Missions reveal secrets of Bremer killing zone

Angela Pownall
Passengers help with the Bremer Bay research into killer whales. Picture: David Riggs.

After trawling through 200 hours of footage from WA's Southern Ocean, researchers are learning more about a unique gathering of killer whales for only a few weeks every year.

Up to 150 orcas congregate off Bremer Bay every February and March in what could be the biggest seasonal aggregation of killer whales in the southern hemisphere.

After the first series of expeditions to the marine hotspot this year, Esperance filmmaker David Riggs said the underwater and surface vision was revealing.

"The killer whales were consistently predating oceanic sunfish, which can get up to 1600 kilos, which is impressive because their diet is primarily blue bottles and jellyfish," he said.

But other groups of killer whales in the aggregation targeted other species.

"One group of 20 or so were seen to tag-team on a grey's beaked whale, following it as it attempted to dive, then ramming it, causing it to eventually drown," he said.

"The killer whales were also targeting surfacing sperm whales, remaining silent as they surfaced, then rapidly approaching and attempting to steal their quarry of giant squid."

Underwater cameras captured more action below the surface.

"Dozens of sharks, both whaler sharks and oceanic blues, along with hundreds of 6-8kg bluefin tuna consistently accompany the killer whales as they patrol throughout the hotspot, opportunistically feeding on scraps from the killer whales' latest feast," Mr Riggs said.

Mr Riggs has watched the spectacle 70km offshore yearly for the past nine years for his research and last year took marine scientists and made a documentary.

He came across the hotspot when investigating the fate of a 3m tagged great white shark that mysteriously disappeared.

Its tag, which washed up on a WA beach, revealed it dived suddenly from the surface to 580m, where its temperature shot up, indicating it was eaten.

There will be expeditions to the "hotspot" in February and March when passengers will be asked to observe and film the activity to contribute to the research.

For information about the tours by Naturaliste Charters, go to whales-australia.com.au/bremer-killer-whales.