2016-12-12 General Committee - Attachments 1, 2, 3 to Item 10 - Oyster Restoration Project

                                                              Ecological Service Professionals
                                                                                   Sustainable Science Solutions

DAF 2009). These estimates do not account for the quantity of dead oyster shell (conch)
removed from the estuary and used for road base or burnt to create lime for cement.
Removing this dead shell would have destabilised the sediment in the estuary and limited
subsequent recruitment onto the remaining oyster banks.
Due to the degradation of these oyster habitats, we currently do not know the natural density
of intertidal or subtidal oyster habitats in the Noosa estuary. However, the average
maximum density of oyster reefs recorded in the USA is 728 ± 102 ind. m-2 for a restored
oyster reef 3 years post deployment (Casas et al. 2015). Therefore, if similar maximum
densities recorded elsewhere also occurred in the Noosa estuary (i.e. 728 ind. m-2) at the
maximum harvest rates (i.e. 6 million oysters per year), then a conservative annual harvest
area of live oysters of 8,241 m2 (but up to 9585 m2 at peak harvest and if density was at the
lower end 626 ind. m-2) would have been required to be dredged or hand harvest to meet the
live oyster harvest records each year, not including dead oysters taken (which were not
recorded). Mechanical dredging, which occurred in the Noosa estuary, usually occurs when
hand harvesting is no longer a viable harvest option due to decreased oyster densities
(Smith 1981). An example of the dredge sled used is provided in Figure 5. Therefore, at the
time when oysters were dredged in the Noosa estuary, the density of oysters was likely much
lower than the maximum 728 ± 102 ind. m-2 recorded elsewhere, so the dredged footprint
was likely much greater than estimated here. Conservative estimates have been used
throughout to ensure that the amount of oyster habitat restored would not substitute habitat
other important habitats within the Fish Habitat Area.




   Figure 5   Historical dredge used from a boat to harvest subtidal oysters (circa 1910) (Smith
              1985).

Furthermore, the current time required to reach marketable commercial size is approximately
2-3 years (DAF 2009), which means that particular leases would likely not have been
dredged more than once every two or three years (a plausible reason the Moreton Bay
Oyster Company initially had three oyster areas in Noosa River to rotate the harvest through
each area), so logically, the actual area harvested was likely much greater than 3 times the
maximum area of live oyster to meet annual harvest demand. A key assumption is that only
live oysters were transported in bags rather than vast quantities of dead shell used for other
purposes. Therefore, the actual biogenic oyster habitat historically present in Noosa Estuary
would have been greater than estimated here.



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