Critical knowledge gaps identified by the cross-sectoral harvest strategy working group are encapsulated within three priority areas for mulloway in NSW:
1) Information on the spatial extent of population structure
Whilst mulloway in NSW have been shown to be part of a single genetic stock along the east coast (Barnes et al. 2015), which is managed at the jurisdictional level (Queensland, New South Wales, Victoria – Earl et al. 2021), the overall general small scales of movement and connectivity (Hughes et al. 2022), and spatial variation in otolith chemistry (Russell et al. 2021), suggest the potential for fine-scale population structuring within the broader stock. Such population structuring may occur over various time scales (e.g. evolutionary, generational or lifetime) relevant to management of the species. Identifying the spatial extent of population structure is therefore critical to inform the potential utility of spatially structured monitoring, assessment, and management of the species in NSW, including the potential need for cross-jurisdictional collaboration with Queensland and Victoria.
2) Refined and updated population life-history parameters
As described above, evidence indicates the potential for fine-scale within-generation population structure of mulloway within NSW, as has been demonstrated elsewhere in Australia (Ferguson et al. 2011). For mulloway in NSW, sub-populations may be subject to variation in environmental variables (e.g. habitat, water temperature, salinity), particularly those that vary with latitude. Such population structure may therefore manifest itself in spatial variability in demographic characteristics, such as growth, size and age composition, and mortality that affect stock productivity and subsequent resilience to exploitation. Information on mulloway reproductive biology was collected in the early 2000s and established size- and age-at-maturity (Silberschneider & Gray 2005), however information on the spatial and temporal extent of spawning is not clearly defined and the body-size fecundity relationship for mulloway in NSW is not well known. An updated examination of spatial variation in size and age structures, growth, mortality and reproductive biology are therefore urgently required to underpin length- and age-based components of future stock assessments for mulloway in NSW.
3) Assessment of gear selectivity and discard/release mortality for the main fishing methods.
Despite the majority of the commercial mulloway catch (~60%) being taken using gillnets (termed ’mesh nets’) in NSW, to date there has been very little research into selectivity, bycatch, discarding and post-release mortality of mulloway caught in this gear. Research on discard (‘release’) mortality from recreational fishing has shown that the two key predictors of mortality are deep-hooking (Butcher et al. 2007) and barotrauma (Butcher et al. 2013, Hughes et al. 2019), however, most of this work was restricted to small mulloway ( 45 cm TL) and no data are available on the fate of larger angled and released conspecifics. Research into the selectivity, rates of discarding and unaccounted fishing mortality of mulloway caught in the main gears and sectors are therefore urgently required (e.g. by defining selectivity functions and rates of discarding and post-release mortality for use in future stock assessment models).
Other knowledge gaps fall under priority areas already being addressed by existing NSW DPI-Fisheries initiatives (e.g. improved fishery data from all sectors, development of fishery-independent survey methods and updated comprehensive ERA; Figure 1).
Successfully fulfilling all knowledge gaps will generate data that will underpin a fourth priority area:
4) Development of a dynamic population model.
This is the essential tool that will be developed to reduce uncertainty in the species stock assessment, service the requirements of the harvest strategy to rebuild the stock, and guide future management to maintain the stock at a level that improves access to, and use of, the resource by all sectors. Any model(s) must also support an expandable assessment approach, capable of determining stock status with reasonable confidence from limited data available during the stock rebuilding phase, but with the ability to integrate additional data sources as they become available (once the rebuilding phase is complete) and maintaining continuity with previous assessments. The role of climatic/environmental drivers on mulloway population dynamics will also be examined within the integrated assessment model(s) that will be developed.
Without the improved knowledge encapsulated in the above priority areas for research, any reasonable assessment of the status of the resource, estimation of appropriate harvest levels, harvest strategy development, and implementation of appropriate management to rebuild the resource and maintain sustainability in future, will not be possible. This will in turn directly impact the magnitude, profitability, and social outcomes derived from the resource. Funding from the FRDC is therefore needed to address these key identified knowledge gaps, representing an urgent research priority for all harvesting sectors of the resource in NSW.
