Westport has partnered with the Western Australian Marine Science Institution (WAMSI) to deliver the $13.5 million WAMSI-Westport Marine Science Program. This 3-year program is developing the latest data, information and modelling on the complex environmental systems and community values associated with Cockburn Sound.
Project 4.1: Snapper connectivity and evaluation of juvenile stocking
Research theme: Fisheries and Aquatic Resources
Researchers: D Fairclough, L Beheregaray, J Sandoval-Castillo, D Vornicu, J Tweedley, A Cottingham, E Fisher, E Lek and M Harrison.
Publication date: January 2025
Understanding how Cockburn Sound snapper connect to the south-west
With the new container port proposed for Kwinana, an already busy industrial area with commercial shipping routes, there was an opportunity to better understand the links between the adult snapper (Chrysophrys auratus) that spawn in Cockburn Sound, and where the juveniles go next.
The research also looked to understand the relative contribution of the Cockburn Sound snapper spawning aggregations to the broader lower west coast stock and determine genetic and morphometric methods for monitoring the occurrence of released hatchery snapper in Cockburn Sound.
Data analyses of genomics were carried out on 765 individual snapper.
What the report found
- The results from the genomic data analysis points to a single and well-connected genetic population within the south-west region.
- Spawning aggregations in Cockburn and Warnbro sounds contribute snapper to the broader, genetically connected, south-western population.
- The highest connectivity was estimated between the Metro and adjacent Metro North oceanic snapper (97% and 100%).
- Demonstrated by the size of female snapper observed, fish that aggregate to spawn in Cockburn and Warnbro Sounds are exclusively very large fish.
- Morphometrics of wild and hatchery-reared snapper differed in many aspects, allowing distinction of such individuals from good quality photographs, demonstrating the potential for these methods to be used in monitoring the hatchery-reared snapper released in Cockburn Sound.
- Since Snapper Guardians commenced in 2014, only four hatchery-reared juvenile snapper have been recaptured and identified from a total of 1,980 juveniles collected by trawl surveys in Cockburn Sound and ~230,000 released hatchery fish across all years.
- Estimated survival rates of hatchery released snapper of less than 1% could be expected by 5 to 6 years of age (the approximate age at maturity and recruitment to the fishery) and 0.1% by 10 years of age.
What the report recommends
- Further work to evaluate whether differences remain between larger hatchery juveniles and those collected during trawl surveys of Cockburn Sound, and between hatchery and wild fish above the minimum legal length for retention of 500mm in the metropolitan and south-west areas of the west coast.
- Future stock enhancement programs require consideration of the economic feasibility of producing sufficient fish and whether that will provide observable benefits and the timing and locations of releases.
- Bespoke monitoring programs of released fish to ensure genetic diversity and improve long-term survival rates.
How Westport will use this report
Westport will use this report to inform its environmental management strategies for the port development, to protect and support marine health in Cockburn Sound.
You can read the full report here.
