One of the issues being discussed among oyster farmers is the death of pacific oysters in Port Stephens near Newcastle. Many farmers have been concerned that it is the POMS virus that has decimated the Pacific Oysters in Georges River, Sydney Harbour and Hawkesbury River. It has been thought by many people that Port Stephens would be the next harbour to be affected due to the proximity to the above places, ocean currents and the possible transference by boat traffic.
A couple of observations are worthwhile at this stage. Worldwide oyster diseases appear to be species specific. eg QX and Winter Mortality with Sydney Rock Oysters, bonamia with Flat Oysters, and now POMS with Pacific’s. Transference can occur quickly in sea water held within non affected oysters eg. Sydney Rocks could transfer the POMS virus and consequently trans-location policies are in place ( monitored by NSW Fisheries) and growers are careful when moving stock and need Fishery’s Permits.
Evidently, 1200 tests have been done on both cultured and wild Pacific’s in Port Stephens and no known disease has been detected. This was reported to growers in Port Stephens at a meeting held last week. The question remains what killed the oysters? Are the animals under stress from some other factor? Observations expressed by growers and fisheries were that water temperatures in November when deaths were first noticed were quite high , rainfall runoff from the land can carry contaminants which could kill oysters but remember Flat and Sydney Rocks Oysters didn’t die and some algal species could be ingested solely by Pacific’s could be toxic. Another consideration is that Pacfics could be nearing the upper latitude for there growing range. Originally they came from a cold water environment in Japan and Korea. So it could be a stress related issue where the oyster becomes vulnerable in this warmer temperate marine environment and dies from some physical factor. Evidently increased mortalities are also occurring in Pacific’s in France due to a Vibro bacteria related issue. This has not been observed here.
The mystery continues and worries growers not only in NSW but Tasmania and South Australia. Growers have been advised that a POMS resistant oyster will not be available for at least 5 to 8 years therefore will not help Port Stephens oyster farmers at the moment.