A trial oyster hatchery in Wilson Inlet will need steady marine exchange to maintain salinity for the spats to continue their promising growth.
Wilson Inlet’s high productivity has shown potential for an aquaculture industry both with mussels and the now-extinct native flat oyster.
Marine biologist Zak Launay, who previously harvested mussels commercially in the inlet, said the oysters could grow to commercial size in about half the time of the standard growth cycle.
L-R: Young oysters in August 2022, the same oysters this year.
Photos courtesy Denmark Bulletin.
Over winter oysters in Mr Launay’s hatchery, growth slowed due to the water temperature dropping below 16C.
He said the peak season for oysters growth occurred in warming temperature and when phytoplankton became abundant.
If this year’s Wilson Inlet sand bar opening allowed for sufficient marine exchange and the subsequent salinity was high enough, close to sea concentration of 35ppt, the oysters could triple in size by the end of summer.
But low salinity due to the poor connection with the ocean in western openings, which maintained the man-made Prawn Rock Channel established in the 1930s as a recreation facility, meant the native oyster was unable to survive.
“This is simply due to low salinity levels in summer,” Mr Launay said.
“The loss of marine characteristics is the most likely reason for its extinction from Wilson inlet.
“There is no other reason.”
He said reinstating the ‘natural conditions’ of sand bar openings would allow for the reintroduction of a native species and for a local aquaculture industry to flourish.
This would provide local seafood and jobs thanks to a sustainable and clean form of primary production.
Mr Launay said the native oyster is an accurate indicator of inlet health.
Allowing for a significant increase in marine exchange would bring more blue water into the inlet.
It was the only way to cease stratifi cation and the subsequent deoxygenation of the bottom layer of water. However, stratification did not occur when salinity in the inlet reaches a level close to sea concentration.
“This is of major importance because the phosphorous released from the sediment is many times what comes down from the catchment, and the main reason for the black ooze along the foreshore,” Mr Launay said.
This article appeared in the Denmark Bulletin, 9 November 2023.
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