By Emma Young
Naturalist David Attenborough has used his TV series Blue Planet II, now showing in Australia, to feature the role West Australian tiger sharks play in the fight against climate change.
It has been 16 years since Sir David Attenborough's Blue Planet and now the sequel, filmed over four years in 39 countries using cutting-edge technology — in some cases being tested on the spot — was hailed Britain's top-rating show in 2017.
Producers, along with local crew members, spent weeks filming in Shark Bay, WA, for the Green Seas episode that alone took 664 hours of diving.
The episode now aired and still available online reveals a hidden side of WA, a vast prairie of seagrass where tiger sharks and green turtles play a ceaseless game of cat-and-mouse.
Producers had searched the world for a place with a seagrass meadow ecosystem sufficiently impressive to get the blue-chip footage necessary to air the segment, allowing Attenborough to tell a wider story.
“In the sundrenched shallows of Australia, kelp is replaced by the sea’s only flowering plant: seagrass,” Attenborough’s signature voice-over said.
“The most extensive of these marine grasslands can stretch for over 8000 square kilometres.
“All across the tropics they are patrolled by tiger sharks. They can grow up to 5 metres in length, and have powerful, crushing jaws.
“Green turtles are their prey. The turtles feed almost entirely on seagrass. A single one can consume up to 2 kilograms of it in a day. But they can never rest easy.”
Healthy turtles would keep well away from an approaching shark, Attenborough said. And just by keeping the turtles on the move, the sharks prevented any one patch of seagrass from being overgrazed.
“That has benefits for us all,” Attenborough said. “A patch of seagrass can absorb and store 35 times as much carbon dioxide as the same area of rainforest. So the prairies and their sharks are surprising allies in the fight against a warming climate.”
Sir David Attenborough in filming for Blue Planet II.
Jessica Meeuwig, director of the Centre for Marine Futures at the University of Western Australia, said the science was “absolutely correct” and seagrass beds could be thought of as carbon credits on a huge scale.
They used sunlight to take carbon from the atmosphere and stored it in their tissues, preventing it from driving climate change.
“So while the oil and gas industries need to limit carbon going into the atmosphere, it can also actually be sucked out of the atmosphere,” Professor Meeuwig said.
“Crucial to seagrass health is the presence of predators like tiger sharks, so we need to protect shark populations in two ways. First, via no-take marine parks and second by managing the increasingly popular activity of shore-based trophy fishing for sharks.”
Professor Meeuwig said science showed that tiger sharks had small chance of surviving the flood of stress hormones caused by being caught, reeled in and photographed, even if they appeared to swim off initially after being released.
“We know they can’t handle stress,” she said. “If the shark is lying placidly while you take a selfie, it’s not a happy shark. These are the very animals vital to the survival of the ecosystems providing the economic benefit of carbon storage. The more we slow the build-up of carbon, the more we slow this terrible journey we’re on to heating our planet.
“Targeting large animals for sport, when they are so important to ecosystem health, seems to be rather short-sighted. These hunters are not catching them to eat.”
Blue Planet II executive producer James Honeyborne said in a statement on the series’ release that the team had witnessed great changes under the water since the release of Blue Planet I, with water warming, coral bleaching and mountains of plastic altering natural systems and harming marine life.
“The health of our ocean is under threat,” he said.
“Never has there been a more crucial time to explore our remotest seas, and to examine what the future might hold for our blue planet.”
Blue Planet II is now showing on Channel 9. The full Green Seas episode is available to watch here.