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Bremer Bay Canyon Orcas

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I was fascinated to learn about this remarkable biodiversity hotspot in the Southern Ocean.

Bremer Bay

Bremer Bay

Bremer Bay Canyon lies 70 kilometres off the south coast of Western Australia. The closest town is the small coastal settlement of Bremer Bay, some 180 kilometres east of Albany. You could be forgiven for wondering what the significance of the canyon is, and why tourists and researchers are drawn to such a remote location.

The answer, in short, is that the canyon is a biodiversity hotspot which attracts a range of large marine species during a six-to-eight-week period each year. Bremer Bay Canyon was only recently discovered and is not yet fully understood.

Great White Shark

Great White Shark

How Was The Canyon Discovered?

In 2013, film makers David Riggs and Leighton De Barros started a venture to discover what had happened to a tagged 3-metre-long Great White Shark. Great Whites, also known as White Pointers, are responsible for most shark related injuries and deaths in Australia, and probably throughout the world. They are top predators with numerous rows of sharp teeth and are known to eat seals, as well as fish.

Shark tagging is used to learn about the behavioural patterns of marine species and their movements. There are several types of tracking device used. In this instance, data was transmitted to satellite from the 3-metre shark. After three months, the tracking device surfaced. Initial data was incomplete as the battery ran out of charge soon afterwards. Remarkably, the tracking device was later found on a beach not far from where the shark had been tagged. The finder sent the recovered tag to CSIRO where the full data set was downloaded.

Apart from the immense distances the shark had swum since being tagged, there were some interesting anomalies found in both the data, and the tag itself. When found, the tag was white and completely clean. This was unusual – any item that has been in sea water for an extended period would usually be covered with algae. In addition, the data showed that the shark had been in an environment with a temperature of 27 Celsius in water of depths of over 500 metres. This data suggested that the shark had been eaten, and the location where this had happened was pin pointed. The question was, what type of animal, and of what size, would be capable of killing and eating a 3-metre-long shark?

Map of Bremer Bay Marine Park

Map of Bremer Bay Marine Park

The search led them to an area of the ocean which had previously been noted as having an abundance of marine life. Species include Orcas, Sperm Whales, Long Finned Pilot Whales, Great White Sharks and other dolphin and shark species as well as many sea birds including albatross.

Why this area exists, and the reasons it is so abundant in marine life at a particular time each year is not yet fully understood. Exploratory work by oil and gas companies indicates that the area is rich in fossil fuels, and that a series of canyons, up to 5000 metres in depth, exist on the edge of the continental shelf and beneath the ocean.

Leeuwin Current

Leeuwin Current

Ocean movement around Western Australia is largely due to the Leeuwin Current, which flows from northern Western Australia southwards. Toward the end of summer, this current slows which allows cold water from Antarctica to fill the canyon. The stream of cold-water releases hydrocarbons from the fossil fuels deep beneath the water and brings them to the surface. This creates a nutrient rich environment which draws marine life to the area. Phytoplankton thrive and grow, and gases are released into the water. The abundance of food promotes growth of many species including squid which grow to massive proportions, as well as crabs and other crustaceans. This in turn attracts pelagic fish and larger marine species including whales and orcas.

Sperm whales migrate through the area, the bulls diving deep beneath the surface to catch giant squid weighing up to 400 kg. As the whale surfaces with its catch, other species approach, keen to have their share of the feast.

The area has been made a marine park for protection and conservation. Researchers are still studying the area and working toward a greater understanding of this unique ecosystem. Tours operate from Albany and Bremer Bay, taking boatloads of enthusiasts out to the edge of the continental shelf where they are captivated by the sight of orcas, whales and sea birds.

Oh, and the answer to that other question – the 3 metre Great White shark was most likely eaten by a larger shark of the same species.

© 2021 Nan Hewitt

Comments

Nan Hewitt (author) from Albany, Western Australia on March 22, 2021:

Yes, I would have thought Orca's might be capable, but there are some very large White Pointers - up to 6 metres in length.

John Hansen from Gondwana Land on March 22, 2021:

A very interesting article, Nan. I was hoping that you would let us know the fate of the shark by the end. I thought maybe Orcas were capable of eating Great White Sharks, but yes, most likely a bigger shark was responsible.

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