Tuesday, March 5, 2024

Where have all the mussels gone?

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Margrit Beemster, The Koondrook and Barham Bridge Newspaper

Research has been conducted in the Yallakool Creek and upper Wakool River near Deniliquin to find an easier way to detect adult freshwater mussels and to better understand why mussels are no longer as plentiful as they once were.

“Unfortunately, we have very little understanding of the current distribution and size of mussel populations,” said Charles Sturt University researcher Dr Nicole McCasker, one of a few researchers in Australia who focus on mussels.

To help address this gap in our knowledge, Nicole leads a research project in the Edward/Kolety-Wakool river system that is trialling the use of side-scan sonar, a technology familiar to many recreational fishers for finding fish, to detect freshwater mussels. 

In September and October 2023, researchers from Charles Sturt University and Austral Research and Consulting undertook side-scan sonar surveys, mapping five two-kilometre reaches of river bottom in Yallakool Creek and the upper Wakool River. A second round of surveys was conducted using different sonar equipment that produces a higher resolution image to try and confirm if the ‘bright spots’ identified in the images from the first survey were actually mussels.

“We are trialling these methods,” said Nicole. “It’s a bit like looking for a needle in a haystack, only we don’t know how many needles there are or if there are any at all! We know that this technology has been used overseas to identify areas where mussels are likely to be, but this is the first time it has been used in Australia. If this survey method works for inland rivers, it has the potential to be used elsewhere in Australia.” 

The project is funded by the Commonwealth Environmental Water Holder’s science program Flow-Monitoring Evaluation and Research (Flow-MER) in the Edward/Kolety-Wakool river system.

Specifically, the researchers are looking for the main two species of large, burrowing freshwater mussels in the southern Murray-Darling Basin – the river mussel Alathyria jacksoni that grows to about 20cm; and the billabong mussel Velesunio ambiguus, that grows to about 12cm. 

“Most people I’ve spoken to have stories of mussels being everywhere when they were children, but now not so much,” said Nicole, who recalls there were plenty about when she was growing up in Kerang, Victoria.

“Mussels play an important ecological role in rivers and wetlands. They are filter feeders so they improve water quality, provide habitat for other animals, and create resources for other organisms.”

Freshwater mussels are also of cultural importance to the First Nations peoples of the Murray-Darling Basin, including local Traditional Owners, the Perrepa Perrepa or Barapa Barapa and Wamba Wamba or Wemba Wemba peoples. 

Speaking at a Knowledge Sharing Day, Jeanette Crew OAM, chairperson of the Yarkuwa Indigenous Knowledge Centre and a Wamba Wamba Pereppa Pereppa Nation woman said, “Mussels were highly significant for our people. Not only were they a major food source, their shells were also used as implements for cutting, scooping and fishing, and for ornamental purposes such as necklaces and that sort of thing.”

The day, held in October at Yarkuwa’s new premises in Hay Street, Deniliquin, was an opportunity for Nicole, Yarkuwa staff and Kolety-Werkul rangers to talk about the types of freshwater mussels in the region, their ecology and important roles they play in their ecosystems.

But as Nicole said, finding mussels in the lakes and rivers of the Murray-Darling Basin isn’t easy. 

“In clear, shallow river systems, researchers can snorkel down and visually count freshwater mussels,” said Nicole, “however, our inland river systems are deep, turbid with lots of snags. Surveys for adult mussels are currently limited to systems that are shallow enough to search for mussels by feeling with your hands or feet. Our research project aimed to trial a sonar scan method to see if we can survey for adults in areas that would otherwise be difficult to sample.

“It’s all about trying to find out where have the mussels gone and how do we get them back. Globally, freshwater mussels are one of the most threatened species alive, but for different reasons. 

“As freshwater scientists, we think river regulation and other changes to rivers in the Murray-Darling Basin have contributed to the decline, so then the next step is what watering/flow regime do we need to bring mussels back? Understanding where they are and where they are not will help us to inform the environmental water managers.”

Nicole is a Senior Research Fellow at the Gulbali Institute, Charles Sturt University. She is interested in hearing from people who have information about freshwater mussels in the Edward/Kolety-Wakool river system. She can be contacted on nmccasker@csu.edu.au or phone 02 6051 9437.

The Koondrook and Barham Bridge Newspaper 11 January 2024

This article appeared in The Koondrook and Barham Bridge Newspaper, 11 January 2024.

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