Habitat and flow requirements of freshwater mussels in the northern Murray-Darling Basin

Between 2017 and early 2020 the northern Basin experienced extreme and prolonged drought. During this time there were reports of extensive mussel deaths across catchments in the northern Basin. The drought provided an opportunity to build knowledge about freshwater mussels and to better understand the extent of population mortality during the drought.

The Commonwealth Environmental Water Office contracted Griffith University to undertake a short-term monitoring project to review existing knowledge about freshwater mussels, and to understand the impact of the drought on mussel populations in the northern Basin.

Key findings from the project included:
The loss of mussel populations across the northern Basin was significant and widespread as a result of the drought and the increased duration of dry conditions.
Cease to flow conditions during the recent drought was longer, sometimes more than double the duration of the maximum cease to flow length in the preceding 37 years.
Site mortality estimates were between 20 and 100% across the northern Basin, which equated to around 2.9 million deceased mussels.
There was a limited proportion of smaller mussels observed, suggesting that they may not be recruiting successfully.
Maintaining low flows and refuge habitat for freshwater mussels is critical to their recovery.

This monitoring project provides valuable information, which will help inform the future delivery of water for the environment in catchments across the northern Basin.