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.
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.
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.
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