Why we need sharks and sharks need us
A MARINE research scientist who has been tracking sharks in Sunshine Coast waters for the past 10 years says we can't live without them.
Dr Jodie Haig works with Ocean and Coast Research has helped tag and track 80 bull sharks to three metres in length since 2006 and has observed their passage between waterways on the Sunshine Coast and those on the Gold Coast.
Her team are now working through the data but what is already apparent is bull sharks require as part of their life cycle access to freshwater systems to have their pups.
An absence of access would ultimately shut down the animals' reproductive cycles but also have other devastating consequences.
As the top predator they play an important role keeping ecosystems healthy, picking off weak crustaceans and fish and in the process weeding out the bottom of the gene pool.
"They pick off weak animals ensuring only strong genes are passed on," Dr Haig said.
"That's how natural selection works.
"As they move to sea they have the same effect.
"They form an important part of the system and keep dolphin, turtle and fish populations healthy."
But more data and information is needed to understand when and why they are likely to use the same areas of beach as humans.
"We have to share it (the marine environment)," Dr Haig said.
"People need to be educated to know when and where to go for safe swimming conditions."
She said detailed study was necessary to understand the recent prevalence of sharks biting surfers in a concentrated area between Byron Bay and Ballina.
The area is a migratory corridor for white sharks and the East Australia current. Whales head north each year to breed and then return south with their pups with sharks following that migration.
"The more animals we tag and follow the better idea we will have of when they are passing through and why," Dr Haig said.
"Without data there can only be speculation.
"People acting out in fear is not in the best interest of themselves and the animals. We need to act on knowledge.
"I agree with the position that humans come first. That attitude is understandable.
"But for biodiversity we need to retain top predators to keep the ocean healthy. We rely on it as much as they do."
Dr Haig said she had not seen a single piece of evidence shark numbers were increasing.
There's a reason, she said, they are on the protected species list.
To better understand what is happening on the NSW north coast it would be necessary for scientists to pool data from a range of sources.
She said shark numbers at Ballina were a concentration of the animals in one place for a specific reason rather than a sign numbers overall were increasing.
Habitat loss, fishing, pollution, shifts in current and temperature and climate change can all be factors.
"Sharks have a home range which is the area they spend their life," Dr Haig said.
They move about depending on their species and can cover the whole of the Coral Sea.
"I've tracked tigers and large dusky whalers that travel great distances between the Barrier Reef and the Coral Sea," she said.
"They can aggregate in a hot spot for a short period for a specific reason whether that be for prey or to breed.
"I've seen them off Fraser Island in number when turtles were hatching. Then they move on. They live over a wide area.
"It's big stuff that needs large scale research into management."