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Tiger sharks are swimming further along Australia’s east coast as ocean temperatures increase, expanding their range south and coming closer to shore.
The warmer waters off the NSW coast are also attracting bull sharks, which are spending more time in Sydney Harbour.
Tiger sharks are the second most dangerous species to humans behind great whites. Bull sharks are the third species most often involved in bites.
While shark attacks are extremely uncommon and fatalities rarer still, the fact Sydneysiders share the city’s waters with the powerful marine predators has been thrown into sharp relief during the past year.
On Monday, a bull shark bit 29-year-old Lauren O’Neill on the leg when she took a dip in the warm evening waters of Elizabeth Bay. Last February, 35-year-old diving instructor Simon Nellist died in a shark attack in Little Bay – the first shark fatality in Sydney since 1963.
The East Australia Current is ushering bull and tiger sharks south as climate change increases the strength of the warm current. Both shark species live in tropical and temperate seas. Their prey, including sea turtles and some species of fish, also move further south with warmer water.
“Bull sharks probably spend up to an extra two months per year in the Sydney region,” Professor Rob Harcourt, a marine ecologist at Macquarie University said. “We’re in the middle of a marine heatwave this year, the water is balmy, so they could stay for even longer now.”
Distribution analysis of 115 tagged tiger sharks shows adult females and juvenile males are expanding their range down the NSW coast towards Tasmania, and they’re coming closer to shore.
“There’s a lot more food closer offshore here,” said Harcourt. “So if they’re coming down with the East Australian Current, they’re going to be popping into shore to get food.”
Tiger sharks tend to rely on scavenging behaviour, preferring to feed at night and in shallow water. They are recognised by the dark vertical stripes on their body that fade with age. They have fairly slender bodies with a large head and square-shaped snout, and can grow to six metres.
Tiger sharks have been responsible for 228 incidents involving people in Australia since 1791, the second-highest number after white sharks, according to data from the Australian Shark-Incident Database.
Most of these incidents have occurred in Queensland. About 38 per cent of tiger shark bites are fatal.
The expanded range of tiger sharks are putting them at risk of greater competition with white sharks, intensifying conservation pressures on both species.
All sharks are critical to the health of ocean ecosystems. White sharks are a protected species in Australia and bull sharks, listed as vulnerable on the International Union for Conservation of Nature (IUCN) red list, play a key ecological role as the apex predators of Sydney Harbour.
Just keep swimming
The great white shark has been responsible for 370 incidents around Australia, most of which occurred in NSW – 151 attacks. Western Australia and South Australia had the second and third most incidents, with 71 and 58 attacks, respectively.
These sharks are found across the world in temperate waters ranging from 10 to 27 degrees (although their preferred ocean temperature is about 20 degrees), making waters off Sydney ideal for them. These sharks are usually found along beaches outside the harbour, such as Manly and Bondi.
Data from the NSW Department of Primary Industries show that juvenile white sharks migrate along NSW coastline over spring and summer.
In a world-first study, researchers from Flinders and Macquarie University gathered hard evidence that white sharks don’t actively hunt humans but rather bite surfers and swimmers due to mistaken identity.
Scientists pinned go-pros to the bottom of tanks at Taronga Zoo and captured footage of sea lions, sharks and surfers.
Then, based on our understanding of shark vision – sharks are colourblind and their sight can be compared to the blurry view of a human without goggles underwater – they developed a virtual visual system to test whether a surfer could be distinguished from a sea lion. The system found it impossible.
The researchers suggested swimmers and surfers with short boards were at most risk of being mistaken for prey, as opposed to people using kayaks, longboards and paddleboards. Lights on the bottom of boards could deter sharks, and the findings could also apply to bull and tiger sharks, the researchers said.
The estimated population numbers of adult great white sharks in waters east of Australia is about 750.
The third most dangerous shark to humans is the bull shark. This was the species that left O’Neill with serious injuries on Monday night in Elizabeth Bay.
Nationally, these sharks have been involved in 200 incidents since 1791.
Bull sharks are known to populate Sydney Harbour in November. Females come in to give birth to their pups – which spend the first years of their lives in rivers and estuaries – and the males follow.
The sharks normally depart around April and swim towards Queensland, but will remain if the waters are warm. They are particularly abundant in Sydney Harbour between January and February.
Bull sharks are also among the only sharks that tolerate fresh water – making the harbour ideal habitat.
Scientists have tagged at least 250 bull sharks across NSW since 2009, including 87 in Sydney Harbour.
Abyss Scuba Diving general manager Rachael Fallon has been working in the industry for 23 years and said she’s never seen a bull, tiger or great white. However, it’s common for divers to see grey nurse sharks, Port Jackson sharks and wobbegongs.
“Some people are nervous about getting in the water to dive, but swimming with sharks is no different to swimming with a dolphin or whale, or a big creature,” she said.
“People have in their head that it will be like Jaws. That it will be big teeth, fast and scary. But really, sharks are graceful and slow.”
Port Jackson sharks are endemic to Australia – meaning they’re only found here – and mostly live in rocky environments near the bottom of the ocean floor in shallow waters, often between May and October. They can give a painful bite.
Grey nurse sharks are found mostly on the east coast of Australia, in shallow coastal waters from the surf zone down to 60 metres.
Fallon said that, for a while, there were fewer grey nurse sharks around Sydney, but it seemed to her they’re returning. Magic Point in Maroubra, Marley Reef in Bundeena and Bushrangers Bay in Shellharbour are among the best spots to see them.
While these sharks look scary due to their fang-like teeth, they are very slow-moving and placid.
How likely are you to get bitten?
After all the shark news this week, it would be easy to think the water is teeming with sharks. But let’s take a look at the numbers.
Between 1852 and 2014, there were 42 shark interactions in the harbour, according to a 2015 review by Taronga Zoo. All but one of those incidents involved bull sharks.
There were 24 harbour bites between 1852 and 1915, 12 between 1916 and 1988, and seven between 1989 and 2014. In the three decades between 1964 and 1995, there were no unprovoked incidents.
Attacks plunged after abattoirs that dumped blood and offal into the harbour shut in 1988, while the construction of sewage outfalls further out to sea between 1984 and 1992 improved water quality.
But as our water ecosystems have become more healthy, sharks – among other animals – have returned. This is a positive thing, marine experts say. With increased numbers of people living along the coast, using the water more and documenting interactions with sharks on mobile phones, it may seem like sharks are everywhere, lurking and ready to pounce.
This is not the case. This year alone, there have been two shark incidents, according to the database. You’re more likely to get struck by lightning than encounter a shark. Five to 10 deaths and over 100 serious injuries are estimated to be caused by lightning every year.
And mosquitos – through transmitting diseases – kill more people in one day than sharks have killed over the past 100 years worldwide, according to the Global Shark Attack File.
If we stick with the animal theme for a minute, between 2001 and 2017, horses killed 172 people in Australia, cows killed 82 and dogs were involved in 53 deaths. In the same period, sharks were involved in only 27 deaths.
Shark bites can be largely avoided by not swimming at dusk, dawn, or after heavy rain, or sticking to ocean pools, netted areas and sea baths.
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According to the search results, the article discusses the increasing presence of tiger sharks and bull sharks along Australia's east coast, particularly off the coast of New South Wales (NSW) and in Sydney Harbour. The warmer ocean temperatures, attributed to climate change, are causing these sharks to expand their range southward and come closer to shore. Tiger sharks are the second most dangerous species to humans, following great white sharks, while bull sharks are the third most dangerous. The article also mentions recent shark attacks in Sydney and highlights the impact of the East Australia Current on the movement of these sharks. Additionally, it mentions the ecological role of sharks and the need for conservation efforts to protect both tiger sharks and great white sharks. The article concludes by providing statistics on shark incidents and emphasizing that the likelihood of encountering a shark is relatively low compared to other risks, such as lightning strikes or mosquito-borne diseases.
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