Massive discovery of juvenile marron in Harvey River shows rehabilitation efforts having an impact

The discovery of a juvenile smooth marron in a South West waterway may not seem extraordinary, but for the researchers who have been rejuvenating the habitat for years, say the discovery is thrilling.

The Harvey River bed has been barren for quite some time, but rehabilitation by Harvey River Restoration Taskforce working with researchers from Murdoch University’s Harry Butler Institute is starting to show signs of success.

As part of the project Marron, more than a meal - Revive our Rivers, big logs have been placed into areas around the waterway to provide habitat for all aquatic animals that call the river home.

The discovery of two juvenile smooth marron taking shelter around some of the first logs installed in Autumn 2021, has project leader Associate Professor Stephen Beatty excited.

Dr Beatty said there was no record of marron in pre-restoration surveys of the area dating back to 2009, and while they did successfully find adults at the site in Spring of 2021, the discovery of juveniles suggests the population may be re-establishing itself.

He said smooth marron returning to the waterway is not only a benefit to the species, but a huge boon for the overall health of the ecosystem.

“Freshwater crayfish are known as ecosystem engineers and play an instrumental role in the functioning of ecosystems,” he said.

Finding the perfect habitat to entice the marron back to the waterway was the first challenge for Dr Beatty and his team. In a study of the ecosystem published in 2019, he found that tree stumps were the perfect habitat for the curious crustacean.

“As any avid recreational marron fisher knows, marron just love the shelter that large wood in our rivers and dams provides,” he said.

“So, putting large wood back in and revegetating the banks of modified sections of rivers will create the habitat that favours marron and also help to create deeper pools that are cooler in the hot periods of the year.

“This will also benefit other native species such as fish.”

Dr Beatty said the most common species found in the modified section of the Harvey River is the eastern Australian yabby, whose overabundance has been damaging to other native crayfish such as gilgies.

When in good water quality areas, the smooth marron often can dominate yabbies and reach a bigger size faster.

Dr Beatty said with the increase in healthier habitat these ecosystem engineers can start to take back their waterway.

“We hope that by providing complex habitat and cooler, deeper pools, the smooth marron can help push out the yabbies and even enable the native gilgie to increase in numbers,” he said.

“Longer term, the revegetation of riverbanks will naturally provide the complex woody habitat at the revegetation site, and also increase the levels of shade and food available for not only crayfish, but also other aquatic species such as native fish.

“We have also shown the restoration site already has a greater diversity of macro invertebrates, which is a great sign of overall improvement in the ecosystem.”

Funding for the ecological monitoring is being provided by the Alcoa Foundation.