About four years ago, Colin Simpfendorfer was diving on reefs in Indonesia’s picture-perfect Raja Ampat region when he noticed the distinct absence of something.
“It’s a beautiful place to dive. We would have expected to see grey reef sharks and white tips,” says the veteran scientist. “But you don’t see sharks for days on end.”
Simpfendorfer, an adjunct professor at Queensland’s James Cook University and a global authority on sharks and rays, has been researching the marine animals since the mid-1980s.
Last week, a global team of shark researchers, including Simpfendorfer, found sharks and rays that live in the open ocean have been dwindling at an alarming rate.
Since 1970, a threefold increase in global fishing rates of sharks coincided with a 71% drop in their numbers around the world. Sharks are targeted by small and large fishing operations, for meat and other products, including shark fins.
“It’s quite devastating to see some of the outcomes,” says Simpfendorfer, reflecting on more than 30 years of study.
The team’s research, published in the journal Nature, involved the complex task of poring over data from fisheries authorities, scientific surveys, and peer-reviewed research to build the most comprehensive picture yet of the health of ocean-roaming sharks.
Many of the sharks are important to Australia’s coastal ecosystems, including great whites and the critically endangered scalloped hammerhead which, like other sharks, are still legally fished in Australia.
The group’s findings suggest three-quarters of these open ocean sharks and rays are threatened with extinction and fill in a big section of the jigsaw puzzle of global shark health – a puzzle that’s intrinsically hard to complete.
There were signs of hope, the research said, because in places where science-backed controls on shark harvesting existed, numbers were stable or recovering.
Meanwhile the public’s awareness of sharks is more often piqued not by their conservation plight – or even when they’re unwittingly eating them – but when they bite humans.
Annual figures showed last week that six of the 10 shark-bite deaths around the world in 2020 occurred in Australian waters.
The rise in fatalities, while tragic, was likely down to chance as the number of shark encounters was only slightly above average.
Around the world, the number of people reporting shark bites each year has been falling steadily in recent years.
That could be another pointer towards falling shark numbers, says Dr Gavin Naylor, director of the Florida Program for Shark Research at the University of Florida, which maintains a corroborated international file of shark bites on humans.
He says with population growth there are more and more people in the water, but this hasn’t translated to more bites.
“If the number of sharks stayed the same then we should see a rise in bites. But we don’t,” Naylor says.
What will rapidly falling shark numbers mean?
As well as sharp falls in the numbers of oceanic sharks, previous research has also found a “pervasive” loss of sharks on tropical reefs, upsetting the ecological balance of these delicate coral-dominated ecosystems.
On Queensland’s coast, peer-reviewed analysis of the state’s coastal shark control program suggests numbers of large sharks, including great whites, tigers and hammerheads, fell by at least 75% over 55 years.
According to the latest research in the journal Nature, global action is needed “immediately” to stop shark populations collapsing and “myriad negative consequences for associated economic and ecological systems”.
Dr Cassandra Rigby, a marine scientist also at James Cook University, who has studied sharks for more than 20 years, said: “The implications of removing sharks is an unhealthy marine ecosystem.”
With Simpfendorfer and others, Rigby is part of the Global Shark Trends Project that’s working to assess the more than 1,200 species of sharks and rays in the ocean.
Her particular passion is the world’s 500 species of deepwater sharks that scientists still have much to learn about. She’s concerned they may also be in peril.
Despite occasionally being “overwhelmed” by the state of the marine ecosystem, she says she’s an optimist.
“We just have to keep pushing for science-based fishing limits. We can now bring some strong science and model the situation (facing sharks) and say that this is the story.”
Marine scientists say removing top predators from ecosystems can have cascading and hard-to-predict effects on marine food webs. Because sharks eat smaller fish and take out the weak and injured, they support the integrity of the whole system.
Simpfendorfer says the threats to sharks from fishing are now well documented and severe. As threats from climate change begin to build, he says it’s even more important to protect shark populations now.
“Fishing is the primary and immediate problem,” he says. “We’re only starting now to get a hint of the climate change effects on sharks … there will be profound effects.
“If we don’t really substantially start to manage these open-ocean fisheries then we have to start imagining a future where there are oceans that don’t have sharks in them, and then the consequences that come from that.”
Will sharks survive?
In Australia, a 2019 assessment led by Simpfendorfer found that of 194 shark and ray species subject to some fishing, 124 were at sustainable levels. But 18 were depleted, and six were depleting and needed to be carefully monitored.
Simpfendorfer says that because sharks are so mobile, any protections they are afforded in Australian waters disappear as they move to other jurisdictions.
“That’s why this is about how they are managing across their range,” he says. “Where you have good management in place, with rules being enforced, then you can sustainably fish these animals. It is possible.”
Dr Jodie Rummer, an associate professor at the ARC Centre of Excellence for Coral Reef Studies at James Cook University, is researching the physiology of sharks and how changing ocean temperatures could affect them.
She says sharks have been in the ocean for about 450m years. “That’s really amazing from an evolutionary perspective, but most of that was without human influence.”
Because sharks reproduce slowly and take years to reach sexual maturity, they’re susceptible to overfishing.
“The advances in technology that are allowing for sharks to be captured so much easier and faster are taking animals out of the population at a much higher rate,” she says. “Everything is happening much faster now than ever before.”
About half of Rummer’s research takes place in the world’s largest shark sanctuary in French Polynesia – an example, she says, of the kind of protection sharks need.
“I guess the bottom line is that, on a global scale, sharks need to be off limits for fishing, as the data show that they are not recovering.”
Simpfendorfer is also optimistic that sharks can recover if enough protections are in place, and points to locations such as the north-west Atlantic where hammerhead and great white shark numbers are recovering.
“Sharks have got a very long evolutionary history and have seen so many other groups come and go,” he says.
“Dinosaurs have been and gone in the time [sharks] have existed. They’re good at surviving.”