By Bianca Hall
There could be fewer than 500 adult breeding great white sharks across almost 60,000 kilometres of Australian coastline, a figure which challenges perceptions the number of white sharks is increasing.
A DNA study of Australia’s great white sharks – the first of its kind into the effective shark population across the continent – showed high levels of interrelation among white sharks on the east, west and southern coasts.
A great white off the Neptune Islands, Spencer Gulf, South Australia.Credit: Getty Images
Experts warn the high level of relatedness among juvenile and subadult Australian white sharks indicates a relatively small adult breeding population.
To conduct the groundbreaking research, scientists mapped the DNA of 650 great whites captured by the NSW shark management program, conducting biopsies and releasing them.
They identified 275 full siblings, and 511 half siblings, of great whites roaming along the east coast, and 12 full-sibling relationships and 29 half siblings in the southern oceans.
Since 2015, the NSW Department of Primary Industries has engaged in the largest shark-tracking project in the world; capturing, tagging and tracking more than 1300 great whites.
Researchers were able to show the sharks in both southern Australia, and the east coast, were closely related and migrated between regions.
They found the great whites tended to congregate in regions based on their life stages, with large subadults and adult sharks in southern waters, and juvenile and small subadult sharks predominating on the east coast.
The study – funded by the NSW Department of Primary Industries Shark Management Strategy and Deakin University – found there were probably fewer than 500 breeding great whites, from which the juveniles and subadult sharks had been born.
Despite this, researchers said, interactions between great whites and people could be increasing, with more people fishing, spear fishing and surfing in great white territories.
Friends, not food: a shark researcher swims with a great white off Oahu, Hawaii.Credit: AP
“Conservation management of white sharks in Australia is complicated by increasing frequencies of human-shark interactions, sometimes resulting in human casualties, leading to public demands for shark control and culling programs,” the study’s authors found.
“Considering our findings, localised threats should be considered a potential risk to the entire Australian white shark population rather than a single subpopulation.”
Over the past 10 years, there have been an average of 20 shark attacks causing injury each year in Australia, in which an average 2.8 people lost their lives each year.
Humane World for Animals marine biologist Lawrence Chlebeck said the data showed a public perception that great white shark numbers were increasing was not backed by evidence.
“Even though fishers frequently spot great white sharks, it’s important that people don’t misunderstand the drivers behind this,” he said.
“Fishers see sharks because sharks are attracted to their activities, and everyone hears about it more because of social media. However, evidence-based research like the population genetic study highlights how white sharks still desperately need protection.”
Based on the results, Humane World for Animals Australia and the Australian Marine Conservation Society called for an immediate halt to the culling of sharks.
Dr Leo Guida, shark campaign manager with the Australian Marine Conservation Society, said the findings were troubling.
“With fewer than 500 breeding adults, the loss of just one of breeding animal is a serious blow to the whole population,” he said.
“White sharks are vital for the health of the ocean. They occupy the top of the food web, keeping it in balance, and without healthy numbers of sharks, food webs can become unstable and potentially collapse.”
Great white sharks, which can live for 70 years, were listed as vulnerable to extinction in 1999, when shark-net data in NSW and Queensland indicated populations had fallen by up to 70 per cent since the 1950s.
However, Queensland’s program, established in 1962, has an exemption from the federal Environment Protection and Biodiversity Conservation Act because it was in operation before the protections were put in place.
A spokesman for NSW Primary Industries Minister Tara Moriarty said the state’s shark management program included a package of methods to alert and protect beachgoers including drones, shark nets and drum lines.
“The NSW government does not fund or operate any ‘shark culling program’,” he said.
“[Our] No.1 priority is the safety of beachgoers while seeking to protect sea life.”
Get to the heart of what’s happening with climate change and the environment. Sign up for our fortnightly Environment newsletter.