Rapid disappearance of large sharks causes ‘ripple effect’ in waters off Queensland

Queensland is known for its big things. It's got the Great Barrier Reef, the Big Pineapple, massive crocodiles, and we should probably also acknowledge Bob Katter's impressive white 10-gallon hat. But when it comes to the size of its sharks, there's bad news.

As shark numbers decline, the diversity of species is also changing for the worse. Records of large apex predators like those seen in the horror movie Jaws are decreasing. And large examples of individual members of species are also becoming rare.

"The average length of species caught is decreasing. So we're catching the smaller species now, as opposed to the bigger species that we used to catch in the past," shark expert Dr Chris Henderson told Yahoo News.

"In the early days we used to catch a whole range of different sharks, but now what we're catching are species that are quite similar."

Related: Beachgoers stunned over fisherman's 'distressing' act with shark

His findings have been outlined in new research from University of Sunshine Coast which used data collected from the Queensland government's shark control program which has been in operation since 1962 and has covered 1,760 km of coastline.

Why are we seeing fewer large sharks?

The research has been published in the journal Communications Biology, and the problem has been linked to domestic and international overfishing, habitat loss and climate change.

The focus of the paper was on a loss of diversity in Queensland waters over the past 60 years. And Henderson believes the problem is having a "ripple effect" and impacting other species lower on the food chain.

"The things we're catching are more reef sharks, smaller bodied sharks that feed mostly on fish. They're not feeding on other sharks, or seals. And by losing the animals that do, we're losing their function in the ecosystem," Henderson said.

Although the research focused on Queensland waters, Henderson believes it's likely other states may also be experiencing similar declines in shark diversity.

"In Australia, and even more broadly, the species that we used to catch on average were much bigger than the species we catch now," Henderson said.

"The paper shows great whites are declining, whalers are declining. And there's other papers that have shown similar things."

Queensland shark net controversies

• Queensland bureaucrats accused of ‘sanitising’ bloody act against shark

• Horror find on Queensland beach leads to call for government rethink

• Dolphins, dugongs and turtles caught in Queensland shark nets

'Ripple effect' of human attacks on sharks revealed

While overfishing is Henderson's biggest concern, he believes there's another factor that is specifically impacting sharks in Queensland waters — the state government's shark control efforts.

The controversial program hires contractors to target and destroy species the government fears could harm beachgoers, including whalers, tigers and great whites.

Because many target species are already in decline, Henderson has urged Queensland authorities to transition away from netting beaches.

“This aim of the [shark control] program is to remove large sharks from the coast to improve swimmer safety, but this has significant impacts on the health of our oceans,” he said.

Politicians call for removal of shark nets after whale trapped

Hours after Henderson's warning about the impact of nets on sharks, the Greens called for an urgent review into what it described as Queensland's "archaic system" of shark control.

This followed conformation that a humpback whale had become entangled in a net off the Sunshine Coast. Unlike NSW, which removes its nets during migration season, Queensland opts to keep them in the water, and this regularly results in high numbers of whale entanglements.

“While the whale has been released, there’s no guarantee it will survive, as the stress of getting tangled can use enormous energy that the whale needs to make its migration journey," Senator Larissa Waters said before noting that since the nets were introduced, 85,000 marine animals including sharks, turtles and dolphins have been killed.

Her colleague Senator Peter Whish-Wilson urged the Federal Government to remove exemptions which allow the Queensland government to use the nets even though they kill endangered species.

“Shark nets are not effective at removing the risk of shark bites to humans," he said.

"Solutions exist that modernise beach safety standards and don’t harm wildlife, yet every year these outdated walls of death cause unacceptable pain and suffering to marine animals."

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