Humans are like ungainly packets of meat when paddling in the ocean and should be easy prey compared to fast-moving fish and seals. So, why are so few people attacked by sharks?
However, recent research indicates that shark attacks in some parts of the world appear to be on the rise. The eastern US and southern Australia have seen shark attack rates almost double in the past 20 years, while Hawaii has also seen a sharp increase. But why?
“Shark bites are strongly correlated to the number of people and number of sharks in the water at the same time,” says Gavin Naylor, director of the Florida Program for Shark Research, which maintains the International Shark Attack File. “The more sharks and people there are in one place, the greater the chance of them bumping into each other.”
This seems like an obvious point, but when you look closer at where attacks are taking place there are some clues as to what might be going on. The large human populations along the southern coast of Australia and the eastern coast of the US mean large numbers of people enjoying the water. But southern Australia has also seen rising numbers of fur seals along its coastline, the favourite prey of great white sharks in the region.
Similarly, seal populations off Cape Cod on the coast of Massachusetts in the US have rebounded in recent years, largely thanks to protection by the US’s Marine Mammal Act introduced in 1972. This has led to increased numbers of great whites in the area too during the warm summer months as they look to feast on the seals that pull themselves out to bask on the beaches.
Sadly, last autumn, Massachusetts suffered its first fatal shark attack in 82 years and growing numbers of shark sightings have led to a string of beach closures.
But there is no real evidence that sharks are actively hunting humans, according to the scientists who study them. Great whites in the North Atlantic, for example, show seasonal movement patterns, migrating thousands of miles to warmer waters further south during the winter months. Some mature adults will venture out into the open ocean for months at a time, covering tens of thousands of miles and diving to depths of 1,000m as they seek prey.
“We are like helpless little sausages floating around in the water,” says Naylor. But despite being potentially such an easy meal, sharks are really not that interested in hunting humans. “They generally just ignore people. I think if people knew how frequently they were in water with sharks, they would probably be surprised.”
However, Naylor believes that the official statistics on shark attacks are probably an underestimate. Most reports come from highly developed countries with large populations and highly active news media. Attacks on remote islands or in less developed communities probably go unreported.
Looking at the statistics for the number of shark attacks last year can reveal some fascinating trends. Last year, there were just 66 confirmed, unprovoked attacks, roughly a 20% fall compared to previous years. Just four of these were fatal according to the International Shark Attack File, although another database of shark attacks records seven deaths. So far in 2019, there have been four fatal shark attacks.
The findings highlight one of the key challenges in understanding why sharks bite humans. There are dozens of different species responsible for bites, each with their own unique behaviour, hunting strategies, prey and preferred habitat – although in many cases the species can be misidentified or not identified at all.
The majority of unprovoked attacks on humans where a species is identified involve three large culprits: the great white, tiger and bull sharks. Yet great whites – the species depicted in the film Jaws and demonised by Hollywood ever since – isn’t just a separate species, but an entirely different taxonomic order from the other two.
“There are 530 different species of shark and there is so much diversity among them. You can’t just group them together,” says Blake Chapman, a marine biologist who has studied shark sensory systems and recently wrote a book on shark attacks on humans. “Different species have such a range in terms of their sensory biology, how they behave, their motivations and the habitats they live in.”
Bull sharks, for example, tend to hunt in shallow, murky water that will require them to rely less on vision and more upon their sense of smell and electroreception, which allows them to detect minute electrical fields produced by their prey.
“(Great) white sharks, which often hunt in very clear water use their vision a lot more and their eyesight is much better,” says Chapman. There is also some evidence that shark teeth may also function as mechanosensory structures – similar to touch – to help the animals learn more about what they are biting.
Naylor believes that in most cases, sharks bites are a case of mistaken identity.
“If these animals are chasing bait fish, the flash of the white sole of a foot from someone kicking on a board might cause them to dart at it,” he says. “When you have a large animal like a tiger or a white shark, which move quickly, a bite is far more likely to be fatal.”
Great whites typically attack from below, delivering a massive catastrophic bite. In some cases, they will withdraw while their prey bleeds to death before returning to eat.
The focus on the risks that sharks pose to us also diverts attention from the far greater threat we pose to their survival due to overfishing and human-induced climate change. Some estimates suggest shark numbers in Australian waters, for example, have declined by between 75-92%.
But for those who are afraid and want to know how to protect themselves from a shark, some advice: punching a biting shark in the gills or poking it in the eyes. Swimming in groups and staying close to the shore are known to reduce the risk of attacks. Wearing dark clothing and avoiding wearing jewellery can also help to reduce the chance of attracting a shark’s attention in the first place.