05-03-2025
Aussies warned of major shark danger: 'Huge numbers'
As millions of Aussies brace for the impact of Tropical Cyclone Alfred, experts are warning of a hidden danger that could linger in the water for days after the wild weather disappears.
From Thursday to Saturday, Brisbane locals can expect wind gusts of up to 125km/h and rainfalls of up to 150mm each day – more than three times the total rainfall for the entire month of February. While rainfall may be heaviest around south-east Queensland, it's also scattered down the coast of NSW, prompting a warning for swimmers to 'stay out of the water' after the rain.
For up to a week after heavy rainfall, the number of bull sharks in rivers and waterways spikes, driven largely by the shark's instinct to scavenge.
'It is likely that dead things get washed out of rivers during heavy rainfall. So obviously they are looking for a free lunch,' Professor Culum Brown from Macquarie University told Yahoo News.
'The other theory is that the freshwater plumes coming into the ocean bring with them lots of nutrients which ultimately encourage plankton growth, which in turn attracts fish. The sharks then chase the fish.'
Prof Brown said there is often a lag between the rain and when the number of sharks spike. But, as shown in a number of studies, the link between the rain and shark activity is clear.
'Several studies, including our own, show that bull sharks do respond to heavy rainfall,' he said. 'One study conducted in Sydney showed that male bull sharks move upstream almost immediately after rainfall and females follow a few days later, but in general bull sharks are attracted to estuaries and rivers during and after heavy rainfall.
'Another study in Queensland found that bull sharks are most often caught in the shark nets when rainfall exceeds 100mm between one and eight days after rainfall. Our own study based in South East Queensland based on data from 1996 - 2022 also found that sharks are more likely to be caught in the shark nets after rainfall.
"In our paper, we also found that 14 out of 15 shark bites in SEQ occurred between one and seven days after rainfall.
'So the take-home message is pretty simple... stay out of the water after rainfall. Particularly stay away from estuaries.'
Over his years as a fisherman and owner of Hunter Shark Jaw Restoration, Joel Nancarrow has noticed an increase in shark activity after rain events and expects "huge numbers" following the Cyclone Alfred's downpours.
"I'm lucky because I'm one of the few remaining shark jaw taxidermists left in Australia, so I'm usually kept up to date on what's being caught," Joel told Yahoo News."In the last two weeks I have received 12 bull sharks, eight tigers and six mako sharks. After this rain, I would expect that they are almost all bull sharks and the numbers will be huge."
Joel feels bull shark numbers have steadily increased over the past decade, and while rain can create more shark activity, he believes the predators are now easily found in any weather conditions.
"If you had asked me the difference in fishing success due to rain 10 years ago, I would have hands down said the flood waters were better. These days, I could take you to any reef along the coast in any weather conditions and guarantee you that we would catch multiple large bull sharks in a short period of time.
"You will find the mid range sharks 200-250kg will be in very big numbers after this rain, in my experience. The XL sharks – 300kg plus – will still be on the reefs and beaches."
In a sandy, protected bay popular with swimmers in NSW, Joel said he's recently caught three bull sharks "well over 300kg" after the beachgoers leave in the late afternoons.
The amount of large sharks he's seen and caught close to shore has led to his choice to no longer swim in the ocean.
"I used to stay out of the water after rain and the usual 6am/6pm feeding times, but things have changed," he said. "I would honestly not swim anymore and while I let my children make up their own mind, they don't either. There's a video on my page from last week where I put a large bait out in the middle of the day and hooked a 300kg shark in under a minute.
"That stuff is terrifying, I don't think I'll ever be back [swimming] in salt water again, the last few years has really opened our eyes. The shark situation that used to be a Queensland thing has well and truly spilled over into NSW."
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