By Ilaria Catizone
Since Pacific Oyster Mortality Syndrome (POMS) first entered Australia in 2010, Tasmanian Pacific Oyster (Crassostrea gigas) growers have been watching the outbreaks along the New South Wales coast, preparing for the inevitable southward journey of the virus across Bass Strait. But when the first Tasmanian outbreak finally occurred in February 2016, it still came as a shock.
The recent Tasmanian outbreak of POMS has killed more than five million dozen Pacific Oysters valued in excess of $12 million.
The Tasmanian oyster industry accounts for 37 per cent of Australian Pacific Oyster production with an estimated farm-gate value of $25 million per year. In Tasmania, the Pacific Oyster industry supports more than 700 jobs, and the POMS outbreak has already caused the loss of at least 80 of these.
Although this POMS outbreak is localised in the south of Tasmania, it has a national impact as Tasmania’s hatcheries located in the infected region supply 90 per cent of Pacific Oyster spat (juvenile oysters) to farmers in South Australia and NSW. Following the outbreak, the movement of spat from Tasmania has been banned and will be restricted in the foreseeable future. This will also significantly reduce production in SA and NSW, representing a further loss of livelihood for about 300 farms with a gross value of production of $60 million a year.
The virus that causes POMS in Australia is the Ostreid herpes virus 1 (OsHV-1). It is the same virus that has devastated Pacific Oyster aquaculture in France, other European countries and New Zealand. Researchers are still unsure how it entered Australia, but more details are being gathered on its biology.
POMS only affects the Pacific Oyster, which makes up 60 per cent of oysters produced in Australia. The virus infects Pacific Oysters of all ages, although juveniles are particularly vulnerable. It is thought that Pacific Oysters can be infected for some time without showing symptoms of the disease, until environmental factors such as high water temperatures trigger an outbreak. Husbandry practices that stress the animals, such as grading or moving them within or between farms, can also increase the susceptibility to the disease.
It is important to note that while POMS is devastating for the oyster it has no affect on human health.
Once POMS strikes, it causes devastating mass mortality within days. Josh Poke grows Pacific Oysters in Pitt Water, near Hobart, and was assessing the damage in early April. “We had 2.4 million Pacific Oysters bigger than 50 millimetres in length in the water when the outbreak hit,” he says. “We are in the process of removing all the dead ones and seeing what’s left. We expect about 50 to 60 per cent losses.”
Josh Poke explains that because of the outbreak his company has been forced to reduce staff to decrease costs. Pacific Oyster supply in the region will likely be low for the next couple of years. In spite of this, he remains positive as the Pacific Oyster farming community in the region is working closely together to cope. “It is good to know you are not alone,” he says. “We will be helping each other out even more than usual during this crisis.”
To help his farm continue, Josh Poke also has about 1.2 million half-grown Pacific Oysters coming from unaffected areas in northern Tasmania to grow-out and sell. The movement of Pacific Oysters from one area to another for growing to market size is a standard practice that now has the potential to save businesses in the south of the state.
Oyster farming locations in northern Tasmania, such as the Circular Head region, have excellent growing conditions, but the large number of dairy farms in the area limits when oysters can be sold directly to market. To overcome this issue, the region routinely grows Pacific Oysters to 40 to 50 millimetres in size then sells them to oyster farms in the southern regions, such as Blackmans Bay and Pitt Water, for grow-out.
The north of Tasmania, fortunately, remains free from POMS so far, so farmers are looking at transferring more Pacific Oysters to the POMS-affected southern areas once water temperatures drop below 16°C, for harvest in the spring before the temperature reaches 20°C. This is working with the hypothesis that as POMS is active in warmer water temperatures, this approach should help protect the Pacific Oysters from infection. This practice is known as ‘window farming’, where the Pacific Oysters are moved to an infected area during a time when the virus is less active.
Executive officer of Oysters Tasmania Neil Stump has been working tirelessly with the industry to mitigate the effects of this outbreak and has had a pivotal role in coordinating activity and briefings with key stakeholders during this crisis.
“We are checking if there are any Pacific Oysters in the north that have not yet been pre-sold to farmers in the south and could be allocated to the worst affected southern growers,” he says.
Although helpful, the practice of growing Pacific Oysters in one area and finishing them elsewhere will only provide short-term relief from POMS. Another short-term solution is to overstock farms with spat to compensate for the expected high mortality.
This is a method adopted overseas but it is very costly and few growers are likely to be able to benefit from it in Tasmania. To help manage the Tasmanian crisis and provide assistance, the Australian and Tasmanian governments announced an assistance package of $7.6 million on 4 April 2016 to assist affected farmers and support recovery of the industry. This comes in the form of concessional loans, contribution towards clean-up costs, waive of licence and other fees for 24 months, and employment of biosecurity officers to assist with recovery arrangements.
Understanding the virus causing POMS and how it spreads as well as what conditions inhibit or assist infection will help Pacific Oyster growers to reduce the impact of POMS in the short term.
Richard Whittington is chair of Farm Animal Health at the University of Sydney and has been involved in POMS research since the virus first appeared in NSW in late 2010.
At that time there was no information about how it spread, which oysters were affected and whether environmental conditions would influence it, he says. “With FRDC funding, we set out to research these questions to eventually provide Pacific Oyster growers with scientifically sound information on which to base their management decisions.”
After two years of intensive research, Richard Whittington and his team have a hypothesis that the virus spreads in seawater attached to plankton. The Pacific Oysters are infected when eating this plankton, but older Pacific Oysters seem to have better resistance to infection. This resistance is further enhanced when growing racks or longlines are raised higher in the water column, which means less time immersed in water.
As the outbreaks in NSW continued beyond 2010, the team also discovered a clear seasonal pattern to the infection. The first outbreak in the Georges River region of NSW has occurred again every year after 2010, followed by a new outbreak in the Hawkesbury River region of NSW in January 2013, which has also happened again in the following years.
While these events are devastating for growers, having made the regions unsuitable for growing Pacific Oysters commercially, they do provide opportunities to better understand how the virus works with a goal of finding a solution.
Researchers now have outbreak maps spanning four years and these show a strong correlation between water temperature and disease activity. This work offers valuable insights for growers, helping to support management decisions about when to bring Pacific Oysters onto their farms and when to harvest.
Another important aspect of Richard Whittington’s work has been on how to protect hatcheries from outbreaks. As younger Pacific Oysters are particularly vulnerable to the virus, hatcheries are at very high risk of having their entire production wiped out by the introduction of POMS.
In a 2014 FRDC project, the University of Sydney team tested two commercially applicable methods of protecting spat in hatcheries. After extensive testing, the methods are now being used by Pacific Oyster hatcheries in Australia and in New Zealand and are proving very successful.
One Tasmanian hatchery has recently been declared POMS free thanks to its application of Richard Whittington’s recommendations on how to protect spat from the virus. These include holding water for 48 hours to settle the sediments prior to running it through the Pacific Oysters and/or filtering the water through a five-micrometre filter.
Both these methods are aimed at removing the plankton from the water, thus also removing the virus that may be attached to it. Most hatcheries also run the water under ultraviolet light to kill the virus as an extra precaution in case any is left after sedimentation and filtration. The water is then replenished with plankton specifically grown under sterile conditions to feed the young Pacific Oysters as they grow.
“What happened in Tasmania is tragic,” Richard Whittington says. “But we knew it may happen, so we were able to prepare the growers by telling them what to expect and how to react to an outbreak.”
The team had fact sheets ready about disinfecting equipment, advice for farmers about how the infection would move through their farm, when it was best to harvest and more. A website (www.oysterhealthsydney.org) is also available for more detailed information. With the experience acquired in NSW over the past four years, Richard Whittington’s team had already been working intensively with growers in Tasmania and SA to gather data specific to their locations that would inform tailored advice for the most effective husbandry practices.
“During an outbreak, we get a lot of anecdotal information about how different practices increase or slow the spread of the virus,” Richard Whittington says. “We value this information and use it to prompt scientifically accurate surveys of the affected farms.”
Researcher and veterinary virologist Paul Hick and PhD student Max de Kantzow, from Richard Whittington’s group, are working on Tasmanian farms to sample Pacific Oysters and assess which practices are best to reduce the impact of an outbreak. Paul Hick’s research has already led to more effective disinfection practices for industry, while Max de Kantzow has confirmed the important role of water temperature through experimental infection trials in the laboratory.
In 2000 the national Pacific Oyster industry and the FRDC showed remarkable foresight by establishing the national Pacific Oyster breeding company, Australian Seafood Industries Pty Ltd (ASI). With POMS arrival, breeding disease-resistant Pacific Oysters is the most important element of the fight against POMS. Industry introduced a levy in 2015 to fund research aimed at fast-tracking the search for Pacific Oysters with high POMS resistance at a young age.
“By the time the Pacific Oysters reach the breeding age of two years old, some show resistance to POMS,” says Matt Cunningham, general manager of ASI. “But the challenge is to breed Pacific Oysters that show a high resistance rate at a much younger age.”
A selective breeding program for Pacific Oysters has been underway in Australia for more than 10 years. Since the disease entered Australia this breeding has mostly focused on breeding for POMS resistance. This means that the industry is well on the way to having resistant Pacific Oysters available for growers.
Unfortunately, the operation of this vital breeding program is entirely funded by the levy collected through sales of oyster spat, which has now stopped because of bans on translocation of spat to unaffected Pacific Oyster growing areas in Tasmania, SA and NSW.
To continue this essential research for the recovery of the industry, Oysters Australia, a national body formed in 2011 by Australia’s community of oyster growers, is looking at other funding options and is investigating how to address the long-term flow-on effects from the outbreak.
The first step is the development of a National Response Plan funded by a $25,000 contribution from the FRDC. This plan will guide all levels of government to provide ongoing support and R&D needed during the recovery of the Pacific Oyster farming industry. The plan will also identify measures to create greater resilience needed for the industry to expand in the future.
Meanwhile, ASI’s 2014 class of Pacific Oysters shows great promise, with some selected families recording 90 per cent survival for one-year-old Pacific Oysters exposed to the virus. More trials are on the way with animals as small as five millimetres from the 2015 group. None of these lines are on farms yet, as they are too young, but some ASI-bred stock is in the water at various Tasmanian farms in combination with other lines.
As ASI breeds new lines, these are provided free of charge to the commercial hatcheries so growers can purchase partially POMS-resistant spat produced from these ASI lines.
Breeding POMS-resistant Pacific Oysters
and understanding the virus to provide best-practice husbandry advice to growers are important complementary approaches to beat POMS in the long term. Developing Pacific Oyster lines that are 100 per cent resistant to POMS will take several years and will be possible only with the continued operation of the ASI breeding program. In the meantime, growers have access to partially resistant Pacific Oysters and the survival rates of these lines can be further enhanced with the right husbandry practices.
ASI’s Matt Cunningham says having the disease in Tasmania could speed up the development of POMS-resistant Pacific Oysters.
“Previously, we would send a sample from our most promising lines to NSW to be infected by POMS and test their response. We would then breed from the siblings of the ones that faired best, as bringing infected Pacific Oysters back to Tasmania was too dangerous from a biosecurity point of view.
“This practice would delay our breeding program as the siblings of Pacific Oysters that proved resistant did not always exhibit the same ability to withstand infection,” Matt Cunningham says. “Now we can infect Pacific Oysters in Tasmania and breed from the actual ones that have proved resistant – a much more accurate breeding strategy.”
FRDC Research Codes: 2011-053, 2012-032, 2015-406