Wilson Inlet could become a thriving commercial fishery for rock oysters and mussels given the correct salinity levels, says aquaculturalist Zak Launay.

The sustainable product feeds on phytoplankton and has the capacity to contribute greatly to the local economy, creating jobs and local fresh seafood.

The native flat oyster once flourished in the inlet but became extinct following the 1930s with a dramatic change in the connection of the inlet to the ocean.

This resulted in a lesser marine environment and altered the salinity below its threshold.

The creation of Prawn Rock Channel Island in the 1930s and western openings of the sandbar to maintain the channel dropped salinity to a level in which the native flat oyster could not survive.

This is unlike in nearby estuaries where the native oyster thrives.

From 2005-2009, Mr Launay established a flourishing mussel fishery and experimented with re-establishing native oysters in the inlet.

During that period he sold mussels through Supa IGA to enthusiastic customers.

But the mussels almost disappeared due to low salinity levels in 2011 when salinity had dropped to 12ppt, or one-third of sea concentration at its seasonal peak.

The mussels are now re-populating the inlet and showing strong growth.

This has been due to the extended opening of the sandbar from 2021 and the resulting high salinity level.

Mr Launay says there are big quantities of oyster shells at the bottom of the inlet demonstrating its abundance until recent times.

The shell, pictured, is from a 2006-2008 research trial he conducted in the inlet.

However, another trial initiated last year shows fast growth of rock oyster due to high productivity from the relatively high salinity levels during last year also as a result of the exceptionally long bar opening.

Mr Launay says the filter feeders are not only part of the ecosystem, often referred to as the canary in the mine, but also a major component of the “blue revolution”.

“Albany is currently investing heavily on this new trend of primary production,” he said.

“Wilson inlet shows similar potential with faster growth given the appropriate salinity levels.

“The main problem impacting Wilson inlet is the low salinity due to poor marine exchange.” Poor marine exchange leads to stratification, when the heavier, blue marine water sits at the bottom of the brackish inlet water without mixing for extended periods.

This process results in de-oxygenation of the bottom layer releasing a higher concentration of nutrients (principally phosphorous) than all nutrients coming from the catchment.

Sediment has been known since the 1990s to be the main contributor to eutrophication of Wilson inlet.

As long as the salinity inside the inlet remains below 35ppt (the sea concentration in salinity) stratification persists, leading to de-oxygenation of the stratified layer and eventually in phytoplankton blooms.

Mr Launay said oysters were unable to live at the bottom of the inlet today due to the frequent deoxygenation.

“Prediction of climate change foresees greater extremes, inevitably resulting in an increase of stratification due to salinity differences,” he said.

“The only way to remediate will be to assess a range of adaptive measures.”

This article appeared in the Denmark Bulletin, 6 April 2023.