equitable, and effective outcomes.
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Habitat loss and fragmentation are major threats to biodiversity. Establishing formal protected areas is one means of conserving habitat, but socio-economic and political constraints limit the amount of land in such status. Addressing conservation issues on lands outside of formal protected areas is also necessary. In this paper we develop a spatially explicit model for analyzing the consequences of alternative land-use patterns on the per-sistence of various species and on market-oriented economic returns. The biological model uses habitat preferences, habitat area requirements, and dispersal ability for each species to predict the probability of persistence of that species given a land-use pattern. The eco-nomic model uses characteristics of the land unit and location to predict the value of commodity production given a land-use pattern. We use the combined biological and eco-nomic model to search for efficient land-use patterns in which the conservation outcome cannot be improved without lowering the value of commodity production. We illustrate our methods with an example that includes three alternative land uses, managed forestry, agriculture, and biological reserve (protected area), for a modeled landscape whose physical, biological, and economic characteristics are based on conditions found in the Willamette Basin in Oregon (USA). We find that a large fraction of conservation objectives can be achieved at little cost to the economic bottom line with thoughtful land-use planning. The degree of conflict between conservation and economic returns appears much less using our joint biological and economic modeling approach than using a reserve-site selection ap-proach, which assumes that species survive only inside of reserves and economic activity occurs only outside of reserves.
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Fisheries management is characterized by multiple and conflicting objectives, multiple stakeholders with divergent interests and high levels of uncertainty about the dynamics of the resources being managed. This conjunction of issues can result in high levels of contention and poor outcomes in the management process. Management strategy evaluation (MSE) can assist in the resolution of these issues. MSE involves assessing the consequences of a range of management options and laying bare the trade-offs in performance across a range of management objectives. Key steps in the approach involve turning broad objectives into specific and quantifiable performance indicators, identifying and incorporating key uncertainties in the evaluation, and communicating the results effectively to client groups and decision-makers. At a technical level, the framework facilitates dealing with multiple objectives and uncertainties in prediction. At the implementation level, it fails if it cannot accommodate effective stakeholder participation and acceptance. MSE shares many features with approaches such as adaptive management and development of management procedures. The principles for implementing the MSE approach are reviewed and practical aspects of its implementation under the Australian Fisheries Management Authority (AFMA) partnership model to fisheries management are discussed. The model stresses stakeholder involvement in all key areas of fisheries management, from stock assessment and setting research priorities, to enforcement and decision-making. Stakeholder involvement, including industry, science, and conservation, extends from membership of the AFMA Board, through Management Advisory Committees to Fisheries Assessment Groups. The benefits and limitations of the AFMA partnership approach are reviewed, both for MSE, and, in a wider sense, in the development of an effective fisheries management system.
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