The real reasons why sharks attack humans
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?
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?
By Richard Gray
9th August 2019
The crystal-clear water beneath 13-year-old Hannah Mighall
darkened for a moment. She was sitting astride her surfboard, enjoying the
warmth of the sun as she and her cousin waited for the next wave in Tasmania’s
idyllic Bay of Fires. Behind them the brilliant-white sandy beach was largely
deserted and the surfing had been good so far.
The sudden shadow below made Mighall instinctively lift her feet
– balls of kelp often broke off nearby rocks and drifted in the surf. “They are
really slimy so I hated touching them,” she says.
But then something took hold of her leg.
The water around Mighall exploded as
a five-metre-long great white shark latched onto her right leg
“It didn’t hurt at first, it was like something gently grabbed
hold of me and then I was in the water,” says Mighall.
To those who witnessed what happened, however, it was anything
but gentle. The water around Mighall exploded as a five-metre-long great white
shark latched onto her right leg, lifted her off the surfboard and shook her in
the air before disappearing underwater.
“It took a few seconds for me to realise it was a shark,” she
says. “When I popped back up from the water I was lying on my back but my leg
was in its mouth. All I could see was my black wetsuit leg, its teeth, pink
gums, teeth and the dark bit under its nose where it meets white. I thought I
was having a nightmare and kept trying to blink my eyes open.”
The shark that attacked Hannah Mighall took an
enormous bite out of her surfboard before it allowed her to bob back to the
surface (Credit: Malcolm Mighall)
Mighall’s cousin, 33-year-old Syb Mundy, who had been sitting on
his own board just a few metres from her, raced over and began punching the
shark in the side of its head. The shark pulled away from him and as it went
underwater it let go of Mighall, lunging instead for her surfboard that was
still attached by a rope to her leg.
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With the board in its mouth, the shark pulled Mighall underwater
for a second time. Moments later she popped back up to the surface with her
damaged board. The animal had bitten clean through the fibreglass and foam.
Mundy grabbed hold of his cousin, put her on his back and
paddled frantically for the shore. Earlier that day Mighall had been practicing
water rescues with another girl during training with her local Surf Life Saving
association, repeatedly being carried into shore as the “victim”. Now she was
doing it for real.
The shark came with us
all the way up to the beach – Hannah Mighall
“The shark was circling us underwater,” says Mighall. “Then this
wave came in and Syb just said, ‘We have got to catch this as it is going to
save our lives.’ I was just tapping the water as I was terrified but he was
really paddling and the wave carried us to shore. The shark came with us all
the way up to the beach as there is a deep gutter running up to it. We could see
its fin as it surfed in on the same wave.”
Luckily for Mighall, among the few people on the beach who
witnessed what had happened that day were a doctor and a nurse. They gave her
vital first aid while waiting for an ambulance to arrive.
More than 10 years later, she still carries deep scars on her
leg that trace the outline of the shark’s mouth. Her right leg is noticeably
weaker than her left – so much so that she has to lift it with her hands when
she wants to kick-start the dirt bike she rides occasionally.
Great white sharks typically attack their prey
from below with great speed, delivering a single devastating bite (Credit:
Getty Images)
Mighall was one of roughly 83 people around the world to be
attacked unprovoked by sharks in 2009. It is a figure that has remained around
the same level over the past decade. The average number of unprovoked attacks between 2013-2017, for example, was 84.
But 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.
The resurgence in seal populations on Cape Cod
on the east coast of the US has led to rising numbers of great white sharks in
areas popular with people (Credit: Getty Images)
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.
We are like helpless
little sausages floating around in the water – Gavin Naylor
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.
Tiger sharks are one of the three main species
responsible for attacks on humans but much of the time they ignore people in
the ocean (Credit: Getty Images)
The reason for the fall – which bucks the overall trend of
growing numbers of attacks – has been attributed to a sharp decline in the number of black-tipped sharks.
These sharks account for many of the bites around the south-eastern US,
migrating down the coast of Florida due to rising sea temperatures that have
led their prey to become more dispersed.
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.
Great white sharks are considered to be the
most dangerous species in the oceans today, but we still know very little about
their life cycle and behaviour (Credit: Getty Images)
“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.
There is some evidence
that shark teeth may also function as mechanosensory structures to help the
animals learn more about what they are biting
“(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.
Chapman believes there may be a complex set of reasons for why unprovoked attacks on
humans appear to have risen in recent decades.
Aside from rising human populations along coastlines, the
destruction of habitat, changing water quality, climate change and shifts in
prey distribution are leading sharks to gather in greater numbers at certain
hotspots around the world.
In 1992, for example, there was a sudden spate of shark bites
off the coast of Recife, Brazil – an area that had no unprovoked attacks for
the entire previous decade. Chapman believes that heavy commercial port
construction in the area damaged large areas of reef and mangrove, potentially displacing species like bull sharks,
which moved to new areas like Recife in search of prey.
Bull sharks are aggressive animals that
typically hunt in water with reduced visability (Credit: Getty Images)
Réunion Island in the Indian Ocean – renowned for its beautiful,
unspoiled marine habitats – has seen a dramatic rise in tourism but in recent
years it has also suffered a growing number of shark attacks by the bull and tiger
sharks that live in the surrounding waters. Since 2011, there have been 11 fatal attacks on Reunion, mainly on
surfers. Those who survive often lose limbs. Researchers have
found that around two-thirds of the Reunion attacks have occurred in turbid water and swells of more than two metres –
the favoured environment for bull sharks, which are thought to be responsible
for most of the attacks.
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.
“A great white in full predatory mode is quite a sight,” says
Greg Skomal, a marine biologist with the Massachusetts Division of Marine Fisheries
who has been tagging and tracking great white sharks since 2009. He should know
– last year, as he was leaning over the pulpit on the bow of a research vessel
while trying to tag a shark, a
large great white breached directly underneath him with its jaws agape.
“It gave me some idea of what a seal feels like,” he says. “I’ve
seen that behaviour a couple of times over the years we have been doing this.
Most of the time we put a camera in the water and the sharks are completely
complacent. We must have done it thousands of times. But on a handful of
occasions they attack straight away, breaking the pole and the camera. It is
like they are in a heightened predatory state where their senses lock onto any
kind of stimuli.
“I wonder if those strikes on people that are not merely
investigative are the result of a person being in the wrong place at the wrong
time with a shark in this kind of heightened state.”
Efforts to tag great white sharks is starting
to provide insights into the behaviour and life cycles of these enormous
predators (Credit: Getty Images)
But for every attack on a person, there are just as many stories
of people who have managed to get up close to these giant predators without any
harm. Take Ocean Ramsey for example, who swam alongside an enormous 20-feet-long great white off
the coast of Hawaii and made headlines around the world.
Skomal and his colleagues are now using new
high-resolution tags that can give the researchers minute
by minute and second by second data on what the sharks are doing.
It is like they are in a
heightened predatory state where their senses lock onto any kind of stimuli –
Greg Skomal
He hopes it might help to answer questions about the behaviour
of these animals as well as about where and how they breed. It could,
ultimately, also help to tell us something about the reasons underlying attacks
on humans, he says.
Some researchers are turning to forensic methods to try and
unravel some of the reasons behind attacks. They are developing techniques to use DNA and bite-mark
patterns to identify species, while others are
examining video footage of attacks and comparing these to injuries to
get a better understanding of what happened.
Data from shark spotters in South Africa have shown that great
whites are more active near the surface, and so more likely to be seen,
when water temperatures are above 14C, during a
new moon and in the afternoon. Other research, however, has suggested that
great whites are more successful hunters at night when there is a full moon.
Many areas now operate shark patrols to spot
sharks before they enter areas used by swimmers and surfers so they can be
alerted (Credit: Getty Images)
Other researchers have suggested juvenile great whites may
attack humans as they hone
their predatory skills, in much the same way that young lions
will experiment with whatever prey they can take on.
But regardless of the reasons for attacks on humans, the risks
involved are still vanishingly small. In Australia the rate of shark attacks is
in the order of 0.5 attacks per million people, while in
the US it is less than 0.2 attacks per million. It is worth noting that in
2018, the US figures dropped to around 0.08 attacks per million while
in Australia they rose to 0.8 attacks per million people.
In Australia the rate of
shark attacks is in the order of 0.5 attacks per million people, while in the
US it is less than 0.2 attacks per million
These figures are blunt instruments, of course. They fail to
account for the comparatively fewer numbers of people who actually use the
water, and the fewer still who swim in water inhabited by dangerous sharks. But
these statistics, however ridiculous or comforting they might seem, do little
to dampen our fear of sharks.
“Fear has played a very important role in our evolution,” adds
Chapman. “Humans don’t need to be eaten themselves by a sabre tooth tiger to
learn to fear them. We learn that fear very quickly from a single story. People
who have never seen a shark before fear them because we hear or watch stories
about them.”
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 over
fishing 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 advise 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.
