The rise and fall of oyster cultivation in the highly urbanized Georges River estuary, Sydney, Australia: A review of lessons learned

Georges River oyster cultivation was one of Australia's earliest aquaculture ventures and became highly productive by the 1970s. However, intensified land use across the catchment was not compatible with maintaining the industry, with oysters acting as a 'canary in the mine' to alert managers to declining condition of urbanized estuaries. Environmental regulations countered some overharvesting and localized pollution issues, but not catchment-scale pollution issues or the spread of disease. The production of Sydney rock oysters (Saccostrea glomerata) was hindered by two major diseases: winter mortality and QX. Winter mortality was first recorded in the river almost a century ago and proved able to cause mass mortality. That ability was countered somewhat by moving the oysters upstream to less saline areas when they were most susceptible to disease. Unfortunately, QX "jumped" from northern estuaries to the Georges River in the mid-1990s and was more prevalent in less saline upstream areas of the estuary. It therefore became difficult and financially unviable to move oysters across the Georges River to avoid winter mortality without becoming more susceptible to QX, and vice versa. In response, some farmers switched production to the exotic Pacific oysters (Crassostrea gigas), which are not affected by winter mortality or QX. This provided only a short reprieve for the industry, as in 2010 Georges River was hit by another disease in Pacific Oyster Mortality Syndrome. Although disease devastated the oyster cultivation industry in the Georges River, the river also provided a valuable base for both the study of oyster diseases and for a breeding program designed to promote S. glomerata disease resistance. It is hoped that lessons from the Georges River can be heeded and used to help other estuaries avoid a similar fate in the loss of their valuable fisheries resources.