Thanks to mainstream media (and a steady stream of shark horror movies) sharks loom large and menacingly as monsters of the deep in the public’s imagination. But new research from an Australian university shows that, much like humans, sharks have friends.
Macquarie University associate professor of biological sciences Culum Brown used acoustic tagging and underwater receivers to study the behavior of sharks in Jervis Bay on the south coast of New South Wales. The Lighthouse, Macquarie University’s online news platform, published his findings.
In a world-first at the Macquarie University Fish Lab, researchers have discovered that Port Jackson sharks like to spend time with other sharks of the same sex and size, sometimes in relationships that last for years. In other words, females have friendships with other females, males with males, and juvenile sharks don’t mix with the grown-ups.
“A lot of it comes down to having similar likes and preferences,” explains Brown. “Human children don’t like to hang out with the oldies because oldies are kind of boring and don’t do anything that children are very interested in, so it’s almost certainly similar in the animal world.”
Studying shark relationships
Brown and his team used acoustic tagging and underwater receivers to record the sharks’ interactions. Afterward they applied social-network analysis to discover that, far from random associations, the Port Jacksons were preferentially hanging out with particular individuals that were similar to themselves.
Such friendships are good for survival, says Brown. Groups of familiar individuals who can predict each other’s behavior are better at foraging for food and staying safe from predators.
“When most people think of sharks they think of mindless killers that are loners,” says Brown. “Nothing could be further from the truth.”
There are hundreds of thousands of Port Jackson sharks down the east coast of Australia from the NSW-Queensland border and around the southern coastline to Perth. In Jervis Bay, where the Fish Lab tags sharks, about 10,000 of them gather during the winter breeding season. Despite an epic 620-mile (1,000 km) migration to Tasmania and back, they return every year to the exact same reefs to reproduce. Macquarie researchers discovered this behavior, never before reported in a shark species.
“Port Jacksons are very, very common, if not the most common shark in Australian waters,” says Brown. “And until we started working on them six years ago we knew almost nothing about them.”
“The thing that struck us was this really high fidelity to these breeding reefs and we thought if they’re doing that, then they must be hanging out with the same animals year after year,” he adds.
“And they are very long lived — a Port Jackson shark doesn’t mature until it’s in its teens, and probably lives more than 50 years. It appeared to us that all the conditions were right for pretty complex social interactions and it turns out that’s true.”
Nothing to fear
It’s also true the distinctive-looking sharks are nothing to fear, says Brown. They are small — the females grow to a maximum of 5 feet (1.5 m), males to 4.2 feet (1.3 m) — and their teeth are for crushing, not tearing. In handling thousands of them over six years, sharks have bitten Brown only twice, and the worst of those was just “a bit of a hickey.”
An earlier Macquarie-led study, published last year, found that Port Jackson sharks have individual personalities. Researchers established this through behavioral tests that exposed the sharks to an uncertain new environment and the stress of human handling. The study noted their level of boldness in the first test and their recovery time in the second. Over repeated trials, researchers observed consistent and distinct responses in individual sharks.
Now, with those personality scores at hand, and through continually recording their underwater interactions, Brown says the next couple of years should produce enough data to determine if the sharks are associating based on personality. Such a finding would further “humanize” an animal with a terrible reputation, and Brown would be happy with that.
“There are far more similarities than differences between animals,” he says. “Not long ago you would have been kicked out of class for trying to humanize an animal, but there’s really been a dramatic shift in attitudes among scientists in the past 10 years; in the past year or two it’s gone berserk.
“One of the things I try and do is impress upon people that animals are really deserving of our respect. I’m not saying they should get the vote but at the very least treat them well and minimize harm. Think about the world from their perspective whenever you’re interacting with them.”
