Wet season flows are essential to the survival of prized freshwater prawn populations in northern Australia, a Charles Darwin University researcher has discovered.

With little known about the ecological role and life history of Macrobrachium spinipes, locally known as cherabin, and with concern that populations are declining, PhD candidate Peter Novak has conducted the first ever study on the lifecycle of the species.

He delivered his findings at a joint congress of the Australian Society for Fish Biology and the Australian Society for Limnology in Darwin on Tuesday, 1 July.

“To understand their natural history, we needed to find out more about their annual migration, and where and when they bred,” Mr Novak said.

He monitored a 400 kilometre stretch, from Katherine to the mouth of the Daly River and through the Edith and Ferguson tributaries over 14 months, surveying more than 4,500 adult prawns and tens of thousands of juveniles and larvae.

“We also collected females with egg clutches of ready-to-hatch larvae and tested the survival rates of the larvae in freshwater over a period of days in the lab,” he said.

“We found that for a larva to survive it needed to reach the saltwater nursery grounds within seven days of hatching. Without their annual migration downstream this species would not survive.”

Mr Novak said their annual journey was timed in tune with river flow and season. The migration began with the rains of the wet season from December to March.

“After the rains, we observed up to one million juvenile cherabin every night for about 30 days in April/May, moving back up the river after the rains, along with other iconic species like barramundi and mullet. The migration was like a replenishing of nutrients and food for the river system,” he said.

Mr Novak’s research about their annual migration will provide valuable baseline data about the species that can now be used to improve management of cherabin populations in the NT.

“Now we not only know how important river flow is to the survival of these cherabin populations, but also how vital the species is in the linkage between freshwater and estuarine food webs,” he said.

“Any developments that might impede the migratory behaviour of cherabin could have significant impacts at an ecosystem scale.”

View a video of Mr Novak’s research. Footage and images are available upon request, or for interviews please contact Amy Kimber on (08) 8946 7619 or 0428 853 425.

Mr Novak’s findings are contributing to Northern Australia Hub project River to landscape connections and biodiversity.

This project is supported by Charles Darwin University, the Northern Australia Hub of the National Environmental Research Program, the Northern Territory Government Research and Innovation Post Graduate Scholarship, and Holsworth Wildlife Research Endowment.

For more information about the joint congress of the Australian Society for Fish Biology and the Australian Society for Limnology visit www.asfbasl.org.au.