The rare Pouched lamprey discovered in the River Torrens
Rare fish are returning to the River Torrens and the Onkaparinga River thanks to an environmental flow program run by the Adelaide and Mount Lofty Ranges Natural Resources Management Board, which is designed to reproduce the kinds of water flows that occurred pre-European settlement.
Two fish, a pouched lamprey and short-finned eel, were discovered by Aquasave – Nature Glenelg Trust (NGT) during recent fish monitoring on behalf of the NRM board.
Aquasave – NGT Fish Ecologist Dr Nick Whiterod says, “The presence of these rare species, along with the continued improvement observed for other species, indicates that these waterways are improving.”
Fish monitoring has been undertaken every autumn and spring since 2012 as part of the program.
The Pouched lamprey was caught in the River Torrens for the first time since 2008.
The short-finned eel was caught in the Onkaparinga River, where it was last seen in 2006.
The short-finned eel discovered in the Onkaparinga River
Dr Whiterod says, “Only single individuals were caught, highlighting how rare these species are in the region.”
Other native fish have shown a steady increase in overall numbers since the environmental flows were first introduced in 2012.
The River Torrens has been impacted by urban development, reducing the diversity of aquatic species. Of an original 16 freshwater fish species, only eight of these persist in the river today.
The environmental flows program, which releases water from reservoirs located in the Onkaparinga, South Para and Torrens River catchments, has been designed to improve biodiversity.
Natural Resources Adelaide and Mt Lofty Ranges Water Projects Officer Joseph Sullivan says releases of water are carefully planned and vary between small flows and higher volume ‘flushes’.
Fish monitoring by Aquasave – Nature Glenelg Trust
“The small flows mimic the occasional rainfall experienced during late spring and early autumn. They help freshen the pools that smaller fish and aquatic animals use as refuges during dry summer periods.
“The higher volume flushes, usually during cooler periods of the year, are intended to mirror higher river flows that existed before settlement and not only help sustain life in the river but also contribute to natural changes in the river channels.”
Fish monitoring helps determine the success of the program and freshwater fish are known to provide a good indication of changes in the environment.
The next round of monitoring will occur in autumn 2017 and Dr Whiterod says that this sampling will help to assess how fish populations have persisted over summer.