High temperatures, not POMS, likely cause of high oyster morality rates in South Australia’s oyster growing regions

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South Australian oyster growers are breathing a sigh of relief with the industry cleared of a potentially devastating disease.

High mortality rates, some up to 60 per cent, were reported at Eyre Peninsula’s Streaky Bay, Coffin Bay and Cowell last week.

This meant the industry, in conjunction with Primary Industries and Regions South Australia (PIRSA), placed a ban on the movement of oysters between bays until more was known about what might have been causing the deaths.

Executive officer of the State’s Oyster Growers Association, Trudy McGowan, said when the ban was put in place it was believed the deaths were heat-related.

But with concerns about the deadly Pacific Oyster Mortality Syndrome (POMS), which has caused millions of dollars of losses in Tasmania, a freeze on moving the shellfish was introduced.

“It [the ban] didn’t have any impact on the sale of oysters, normal oysters still go to sale, but it was just precautionary from a biosecurity point of view that we don’t move stock between bays.

“It was just in case one bay did have some type of disease then we obviously don’t want to move it to another bay.”

Ms McGowan said extensive tests have been done by PIRSA and all the test results have come back negative to POMS, which the industry was pretty confident would happen.

Temperatures a contributing factor

She said the issue could be related to recent high temperatures.

“The heat causes issues and sometimes there is not a lot of food in the water either and in this situation it is most likely that it was a combination of those types of things that cause the stress to the oyster and their mortality.”

She also said the problems have been compounded by a shortage of spat, which has seen younger-than-normal oysters being put out to grow as the industry plays catch up on an oyster shortage.

“It is a bit of a catch 22 situation because you want to get your spat out and everybody wants to get it into the water, but this is not the best time.

“Hopefully by next year as people fill their farms we’ll be back into a more normal timeframe and people will then be able to spread their spat out and we’ll avoid these types of situations.”

Always monitoring

Trudy McGowan said with the recent hot weather with some growing areas seeing temperatures in the high 40 degree Celsius, growers would need to look at the farm practices.

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“The growers will continue to monitor water temperatures and what is going on and we will manage for those extreme conditions, that is just part of the adaption of farming.

She said they would also continue to test whenever there was a higher amount of mortalities.

“The ban has been lifted and last year we had a number of times that we reported and nothing came through that was positive.

“It is just a precautionary measure that we take and while the temperatures are high it is something that we are just very aware of.”

Ms McGowan said they would also keep supporting growers, but she said growers were part of a “pretty resilient industry”.

“It’s farming and it is a risk that you take unfortunately and it is devastating for the growers, but it is part of the process that they work through and it is no different to land farming.

“These guys are strong and they seem to be able to deal with it because farming is not an easy business,” Ms McGowan said.