Analysis of farm management strategies following herpesvirus (OsHV-1) disease outbreaks in Pacific oysters in Tasmania, Australia

The microvariant genotype of Ostreid herpesvirus 1 (OsHV-1 μVar) has severely disrupted oyster production in Europe, New Zealand, and Australia by causing repeated and seasonal outbreaks of mass mortality in Pacific oysters (Magallana gigas). The virus was first detected in Tasmania, Australia, in January 2016, and mortalities of up to 87% were reported (de Kantzow et al., 2017). This study surveyed 95% of Tasmanian oyster farmers in OsHV-1 infected growing areas one year following initial detection, and recorded mortalities and associated farm management strategies in the 2016/2017 season, compared with the initial outbreak and before OsHV-1 occurrence. The survey was comprised of 37 open- and closed-ended questions, with data collected on background information, mortalities, environmental, genetic, and husbandry information. Perceived business viability was overall strong (75%), with changes to farm management occurring on 88% of leases in response to the virus. Commercial oyster farming businesses ranked handling regimes and stocking densities as the most important husbandry factors for influencing mortalities. Water temperature was ranked as the most important environmental factor, with 60% of businesses considering mean water temperature of 18- < 20 °C sufficient to activate disease. Mortalities for oyster size classes across multiple years are also reported. This survey has provided an expedient and cost-effective method to obtain information on the impact of a highly virulent disease and associated environmental conditions across an industry. These results will inform future management strategies and associated research.