Native congolli are the most abundant small-bodied fish species in the Lower Lakes for the first time since surveys began in the mid-2000s.
The delivery of water for the environment to the Lower Lakes and Coorong in recent years has enabled congolli and other species of fish to migrate from the Coorong into Lake Alexandrina through fishways.
Adrienne Rumbelow from the Department for Environment and Water said monitoring by the University of Adelaide had shown a steady increase in the proportion of congolli in the Lower Lakes since the drought.
“Congolli spend different parts of their lifecycle in fresh water and salt water. Adult females live in fresh water and migrate downstream from Lake Alexandrina to the Coorong estuary and Southern Ocean in winter to breed,” she said.
“In late spring and summer tiny juveniles migrate upstream from the estuary to Lake Alexandrina via the fishways at the barrages.
“During the Millennium Drought there was no fresh water flow from the River Murray to the Coorong, meaning females could not access the ocean to breed.
“Fishways on the barrages were closed from 2007–2010 (the approximate lifespan of the congolli), obstructing the upstream migration of juveniles. This resulted in a catastrophic drop in congolli numbers, and there were big concerns we were facing a local extinction of this species.”
Ms Rumbelow said the present high numbers of congolli in the Lower Lakes were a direct result of the recovery of water for the environment as part of the Murray-Darling Basin Plan and delivery to the Lower Lakes and Coorong in recent years.
“Since September 2010, continuous fresh water flows from Lake Alexandrina to the Coorong estuary have been provided through fishways, meaning congolli, among other species, have had opportunities to migrate from the Coorong into Lake Alexandrina,” she said.
“Winter flows from the Goulburn River in Victoria have also played an important role in recovery. The timing of these flows reaching the Lower Lakes has coincided with the downstream migration season of female congolli, allowing access to marine spawning grounds.”
Congolli are a key prey of the mulloway, an important recreational and commercial fish of the Coorong and Murray Mouth. In the Lower Lakes, congolli provide food for larger fish such as golden perch and for fish-eating water birds like pelicans and cormorants.
Water for the environment has been provided by the Commonwealth Environmental Water Office and The Living Murray program (Murray-Darling Basin Authority).
Monitoring is funded by The Living Murray, a joint initiative of the South Australian, New South Wales, Victorian, Australian Capital Territory and Commonwealth governments, and coordinated by the Murray–Darling Basin Authority.