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Steven
Spielberg was given a stinker when he signed on to
direct
Jaws. The script wasn’t finished, Richard Dreyfus hated
his
character’s development, and the first mechanical shark
sank
as soon as it was put in water. But because of the movie’s
success,
he became powerful enough to make any movie he
wanted.
Jaws is the reason we were given Schindler’s
List and
Close Encounters of the
Third Kind.
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Every time there is a sighting or an attack, the media goes
out of its way to tell us how rare the attacks are. Every news report includes
a disclaimer that attacks occur once in a blue moon. They usually make some
comparisons: you’re more likely to be killed by a cow than by a great white
shark; you’re more likely to be bitten by Luis Suarez – you know, things like
that.
But is it true? Are sightings and attacks by great white
sharks rare and staying rare? Or has the faster news cycle led to the need for
more sensational stories and therefore more coverage? It may be a bit of both.
More people swim in the oceans now than in the 1700’s or
1800’s. The reasons are many – more leisure time, more information about open
water (lack of sea monsters), and a big increase in world population. So maybe
the attacks reflect an increase in pruny people.
The International Shark Attack File (ISAF) at the University
of Florida states that attacks have been increasing each decade since the early
1900’s, although there was a dip in the late 70’s and early 80’s. The ISAF says
because they had a lapse in their record keeping, but I think it was due to the
Jaws effect.
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People
used to sail within sight of land because they feared
falling
off the Earth and the sea monsters that lived in open
water.
They weren’t going to swim out there! It wasn’t until
1875
that someone swam the English Channel, and it didn’t
happen
again for 31 years. Of course sea bathing, or wading,
was
popular, but most often the sea water was
brought
to pools on land.
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On the west coast of North America, an older study severely
underestimated the number of great whites because of sampling biases, so a 2014 study re-evaluated this study and generated a number of more than 2000 for just
those around California. Another 2014 study on the east coast of North America
showed a dip in 1970’s but a steady increase in the number of great whites
since the 1980’s.
A third 2014 study in Australia linked bite risk to
increased shark numbers and suggested that this increase was due to an increase
in whale numbers. Add to this upshot in population a study that used radiocarbon dating of vertebral columns. The authors showed that male great
white sharks can live up to 73 years, much longer than previously assumed. More
great whites living longer lives than we thought? Sounds like a recipe for more
attacks.
The reason for this –
humans probably. In 1972, the Marine Mammal Protection Act was passed.
This made the killing of any marine mammal (dolphins, seals, whales, etc.)
illegal. This was joined by the international moratorium on commercial whaling
passed in 1982. As a consequence, marine mammal numbers have been on a steady
rise. Yum, more food for sharks. More food means more surviving sharks; more
adult sharks means more baby sharks.
Helping this survival rate was a 1997 ban on the hunting of
great white sharks. I don’t know a better way to increase the number of sharks
than to stop killing them. So – there are more sharks, is it too weird to think
that there might be more attacks?
But there are problems in counting attacks. The perpetrators
eat the evidence in most cases. We may be significantly underestimating the number of
fatal attacks just because we don’t have bodies to count.
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The
great white shark (1, Carcharodon
carcharias), the bull shark
(2,
Carcharhinus leucas), and the tiger
shark (3, Galeocerdo cuvier)
are
responsible for the majority of unprovoked attacks on humans
in
open water. The great white swims in temperate and tropical
water
around the world. The bull is in coastal water and rivers
around
the world, but the tiger shark lives in tropical and
subtropical
waters. Tigers only come about halfway north in the
US.
Could you tell which one was gnawing your leg off?
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Get hit by a car – sure, try to get the license plate number
and you might be able to get some satisfaction. But unless it’s a really
unusual looking shark, I don’t think you’re going to get a call saying the
private detective you hired has found him. Moby Dick, maybe, but a shark that
looks like every other shark – nope.
But there’s an exception. Were you chewed on in a coastal
river or river-fed lake? Then it was probably a bull shark. Bull sharks are exceptions
amongst sharks. Most sharks are able to live in saltwater because they have a
way of stopping the loss of cellular water to the high salt environment they
live in. Most sharks accomplish this by storing a huge amount of chemical
called urea. See this post for more information.
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There
are very rare sharks of the Glyphis
genus that can
live
in brackish waters as well. They live in southeast Asia
and
Australia, but they are very mysterious and aren’t
sighted
often. This is a bull shark found in a golf course
lake
in Australia. If bitten while in a river or lake, think
bull
shark, not Glyphis.
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This is important because bull shark attacks are the most
likely to be fatal -if you can believe the statistics. So the coastal rivers
aren’t as safe as you thought, but at least you’ll know who’s gnawing your leg
off.
Contributed by Mark E. Lasbury, MS, MSEd, PhD
Mark is writer and educator in the areas of science and
history
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