A scarred great white shark cruising through Australian waters
Philip Thurston/Getty Images
Great white sharks avoid places where they have been caught, which might give us a way of deterring them from hunting near swimmers.
It’s a flight response, says Paul Butcher at the New South Wales Department of Primary Industries in Australia. “It’s the same with almost any animal and the same with sharks.” The animals later “resume their normal migratory movements as if nothing ever happened”, he says.
Butcher and his colleagues have been using SMART (Shark Management Alert in Real Time) drumlines: baited hooks on buoys located 500 metres off the coast of about 20 popular areas in New South Wales. Each of the 305 total drumlines is equipped with a system that notifies local response teams, who aim to reach any hooked shark by boat within 30 minutes of the animal taking the bait. The lines are set anew each morning and collected later that day so they aren’t left overnight.
The teams record the shark’s size and health and tag it. They then move sharks deemed as more of a threat to swimmers – great white, tiger and bull sharks – another 500 metres offshore and let them go. Other species, such as hammerhead and grey nurse sharks, are released where caught.
Butcher and his colleagues monitored 36 great white sharks (Carcharodon carcharias) that were equipped with dorsal fin-mounted satellite-linked radio transmitting tags after being caught at five sites in 2016. During the first three days after the sharks’ release, they all moved away from the beaches where they had been caught and stayed mostly offshore.
“Although sharks gradually moved closer to the shore 10 days after release, 77% of the sharks remained more than 1.9 km away from the coast and an average of 5 km away from where they were tagged,” wrote the researchers in their paper.
In addition, the sharks were still being detected, via the tracking equipment, for an average of nearly 600 days after their release, showing that the programme doesn’t increase the risk of them dying.
Since 2015, more than 1100 great whites, with an average length of about 2.6 metres, have been caught on the SMART drumlines, with more than 400 recapture events, says Butcher.
The drumlines are part of a larger attempt in New South Wales to find non-lethal ways to keep great white, tiger and bull sharks away from people in the water. Drones are now flown at up to 50 beaches to look out for sharks and other potential threats during school holidays, and the department runs 37 shark listening station buoys that detect when tagged target sharks pass nearby. This information is then sent to the public via the SharkSmart app.
This suite of tools could one day mean that controversial beach meshing nets, which in New South Wales alone captured 228 animals in the 2022/23 reporting period, can be removed. Of these 228 animals, only 85 were released alive and more than 200 were non-target species, including turtles, dolphins and seals.
David Booth at the University of Technology Sydney says the study’s findings are very good news. “And to still be re-sighting the caught and released animals years later is pretty impressive and certainly better than slaughtering them,” he says.
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