What the fish! The latest fish survey results from the Marne Saunders catchment in 2023

The Marne River and Saunders Creek do not have regular flow. By autumn each year, these streams dry out to a few pools or waterholes persisting in certain parts of the catchment. These pools become refuge areas for aquatic species that need water to remain alive, including fish. Each autumn, fish experts from Nature Glenelg Trust survey approximately 10 water sites (up to 16 pools or waterholes depending on the year and season). Over 20 years of data has been collected, which means we have a good understanding of how fish respond to seasonal stream flow conditions along the Marne River and Saunders Creek. The data shows the long-term trend in fish population dynamics, indicating when there is recruitment with young fish born and surviving, and where non-native fish are becoming more dominant.

Unfortunately, the overall trend shows a decline in native fish populations. The good news is that over the last 3 years, with wetter weather and winter rainfall, there has been water flowing in the catchment which has resulted in stabilisation in fish populations since 2019-2020 when no flow was recorded through the Marne Gorge.

Break-out box – Earlier in this story, you may have noticed that the images of Jutland road in autumn and spring 2020 showed water and stream flow. This is interesting, because this site is the last one before the stream enters the gorge and the streambed was so dry that water flow didn’t make it all the way from the upper catchment to the gorge below and out onto the plains.

In 2023, bumper numbers of the little native fish named obscure galaxias were caught during the survey, and it was the highest number of this fish species caught when compared to the last 5 years.

Once the Marne River reaches the plains there are less instream pools and water holes, although the area around Black Hill was renowned for the permanently flowing springs that occurred in the stream bed. These were home to the river blackfish, a threatened species. Almost all of these springs have dried up with only a few now remaining downstream of Black Hill. The presence of this fish species in the annual survey has been a bit hit and miss over the last 20 years, and in most years only a single river blackfish is caught. Over the last 30 years, the Marne River has only flowed and connected with the River Murray three times (1992, 1996 & 2004). This has resulted in unfavourable conditions for the river blackfish to spawn and reproduce which is causing this species to decline.

Connection of the Marne River and Saunders Creek with the River Murray is now rare due to water resource development and land use changes across the whole catchment. In addition, the changing climate is resulting in a declining trend in rainfall and runoff water needed to create stream flow. This is similar to what is happening in the neighbouring Barossa Valley, where a water security plan has been developed to guide a sustainable water future to 2050.

In 2022 the landscape board funded a Grassroots Grant project to undertake continuous salinity monitoring by community members in the spring-fed pools where the river blackfish occur. We are also looking at alternative monitoring methods that may provide a better understanding of fish numbers and locations in the hope that solutions can be found to keep this iconic fish species in the catchment.

What can you do?

• Sign up to be a part of WaterWatch, and record when you see flow in the river near you.
• If you live in the hills and have a low flow device on your dam, do a seasonal check on your device to make sure it is in working order. It is critical that any low flows from summer and autumn rainfall bypass dams as this water is essential to keeping these native fish populations alive. More maintenance guidelines

Dr Nick Whiterod, Nature Glenelg Trust

The fish surveys are a partnership between Nature Glenelg Trusts and the Murraylands and Riverland Landscape Board through funding from the landscape levies.