Editor's Choice - Ecosystem based fisheries management: linking existing models to form a practical decision support tool
August 2013 (Issue 50:4)
Dichmont, C. D., Ellis, N., Bustamante, R. H. Deng, R., Tickell, S., Pascual R., Lozano-Montes, H., and Griffiths, S. (2013). Evaluating marine spatial closures with conflicting fisheries and conservation objectives. Journal of Applied Ecology, 50, 1060-1070.
It impossible to retain resources in a pristine state and simultaneously extract benefits from them. Consequently, the challenge for researchers in the field of resource management is to provide decision makers with trade-offs among alternative management goals in a way that highlights the outcomes of alternative management policies in a transparent, yet scientifically rigorous manner. As shown by this Editor’s Choice, fisheries are at the forefront of developing the tools to provide scientific management advice by linking decision support techniques, population and ecosystem modelling and statistical analysis.
Traditionally, the advice provided to fishery managers has focused on the trade-offs between short- and long-term yields and between future resource size and expected future catches (Beverton & Holt 1957; Quinn & Deriso 1999). However, managers recognize that there are additional trade-offs to consider when selecting fishery catch and effort controls. Ecosystem-based Fisheries Management (EBFM) “recognizes the physical, biological, economic, and social interactions among the affected components of the ecosystem and attempts to manage fisheries to achieve a stipulated spectrum of societal goals, some of which may be in conflict” (Marasco et al. 2007). While the principles which should underlie EBFM, and some guidelines for their implementation, have been developed (Francis et al. 2007), practical analytical tools are still lacking. In the absence of such tools, it will be impossible to identify the tactics needed to address the multiple objectives of EBFM, such as which areas should be closed to fishing, and the ideal number of vessels.
Prawn fisheries have the potential to have major impacts on habitats and ecosystems through direct impacts on substrate, and by removing many species in addition to the target species. Most studies of the impacts of prawn fisheries on ecosystems and habitats have focused on fisheries in temperate zones, although large prawn fisheries occur in species-rich tropical regions. These fisheries take many species as bycatch, including species that have been identified as threatened or endangered. Australia’s Northern Prawn Fishery is the most valuable fishery managed by Commonwealth Government of Australia. It is a trawl fishery which operates in the Gulf of Carpentaria and across northwest Australia. The fishery has been certified as sustainable in a single-species sense, and is managed using limits on fishing effort, gear restrictions, and closed seasons and areas. Although vessels are required to use Turtle Excluder and Bycatch Reduction Devices, the fishery is known to take over 350 teleost and elasmobranch species (Stobutzski et al. 2001) and to have a large footprint on the habitat.
Spatial management is considered a powerful tool to address ecosystem impacts, but could have undesirable consequences on the target fishery and hence the profitability and social sustainability of the fishery. Dichmont et al. have developed a decision support tool which links and integrates models which represent several major ecosystem and fishery impacts within a single framework. Dichmont et al. develop a Management Strategy Evaluation (MSE) framework (Bunnefeld et al. 2001) and use it to contrast four spatial management strategies. The results from the modelling allow the consequences of each alternative policy to be summarized in terms of spatially explicit performance measures which address management goals which range from the yield from the fishery to impacts of benthos. MSE involves simulating all aspects of the system being managed, including the underlying biological system, how it is monitored, and the selection and implementation of regulations (Fulton et al. 2011). A key aspect of MSE is representations of uncertainty, including that associated models, monitoring, and implementation of regulations.
The MSE includes a demographically detailed model of the two prawn species which are the targets for the fishery, and a spatial ecosystem model (EcoSpace) which captures the dynamics of 53 functional groups, including other species of targeted prawns, and represents habitats throughout the Gulf of Carpentaria. The set of models on which the MSE is based also includes a vessel dynamics model which describes the movements of vessels given the constraints imposed by spatial and seasonal closures. The effort distribution is input for other models used in the paper to evaluate benthic impacts and the consequences of fishing on threatened and endangered species. Dichmont et al. evaluate four spatial management strategies, including a status quo, and strategies which aim to minimize (a) direct and indirect ecosystem impacts, (b) the number of species at risk, and (c) impacts on the benthos.
Graphical summaries of model outputs chosen to quantify the management objectives allow the trade-offs among the management objectives to be highlighted. These summaries are developed with decision makers, in order to be of direct help in decision making. The status-quo is shown to have relatively minor impacts on the ecosystem generally. Strategies which aim to achieve specific management objectives are shown to perform best for those management objectives, but the size of the improvement over the status-quo differs markedly among strategies, highlighting to managers how much improvement is possible. In addition, strategies which aim to reduce ecosystem impacts lead to displacement of effort to regions currently not subject to high levels of fishing.
Although MSE frameworks have been developed in the past for fisheries decision making (Fulton et al. 2011), those frameworks are very complicated and require data and parameter estimates which are rarely available, as is the case for the Northern Prawn Fishery.
Dichmont et al. was selected for this Editor’s Choice because it links models which have been developed previously for individual aspects of EBFM to make maximum use of existing tools, thus providing decision makers with information on how alternative management policies impact a broad suite of management goals. The approach is applied to a prawn fishery off the coast of northern Australia. However, it could be applied to other fisheries in which there are multiple conflicting objectives and where models have been developed for individual EBFM objectives. More generally, it could be applied as a decision support tool in areas beyond fisheries, including terrestrial spatial planning, harvesting of game, impacts of climate change and ocean acidification, and extended so that outcomes are represented in the form of metrics which quantify key ecosystem services.
Beverton, R. J. H. & Holt, S. J. (1957) On the Dynamics of Exploited Fish Populations, Fishery Investigations Series II Volume XIX, Ministry of Agriculture, Fisheries and Food
Bunnefeld, N., Hoshino, E. & Milner-Gulland, E. J. (2011) Management strategy evaluation: a powerful tool for conservation? Trends in Ecology and Evolution, 26, 441-447.
Francis, R. C, Hixon, M. A., Clarke, M. C., Murawski, S. A. & Ralston, S. (2007). Ten commandments for ecosystem-based fisheries scientists. Fisheries, 32, 217-233.
Fulton, E. A., Link, J. S., Kaplan, I. C., Savina-Rolland, M., Johnson, P., Ainsworth, C. et al. (2011) Lessons in modelling and management of marine ecosystems: the Atlantis experience. Fish and Fisheries, 12, 171–188.
Marasco, R. J., Goodman, D., Grimes, C. B., Lawson, P. W., Punt, A. E. & Quinn, T. J. II (2007) Evaluating marine spatial closures with conflicting fisheries and conservation objectives. Canadian Journal of Fisheries and Aquatic Sciences, 64, 928-939.
Quinn, T. J. II & Deriso, R. B. (1999) Quantitative Fish dynamics. Oxford University Press, New York.
Stobutzski, I. C., Miller, M. J., Jones, P. & Salini, J. P. (2001) Bycatch diversity and variation in a tropical Australian penaeid fishery; the implications for monitoring. Fisheries Research, 53, 283-301.
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