Dredging river mouth ‘best way’ to bring back fish
Dredging of the shallow Noosa River mouth is the best way to reduce sediment and help bring back marine life biodiversity, according to the panel of experts behind the latest system health study.
A panel led by University of Queensland's Professor Greg Skilleter recommended a similar program of target dredging to that which occurred in 1998.
A report released by the panel said plans should be made for opening the mouth of the estuary at a time when there were "peak spring tides and possibly predicted rainfall".
"Opening the estuary at this time would provide an opportunity for accumulated fine sediments to be flushed from the system," the report said.
"This is no longer possible due to the restricted opening and reduced tidal prism.
"Once flushing has been achieved, maintenance of dredging channels through the shallow lakes should be established and discussion should be held with the relevant government agencies about establishing designated 'go slow zones'."
These zones would be to reduce wash from boats eroding shorelines, which prevents the re-establishment of seagrass and shallow mangroves.
The report said if sedimentation and resuspension was shown to be reduced after flushing and dredging of channel, there was an opportunity for replanting seagrass and mangroves in "areas where these flowing marine plants were once known to be present".
The 2018 study was the third component of the Bring Back the Fish research program, a joint initiative of the Noosa Biosphere Reserve Foundation, Noosa Parks Association and The Thomas Foundation, aimed at understanding how to improve biodiversity in the Noosa River.
Professor Skilleter has previously expressed surprise at the very low numbers of prawns and other small animals that were found in comparison to 20 years ago.
His team was most alarmed by a 30-65 per cent decline in small animals that lived in the sand and mud and made up a key component in the diet of many fish and crabs.
"The overall conclusion was that the abundance and diversity of the benthic animals in the Noosa River is now severely depleted compared with historical levels," Professor Skilleter said.
He told ABC radio a study done for Noosa Council 20 years ago looking at the river mouth dredging impacts showed there was disturbance to the system, but the river recovery was similar to that after a natural flood event.
In 1998 a UQ research team was given $65,000 by Noosa Council for UQ zoology and entomology honours student Andrew Pryor and PhD student Samantha Miller to investigate the effects of dredging on important fish habitats in the area.
The "before and after" examination of the impacts on marine fauna of a dredging program was supervised by Professor Skilleter.
The dredging involved removing sand from the mouth of the Noosa River to build up the depleted Noosa Spit.
"Mr Pryor's work examined the impact of dredging on animals such as small worms and crabs which live in the estuarine sand," Professor Skilleter said at the time.
"He found the community had changed in terms of species dominance since the dredging.
"Ms Miller's work found colonisation of the new sand areas on the spit by worms, clams and juvenile fish had taken place very quickly although further investigations are needed to determine whether this will result in a positive outcome for fisheries in the area."