WRL puerulus settlement has been unexpectedly low over the past two settlement periods, with the most recent settlement period (2008/09) being the lowest on record. This extremely weak settlement has occurred despite environmental conditions being favourable for an above average settlement (i.e. a strong Leeuwin Current, warm sea temperatures and la Nina like conditions).
The recent poor settlements could be attributed to a number of possible scenarios, including, reduced egg production from depleted brood stock or a shift/change in oceanic conditions possibly due to climate change. Understanding what scenario(s) are responsible will be crucial for the effective conservation and management of the WRL stock, and ultimately the longevity of the fishery. Anecdotal evidence suggests that colonisation of the puerulus collectors by a number of other species commonly found during processing of these collectors have also been extremely low in recent times. Beginning to examine of the marine flora and fauna communities colonising the puerulus collectors over a range of 1200 km during this time of extremely low settlement (i.e. prior to the end of the settlement season in April 2009) and determining how these communities vary in relation to the varied environmental conditions experienced, will provide valuable information as to what may be influencing puerulus settlement. If settlement of other marine flora and fauna show a related response to that of the WRL pueruli, it could indicate environmental change may be responsible for the decreased settlement. This data will complement other research, such as the oceanographic modelling application (JM010) submitted by DoF and is crucial to the effective management of the WRL fishery. Furthermore, this spatial analysis conducted on a monthly scale has the potential to further identify possible indicator species of localised environmental conditions that could continue to be monitored as part of the standard WRL puerulus monitoring program.

The need for this project was identified through the ESD/EA Risk Assessment workshops held for the Shark Bay and Exmouth Gulf trawl fisheries in May and October 2001. Research is required to provide baseline data on biodiversity on and off the trawl habitats in Shark Bay and Exmouth Gulf to allow an assessment of the effects of trawling on bycatch and to set up reference sites for long-term monitoring of the environmental impact of trawling. The study will examine seasonal variation in biodiversity and efficiency in capture of bycatch species to provide a rigorous scientific basis for determining references sites in other fisheries. Understanding seasonal variability will allow the selection of the appropriate timing of long-term monitoring. Depletion experiments will ensure that bycatch catch per unit effort is related to actual abundance. The sampling undertaken in Shark Bay will cover both prawn and scallop ESD requirements to enable similar reference sites to be established in all WA trawl fisheries. Bycatch issues in the Shark Bay and Exmouth fisheries were identified as a moderate risk through an Ecological Risk Assessment workshop. There is a need for a better understanding of the faunal composition and habitat preferences of bycatch species in both trawled and untrawled areas will aid in determining the most appropriate level of risk to bycatch species. This may allow management strategies to be developed to ameliorate any detrimental impacts on those species that are found to be highly vulnerable to trawl impacts. This information will also enable the Department of Fisheries and industry to effectively respond to information required by Environment Australia on the risk level, objectives, performance indicators and management responses for each issue in order to continue to provide quality and highly valued seafood to both export and local markets. It will also provide a basis to answer queries from conservation and community groups.