MEDIA RELEASE: Spying on barra in the Top End

A group of Top End barra may not have million dollar tags but the reward for tracking their movements could mean a richer environment for everyone.

More than 100 barramundi have been tagged in the Roper River in a joint project to determine the water flows and levels that barramundi need to breed and survive in the river system.

And the results have surprised researchers with several fish travelling more than 100 kilometres over several days.

NT Department of Environment and Natural Resources (DENR) program co-leader Dr Peter Dostine will present the initial findings of the Roper River barramundi tracking program at the 2016 Territory Natural Resource Management (TNRM) Conference in Darwin today.

About 40 “acoustic listening stations” have been placed on the riverbed over a 300-km stretch of the river between Elsey Station, near Mataranka, to the mouth of the Roper River.

These stations listen for unique sound signals, similar to Morse code, emitted from electronic tags implanted in the fish.

When a fish swims past a station, its identity, date and time are recorded to allow the researchers to continuously follow the movements of each tagged fish.

Dr Dostine said the project is the largest application of this method to track fish in a river system in the NT and will help understand the impacts of development on spring-fed rivers.

“We want to better understand the impacts of river flow on the migration movements for the barramundi, which swim between freshwater and estuarine habitats for spawning,” he said.

Barramundi tracking began in the Roper River in October 2015 as a joint project between NT DENR, Charles Darwin University (CDU), NT Fisheries and Yugul Mangi Rangers from Ngukurr.

The rangers helped set up the receivers, which have also been located around potential barriers to movement such as the Roper Bar and different cascades along the river.

CDU program co-leader David Crook said the initial research findings were surprising, considering how far some of the barramundi swam, while some adult female barramundi chose to stay in freshwater habitat rather than move to the estuary waters for spawning.

“One metre-plus fish has moved more 400 kilometres since March, swimming down to the mouth of the river, back to the Roper Bar and then back to the mouth, while a couple of fish swam more than 60 kilometres upstream within two days of being tagged,” Dr Crook said.

“The species is thought to change from male to female at three to five years of age, but we have found 11-year-old females in the freshwater that are not spawning or changing to male at all during their life history. This flexible migration behaviour seems to explain why we are finding metre-plus fish in freshwater.”

Dr Dostine said the barramundi transmitters have a 1300-day life, which will bring the project up to April 2019, but they are hoping to be able to extend the project as more researchers identify different fish to track, such as the endangered sawfish.