Models are key tools for integrating a wide range of system information in a common framework. Attempts to model exploited marine ecosystems can increase understanding of system dynamics; identify ...major processes, drivers and responses; highlight major gaps in knowledge; and provide a mechanism to ‘road test’ management strategies before implementing them in reality. The Atlantis modelling framework has been used in these roles for a decade and is regularly being modified and applied to new questions (e.g. it is being coupled to climate, biophysical and economic models to help consider climate change impacts, monitoring schemes and multiple use management). This study describes some common lessons learned from its implementation, particularly in regard to when these tools are most effective and the likely form of best practices for ecosystem‐based management (EBM). Most importantly, it highlighted that no single management lever is sufficient to address the many trade‐offs associated with EBM and that the mix of measures needed to successfully implement EBM will differ between systems and will change through time. Although it is doubtful that any single management action will be based solely on Atlantis, this modelling approach continues to provide important insights for managers when making natural resource management decisions.
The correct prediction of the shape and strength of density dependence in productivity is key to predicting future stock development and providing the best possible long‐term fisheries management ...advice. Here, we identify unbiased estimators of the relationship between somatic growth, recruitment and density, and apply these to 80 stocks in the Northeast Atlantic. The analyses revealed density‐dependent recruitment in 68% of the stocks. Excluding pelagic stocks exhibiting significant trends in spawning stock biomass, the probability of significant density dependence was even higher at 78%. The relationships demonstrated that at the commonly used biomass limit of 0.2 times maximum spawning stock size, only 32% of the stocks attained three quarters of their maximum recruitment. This leaves 68% of the stocks with less than three quarters of their maximum recruitment at this biomass limit. Significantly lower recruitment at high stock size than at intermediate stock size was seen in 38% of the stocks. Density dependence in late growth occurred in 54% of the stocks, whereas early growth was generally density‐independent. Pelagic stocks were less likely to exhibit density dependence in recruitment than demersal and benthic stocks. We recommend that both the degree to which productivity is related to density and the degree to which the relationship changes over time should be investigated. Both of these aspects should be considered in evaluations of whether sustainability and yield can be improved by including density dependence in forecasts of the effects of different management actions.
Ecosystem-based management (EBM) of the ocean considers all impacts on and uses of marine and coastal systems. In recent years, there has been a heightened interest in EBM tools that allow testing of ...alternative management options and help identify tradeoffs among human uses. End-to-end ecosystem modelling frameworks that consider a wide range of management options are a means to provide integrated solutions to the complex ocean management problems encountered in EBM. Here, we leverage the global advances in ecosystem modelling to explore common opportunities and challenges for ecosystem-based management, including changes in ocean acidification, spatial management, and fishing pressure across eight Atlantis (atlantis.cmar.csiro.au) end-to-end ecosystem models. These models represent marine ecosystems from the tropics to the arctic, varying in size, ecology, and management regimes, using a three-dimensional, spatially-explicit structure parametrized for each system. Results suggest stronger impacts from ocean acidification and marine protected areas than from altering fishing pressure, both in terms of guild-level (i.e., aggregations of similar species or groups) biomass and in terms of indicators of ecological and fishery structure. Effects of ocean acidification were typically negative (reducing biomass), while MPAs led to both 'winners' and 'losers' at the level of particular species (or functional groups). Changing fishing pressure (doubling or halving) had smaller effects on the species guilds or ecosystem indicators than either OA or MPAs. Compensatory effects within guilds led to weaker average effects at the guild level than the species or group level. The impacts and tradeoffs implied by these future scenarios are highly relevant as ocean governance shifts focus from single-sector objectives (e.g., sustainable levels of individual fished stocks) to taking into account competing industrial sectors' objectives (e.g., simultaneous spatial management of energy, shipping, and fishing) while at the same time grappling with compounded impacts of global climate change (e.g., ocean acidification and warming).
•Sensitivity analysis of an end-to-end Atlantis model of the Eastern English Channel.•Morris screening analysis with growth, mortality, and reproduction parameters.•All parameters important for ...system stability.•Bottom-up effects (plankton and some invertebrate parameters) stronger role than top-down.
There is growing interest in using mechanistic ecosystem models for ecosystem-based management, as they have the advantage of capturing both bottom-up and top-down processes as well as system interactions from food web structure, spatial constraints, and human activities. However, they have the disadvantage of requiring many parameters, many of which are unknown and must be estimated or calibrated to available data. Sensitivity analysis (SA) is an important part of simulation model development in order to understand model uncertainty and which parameters are more or less influential, but has been relatively neglected with Atlantis models due to the large number of parameters and long simulation run time. The Atlantis Eastern English Channel (Atlantis-EEC) model has been applied to investigate ecosystem dynamics and processes as well as fishery management scenarios. Here we present the results of a SA of growth, mortality, and recruitment parameters, which are parameters particularly difficult to measure and thus commonly tuned through model calibration. To manage the large number of parameters in the model, we used a Morris screening approach. This method can efficiently provide information on parameter main effects and interactions/non-linear effects with relatively few simulations. We performed an initial SA including all groups on 90 parameters, where we found that the most important drivers of system dynamics and biomass across groups were: (1) plankton growth and mortality rates and (2) top predator's fixed recruitment and juvenile mortality rates. We then performed a follow-up SA on a subset of 61 parameters, excluding top predators and plankton groups from the analysis. We found that all parameters were important for system stability, while individual groups’ biomass were generally most influenced by their own parameters and a subset of benthic invertebrates. Nonlinear/interaction effects were widespread, demonstrating the prevalence of feedback loops in the trophic structure, and the importance of bottom-up effects and, to a lesser extent, top-down effects. The information gained from this SA provided a better understanding of the model structure. It also allowed us to make recommendations on the general Atlantis model calibration process as well as suggesting which parameters may be most important for propagation of uncertainty in model scenarios.
•Von Bertalanffy growth parameters are used to inform the spatial structuration of an exploited species.•Spatial differences in asymptotic length reinforce the metapopulation hypothesis.•Growth ...parameters estimates differ depending on the type of data used - scientific survey or commercial fisheries.
In fisheries science, a mismatch between the delineation of a fish stock and the underlying biological population can lead to inaccurate assessment and management. Previous results suggested a potential spatial structuration of the Eastern English Channel (EEC) stock of common sole, Solea solea, in three sub-populations. In this article, we propose to investigate the spatial population structure of common sole in the EEC using the von Bertalanffy Growth Function parameters as indicators of population segregation. In order to test the sub-population hypothesis and evaluate its robustness to data sources, we developed three models, all including an area effect on growth parameters. The first model was aimed at testing a potential data source effect (in addition to the area effect) using commercial and scientific survey data jointly. The two other models used either scientific survey or commercial fishery data and focused on spatial differences in growth parameters. Our results showed that the growth parameter estimates indeed differed depending on the type of data used, with higher estimated asymptotic length and length at age two (L2) using commercial data. They also highlighted spatial differences in asymptotic length, consistent between models, which tend to confirm a spatial structuration of sole in the EEC. While these results need to be strengthened by marking and genetic studies, they constitute a first step towards a better understanding of the population spatial structuration of common sole in the EEC.
A key component of ecosystem-based fisheries management (EBFM) is explicit consideration of trade-offs. Ecosystem models can be used to quantify trade-offs and focus discussion around objectives. ...Given large structural uncertainties inherent in ecosystem models, however, comparative approaches are recommended to identify results that are robust to model formulation. We developed ecosystem models of the continental shelf and slope of New South Wales, Australia, using two ecosystem modelling frameworks, Atlantis and Ecopath with Ecosim. The models were calibrated to emulate large-scale changes in ecosystem structure between 1976 and 1996, as predicted by data from fishery-independent trawl surveys. Calibrated models were projected forward under a range of “optimal” fishing efforts designed to achieve economic, conservation or biodiversity objectives. While there were large differences in model predictions for individual species, the models gave very similar qualitative results when ranking fishing policies and describing trade-offs. Our results illustrate the importance of identifying fishery objectives before build-up of fleet capacity, and the need to consider trade-offs when simultaneously stating multiple ecosystem-level goals. Our finding that structurally-distinct ecosystem models can provide consistent qualitative advice highlights the capacity of ecosystem models for informing strategic management questions, even in the presence of considerable uncertainty in ecosystem-level processes.
Modelling marine protected areas: insights and hurdles Fulton, Elizabeth A.; Bax, Nicholas J.; Bustamante, Rodrigo H. ...
Philosophical transactions - Royal Society. Biological sciences,
11/2015, Letnik:
370, Številka:
1681
Journal Article
Recenzirano
Odprti dostop
Models provide useful insights into conservation and resource management issues and solutions. Their use to date has highlighted conditions under which no-take marine protected areas (MPAs) may help ...us to achieve the goals of ecosystem-based management by reducing pressures, and where they might fail to achieve desired goals. For example, static reserve designs are unlikely to achieve desired objectives when applied to mobile species or when compromised by climate-related ecosystem restructuring and range shifts. Modelling tools allow planners to explore a range of options, such as basing MPAs on the presence of dynamic oceanic features, and to evaluate the potential future impacts of alternative interventions compared with 'no-action' counterfactuals, under a range of environmental and development scenarios. The modelling environment allows the analyst to test if indicators and management strategies are robust to uncertainties in how the ecosystem (and the broader human–ecosystem combination) operates, including the direct and indirect ecological effects of protection. Moreover, modelling results can be presented at multiple spatial and temporal scales, and relative to ecological, economic and social objectives. This helps to reveal potential 'surprises', such as regime shifts, trophic cascades and bottlenecks in human responses. Using illustrative examples, this paper briefly covers the history of the use of simulation models for evaluating MPA options, and discusses their utility and limitations for informing protected area management in the marine realm.
Simulating fish larval drift helps assess the sensitivity of recruitment variability to early life history. An individual-based model (IBM) coupled to a hydrodynamic model was used to simulate common ...sole larval supply from spawning areas to coastal and estuarine nursery grounds at the meta-population scale (4 assessed stocks), from the southern North Sea to the Bay of Biscay (Western Europe) on a 26-yr time series, from 1982 to 2007. The IBM allowed each particle released to be transported by currents, to grow depending on temperature, to migrate vertically depending on development stage, to die along pelagic stages or to settle on a nursery, representing the life history from spawning to metamorphosis. The model outputs were analysed to explore interannual patterns in the amounts of settled sole larvae at the population scale; they suggested: (i) a low connectivity between populations at the larval stage, (ii) a moderate influence of interannual variation in the spawning biomass, (iii) dramatic consequences of life history on the abundance of settling larvae and (iv) the effects of climate variability on the interannual variability of the larvae settlement success.
•We simulated the drift trajectories of sole eggs and larvae at large spatial (four stocks) and temporal (26 y) scales;•We used an IBM coupled online to a hydrodynamic model;•We emphasized:•The very low to moderate connectivity between populations at the larval stage•The moderate influence of spawning biomass variations on recruitment•The influence of life history and climate variability on the amount of settled sole.
A scavenger is an animal that feeds on dead animals (carrion) that it has not killed itself. Fisheries discards are often seen as an important food source for marine scavengers so the reduction of ...discards due to the Landing Obligation may affect their populations. The literature on scavenging in marine ecosystems is considerable, due to its importance in the trophic ecology of many species. Although discards undoubtedly contribute to these species’ food sources, few can be seen to be solely dependent on carrion (including discards). Ecosystem models predicted that discards contributed very little to the diet of scavengers at a regional scale. A reduction in discards through the Landing Obligation may therefore affect populations for a few species in some areas, but generally this is unlikely to be the case. But it is challenging to identify how important discards might be to scavengers, as they are taxonomically diverse and vary in the role they play in scavenging interactions.
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