Australia wipes out distinct tiger shark population before it was discovered

·Environment Editor
·3-min read

Australia wiped out a genetically distinct population of tiger sharks before it was even known they existed, new research indicates.

DNA samples from 1910 to 1960 show the sharks were flourishing on the east coast, and still existed in the wild through the 1990s.

By 2000, evidence of their presence disappears.

Two images of tiger sharks side by side.
Because tiger sharks (galeocerdo cuvier) migrate, discovery of the genetically distinct population came as a surprise. Source: Getty (File)

Speaking with Yahoo News Australia on Monday night, lead author Dr Alice Manuzzi from the Technical University of Denmark said the decline appears to coincide with two factors:

  • Introduction of shark control programs

  • Increases in commercial shark fishing

“Localised depletions of tiger sharks could be more common than we anticipated,” she said in an earlier statement.

“We should consider localised protection measures, such as local seasonal closures or marine reserves to properly match the geographic scale of the population.”

Conservationists warn tiger sharks threatened by government policy

Dr Manuzzi’s call for better shark conservation was echoed by campaigners calling for an end to shark net programs in Queensland and NSW.

Australian Marine Conservation Society (AMCS) and Humane Society International (HSI) are currently investigating whether they can nominate tiger sharks as a threatened species.

A 2019 study found the species' numbers had declined by 71 per cent in just 33 years across Australia's east coast.

A Sea World rescuer watches a whale that was tangled in drumlines.
A whale became entangled in shark nets off Surfers Paradise on Thursday. Source: Sea World

AMCS shark expert Dr Leonardo Guida characterised the study’s results as a “canary in the coal mine”, adding an urgent tiger shark population count and independent fishing monitoring are needed.

“Tiger sharks are caught incidentally in the commercial fisheries of New South Wales and Queensland and are kept for their meat and fins,” he said.

“In Australia, their numbers are declining and fishing rules specific to this species are sorely needed.”

HSI marine biologist Lawrence Chlebeck called for a modernisation of Australia's "uselessly destructive" shark control mechanisms, which are known to also kill dolphins, sea turtles and whales.

"These programs contribute to the ongoing decline in tiger sharks on Australia’s east coast," he said.

"This species is vital to the health of delicate marine ecosystems, including the Great Barrier Reef."

Tiger shark population find came as a 'surprise' to researchers

Maintaining complex genetics is essential to ensuring species are able to remain healthy when stressed by environmental changes. This can include climate change, hunting and disease.

A list of facts about sharks next to an image of a grey nurse shark.
Source: Yahoo / Getty

Dr Manuzzi told Yahoo News Australia the discovery of the distinct tiger shark population was a “surprise”.

Her team, which included researchers from the University of the Sunshine Coast were able to access historical samples of shark tissue, by delicately drilling into museum specimens.

Because large predators like tiger sharks migrate, it was not thought they would be cross-breeding with individuals.

While it's unclear whether this new “southern population” which existed as far south as Victoria was visually different, they are believed to have been more residential in behaviour.

“We assumed they’re big enough, they move enough, that we thought fishing was not affecting keeping the population healthy,” Dr Manuzzi said.

“But actually with this study, we can see that that's not true.

“Even sharks, like the tiger shark, and many other migratory sharks that move a lot can actually be affected in a short timeframe.”

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