The Great Australian Bight and Great White Shark cage divers – Cosmos

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Cosmos » Nature » The Great Australian Bight is in better shape than we thought, which is good news for the Great White Shark cage divers
Imma Perfetto
For many years the southern half of the Australian continent, unimaginatively named “the Great Australian Bight,” has captured little attention, and has not been known for marine science. But a greater focus has been placed on the region, partly due to the suggestions over the years that it might be rich in deep sea oil, as well as its whale population.
It is now much better understood, and this week two papers reveal it’s in good shape.
The Neptune Islands, off the Eyre Peninsula at the eastern most point of the GAB, in South Australia, is one of only few places in the world (and the only one in Australia) where people can cage dive with great white sharks.
New research says human activity has not deterred the great whites from the area.
The effect of great white (Carcharodon carcharias) cage-diving tourism on shark residency has been tracked over  two decades with data collected by tour operators and eight years of independent scientific monitoring and research.
Professor Charlie Huveneers, Director of Flinders University Marine and Coastal Research Consortium and leader of the Southern Shark Ecology Group, says that shark residency increased in the late 2000s at the same time as a rise in cage-diving activity.
“White shark residency has returned and remained at baseline levels since 2013, showing that adequate regulations and good industry practices can minimise impacts on white sharks and ensure long-term sustainable wildlife tourism,” says Huveneers, who is a senior author on the paper.
Deputy Premier and Minister for Climate, Environment and Water Susan Close says the State Government is committed to ongoing research to continually improve understanding of the effect of great white shark tourism on the sharks themselves.
“These businesses and their commitment to sustainable management of shark cage diving have established Port Lincoln and the Eyre Peninsula as the premier destination for this activity,” she says.
“White shark cage diving is a unique eco-tourism experience where you can get up close and personal with the largest predatory fish on the planet.”
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Only a stone’s throw away in the Great Australian Bight, researchers have taken another step towards understanding the region’s vast marine food web.
They have described how the ocean’s tiniest plants, called pico- and nano-phytoplankton, underpin the stock of macroscopic zooplankton species – floating or weakly swimming aquatic animals that rely on water currents to move any great distance – that make up the base of many marine food webs.
“Every drop of seawater contains thousands of individual plankton,” says Dr Mark Doubell, an oceanographer from SARDI, and co-author of the new study in Oceanologia.
“The analysis of over 10 years of water samples undertaken in this study has deepened our knowledge of the composition of the planktonic ecosystems which are fundamental to the health and productivity of our marine ecosystems and the fisheries they support.”
The GAB supports a diversity of species ranging from extensive seagrass beds and kelp forests to the strange leafy seadragon (Phycodurus eques), and the immense blue whale (Balaenoptera musculus).
Before now it was generally understood that the Bight is very low in plankton biomass, except for during summer when the nutrient supply by upwelled ocean currents triggers phytoplankton (also known as microalgae) blooms.
But by undertaking a comprehensive study of the plankton variability in the eastern Great Australian Bight, the team discovered that, actually, the region produces enough smaller types of phytoplankton year-round to underpin a relatively stable stock of zooplankton.
“Our findings bust the myth of the Bight as an oligotrophic (deficiency of plant nutrients) ocean,” says co-author Jochen Kaempf, oceanographer and associate professor in the College of Science and Engineering at Flinders.
“Instead, the findings point to a year-round supply of nutrients fuelling the marine food web, most likely related to a high degree of nutrient recycling of the region.”

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Originally published by Cosmos as The Great Australian Bight is in better shape than we thought, which is good news for the Great White Shark cage divers
Imma Perfetto is a science journalist at Cosmos. She has a Bachelor of Science with Honours in Science Communication from the University of Adelaide.
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