Native congolli being returned to the river after survey. Photo: CEWO
Posted: 7 May 2020
The latest fish survey results in the Lower Murray region have water managers excited. Congolli, a native Australian fish, is the most abundant small-bodied fish species in South Australia’s Lower Lakes for the first time since surveys began in the mid 2000’s.
This is a big bounce back for a species that suffered significantly during the Millennium Drought. Its recovery is due to environmental flows restoring the connection between the Lower Lakes, the Coorong estuary and the sea, which is essential for the survival of native fish such as congolli.
Congolli spend different parts of their lifecycle in fresh water and salt water. The adult females live in fresh water most of the year round. Each winter they swim downstream to the Coorong estuary and Southern Ocean to breed. In late spring and summer, juvenile congolli migrate back upstream via fishways at the barrages, to complete their lifecycles in the freshwater of the Lower Lakes.
"Congolli numbers dropped drastically during the Millennium Drought, when the River Murray stopped flowing to the Coorong from 2007 to 2010. Fish couldn’t access the salt water of the Coorong and the Southern Ocean to breed and there were concerns they would become locally extinct"
— Commonwealth Environmental Water Holder, Jody Swirepik.
Congolli are a key prey of the mulloway, an important recreational and commercial fish of the Coorong and Murray Mouth. Congolli are also food for larger fish such as golden perch and for fish-eating water birds like the iconic pelicans of ‘Storm Boy’ fame.
Since 2010, water for the environment has been critical in maintaining a continuous flow through the barrages—at times, accounting for 100% of the flow from the Lower Lakes into the Coorong. This has allowed the connection between the River Murray, Lower Lakes, the Coorong and the ocean to stay open, resulting in a boom in congolli, and other fish populations.
“We deliver water for the environment to achieve multiple benefits along the whole length of the river,” Ms Swirepik said, “Most of the water for the environment that makes its way to the Coorong has already benefitted sites upstream.”
Winter flows delivered to benefit plants along the banks of the Goulburn River, are the same flows that make their way along the River Murray and through to the Coorong to support the downstream migration of the female congollis. Similarly, spring flows delivered to benefit Barmah-Millewa Forest on the mid-Murray, make their way to the Coorong in late spring and summer in time to support the upstream migration of juvenile congolli.