Project number: 2003-046
Project Status:
Budget expenditure: $378,224.93
Principal Investigator: Ian Brown
Organisation: Department of Agriculture and Fisheries EcoScience Precinct
Project start/end date: 29 Jun 2003 - 22 Feb 2008


In his assessment of the Queensland spanner crab fishery for exemption from the export controls of the EPBC Act, the Federal Environment and Heritage Minister recommended that arrangements for joint monitoring and assessment of the shared stock of spanner crabs be made, with a view to eventual co-management. This process needs to be addressed before the next Commonwealth review of the fishery in five years’ time. While the development of complementary management arrangements is ultimately a core-business function of the two State governments, the evaluation of existing monitoring and assessment paradigms and the synthesis of a common reference point-setting process clearly requires significant collaboration between scientists, modellers and statisticians.

A workshop involving scientists and fishery managers from Queensland and NSW was held recently (27 September ’02) to examine collaborative options with regard to research and management in the spanner crab fisheries. The meeting agreed that there is a need to conduct simultaneous field trials of the two States’ monitoring surveys, to determine their relative cost-effectiveness as fishery-independent measures of stock abundance. The broad principles of such an exercise were agreed to, and details of the experimental design were fleshed-out at another meeting of research collaborators in NSW in late November.

Previous work aimed at estimating growth rates in spanner crabs has yielded highly divergent results, and none has provided a reliable estimate of age at recruitment. It is essential that this knowledge-gap is bridged because an estimate of age at recruitment is crucial to the successful development of age-based assessment models. Ideally such a model, tuned with the LTMP fishery-independent survey data, would replace the simplistic CPUE regression-based model.

While the fishery-independent spanner crab monitoring programme will overcome hyperstability problems inherent in the commercial statistics, it still requires the use of commercial gear, and is therefore subject to the same problems of variable catchability. These are presumably related to behavioural cycles of the crabs, habitat patchiness, and the effects of environmental factors such as water temperature. The impact of these factors on catchability needs to be investigated if survey and commercial CPUE data are to be interpreted correctly and the assessment process significantly improved.


1. Determine the age at which spanner crabs recruit to the fishery.
2. Develop a common methodology for monitoring and assessing the Australian spanner crab stock.
3. Exploratory investigation of sources of variability in apparent population density.

Final report

ISBN: 978-0-7345-0394-7
Author: Ian Brown
Final Report • 2009-03-12


Spanner crabs (Ranina ranina) represent a valuable single-species fishery in Queensland. Although a transparent and effective assessment process was developed some years ago for setting the commercial total allowable catch (TAC), additional information was needed to reduce some of the uncertainty in assessments, and to incorporate fishery-independent information from the DPI&F Long-Term Monitoring surveys into the process. The exploited stock crosses State boundaries and extends into northern NSW waters, but historically quite different approaches to monitoring and assessment have been developed by the two States. 
This project set out to clarify conflicting estimates of growth rates, develop an integrated (stock-wide) system for monitoring and assessing the status of the resource, and to examine some environmental variables believed to be responsible for influencing catch rates.

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