In South Australia and all other countries spionid polychaete (‘mudworm’) infestations are a major problem for oyster growers and have large financial impacts, it has been recorded by individual oyster growers to lose up to $50,000 in stock in one year. There are 150 licensed oyster growers in SA and if this loss caused by mudworm was calculated at 5% of the extreme cases at $2500 per licence holder the economic cost to industry would equate to $375,000 per annum. These losses may not be through mortality, but growers experiencing mudworm problems provide extra oysters when selling to their buyers to compensate for losses from mudworm infestations. In South Australia the species causing damage are not well known. It is for this reason that South Australian Oyster Research Council (SAORC) want to implement a survey to gain an understanding of mudworm species found in SA to assist industry with the management of this pest.

The industry views the need to understand and control mudworm infestations as the losses caused by these worms could potentially be reduced if known species are identified and management techniques can be put in place to reduce infestation rates. However, the farmer’s ad-hoc management approaches have failed to stop or reduce mudworm infestation rates, as farmers have reported that with even the best management practices they still experience mudworm infestations. Due to this, the South Australian Oyster Research Council has identified two experts in mudworm identification to work with SA scientists to survey mudworm species and suggest management practices to SA oyster growers to potentially reduce the problem. Mudworm surveys have been conducted in many other oyster growing areas and different species have been identified which have different life cycles, hence, different forms of management practices are required to reduce infestations.

If this project can achieve a 50% reduction in mudworm infestations or mortality after harmful species have been identified and farmers have implemented management techniques developed through the extension training workshop, the savings to growers will be approximately $187,500 dollars over the next year. The reduction in oyster growers production costs is a small component, the benefits will be seen in the future through increased consumer confidence, hence, increased sales of SA oysters.

In addition, minimising the impact of mudworm on the Pacific oyster aquaculture industry in SA will also strengthen the confidence of new growers and investors in this industry thereby encouraging its further development.

For at least the last 12 years SA growers have noticed unexplained mortality of Pacific Oysters. Tests for Pacific Oyster Mortality Syndrome (OHSV-1uvar) have come up negative each time.

The mortality was first documented in Smokey Bay and is now documented in all the major producing Bays in South Australia, including Coffins Bay, Smoky Bay, Cowell and Ceduna (Denial Bay). Mortality rates have been increasing over time. Losses of between 5-20% each year which equates to between $1.8-$7 million per annum.

Mortalities are generally associated with seasonal temperature related stress in the animals. The timing of the mortalities varies from year to year within specific bays. Mortlaities do not follow a geographical distribution with some sites more affected than others. Anacodatal advice from growers indicates that sites with slower growth rates don’t suffer as badly has highly productivity bays.

In recent years, mortalities have been experienced in the major producing bays. Anacdotal adivce from growers indicates that mortality is particularly in smaller to medium size oysters, but mortality is also occuring in mature stock.

There does seem to be a genetic link to the mortality with anacdotal reports of 100 % mortality of certain “batches”. Given this link the breeding program is breeding for resistance to these unexplained mortality events. Susceptibility varies depending on the family line.

In response some growers are lifting the height of the oysters which reduces the mortlaity rate but slows the growth rate and increases the growout time. There is concerm within the industry that this is not an economically viable solution in the long term.

Research has been proposed to investigate unexpained mortality however industry are supportive of an epidemiological analysis of exisiting data and knowledge to narrow the likely causes so that any future research is focused on likely causes.