Secrets of the orcas
A stretch of ocean off Western Australia consistently attracts the largest known aggregation of killer whales in the Southern Hemisphere. But what lures them, and other large marine creatures, to the pinprick in the vastness remains a mystery.
A stretch of ocean off Western Australia attracts the largest known aggregation of killer whales in the Southern Hemisphere.
TATTY, EL NOTCHO, A380, Isosceles. These are the names given to the killer whales of Western Australia’s little-known Bremer Canyon. Found 65km out from a remote stretch of coastline 500km south-east of Perth, each year this deep-sea cleft becomes a temporary home to the largest known group of killer whales in the Southern Hemisphere. Exactly why, where they come from – and where they go to next – are as yet all unknowns. The comical monikers relate to their dorsal fin characteristics or body size, and reveal the attachment that visiting scientists, researchers and boat crew have developed for the ephemeral population of more than 100 orca, which appears seemingly from nowhere each January and lingers until mid-April.
Daily expeditions by Naturaliste Charters, and David Riggs, the Esperance-raised documentary filmmaker they’ve teamed up with, have been set up to uncover these baffling unknowns. Numerous scientists, some of whom join the voyages for months at a time, have also been recruited to help.
David began researching this biodiversity hotspot near the edge of the continental shelf in 2003. Two years later, he noticed an uncanny aggregation of killer whales in the same area, and began looking into marine activity in the Bremer Canyon for a documentary.
Experts believe pressurised hydrocarbon systems beneath the sea floor are leaking methane gas, fuelling an ecosystem of bacteria that uses methane as an energy source. Other organisms, such as phytoplankton, crustaceans and squid, feed on the bacteria, and, in turn, attract larger marine life – from giant squid to sperm whales, blue sharks, great whites, sunfish and eagle rays – which make attractive prey for killer whales.
Deep-sea life has been attributed to hydrocarbon sources at numerous sites around the world, but further research is needed to prove its occurrence at Bremer. With plans in place to send investigative equipment down to the sea floor, David is hopeful that it’s only a matter of time. What he can say with certainty is that, of 36 canyon systems along WA’s south coast, this is the only one known to have such intense activity. And most of it occurs within a tiny zone, only 8km across.
But why isn’t it there all year round? David and Norwegian scientist Martin Hovland believe that the warm Leeuwin Current, which sweeps around the far south-western corner of Australia, seasonally suppresses or distributes rising nutrients.
“Picture a tree waving in the breeze,” David says. “When summer comes around, you get a south-easterly change and that pulls the Leeuwin Current up, like a big bubble of water.”
Although a 2013 documentary shone a light on the wonders of Bremer Canyon, David fears that deep-sea petroleum mining may eventually occur in the area, depressurising the hydrocarbon,
causing the food source to evaporate and altering the ecosystem forever. For now, existing exploration permits have been cancelled and, in early 2016, both state and federal politicians met with David to assess the area’s attributes. For David, the creation of a marine park isn’t enough; he wants an oil and gas exclusion zone to be established.“There’s never been any suggestion of this place being afforded proper protection,” he says.
One way David and his partners hope to gain support for the canyon is by taking visitors to see the killer whales, using part of their fares to fund research by onboard scientists, and asking spectators to contribute photos and videos to an online database.
ABOARDTHE CETACEAN EXPLORER, we journey away from Bremer Bay’s sleepy harbour under a cloudless sky. We soon spot common dolphins shooting through the surface of the water like skimming stones. It’s a calm day, but a large swell still causes the boat to climb, rattle and slap its way through the sea. Most of the visitors are out on deck, inhaling sea air and staring at the horizon. Many are queasy but no-one is ill; according to the crew, a common experience is raging waters, a 4m swell, stinging spray from high winds and across-the-board seasickness.
Seated in the sunshine, we watch a black-browed albatross sweep over our wake like a slow-motion pendulum. It glides in wide arcs, the tip of its black-and-white wing all but kissing the water as it changes tack.
We power out to the 5000m-deep canyon’s edge, losing sight of land save for a giant sand dune. The skipper lets the engines idle and all eyes search for ‘the blow’, a puff of vapour exhaled by a killer whale seconds before it surfaces, closely followed by that unmistakeable black fin.
We’re also told to look for clusters of seabirds dog-fighting above the water. “The orcas are messy eaters,” says skipper Mal Bush. “It’s like when we eat a taco, only with no hands.” The birds eagerly scoop up the fishy debris.
As we scan the silky ocean, Rebecca Wellard from the Centre for Marine Science and Technology at Curtin University tinkers with aquatic audio equipment. She’s doing her PhD on the bioacoustics of Australian killer whales, observing their underwater whistles, burst pulse sounds and echolocation clicks. She then compares them with pods in Ningaloo Marine Park, others in the Northern Hemisphere and south to Antarctica. “I’m trying to see if populations in Australia have their own dialect,” she says.
After three years of field study, she’s noticed the whistles emitted in Bremer are similar to those elsewhere. But their burst pulse sounds seem to be more localised – something she
We spot dolphins shooting through the surface of the water like skimming stones.
hopes to pinpoint.“There are acoustic clans within the Northern Hemisphere. They can tell these clans, these family groups, by their different dialects,” she says.
“I also want to describe the Bremer population’s call repertoire. If we could understand what killer whales in Australia actually sound like, I can look at other noise loggers and see if these particular killer whales are moving in different parts of Australia. It’s a really non-invasive way of us tracking the animals.”
Interestingly, Rebecca has observed that the killer whales that come to Bremer Canyon don’t appear at Ningaloo Marine Park. “We have no idea where they go,” she says.
Rebecca, whose work has been supported by the AG Society, has a low-frequency noise logger to record sounds deep under water. Left for 12 months at a time, it reveals the Bremer Canyon’s soundscape: from pygmy blue whales (see AG 133) and dolphins, to southern right and humpback whales, and boat traffic.
During each expedition, Rebecca also deploys a handheld hydrophone over the side of the boat to listen in real time.When the boat is moving, a towed hydrophone array provides her with insights into what’s beneath.“On the back are three GoPro cameras, so I can get concurrent acoustic and visual behaviour,” she says.“It’s the first time it’s been done in Australia on killer whales.”
In this instance, there’s no other existing data with which to compare her findings; she’s at the scientific frontier. It’s exactly this – the mystery of the killer whale – that keeps her enthused. “We don’t know anything about them in Australia and they’re the apex predator, the king of the ocean,” she says.
The upside of rough days at sea is that the orcas tend to chase food more fiercely and breach more readily. By midday, we’re starting to worry that the biggest of the dolphin species is a no-show.Then, two triangular dorsal fins are spotted: bull killer whales.The boat turns, and a pod of six break the surface almost simultaneously, about 200m away.They trace an imaginary line, patrolling back and forth.
“They move frightfully fast,” says Mal.“They can keep up with you when you’re travelling 60km an hour. They’re smart and emotional, too.”
Over the next few hours, all within about 160ha, we come across numerous pods roving the sea. Most individuals keep their distance – about 50m away – but occasionally one or two inquisitive whales playfully approach, diving under the boat at the last second. Each instance delivers audible gasps from their human audience.
As we turn to leave, a false killer whale pod joins us, leading the boat, hugging its sides and chasing its wake. Smaller and grey, they may mimic their fiercer cousins, but they’re no match for the power and presence of the Bremer Canyon’s killer whales. FOLLOW Rebecca Wellard’s scientific field work on her facebook page: www.facebook.com/orcatalkoz