Publications: Research reports and publications

OsHV-1 mortalities in Pacific oysters in Australia and New Zealand: the farmer's story

  • Castinel A,
  • Fletcher LM ,
  • Dhand N,
  • Rubio A,
  • Whittington R,
  • and Taylor M
1 September, 2015
Cawthron Report 2567. Prepared for the Ministry of Business, Innovation and Employment (MBIE).


Since 2010, disease outbreaks involving Ostreid herpesvirus type 1 microvariant (OsHV-1) have had dramatic impacts on Pacific oyster production and farmers' livelihoods across New Zealand and in New South Wales, Australia. These episodes of mass oyster mortality, known as Pacific Oyster Mortality Syndrome (POMS) in Australia, have highlighted the complexity of disease management in the marine environment. Oyster farmers' management decisions may have played a role in the extent of the OsHV-1 mortality outbreaks. But neither their perceptions of disease risk nor their management decisions have been documented within the context of biosecurity preparedness and operational risk.

We conducted structured, face-to-face interviews with oyster farmers in New South Wales Australia and New Zealand with the aim of capturing their views on disease risk and on strategies to prevent or manage OsHV-1 and other disease outbreaks on their farms. Participants were chosen to maximise diversity of views and practices in the Pacific oyster farming industry in both countries. The questionnaire was organised in five sections: (1) participant characteristics; (2) experience with OsHV-1 mortalities (POMS); (3) support during the disease crisis; (4) risk management strategies; and (5) risk and preparedness.

Twenty-two farmers (half from New Zealand and half from Australia) were interviewed about their experiences with POMS and other oyster diseases. Nearly all participants reported that the oyster mortalities had a devastating impact on their morale, particularly in New South Wales estuaries where growers tend to form a close community. During the disease crisis, governments in both countries remained a trusted source of advice, on a par with industry sources and other oyster farmers. For routine advice on animal health, participants preferred to consult the farming industry or the internet, though most respondents admitted that they were not likely to seek technical advice in the absence of disease on their farm. Overall the governments' responses to POMS left a mixed impression, with over 40% of participants having either no opinion or nothing positive to say about the experience. Movement controls were a positive point for 16% of farmers, but for 29% of them it was a negative factor, contributing to a slow and unstructured response.

Amongst the preventive strategies explored in the interview, adopting a collective risk management plan and varying the sources of spat (juvenile oyster) were seen as the two most effective approaches. On-farm biosecurity measures were ranked third in terms of perceived effectiveness but were the most likely to be applied of all proposed measures. The discrepancy between perceived effectiveness and inclination for uptake suggested limitations in the potential feasibility of some preventive strategies. In contrast, ranking of effectiveness and practicality of control strategies were more consistent. Stopping movements of stock and gear and zoning of farming areas by OsHV-1 status received the most support.

Following POMS, most affected farmers and more than half of unaffected farmers changed their approach to growing oysters, by modifying their husbandry techniques or adopting a different operational strategy. When asked about taking business risk in the near future, the group was clearly divided: 41% were not ready to take any risk whilst the rest of the respondents were considering changes such as diversifying species, investing in hatchery spat and in new, more versatile infrastructure, or a mix of these initiatives. In terms of biosecurity readiness, the majority were confident that their business was as prepared as it could be to overcome disease challenges. Interestingly, even after the POMS event, only half of the respondents said they had a plan to cope with mass mortalities on their farm. But this aspect will need to be further explored as the concept of 'preparedness and planning' may not have been appropriately explained or understood by participants.

During the course of the project, the research team received funding from the New Zealand government to hold a two-day knowledge exchange between farmers, scientists and government to share views on oyster disease risk perceptions and management. Participants were farmers from New South Wales Australia and New Zealand, who had taken part in the survey. This meeting was an opportunity to present and confirm the study preliminary findings through consensual validation.

Based on the findings from the interviews, this research identifies potential strategic directions for an industry facing increasing environmental challenges in both countries. Disease prevention and control strategies should be included in business risk management plans for the shellfish farming industry. Farmers, scientists and governments will be more successful if they work in partnership to develop practical and effective measures to manage diseases as well as pests in the aquatic environment. Collaboration between all parties to optimise resources, expert skills and knowledge should be actively encouraged and enabled at all levels including industry, research and regulating bodies.