Improving the effectiveness of age-abundance indicators in the management of fisheries in Queensland, Australia

O'Neill, Michael Francis (2015). Improving the effectiveness of age-abundance indicators in the management of fisheries in Queensland, Australia PhD Thesis, School of Geography, Planning and Environmental Management, The University of Queensland. doi:10.14264/uql.2015.1106

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Author O'Neill, Michael Francis
Thesis Title Improving the effectiveness of age-abundance indicators in the management of fisheries in Queensland, Australia
School, Centre or Institute School of Geography, Planning and Environmental Management
Institution The University of Queensland
DOI 10.14264/uql.2015.1106
Publication date 2015-12-03
Thesis type PhD Thesis
Supervisor Ron Johnstone
Total pages 144
Language eng
Subjects 0704 Fisheries Sciences
0104 Statistics
0102 Applied Mathematics
Formatted abstract
The development of fishery indicators is a crucial undertaking as it ultimately provides evidence to stakeholders about the status of fished species such as population size and survival rates. In Queensland, as in many other parts of the world, age-abundance indicators (e.g. fish catch rate and/or age composition data) are traditionally used as the evidence basis because they provide information on species life history traits as well as on changes in fishing pressures and population sizes. Often, however, the accuracy of the information from age-abundance indicators can be limited due to missing or biased data. Consequently, improved statistical methods are required to enhance the accuracy, precision and decision-support value of age-abundance indicators.

This research uses three case studies as the basis for improving the effectiveness of ageabundance indicators in fisheries management: eastern king prawns, stout whiting and spanner crab.

The case study species were chosen to demonstrate different aspects that age-abundance indicators need to adapt to. The case studies contrast different life history characteristics (e.g. varied lifespan), fishery management (e.g. effort versus harvest restrictions) and fishery challenges (e.g. fishing power bias and high operational costs of fishing for eastern king prawns; inconsistent data for stout whiting; need for more comprehensive management methodology for spanner crab). Collectively, the case studies form the scientific detail of the thesis.

The first case study developed new methodology for the calculation of abundance indicators and reference points for eastern king prawns. Bio-economic indicators were standardised for calibrating simulations and identified catch-rate levels that were effective for monitoring profitability and useful in simple within-year effort-control rules. Favourable performance of catch-rate indicators in management was achieved only when a legitimate upper limit was placed on total allowable fishing effort. The findings inform decision makers on the uncertainty and assumptions affecting economic indicators.

For the second case study, a new catch curve methodology was described for estimating annual survival fractions of stout whiting. The method analysed individual fish age-abundance data such as length and age by using Gaussian finite mixtures and was designed to overcome fishery dependent sampling issues, assuming that only fish ages within each length category were sampled randomly and that fish lengths themselves were not. The analysis improved estimates of stout whiting survival in waters along Australia’s east coast. The catch curve mixture model applies naturally to monitoring data on fish age-abundance and is applicable to many fisheries.

In the third case study, revised abundance indicators were developed to achieve more responsive spanner crab management. Simulations identified harvest and catch-rate baselines to assisting setting quotas that ensured sustainable crab biomass. The management procedure is robust against strong trends in catch rates and adaptable for use in many fisheries.

The following strategies were identified for the case study fisheries to improve the usefulness of age-abundance indicators in determining management decision making reference points:
• Eastern king prawns – the combined approach of setting target fishing effort near the level for maximum economic yield and a secondary in-season lower limit on catch rates.
• Stout whiting – a mean survival fraction calculated over the two most recent years and evaluated against a target fraction corresponding to the years that best represented stable and profitable fishing.
• Spanner crab – precautionary levels of base quota set below average harvests and above average catch rate reference points ensured robust performance of the management procedure.

The general basis of indicator management was not different between species or method of harvest regulation. The analysis procedures adapted allowing application to each species.

The case studies also demonstrate the use of modernised frameworks for generating and using indicators in fisheries management in Queensland. Mitigation of indicator variance iii and high risk management strategies rests with setting conservative reference points and decision rules to enable active management. The systems described can help improve and measure sustainable and economic outcomes of other fisheries, both in Australia and globally.
Keyword Fisheries

Document type: Thesis
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Created: Mon, 23 Nov 2015, 21:34:49 EST by Michael O'neill on behalf of Scholarly Communication and Digitisation Service