Data Story: Shark Attacks Rise as Humans Increasingly Impact Oceans

data-analysis-of-sharks

An analysis of over a century of reported shark attack data shows that attacks are on the rise. But it also offers some hints at the reason why: increasing human influence and interference in the oceans.

Reported shark attacks since 1970.

Reported shark attacks since 1970.

Shark attacks are on the rise in general, and provoked attacks — incidents in which a shark was confronted with some sort of human interference — are on the rise as well. 

The pattern of attacks is also changing. For example, attacks involving tiger sharks and bull sharks — two of the most aggressive species — seem to be moving northward as climate change warms ocean waters. Below, we can see that the percentage of yearly attacks occurring north of the latitude 32 line (blue) appears to be on the rise for both species.

tiger-shark-attack-data
bull-shark-attack-data

Collectively, tiger and bull sharks account for roughly half of all reported shark attacks in most years. And the rise in more northern attacks by these species reinforces what marine biologists have already observed. Bull sharks, for example are mating further north in response to warming waters. Many other shark species have shown similar movement patterns.

Our analysis did not find any significant change in the number of "northern" shark attacks involving white sharks (including the famed great white). But there's an interesting biological reason why white sharks might not be moving north in response to rising water temperatures when other species apparently are.

Most sharks, including tiger sharks and bull sharks are cold blooded (ectothermic), which means that their body temperature matches the water around them. Because of this, they may be particularly sensitive to changing water temperatures. White sharks, on the other hand, are warm blooded (endothermic), and thus may be less likely to alter their behavior based on ambient water temperature changes.

Since most sharks are cold blooded, though, the data suggests that as ocean temperatures rise, swimmers, surfers, and boaters in more northern climates can probably expect an increase in the number of sharks — and consequently the number of shark attacks — in their seas.

Of course, it's worth remembering that shark attacks are still tremendously rare. You are far more likely to be struck by lighting, for example, than attacked by a shark. Fatal incidents are rarer still. The data set we analyzed, which contains data on more than 6,000 human-reported shark attack incidents, includes just a few reported fatalities each year. Given that humans reportedly kill about 100 million sharks per year, it's pretty clear that sharks have more to fear from us than we from them.

Still, if you want to minimize your chances of bumping into a shark, the data suggest you should put your surfboard in storage. Surfing has been the single activity most associated with shark attacks every year since 1980. Swimming and fishing are the second- and third-most common activities associated with reported shark attacks, respectively. 

shark attack data by activity

However, surfing and fishing shark attacks were quite unlikely to be fatal. Swimming, bathing, and various diving activities (diving, scuba diving, snorkeling, spearfishing, etc.) had a significantly higher percentage of fatal attacks.

shark in the water sign

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