Oyster mortality

Why report oyster mortality?

Early reporting to NSW DPI of suspected oyster disease will result in an investigation, and determination if disease is the cause. Rapid reporting of unexplained mortalities can make the difference between minimising impacts through improved stock management and extensive stock losses (if not reported or managed early). Early detection can assist with eradication or control of disease and the identification of practical measures to minimise the impact on businesses, and help protect stock against loss.

A number of oyster diseases pose significant threat to the NSW oyster industry. These are included as either Prohibited Matter listed in the NSW Biosecurity Act 2015 or as Notifiable Pests and Diseases listed in the NSW Biosecurity Regulation 2017.

Some examples of these diseases include:

  • QX disease (caused by Marteilia sydneyi)
  • Pacific Oyster Mortality Syndrome (POMS; caused by Ostreid herpesvirus microvariant -1)
  • Winter Mortality (causative agent currently under review, previously thought to be caused by Bonamia [Mikrocytos] roughleyi).

All unusual mortality suspected to be the result of any disease must be reported to NSW DPI. This is a requirement under the NSW Biosecurity Act 2015 and is also an Aquaculture Permit Condition under the NSW Fisheries Management Act 1994.

Protocol for reporting oyster mortality

In the event that suspected oyster disease events or unusual mortality is observed:

1. Notify DPI within 24 hours. This can be done by contacting any of the following:

  • Emergency Animal Disease Watch 24 hour hotline 1800 675 888
  • Aquatic Biosecurity Risk Management team (02) 4982 1232
  • Your local NSW DPI Fisheries office and ask to speak to a Fisheries Officer

2. Record all relevant information details. Your report will be referred to the Aquatic Biosecurity Risk Management team and an officer may arrange for samples to be collected for laboratory analysis.

Use this Oyster Health Diagnostic Submission Form (PDF, 30.86 KB) template to help capture as much information as possible, including:

  • the species of oysters experiencing mortality and % estimate of stock lost
  • the date mortality was first noticed and any changes in % mortality estimate since
  • the date the stock was last inspected prior to mortality being noticed
  • the estuary and location within estuary, including lease number(s)
  • the type of cultivation used (e.g. trays, baskets, cylinders)
  • whether the oysters were wild caught or hatchery reared
  • if there are any other oyster species or nearby wild oysters also experiencing mortality
  • observations of changes in temperatures, rainfall, salinity or other water quality observations
  • any other information, such as whether stock has been recently handled or relocated

Oyster mortality is often due to predation or environmental effects such as heat or freshwater input and may not be the result of a disease. Even so, it is important that all events of unusual or unexplained mortality are reported. Some unusual mortalities may potentially be a result of diseases which are not visually/obviously apparent. DPI encourages farmers to report unexplained mortalities to the department so that a disease investigation can be initiated.

Oysters on checker plate