Four shark attacks in 48 hours have renewed calls for a shark cull in New South Wales, as two victims remain in critical condition, and 20 Sydney beaches remain closed.
Rob Harcourt, emeritus professor of marine ecology at Macquarie University, surfs daily at Bondi or North Steyne in Manly— where one of the four tragic shark attacks occurred on Monday.
The shark expert has rejected urgent calls led by former Prime Minister Tony Abbott to cull Sydney Harbour’s shark population.
“Three shark attacks in three days in Sydney. This didn’t happen because of the weather or the time of day, it happened because there are too many sharks,” Abbott posted to Facebook on Tuesday. “It’s way past time to reintroduce the shark fishery.”
Ex-pro surfer Dayyan Neve, who helped save fourth shark attack victim Andre de Ruytor on Sydney’s northern beaches, echoed Abbott’s sentiment: “Culling should be up for debate as an option in consultation with surfers and fisherman,” he told The Daily Telegraph.
While emotions and fears are understandably high following the attacks, Professor Harcourt tells The Lighthouse it’s vital our response to them is led by science.
“Culling the shark population won’t do anything,” he said. “Calling for more culling is a knee-jerk response to this tragedy. The reality is, we already have a culling program. We’ve been doing this since 1931, nearly 100 years. The call for culling is a 19th century response to a 21st century problem.”
The movements and behaviours of the Sydney Harbour bull shark population have been studied for years.
“Thanks to the huge effort by NSW Fisheries to track hundreds of sharks, we know that sharks move in a different pattern when feeding, compared to when they are moving between places,” Harcourt explains.
After a period of heavy rainfall (above 20mm), Sydney’s 100-year-old sewage pipes overflow and flush into the harbour, attracting schools of baitfish.
The baitfish feed in the sewage, and the bull sharks follow to feed on them in the turbid, brackish water.
That’s why marine researchers are urging the public to wait 72 hours after a downpour to swim in the harbour, and at least 24 hours to swim or surf at ocean beaches.
“The conditions that are optimal for bull sharks to come and bite you are actually the same conditions for you to get really sick. It’s a double whammy,” Harcourt said.
The spate of attacks isn’t due to the number of sharks in the harbour, he said, “but our rapidly changing climate.”
“It’s not that there’s suddenly more sharks this summer, but there’s certainly more people in the water. The water is also particularly warm this season."
"The bull sharks come down and spend the summer in the harbour. Because the water is warming up so quickly, they come earlier, they stay longer, and they go back later.
“With the heavy rain we’ve just had, the fresh water mixing with the harbour water brings the food of the bull sharks close to the shore around those rocky reefs.”
Adding, “that’s exactly where” 12-year-old Nico Antic was swimming when the young boy was attacked on Sunday at Shark Beach.
Bull sharks, unlike most other sharks, are very tolerant of fresh water. They feed a lot on fish that gather in those plumes of brackish and fresh water.
They attack in bad light, at dawn or dusk and in murky water.
“The strongest predictors of shark feeding behaviour are very heavy rainfall and warm ocean waters, both of which we’ve had in abundance,” Harcourt said.
Personally, he utilises free government website Beach Watch to keep an eye on real-time pollution levels at his local beaches: “If the water is dirty, I wouldn’t go in.”
NSW Premier Chris Minns has ruled out a shark cull, saying instead the state’s “warning system and communication needs to be beefed up,” at high-risk times such as during the recent stormy weather.
“I think you have got to look at the circumstances, the brackish water, whether there’s better communication that we can give to the people of NSW and Sydney,” he said.
Australian wildlife scientist Vanessa Pirotta says the attacks “should be a catalyst for renewed national education about sharks”— not culling.
Pirotta appeared on Nine’s Today on Wednesday morning to urge the public to beware ocean swimming after heavy rain.
“As a marine scientist, I personally do not support a cull,” Pirotta said, telling Lighthouse she believes that suggestion is “a result of people being misinformed.”
She would like to see shark safety education carried out “from school levels up.”
Pirotta envisions safety tips about not swimming in the harbour at dawn or dusk, or after heavy rainfall, entering the national consciousness in a similar way to ubiquitous beach safety messages like ‘swim between the flags.’
“These awful events highlight the need for investing in science and better science communication, not fear,” she said.