optimising the investigation of unexplained oyster mortalitY
BUDGET EXPENDITURE: $17,500
PRINCIPLE INVESTIGATOR: Oysters Australia
ORGANISATION: Oysters Australia
PROJECT CODE: 2025-35
PROJECT STATUS: Completed
BACKGROUND
The health of farmed oyster stock is fundamental to the commercial viability of Australia’s oyster industry. Despite farmers’ best efforts to maintain healthy, high-quality oysters, even the most experienced growers are vulnerable to losses in the dynamic and often unpredictable marine environment. Part of this challenge is that oysters are encapsulated within their shell, making it difficult to detect problems until mortality occurs. Unlike other aquatic or terrestrial animals, this hidden physiology complicates timely investigation. In New South Wales, it’s not uncommon for growers to cite a 30% mortality rate across the production cycle, a broadly accepted norm that underscores the persistent risks facing oyster health.
Targeted testing for a narrow range of ‘notifiable’ pathogens has failed to identify a likely cause in recent large-scale mortality events. Broad and in-depth investigation into all possible infectious and non-infectious causes remains largely unexplored.
Unexplained mortality events occur without a clear cause; they have an unknown aetiology. They have not been found to be associated with any notifiable oyster pathogen, obvious environmental stressor, or restricted to a particular management practice. This highlights the complexity and uncertainty surrounding such events, emphasising the need for further investigation and collaborative inquiry.
PURPOSE OF THE WORKSHOP:
On the 20th August 2025, Oysters Australia convened a workshop on the topic of oyster mortality of unknown aetiology. The workshop set out to review and develop a more robust framework to investigate and respond to unexplained mortality events by refining the investigative framework, clarifying the role of government, aquatic animal veterinarians, and researchers, and identifying practical tools and resources to support growers.
By fostering collaboration between industry, researchers, private consultants, universities and government, the workshop sought to shape a targeted, cost-effective program of work that enables the industry to more effectively detect, investigate, and respond to unexplained mortality events.
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