Sharks, Sound and the Question Nobody Seems to Be Asking

Every time there is a shark attack, we're told about the victim, we interview witnesses, we speak to the paramedics and the surf lifesaver who was on hand to help, and then the conversation inevitably turns to drones, shark nets, SMART drumlines and helicopter patrols.

Yet despite all the coverage, there is one aspect of shark management that is rarely discussed.

Few Australians realise there is an extensive underwater listening network operating off our coastline, quietly tracking sharks using acoustic technology.

Given sharks are known to be highly sensitive to sound and vibration, I find myself wondering why more people don't know this system exists, and whether enough questions are being asked about the role sound plays in the underwater world these animals inhabit.

After all, we're not talking about a handful of devices. We're talking about hundreds of underwater listening stations, thousands of acoustic tags and sharks carrying devices that emit unique sound signals. Together, they form an enormous technological network operating beneath the surface of Australia's oceans, largely out of sight and, for most of us, out of mind.

So why does almost nobody know about it?

Given sharks are known to be highly sensitive to sound and vibration, why isn’t there more public discussion about the technology itself?

Now before anyone rolls their eyes, calls it a conspiracy theory and dismisses the question out of hand, let’s start with what we know.

Sharks absolutely hear sound.

Research into shark hearing and behaviour dates back more than six decades. In a landmark 1963 study published in Science, marine biologists Donald Nelson and Samuel Gruber found that large sharks in their natural environment were attracted to low-frequency pulsed sounds, particularly those between 20 and 60 hertz. The sharks responded to these sounds but showed little interest in higher-frequency signals or continuous low-frequency noise.

Since then, scientists have learned that sharks navigate a remarkably complex sensory world. Many species can detect frequencies up to around 1,000 hertz and use a specialised sensory system known as the 'lateral line' to detect water movement, pressure changes and disturbances in their environment.

In practical terms, this means a shark can often sense struggling prey, nearby animals and activity in the water long before it can see them. Put simply, sharks live in a world of vibration and don't experience the ocean the way we do. While humans rely primarily on sight, sharks navigate a world rich in sound, vibration and movement.

Australia has built one of the largest shark-monitoring networks in the world.

According to the NSW Government, sharks tagged by researchers are fitted with acoustic transmitters that emit unique sound signals. These tagged sharks can then be detected by a network of 37 real-time listening stations positioned along the NSW coastline from Tweed Heads to Merimbula. The system is designed to improve public safety by alerting authorities when tagged sharks pass within range of a receiver. (SharkSmart⁠)

What many people don't realise is that this network has been operating for more than a decade. Introduced as part of NSW's Shark Management Strategy, the technology was designed to improve our understanding of shark movements and provide beachgoers with an additional layer of protection.

The broader Australian network is even larger, with hundreds of acoustic receivers deployed through the Integrated Marine Observing System (IMOS) and a range of state and federal research programs. Together, they form one of the most extensive marine animal tracking systems in the world. (animaltracking.aodn.org.au)

A submission to a parliamentary inquiry examining shark mitigation measures argued there was limited publicly available information demonstrating comprehensive environmental impact assessments relating to acoustic tagging programs and their potential effects. (Australian Parliament House⁠)

Which raises an obvious question: if sharks are highly sensitive to sound and vibration, and Australia has spent millions building one of the world's largest acoustic shark-monitoring networks, shouldn't we know whether that technology has any effect on the animals it is designed to track?

The question becomes even more interesting when viewed against the broader trend in shark incidents.

According to the Australian Shark Incident Database, Australia recorded an average of around three unprovoked shark incidents a year during the 1950s. That figure rose to approximately 12 incidents annually during the 2000s and is now sitting at between 21 and 27 incidents a year during the 2020s, depending on the dataset and methodology used.

Australia's acoustic shark-monitoring network was introduced from 2015 onwards. Since then, shark incidents have continued to occur, with Australia recording an average of almost 29 shark encounters a year over the past decade, compared with around 16 a year during the 2000s.

Of course, correlation is not causation, and scientists point to numerous possible explanations, with the reasons remaining the subject of ongoing debate. What is not disputed, however, is that despite significant advances in shark-monitoring technology, the long-term trend in shark incidents continues to move in one direction.

The purpose of Australia's acoustic shark-monitoring network is straightforward. Researchers use acoustic tags and underwater listening stations to better understand shark movements, improve public safety and, ultimately, reduce the risk of shark encounters.

So what exactly is happening beneath the surface?

If researchers are actively exploring whether certain sounds can deter sharks, given the increasing number of incidents, is it unreasonable to ask whether some sound-based technologies may also have unintended consequences? And if shark incidents have continued to rise despite significant investment in monitoring technology, shouldn't we be curious about every possible factor that may be influencing shark behaviour?

Beyond the debate over whether acoustic monitoring systems are helping or harming, there is a more fundamental issue: most Australians have little understanding of the increasingly complex acoustic environment operating beneath our oceans.

Between tagged sharks, underwater receivers, vessel traffic, ferries, sonar, marine construction and countless other sources of noise, the modern ocean is a very different place from the one researchers first studied decades ago.

The question is not whether sound matters to sharks. We already know it does.

The question is whether we fully understand the cumulative effect of all these sound sources on the animals we share our coastline with.

I have not found evidence that the listening stations or tags attract sharks.

Yet, equally, I have not found a publicly available study specifically designed to test whether the acoustic monitoring network itself changes shark behaviour around beaches.

And if we don't know, how do we find out?

Because perhaps the most important questions are not the ones we're asking after a shark attack.

Perhaps they're the ones we're not asking at all.