Perkinsus olseni is a pathogenic alveolate protozoan parasite that causes mortality, morbidity, and quality degradation in Australian abalone. For this Fisheries Research and Development Corporation (FRDC) co-funded study we investigated the economic impact of P. olseni on Australian abalone fisheries and assessed whether the common practice of shucking at sea increases disease transmission risk, particularly in the Western Zone of South Australia (WZSA) where Blacklip (Haliotis rubra) and Greenlip (H. laevigata) Abalone are commercially harvested and viscera discarded at sea.
Since 1980, P. olseni has caused widespread mortality in New South Wales and South Australia, resulting in tens of millions of dollars in economic losses through catch rejections and displaced fishing effort. Environmental analyses revealed correlation between P. olseni presence and higher maximum water temperatures, suggesting climate change may exacerbate disease spread.
To investigate transmission risks, we studied the fate of infected viscera discarded at sea and whether the parasite survives transit through the digestive system of fish. Baited video trials and diver observations demonstrated that discarded viscera are rapidly consumed, primarily by the wrasse Notolabrus tetricus. Laboratory experiments confirmed that P. olseni not only survives gut transit through these scavenging fish, but that scavenged P. olseni sporulate more frequently than they do in seawater or synthetic medium, increasing the likelihood of disease transmission to healthy abalone. These findings confirm that shucking at sea and discarding viscera overboard increases infection pressure and may facilitate spread of the parasite to new areas.
The research supports the current practice of landing Blacklip Abalone whole from affected areas in the WZSA and recommends extending this requirement to Greenlip Abalone in these areas despite their lower visible infection rates. Given warming ocean temperatures may favour P. olseni and the proximity of Abalone Viral Ganglioneuritis to the region, ceasing all disposal of abalone material is recommended as a critical biosecurity measure. Industry, managers, and policymakers should collaborate to overcome challenges associated with landing whole abalone or retaining shell and gut, potentially exploring value-adding opportunities from viscera and shells while reducing disease transmission risks. Fisheries management strategies to address this biosecurity risk are currently under review.