Scientist says shark numbers aren’t booming but they do love an international roadtrip

A spate of east coast attacks have bred fear of rapid growth in shark populations, however a Kiwi surfer and scientist says the numbers simply don't add up. 

• “The great white [shark] cannot reproduce as quickly as the narrative of population explosion suggests,” Riley Elliott, who has been tagging sharks in New Zealand since 2024, told the Mid North Coaster. 

Growing concern: A number of prominent politicians, including former prime minister Tony Abbott and Queensland MP Bob Katter, have called for shark culls in response to recent attacks.

• Last month a 35-year-old mother was pulled from between the flags at Coogee Beach in Sydney in a critical condition after a shark attack. 

Local incidents: In January, a 39-year-old surfer had his board bitten by a suspected bull shark at Point Plomer near Crescent Head, while a Swiss tourist was killed and her partner seriously injured in a shark attack at Crowdy Bay last November. 

Up-and-coming local surfer Kai McKenzie lost a leg in a great white attack near Port Macquarie in July 2024. 

Learning opportunity: Better known as the “Shark Man”, Riley Elliott has been studying the migratory patterns of great whites for years.

The results have been illuminating.

• “I've tagged 30 sharks down on Stewart Island, the bottom of New Zealand, and about a third of them go to east Australia and spend the entire winter there,” he said.

Joe’s journey: One tagged great white, named Joe, has a particular penchant for international travel.

“He went from Stewart Island down to the South Antarctic Islands, which is like 700 kilometres below New Zealand, halfway to Antarctica.”

Joe then travelled to NSW, before heading north to the Great Barrier Reef and eventually returning to the North Island of New Zealand. 

Are there more great whites?: While increased sightings anecdotally suggest that shark populations are booming, Elliott said the figures don’t reflect that. 

He said the effective population size for great whites, which is the number of adults that are breeding, remains around 270 in the Southwest Pacific, while around 50 a year are killed through shark nets, drumlines and fisheries bycatch.

What about bull sharks?: While great whites are highly migratory, bull sharks are a much more localised species.

Elliott says bull sharks can learn to associate boats or wharves with food, which can lead to increased numbers in specific areas. But that does not mean the population has rapidly expanded.

• “There's a big difference between observing more sharks and there actually being more sharks.
  
  “If there were just way more sharks and they just had blood on their mind, there'd be people getting bit every day, but there's not.”

Perfect storm: So, if numbers haven’t exploded, why are we getting more incidents?

Elliott said shark interactions often occur in “clusters” and are due to a number of variables, including the availability of prey, water temperature and water quality. 

• “You can create a perfect storm where you've got feeding sharks in murky water with people going surfing and flashing the white soles of their feet,” he said.
  
  “A cluster suggests a multitude of animals have probably gone to that area for the same reason.” 

What is the answer?: Elliott said the evidence is clear that shark nets and drumlines “don't give the fence protection that people think they do”, but is far more enthusiastic about NSW’s move to increase drone surveillance at beaches, including on the Mid North Coast.

He has rubbished calls for large-scale shark culling and argues for greater data gathering through ongoing tagging programs. 

Research has shown culling programs do not reduce the long term risk of shark attacks and have a negative impact on ecosystems. 

Sponsoring sharks: The movements of Elliott’s tagged sharks can be tracked on the Great White App, and the general public can sponsor a shark to support the work.

Click here for more information. 

Image credit: @thelifeofrileynz.