‘Overcatch’ or ‘fouling’, whereby juvenile oysters (wild spat) or other aquatic organisms attach themselves to semi-mature oysters, is the largest farming challenge for Sydney rock oyster (SRO; Saccostrea glomerata) growers in Australia and represents a major barrier to efficient and sustainable production (Wayne Hutchinson, FRDC, personal comm.; Durr & Watson, 2010). Without timely intervention, fouling often renders the oysters unmarketable, leading to substantial proportions of product being discarded or having growth rates considerably slowed (Watson et al. 2009; Adams et al. 2011). It is estimated that 30–50% of SRO grown in Qld and northern NSW are wasted as a result of fouling with a potential value of $13–30 million/annum (Tim Prowse, QOGA, personal comm.; FRDC, 2022); this is either because the products become unsellable or due to losses associated with current overcatch control treatments. The inability to effectively manage overcatch has contributed considerably to the decline of Qld’s oyster industry over the last century, and similarly remains a significant financial impost to NSW oyster growing operations (de Nys et al. 2002; Cox et al. 2012).

At present, oyster growers typically attempt to mitigate the impacts of overcatch using methods like air drying and heat immersion; but both are labour intensive, have no clear guidelines or benchmarked specifications to support new growers in their implementation, and can result in significant mortalities or even total crop losses if undertaken incorrectly (Fitridge et al. 2012; 2014; Mayrand et al. 2015). While two relatively new technologies exist that hold promise for successfully managing overcatch, namely the ‘cold shock’ hypersaline system and FlipFarm system (Cox et al. 2012; Jackson, 2021), these have not yet been widely trialled or adopted in Australian oyster growing regions. There is thus a pressing need to better understand the optimal parameters for effectively eliminating overcatch while retaining host oyster health in commercial production settings.

The proposed project will respond to this longstanding need by evaluating and comparing the efficacy, practicality and cost-effectiveness of these various existing and emerging overcatch control methodologies under the same commercial environment, location and stock. Trials of these four treatments (air drying, heat immersion, cold shock system, FlipFarm system) will be carried out at established oyster leases in Qld’s Moreton Bay region, which is particularly prone to the impacts of fouling and therefore offers the ideal location to determine the efficacies of different methods in controlling overcatch in on-farm settings. The location also has no pre-existing incidences of QX disease that is currently decimating many other SRO growing regions in NSW and Southern QLD. The findings from this work will provide essential outputs, including validated methods and Best Management Practices (BMPs), which will be widely disseminated to the national oyster industry through various relevant forums.

With the Qld government in particular seeking to rejuvenate its oyster industry (McDougall, 2020), and the entire Australian oyster industry looking to expand and boost production (Oysters Australia, 2020), the timing of this project is optimal. The results will not only assist new growers entering the industry, but they will also provide essential learning to established growers throughout Australia who experience significant oyster losses and labour costs associated with overcatch management. The project also aligns with the Oysters Australia Strategic Plan 2020–2025 to (i) increase the sustainable, efficient production of oysters and their management on farm; (ii) manage industry risks; and (iii) increase industry knowledge, skills and networks. It will further help to meet the objectives of the FRDC’s R&D Plan 2020–2025, particularly Outcome 1 (i.e., ‘growth for enduring prosperity’), by providing the oyster industry with genuine opportunities to reduce crop losses, increase profitability, expand production and enhance their reputation in a stewardship context. From a broader societal perspective, the project outcomes will be crucial in building a properly functioning circular economy in the oyster industry, by preventing the creation of waste in the first place.