Freshwater Mussels in the Murray Darling Basin

They are amazing biofilters, playing a crucial role in keeping rivers healthy. An abundant food source for First Nations Peoples, Freshwater Mussels are a critically important part of the web of life.

Once, they were second only to fish as the dominate life by weight in inland rivers.

The severe drought of 2017-2020, exacerbated the problems caused by decades of over extraction and mis-mangement of water in the Murray Darling Basin and the unthinkable happened – many rivers dried up completely. The Darling-Baaka was a series of small, green disconnected pools from Bourke to the Murray. The Macquarie-Wambuul was cut of at Warren, completely drying out the Macquarie Marshes and the Lower Macquaire.

Rightfully, the fish kills that resulted shocked and horrified the community. But the loss of an estimated 2.9 million Freshwater Mussels is a lesser known ecological catastrophe.

This post includes an article that appeared in The Conversation, and lower down a published study of the habitat and flow requirements of the Freshwater Mussels.

The internationally significant Macquarie Marshes is the only place in the northern Basin where remains of all three species of Freshwater Mussels that live in the basin were found. It is home to the biggest and oldest Freshwater Mussel remains that were found in the study, with one specimen measured at 137.2mm.

The presence of large, old Freshwater Mussels in places like the mid Darling-Baaka Rivers and the Macquarie Marshes proves that the natural wetting and drying patterns of these systems never included completely drying out, like they did in 2017-2020.

The Conversation – Academic rigour, journalistic flair

Professor Alan Lymbery – Jan 12th 2022

Freshwater mussels are dying suddenly and in the thousands, with each mass death event bringing these endangered molluscs closer to extinction. Tragically, these events rarely get noticed.

Read the full article here

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

Report to the Commonwealth Environmental Water Office
November 2020

Fran Sheldon and Nicole McCasker
Co-authors: Michelle Hobbs, Paul Humphries, Hugh Jones, Michael Klunzinger and Mark Kennard

Australian Rivers Institute, Griffith University

Institute of Land, Water and Society, Charles Sturt University

The authors respectfully acknowledge the Traditional Owners of the lands and waters of the Murray-Darling Basin, particularly those whose lands we walked on in this study, across the Darling, Barwon, Macquarie, Namoi, Gwydir and MacIntyre rivers. We acknowledge that Aboriginal peoples have cared for the rivers for millennia, and pay our respects to the Elders, past and present.

Executive Summary
Freshwater mussels are considered ecosystem engineers of rivers; they modify substrates through burrowing, mediate water quality through filtration, provide food and habitat for other organisms and play a significant role in the biogeochemical cycling of nutrients and are also seriously threatened globally. The rivers of the northern Murray-Darling Basin (MDB) are home to three species of freshwater mussel – the large ‘river mussels’ Alathyria jacksoni and Alathyria condola and the smaller ‘floodplain/billabong mussel’ Velesunio ambiguus. As sedentary, long-lived organisms, obtaining an understanding of the habitat requirements of resident freshwater mussels will provide insights into the natural hydrology of Australia’s inland rivers, and the potential role healthy populations of freshwater mussels could play in influencing water quality through biofiltration. This project was conceived in response to the extensive drought in the northern Murray-Darling Basin between 2017 and early 2020 and the reports of extensive mussel mortality. The specific aims were to review existing knowledge and identify knowledge gaps in relation to environmental water requirements, life history, physiological tolerances and habitat requirements and cultural significance of freshwater mussels in the Murray-Darling Basin, improve baseline understanding of distribution and structure of freshwater mussels in the Northern Basin and make recommendations for land and water management to protect freshwater mussel populations. This was achieved through a predictive analysis of mussel distribution, and analysis of the hydrological conditions during the drying event and a field survey to establish the extent of mussel mortality at sites across the northern Murray-Darling Basin……….

……… The combination of rapid and quantitative surveys used in this study suggest that the loss of mussel populations across the northern Murray-Darling Basin resulting from the drying conditions of 2017- 2019 is significant and widespread. This is a cause for concern given the longevity of mussel individuals and the poor evidence of widespread recent recruitment. Based on our analyses we make the following five (5) broad recommendations:

  • Recommendation 1: that further research needs to be undertaken to understand the biology of freshwater mussels in the northern Murray-Darling Basin, including their reproduction, recruitment, growth patterns and diets, as well as their role in the ecosystem of the northern Murray-Darling Basin Rivers – not least because, besides fish, they were historically the dominant animal by weight in these rivers.
  • Recommendation 2: that a focus be made on monitoring freshwater mussel recovery in both the short- and long-term. This should include an understanding of which fish species act as hosts and what conditions are required for successful recruitment and establishment of juveniles.
  • Recommendation 3: that the importance of low flows and refugial habitats, reaches and waterholes, be formally recognised for freshwater mussels in the northern Murray-Darling Basin and the flow requirements of freshwater mussels be incorporated into flow management plans.
  • Recommendation 4: that the role of refugial reaches and waterholes in the landscape persistence of mussels and fish be recognised and the flow required to maintain the integrity of these physical places in the channel network be understood and incorporated into flow management plans. This would require a basin- wide perspective of the Water Sharing Plans and Water Resource Plans to ensure the critical area of the Barwon-Darling River has adequate flows for long-term population survival.
  • Recommendation 5: that a specific Freshwater Mussel Recovery Plan be developed in consultation with the communities of the northern Murray-Darling Basin and this plan articulate with Fish Recovery Plans.

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