Part 4 - The Scientists
By Angie Davis
Understanding the Apex – the science
If there’s one thing that the sudden increase of shark incidents along the east coast of Australia has taught us it is that the wider public know very little about White Sharks. What science tells us is there are 510 species of shark worldwide, and 182 of these sharks have been found in Australian waters.
According to Physical Oceanographer and Byron Bay local Malia Rouillon, “the types of sharks implicated in the majority of unprovoked attacks on humans in Australian waters are the White Shark (Carcharodon Carcharias), Tiger Shark (Galeocerdo Cuvier) and the Bull Shark (Carcharhinus Leucas)”, accounting for 96 per cent of fatal shark attacks in Australia. “Given that Australia is well known for its beach culture, with 35,000km of coast, containing an estimated 11,900 beaches…it is not surprising that it has a relatively high rate of shark attacks,” said Rouillon.
Kent Stannard, founder of Tag for Life, recognized the potential threat for increased interaction between sharks and humans over 15 years ago. Talking with his friend, Australian surfing legend Wayne Lynch, the two identified that there were more people using the water, surfers were moving further afield exploring newer and more remote locations, and that chances of shark attacks on humans would subsequently increase. Tag for Life has been a mechanism that has helped fund and facilitate scientific research into White Sharks particularly with Barry Bruce, Australia’s preeminent White Shark scientist, and the CSIRO. Stannard had the network and ability to support the science and is passionate about it being distributed. “The purpose of science is to uncover the truth, and get the truth to the public.”
“White Sharks were protected back in the 80s as a result of their numbers being severely depleted through commercial and recreational fishing activities, so it’s highly probably that their population is now increasing, combined with an increase in the populations of their prey species.”
Barry, Kent and their teams have identified the cold waters around the eastern Bass Strait area, which is highly rich in essential nutrients, as the birthplace and pupping ground of White Sharks. They tend to spend the first season of their life here, before migrating north to the warmer waters of Port Stephens for the next five to six years.
“The pups are between 1.2 to 1.5 metres in length, look identical to the parent and are left to fend for themselves. During this juvenile phase they are feeding inner shore on fish and ray species and do regular excursions out to the edge of the continental shelf before returning to inner shore waters.”
According to Stannard, the sharks will spend about 75 days around the beaches south and north of Port Stephens from late winter through to late spring, before heading back to eastern Bass Strait over the summer to autumn months. There has never been an attack on these beaches despite the presence of swimmers and surfers.
“White Sharks are migratory animals, constantly on the move, moving with food sources. The environment has shifted in a way that has become favourable for White Sharks to be there on the north east coast now.”
The tagging program’s results suggest that there has been a drop in the number of juvenile sharks in the Port Stephens area, poising the question: “have they moved north?” In their next stage of life being sub-adulthood, these sharks would be around 3.4 to 4 metres in length, which is consistent with the estimated size of sharks being observed around the Ballina/Byron Bay area. “These sharks extend their range of migration up and down the eastern seaboard of Australia from the southern Barrier Reef down through Bass Strait. This would require vast amounts of energy expenditure and as a result their meal requirements become greater, they become more opportunistic and begin to add other species to their diet, including energy-rich sources such as seals, dolphins and whales.”
“You are experiencing warmer sea temperatures in the Northern Rivers areas at the moment, unusually high for the winter months. The East Australian Current (EAC) appears to be hugging tighter to the coast…and with it prey and predatory species.”
Rouillon believes that the recent increase in shark activity is based around the “hungry shark” theory. “ The recent shark attacks and encounters are focussed around the two lunar cycles after the first whales have made their migration. White Sharks are not feeding constantly. Their liver is like a battery and allows them to go weeks and months without eating.” The El nino effect has led to a later migration than usual of the whales, meaning they are more clustered together, resulting in less feeding opportunities for some of the White Sharks during a key stage of their feeding cycle, “therefore a small amount of hungry sharks have been getting desperate and peaked up to feed on the full moon. This has resulted in more negative shark encounters in the region.”
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