10 October 2023
Commercial fishers in Queensland and the Northern Territory are playing a vital role in sawfish research with researchers from Australia’s national science agency CSIRO, and Charles Darwin University.
Together these teams have tagged and tracked more than 40 sawfish. One of these was a Largetooth Sawfish measuring more than five metres that swam an incredible 1000 kilometres in two months.
Sawfish are extinct in many places worldwide. Although they still survive in northern Australia, conservation managers are concerned about low population numbers as individuals are often caught in fishing nets by accident. To date, scientific data on sawfish populations in Australian waters has been negligible and it has been difficult to determine just how critical the sawfish situation is, or how best to protect them.
This new tagging data are helping researchers better understand the movement and survival of sawfish released from fishing gear, which is critical for conservation efforts, and some surprising findings have been made.
CSIRO research scientist Dr Richard Pillans said out of the 40 tagged so far, the biggest was a massive 5.7 metres long.
“Amazingly, this giant sawfish swam 1000km in a two-month period: from the west side of Cape York, to near Croker Island off the coast of the Northern Territory,” Dr Pillans said. “I was completely astonished by the distance and speed this adult sawfish travelled. By recovering the tag, we also got data on swimming depth and temperature throughout the track.”
Researchers worked in close collaboration with commercial fishers in Queensland and the Northern Territory to help paint a better picture of sawfish survival rates. Fishers are now recording the sawfish they catch, collecting tissue samples, and tagging animals with satellite transmitters to determine post-release survival rates and the distance they travel.
“We know that fishers catch sawfish accidentally as ‘bycatch’ in their nets,’ Dr Pillans said. “The sawfish’s extended snout, or rostrum, has teeth along its edge, so when they come into contact with a net, they can get very entangled. What we don’t know is how many sawfish there are and what impact bycatch is having on their population status.
“Given they can grow up to seven metres with about two metres of that being rostrum, releasing them can be an extremely hazardous undertaking. We are working with the fishing industry to assist them and us understand the species better. This collaboration is crucial in helping to conserve Australia’s remaining sawfish population.”
Just getting access to the data has proved to be an adventure for Dr Pillans, his doctoral student Julia Constance, and the Garngi Indigenous Rangers of Croker Island.
The tag had to be physically retrieved after automatically detaching from the 5.7-metre sawfish. Luckily it washed ashore on the remote beach at McCluer Island and an urgent helicopter flight was organised to get it.
“We knew its location within about 500 metres, but when you’re looking for something half the size of a stubbie that’s a lot of beach to cover.”
“We knew its location within about 500 metres, but when you’re looking for something half the size of a stubbie that’s a lot of beach to cover,” Dr Pillans said.
The team found the tag 45 minutes after landing on the island’s beach.
“We are all really pleased to have this new information on sawfish movements,” Dr Pillans said. “This has given us all a big boost. It just goes to show how much can be achieved when the fishing industry, Traditional Owners and scientists work on research as a team.
“The reality is we wouldn’t have been able to collect this level of data in this short space of time without the collaboration of the fishing industry and it is exciting working towards a common goal of ensuring sustainable management of our threatened marine life.”
This project is supported with funding from the Australian Government under the National Environmental Science Program (NESP). The NESP has provided more than $1.1 million in funding since 2021 to support further research into sawfish.
Download video footage of the tagged sawfish here. The short video clip shows a commercial fisher in Queensland Gulf of Carpentaria inshore net fishery (barramundi gillnet fishery) releasing a Largetooth Sawfish. The second (longer video clip) shows CSIRO/NESP research with APN Rangers and commercial fishers at Archer River, Queensland.
Download still images here.