Warning climate change could keep bull sharks in Sydney waters ‘year-round'
The James Cook University research shows that bull sharks, which spend their winters in Queensland, are now on average staying 15 days longer off Sydney's coast in the summer than they did 15 years ago.
JCU postdoctoral research fellow Nicolas Lubitz said rising water temperatures were to blame.
'We did a climate analysis of water temperatures of the coast around Sydney and found that average temperatures during the period from October-May each year have been increasing over the past 40 years,' he said.
'We've been tracking migratory bull sharks moving seasonally between Queensland and NSW, specifically the area off Sydney for 15 years, and now on average they're staying 15 days longer than they used to back in 2009.'
The change in migration patterns would extend the potential for human-shark encounters, Dr Lubitz warned.
'Sydney is Australia's most populated city, where bull sharks disappear during the wintertime and migrate back to Queensland during the cooler months, as bull sharks avoid long-term temperatures below 19 degrees,' he said.
'But if they're staying longer, it means that people and prey animals have a longer window of overlap with them.'
According to the Australian Shark Incident Database, nearly all shark encounters in Sydney Harbour with humans involve bull sharks.
They are considered one of the world's most dangerous and aggressive shark species.
In March this year, Sydney woman Mangyon Zhang was attacked by a bull shark at Gunyah Beach, Bundeena, south of Sydney.
Ms Zhang survived the attack.
'She has quite a severe laceration to her outer right leg, to the bone, calf and thigh, and inside thigh,' her partner Maria Masutti said in a social media post.
'She lost quite a lot of blood and had transfusions.'
Dr Lubitz also said if warming trends persisted, bull sharks could inhabit the waters off Sydney 'year-round'.
'While the chances of a shark bite, and shark bites in Australia in general, remain low, it just means that people have to be more aware of an increased window of bull shark presence in coastal waters off Sydney,' he said.
Wildlife scientist Vanessa Pirotta said the research could inform how the public interacted with the marine environment.
'As a whale scientist as well, a lot of these animals are economically profitable for us,' Dr Pirotta told NewsWire.
'People will pay to swim with sharks, people will pay to whale watch.
'Their presence is so important for us, not only ecologically but also economically.'
Dr Lubitz also said the changing climate could alter bull shark breeding patterns, pushing the predators to new breeding grounds further south.
'If that trend persists, there's a fair chance that a lot more tropical species are going to be pretty much year-round in the Sydney area, which obviously changes the whole dynamic,' he added.
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