Qualitative mathematical models to support ecosystem-based management of Australia's Northern Prawn Fishery

A major decline in the catch of the banana prawn [shrimp], Penaeus (Fenneropenaeus) merguiensis, occurred over a six-year period in the Weipa region of the northeastern Gulf of Carpentaria, Australia. Three main hypotheses have been developed to explain this decline: (1) prawn recruitment collapsed due to overfishing; (2) recruitment collapsed due to a change in the prawn's environment; and (3) adult banana prawns were still present, but fishers could no longer effectively find or catch them. Qualitative mathematical models were used to link population biology, environmental factors, and fishery dynamics to evaluate the alternative hypotheses. This modeling approach provides the means to rapidly integrate knowledge across disciplines and consider alternative hypotheses about how the structure and function of an ecosystem affects its dynamics. Alternative models were constructed to address the different hypotheses and also to encompass a diversity of opinion about the underlying dynamics of the system. Key findings from these analyses are that: instability in the system can arise when discarded fishery bycatch supports relatively high predation pressure; system stability can be enhanced by management of fishing effort or stock catchability; catch per unit effort is not necessarily a reliable indicator of stock abundance; a change in early-season rainfall should affect all stages in the banana prawn's life cycle; and a reduced catch in the Weipa region can create and reinforce a shift in fishing effort away from Weipa. Results from the models informed an approach to test the hypotheses (i.e., an experimental fishing program), and promoted understanding of the system among researchers, management agencies, and industry. The analytical tools developed in this work to address stages of a prawn life cycle and fishery dynamics are generally applicable to any exploited natural resource

Importance of trophic information, simplification and aggregation error in ecosystem models

Ecosystem models are becoming increasingly important as pressure from fisheries intensifies and ecosystem-based fisheries management becomes more widely used. Trophic webs often form the basis of ecosystem models and ecosystem-specific dietary information is crucial for optimal model performance. This is particularly the case if model predictions are used in management decisions. The Tasmanian live fish fishery for banded morwong was used as a case study to investigate the importance of trophic information, model simplification and aggregation error on ecosystem model results. Dietary analysis of 6 commonly captured reef fish was undertaken. Significant trophic overlap was found between blue throat wrasse Notolabrus tetricus and purple wrasse N. fucicola, and banded morwong Cheilodactylus spectabilis and bastard trumpeter Latridopsis forsten. Marblefish Aplodactylus arctidens and long-snouted boarfish Pentaceropsis recurvirostris had significantly different diets from other species studied. Using this information, a detailed qualitative model was produced and then simplified through the aggregation of variables. Variables were aggregated using 3 methods: Euclidean distance, Bray-Curtis similarity, and regular equivalence for inclusion in 3 simplified models. Variable aggregation is undertaken in many studies and may create aggregation error. Each aggregation method produced a different proportion of incorrect model predictions as a result of aggregation error. The model simplified using regular equivalence produced the least aggregation error and a web structure aligned with the dietary analysis. More widespread use of these methods in fisheries management should be considered

Evaluating how food webs and the fisheries they support are affected by fishing closures in Jurien Bay, temperate Western Australia

This project built on collaborative research in the Jurien Bay Marine Park to develop quantitative models of the ecosystem in this region (Ecopath, Ecosim and Ecospace) and qualitative models of different parts of the ecosystem. These models were used to evaluate the effects of different management options, such as controls on fishing effort and different spatial closures, on fished species (e.g. Western Rock Lobster, Dhufish, Pink Snapper) and the trophic interactions in the ecosystem. In addition to evaluating different management options, the process of developing the model through a series of workshops provided a mechanism for integrating research from previous studies and building understanding about the ecosystem and model among researchers, managers, fishers. The Ecopath model consisted of 80 functional groups (more than 200 species), including 31 fish groups, 26 invertebrates, 11 primary producers, two marine mammals, two seabirds and eight non-living groups. The Advisory group for the project, which had representatives from the Department of Fisheries WA, Department of Environment and Conservation, RecFishWest, RLIAC, and WAFIC, provided directions for developing the management scenarios for evaluation by the quantitative models, including recent changes to fishing regulations in the West Coast region. The final stage of the model can address key ecological questions in the system and explore the dynamics of target species such as Western Rock Lobster and top predators under different fishing regimes. The benefits from the spatial closures, evaluated by Ecospace, vary greatly between species – they were much more effective for relatively sedentary species such as Dhufish and Pink Snapper than migratory species such as sharks

A framework for understanding cumulative impacts, supporting environmental decisions and informing resilience based management of the Great Barrier Reef World Heritage Area: Final Report to the Great Barrier Reef Marine Park Authority and Department of the Environment

This project was commissioned by and developed with the Department of the Environment and the Great Barrier Reef Marine Park Authority (GBRMPA) to develop a qualitative framework for understanding cumulative impacts on the resilience of coral reef and seagrass ecosystems to inform decision making in the Great Barrier Reef World Heritage Area (GBRWHA). This report is the result of close collaboration between the Australian Institute of Marine Science (AIMS), GBRMPA, Department of the Environment, the Commonwealth Scientific and Industrial Research Organisation (CSIRO) and the University of Melbourne. The Great Barrier Reef is facing a range of pressures, and supporting the resilience of the Reef has become a central focus in its management. A key challenge for managers is to understand the cumulative impacts of multiple stressors and incorporating this knowledge into management decisions. The Cumulative Impact and Structured Decision-Making (CISDM) framework represented in this report is designed to assist Great Barrier Reef Marine Park managers and stakeholders in this challenge. The framework uses qualitative and probabilistic modelling to provide a systems-level understanding of how cumulative stressors affect coral reefs and seagrass ecosystems in the GBRWHA. These ecosystems underpin matters of national environmental significance (MNES), including the outstanding universal value (OUV) of the GBRWHA. This report forms one part of the department's program of work funded under the Sustainable Regional Development Program to support the Strategic Assessment of the Great Barrier Reef World Heritage Area.This record includes 2 *.NETA files as mentioned in the report on page 38. These files are specific to an application called Netica. Please see https://www.norsys.com/netica.html for more information

Identifying key dynamics and ideal governance structures for successful ecological management

Estuaries around the world are often degraded and subject to issues surrounding effective management and governance. Without substantial changes in the overall management of many catchments, there is a risk that estuarine health will further decline, causing serious social and economic impacts. The Peel region is one of Australia's fastest growing residential areas and the social and economic wellbeing of the local community is tied to the health of the Peel-Harvey estuary. This estuary is the largest in south Western Australia and has for decades incurred considerable anthropogenic impacts. This study uses the Peel-Harvey estuary as a case study for the assessment of governance structures and ecosystem dynamics using qualitative models. Each model highlights drivers that impact the most important assets, water quality and general environmental quality. Potential management strategies are identified to tackle ineffective monitoring and regulation of impacts, overlapping responsibilities between different public infrastructure providers, and a lack of accountability. Incorporating 'ideal' management strategies into 'future' models clarified paths of governance and provided better delivery of outcomes. Strong environmental and nutrient management were integral to effective environmental governance, as was the need for whole-of-government environmental decisions to be made in the context of predicted longer-term benefits for all sectors, including the general community. The assessment of social-ecological structures, issues and potential management strategies using qualitative models identified mechanisms to achieve effective management and resulted in predictions of increased environmental quality, as well as increased social and economic values

Modelling coastal planning in southwest Western Australia: Complexity, collaboration and climate adaptation

This action-research project investigates the extent to which current coastal planning arrangements can respond to climate change impacts such as coastal erosion and recession in the southwest of Western Australia. The complex social ecological system that comprises coastal planning in the region was modelled in a collaborative process. This took the form of a major action research workshop followed by further small workshops and interviews with key actors. The modelling process has implications for coastal planning as it shows that despite recent changes to coastal planning policy there are still significant areas of liability resulting from climate change that are not yet accounted for by governance. More generally, private and public coastal developments in WA are in a phase of rapid growth, with observable degradation of the coastal environment. Within the context of the model system, this implies that the positive feedback subsystems are strongly driving the system, and current levels of response to public liability and environmental advocacy are relatively weak and inadequate to achieve sustainable coastal management. For this system to be stable requires that negative system feedback be stronger than positive feedback. Future modelling efforts will investigate potential interventions and restructuring of governance system to achieve goals of sustainable development. Thus far, the main use of the model has been as a heuristic device to discuss the coastal planning system with key informants, and to identify constraints and opportunities to coastal adaptation through the planning system

An integrated monitoring framework for the Great Barrier Reef World Heritage Area

Monitoring provides important feedback on how social and environmental systems are tracking and whether or not human activities, including management activities, are having an impact. This paper describes an approach applied to develop an integrated monitoring framework to inform adaptive management of the Great Barrier Reef World Heritage Area, a complex, multi-jurisdictional, multi-sectoral marine system of international importance. It identifies the gaps and opportunities to integrate the existing long-term, short-term and compliance-related monitoring and reporting initiatives to provide the information for more effective and efficient (adaptive) management of the Great Barrier Reef World Heritage Area. And as importantly it aligns expectations among different agencies about how monitoring will inform management. Fifty two high priority values, processes and pressures for management were identified along with 65 existing monitoring programs. Developing the monitoring framework was useful in several ways. First it brought together scientists, policy-makers, managers, and other interested stakeholders with different agendas, philosophies and incentives and established a common purpose, lexicon and language for an integrated monitoring program. Second, it highlighted the importance and usefulness of qualitative conceptual models as a framework for focused discussion around a set of hypotheses with relevance for management. Third, the process started an important conversation about defining and setting a realistic number of monitoring priorities for management. Finally, it has provided direction for how to build on existing initiatives to develop an integrated monitoring program for a globally significant world heritage area