Ensuring that connectivity and stock dynamics are well understood is crucial to determining the appropriate scale for fisheries management and assessment.
There is strong industry and management interest in determining the extent to which connectivity and stock dynamics of snapper along the west coast might have changed over time reflecting changes in environmental conditions and stock abundance.
There is a need to reassess the most appropriate scale for management of the snapper resource in WA under the new Aquatic Resources and Management Act.
There is a need to evaluate whether active-acoustic methods can improve capacity to monitor the spatial distribution and abundance of snapper in key spawning aggregations and whether these methods are complementary to the existing approaches used to assess snapper stocks in the GCB and WCB and elsewhere in Australia.
Final report
This report describes a collaborative project focused on Snapper (Chrysophrys auratus) carried out between 2018 and 2021 by researchers from the Western Australian Department of Primary Industries and Regional Development (DPIRD), Flinders University, University of Adelaide, University of Western Australia, and CSIRO. The project was co-funded by the Fisheries Research and Development Corporation and had three key aims, which were motivated by questions raised by commercial fishers in the Gascoyne and West Coast bioregions of Western Australia, about C. auratus stock structure in relation to current fishery management boundaries and the methodologies used to assess these Snapper stocks.
Firstly, the biological connectivity of C. auratus in waters offshore of Shark Bay (in the Gascoyne Coast Bioregion) and to the south off an area between Kalbarri and Geraldton (in the West Coast Bioregion) were investigated using population genomics, otolith chemistry and larval dispersal modelling. These studies identified, for the first time, nursery grounds inside Shark Bay that are attributable to the Gascoyne oceanic Snapper stock, confirmed the larval transport pathways linking these with known spawning grounds around islands off Shark Bay and commenced the development of a recruitment index for this stock.
Secondly, a novel fishery-independent survey method, combining acoustics (sonar) with underwater cameras, termed acouptics, was trialled for monitoring C. auratus stocks off Shark Bay. The study has shown that these active acoustic methods can be used to monitor Snapper aggregations and estimate numbers of fish/biomass, providing a potential addition to the future Snapper assessment toolkit.
Thirdly, this project explored if there had been any changes in the biological characteristics of C. auratus in oceanic waters of the Gascoyne Coast Bioregion and northern West Coast Bioregion over the past 30 years. The study demonstrated changes in maturity of Snapper in the Gascoyne, with the updated parameters used to inform the most recent (2022) assessment of this C. auratus stock.
The outcomes of this project will provide the basis for a review of stock assessment approaches and management arrangements for C. auratus on the West coast of Australia. Outcomes of the acouptics work provides a conceptual basis for application in C. auratus assessment research elsewhere in Australia and New Zealand.
