By Debbie Koenig
The Discovery Channel’s annual “Shark Week” has been feeding America’s shark obsession since 1988. With shows spotlighting gruesome shark attacks, gripping battles between sharks and seals, white shark “hotspots,” and other terrifying fare, it’s enough to make a person rethink swimming in the ocean.
But how dangerous are sharks to humans, really? To find out, WebMD interviewed Gavin Naylor, Ph.D., director of the Florida Program for Shark Research (FPSR) at the Florida Museum of Natural History. Along with performing original research, FPSR maintains and investigates the International Shark Attack File, a comprehensive database of all known shark attacks throughout the world.
Our interview has been edited for clarity and length.
WebMD: Roughly how many sharks are there in United States waters? Are there more now than there used to be?
Dr. Naylor: It’s hard to say how many. The usual method used to estimate is called capture-mark-recapture. We capture and tag a bunch of animals. If those are the only animals in the area and we tag them, there’s a high probability we’ll recapture only marked ones. But if we tag 100 and there’s a population of 1,000,000, we’ll recapture far fewer with tags. Based on the proportion of tagged animals we recapture, we can estimate how many are out there. But it’s not perfect. It doesn’t account for the fact that animals move. The honest answer is we don’t know.
We do know the numbers are declining, though. With shark-fishing tournaments we used to see hundreds of sharks lined up, now we see one or two. Also, the price of fins is going up in places where they eat shark fin soup—there’s not enough supply to meet the demand.
WebMD: Which parts of the country’s coastlines see the most shark activity?
Dr. Naylor: Florida sees about half of the country’s shark bites. We have a lot of coastline and also very warm water, plus nice beaches. Millions come here to swim, and in warm water we have a lot of sharks sharing the habitat. We get blacktip sharks, bull sharks, tiger sharks, sandbar sharks, and some other, rarer ones.
What’s interesting isn’t that Florida has more shark bites, but that very few are ever fatal. They’re mostly by blacktip sharks, which target fish. Usually when they bite a human it’s a mistake. They’re predators, and they live by quickly responding. They see a flash of white and attack it. Once they realize, “Whoa, that’s not what I thought it was,” they get out as fast as they can. They’re probably as frightened as the humans.
WebMD: How common are shark attacks?
Dr. Naylor: Worldwide there are about 150 bites each year, and about half are unprovoked. Provoked is when someone wants a picture and grabs a shark, or is out spearfishing, or trying to ride the shark—what we call stupid human tricks. Those we don’t blame the shark for, since they’re responding as anybody might who’s riled up.
The incidence of bites seems to be very strongly correlated with the number of sharks in the water at the same time as a lot of people. Sharks are usually off-shore so we want to figure out, when is there a high probability of encountering a shark? What brings them in-shore? The data seems to suggest that it’s when the bait fish, the food they feed on, come in. The sharks will follow them, and if there are people in the water they may get bitten.
The specifics change from one species to the next. What explains bites from blacktip sharks doesn’t explain bites from white sharks. I tell people that a white shark is as different from a blacktip shark as a hamster is from a kangaroo. The divergence between these animals occurred millions of years ago.
WebMD: Which species of shark are most likely to attack a human? Are there any that we can swim with safely?
Dr. Naylor: There are 520 different species of shark, but only about a dozen that are ever implicated in biting people. Only three out of the 520 are responsibility for 99% of fatalities: white sharks, bull sharks, and tiger sharks.
WebMD: Is there any way to defend yourself if a shark were to bite you?
Dr. Naylor: Go for the nose, eyes, or gills. The gills have spikes and you can get badly sliced, so don’t grab—just hit. As for the eyes, I’d poke there. The nose is fairly sensitive, so hit it as hard as you can.
As with any predator, a shark will bite something and then leave for a while. They know that most prey items will fight back. Seals can deliver tremendous damage to a shark. So the shark will bite and leave, to let the prey get weaker, then come back. If you show tenacity as it’s biting you, it’ll think twice about returning.
WebMD: Is there anything the beach-going public needs to consider before diving in?
Dr. Naylor: You never want to go swimming alone. You’d be well advised not to go at dawn or dusk. Sharks are active then, and they can see you better than you can see them. Don’t splash around or make a lot of commotion; that brings in curious sharks. If you ever see bait fish jumping out of the water, it’s because they’re being chased by something. Reverse out of the water purposely and quickly. Keep your eye on where you think the animal chasing the bait fish is. Don’t turn your back to it—you want to be able to avoid it last-minute or clock it on the nose or eyes.
WebMD: With more people having drones now, videos are surfacing of sharks swimming close to bathers. It looks like those people are in real danger, but are they?
Dr. Naylor: People are in close proximity to sharks far more than they imagine. They just don’t bother us. Talk to any hardcore surfers—they see sharks every day. It underscores that they’re not really out to get people. If they were, there’d be 10,000 bites a day.
You have a much higher chance of getting hit by a car on the way to the beach. If people worried as much about their health as they do shark bites, we’d be the healthiest people in the world.
WebMD: How is climate change affecting sharks' patterns or behaviors?
Dr. Naylor: It’s reasonable to think that as the climate changes, and it is changing, food sources will move into different areas. Predators that feed on them will follow. So it’s reasonable to think it will produce different distribution patterns and sharks will go to places they haven’t previously. But we don’t want to pile on and say definitively, “Climate change will increase shark attacks.” In some places human shark interactions could go down! They’ll follow the food, and sharks can go large distances.
WebMD: Why are sharks necessary for a healthy ocean?
Dr. Naylor: Sharks, most of them, are apex predators, at the top of the food chain. Those in that position regulate the population numbers of the ones underneath, which then regulate the ones beneath that group, and so on. If you remove an apex predator it can have an outsize effect, cascading down the food chain.
So we know that without sharks there would be a shift in dynamics, but we don’t know exactly what that shift would be. Would there be an explosion of anchovies, or seaweed all over the beaches, maybe red tides? There’d be a new equilibrium set up, very different from what we’re used to. We don’t have enough information to predict what that would be.
But we do think they play a very important role. Many more fish in the ocean are fed on by sharks than there are sharks.