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Image 1 for The world’s biggest tiger sharks reside at Norfolk Island – why is that?

Jack Entwistle and mate surfing Norfolk Island – from an article in PLB some years ago, with photos by Zach Saunders.

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The world’s biggest tiger sharks reside at Norfolk Island – why is that?

11 July 24


“You need something special to be able to sustain that many large sharks.” Scientists are trying to figure it out – as reported by Perth Now:

Australia’s Norfolk Island baffles scientists with tiger sharks reaching greatest lengths on Earth

Baffled scientists are on a mission to discover why Australia’s remote Norfolk Island has become a breeding ground for the world’s largest tiger sharks.

Biologists Charlie Huveneers, Lauren Meyer, and Adam Barnett visited the South Pacific island to discover why the ferocious creatures had become so prosperous in the region, with their population density also topping the charts.

“This was the most tiger sharks we had ever caught in one day and they were the biggest males and biggest females we had ever seen,” Dr Meyer told National Geographic.

Related to the great white and typically measuring nine feet (2.7m), Norfolk Island’s striped visitors often reach the terrifying lengths of 15 feet (4.6m).

Though despite the mammoth creatures lurking beneath, corners of the island did offer sanctuaries for swimmers to snorkel and frolic without the threat of being eaten.

The scientists’ venture to channels brimming with the creatures was fuelled as much by conservation pressure as their hopes of identifying what made the predators unique.

Tiger sharks are known to be near-threatened by extinction largely due to excessive fishing.

Noting the island’s history as a penal colony and cattle ranch, Dr Meyer had a theory that the species had been dining at the “drive-through hamburger joint” due to the dumping of internal organs off the coast.

“You need something special to be able to sustain that many large sharks,” Professor Huveneers said of the sharks’ diet.

A study of various elements suggested only 10 per cent of what they consumed could be attributed to cows, which came as a surprise.

Shockingly, their results suggested a staggering 52 per cent of the species’ diet was sea birds — describing the cattle waste, known as offal, as just “a bit of dessert”.

It turned out, Norfolk Island’s coastline menu was more KFC than McDonald’s.

The wedge-tailed shearwater is a type of seabird known to descend upon the island in the tens of thousands, which researchers deemed easy prey for sharks feeding at a particular time of day.

“That seabird rafting behaviour at dusk is the perfect opportunity for sharks to come up and use their big, flat noses to suction these birds off the surface,” Dr Meyer said.

Surprisingly, the shark species was found to frequent the coastline only five months a year when there was no shortage in food to sustain them across every season.

While further data showed some evidence the creatures used Norfolk Island as a breeding ground before fleeing to the safer waters of New Caledonia to give birth, their attraction to the remote dwelling remained largely unsolved.

“We’re getting closer to the answer, but it’s certainly not a slam dunk,” Professor Huveneers said.

- AUTHOR: ZACH MARGOLIUS

- SOURCE:   PERTH NOW

-  ORIGINAL ARTICLE HERE



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