Last weekend I decided to explore the lower reaches of Mooney Mooney Creek from its meeting point with the Hawkesbury, riding on a rising tide. After my spooky solo paddles in Mangrove Creek, I had a hankering for the open horizon and a bit of human life around me. From my put-in at Deerubbin Reserve beside the freeway, and all the way round Spectacle Island, a nature reserve in the mouth of the creek, the constant hum of the traffic and the echoing rumble of trains crossing Brooklyn Bridge remind you that “civilisation” isn’t far away.
Low tide at Mooney Mooney Creek means mud and oyster leases. The lingering blue haze from last week’s hazard reduction burns descended on the poles and frames, forlorn in the shallows, blurring them into beautiful abstracts.
The story of oyster farming in the Hawkesbury in recent times is a sad one, full of strange historical ironies.
People have been harvesting shellfish from the shores of the river for a very very long time and Sydney rock oyster has been farmed in Broken Bay since the 1880s. In those days oysters were dredged from the estuary floor and after the meat was eaten, the shells, along with those from ancient middens, were burnt to make lime for mortar.
But in 2004, after a hundred years of farming oysters here, Qx disease hit the Hawkesbury.
The “Q” in the name stands for Queensland. The Sunshine State produces a 10th of the oyster harvest it did in the nineteenth century, thanks to Qx and to the oyster-infesting mudworm (introduced from New Zealand in the 1880s along with imports of oyster spat). The “x” was a scientific shorthand for “what the hell is this anyway? We really don’t know”. Since then, researchers have figured out that Qx is caused by Marteilia sydneyi, a single-celled organism that during the summer infects oysters, causing them not just to slowly starve to death, but also to reabsorb their own gonads (nasty!). The parasite then releases spores that cycle their way through a polychaete worm, Nephtys australiensis, in the winter, before reinfecting the oysters the following season.
M. sydneyi isn’t always the kiss of death. The parasite is found in estuaries all along the coast of NSW and Queensland, even in “low risk” areas where Sydney rock oysters are still being commercially grown. Environmental stress, it seems, triggers outbreaks of Qx and surprisingly few wild Sydney rock oysters, the ones I saw lining the rocky shores of Mooney Mooney Creek, die from Qx. Which is good, if mysterious, news.
So, facing of losses of over 90% of the harvest, what could save the oyster industry in the Hawkesbury?
It was noxious pest to the rescue.
The Pacific oyster, farmed in Japan for centuries, was smuggled into Port Stephens in the eighties and spread quickly through the intertidal zones of New South Wales. It’s a fecund and fast growing bivalve, planktonic eggs and larvae travelling far and wide, crowding, outgrowing, and sometimes settling on and smothering native rock oysters. A “selfish shellfish”, in the words of one inspired Tasmanian subeditor.
The very qualities that have made the Pacific oyster such a hateful invader came to the rescue of the Hawkesbury farmers in 2005. A process for producing sterile “triploid” Pacific oysters had been developed in North America in the 1980s, with the aim of pumping out meatier shellfish fast. When fertility mean spawning 40 million eggs in a season (not to mention changing sex several times over a lifetime) avoiding reproduction saves a lot of energy.
Local farmers restocked with these “triploid” Pacific oysters. As well as being immune to Qx, they were ready to harvest in less than two years compared to the three and a half years it takes rock oysters to reach the table. The new “tamed” Pacific oysters took the Hawkesbury by storm.
And then in 2013 disease struck again. Millions of oysters were wiped out overnight by a virus that affected Pacific oysters and Pacific oysters alone.
Like the oyster itself, the scientifically spawned sterile “triploids”, and indeed the settlers that farm them, “oyster herpes” or POMS (Pacific Oyster Mortality Syndrome), first seen in France in the late noughties, had circled the globe to Broken Bay.
Only three oyster farming businesses are still going in the Hawkesbury these days, hanging on for scant supplies of Qx resistant rock oyster spat, first found amongst the survivors of the Georges’ River outbreak in the mid 1990s.
Right now, the derelict oyster farms are mostly places for posses of pied cormorants to hang out.
But there’s still plenty of life to be found at Mooney Mooney at low water: globe trotters like the eastern curlew, exhausted after a long flight south, and locals like the rock warbler that only lives on Sydney sandstone, compensating for its drab colours and homebody ways with a goth-style nest of grass and spider webs it hangs in the darkness of caves and crevices. And I clocked a new heron record – twenty at least, catching crabs in the mud of low tide.
References
Michael C Dove, John A Nell, Stephen Mcorrie and Wayne A O’Connor “Assessment of Qx and Winter Mortality Disease Resistance of Mass Selected Sydney Rock Oysters” Journal of Shellfish Research 32(3) 681-87 doi: http://dx.doi.org/10.2983/035.032.0309
Wayne A O’Connor and Michael C Dove “The changing face of Oyster Culture in New South Wales, Australia” Journal of Shellfish Research, Vol. 28, No. 4, 803–811, 2009.
J.A. Nell “The history of oyster farming in Australia” Marine Fisheries Review 63(3), 14-25
