1. The canaries of our estuary
Laurie Derwent
Oysters
The canaries of our estuary

2. Laurie Derwent 4th generation oyster farmer
Joined NSW Fisheries May 1978
Oyster pollution disaster August 1978
Various Fisheries & Maritime roles to BA (Geog) and Dip. Law.
Post retirement projects

3. Oyster Species in Georges River
Sydney rock oyster (Sassostrea glomerata) (Previously Saccostrea commercialis)
Flat oyster (Ostrea angasi)
Pacific oyster (Crassostrea gigas)

5. Advantages and disadvantages of being a filter feeder

6. Stuck on a rock or another hard place
Your food comes to you. You can’t chase it but if you are cultivated your farmer may be kind (or lucky) in choosing your environment.
You are what you eat – other than your filter system you have no choice in the diet.
Food etc can be originate from a range of sources.
The good the bad and the crappy.
It’s hard to escape from predators or parasites. Sometimes a hard shell is just not enough.

7. Natural oyster mortality causes
Predators: Fish especially on spat. ‘Choosing’ the place where you catch can determine your fate.
Heat: limits the habitat by locality and in the intertidal range.
Winter mortality Mikrocytos roughleyi: apparently a natural disease (2-3 micron parasite known since at least 1924)
Overcrowding: Competition for space / access to food can lead to ‘suffocation’ or starvation.

8. Oyster cultivation methods in Georges River
‘Catching’ the oysters and
taking them to the most suitable habitat
for survival and growth.
‘Highway oyster farming’

9. Shell Bed at Lime Kiln Bar 1990’s
Photo: NSW DPI

10. Oyster Sticks
Photo: NSW DPI
Salamander Bay Pt Stephens

11. A Good Catch
Charles Percy Derwent on right

12. Tray cultivation: Oatley Park
Photo: NSW DPI

13. Source: NSW DPI

14. 30 people employed (Derwents and Drakes)
Neverfail Bay
Neverfail Bay
Neverfail Bay served each day as the interface between Georges River Leases for movement of spat, materials and for dispatch of 1000s of bags of oysters each year.
30 people employed (Derwents and Drakes)
30+ punts and launches.
Photo 1997

15. What Happened? Mudworm (esp. Polydora websteri)
Urban runoff: Industrial and land development
Sewage Pollution = Food Poisoning Purification
Oil spills & clean up (dispersants): World Encouragement 1979
TBT – Tributyltin antifoulants (French ban 1982, NSW Mar 1989 – after 1 year industry campaign)
QX – (Martelia sydneyi) – protozoan parasite
POMS – Pacific Oyster Mortality Syndrome (OsHV-1 micro variant). France 2008, Georges R 2010, Tas Feb 2016.

16. Source : Qld Museum
QX infected Sydney rock oyster on right – note colour of the ‘gut’

17. What else? - Poor catches (at least by 1976),
Boat wash, (physical damage and turbidity), Look what they’ve done to my seagrass (zostera posidonia)
Heavy metals
Acid sulphate soils (worse in other estuaries)
No jellyfish?
Don’t forget the little guys (plankton, invertebrates, fish larvae etc

18. How did humans contribute to each of these problems?
Mudworm – NZ imports
Sewage pollution - (oysters were not really bothered)
TBT – why did it take so long to ban in NSW?
QX Was this introduced or inevitable after stress.
POMS - a world problem – travels with shipping?
Others: Insufficient controls on pollutants including runoff from development, boat wash

19. Neverfail Bay 2007
Source:
Google Earth

20. Neverfail Bay 2008

21. Breakfast of Champions 1956
Photo: Daily Mirror