Diving Into The Deep World Of Sharks

JOHN DANKOSKY: This is Science Friday. I’m John Dankosky. You know how it goes. As summer approaches and people head to the beach, you start to see more and more stories about people encountering sharks. But my next guest points out every story with a headline like, big sharks spotted near beach, could also be written as, fish swims in water. It’s home.

Sharks have this kind of mythic status like an aquatic T-Rex, but our fascination with their apex predator status leads to coverage that can be over the top, misguided, and sometimes even harmful to the goal of conserving and protecting threatened species.

Dr. David Shiffman is a faculty research associate at Arizona State University, and he’s the author of the brand new book Why Sharks Matter– A Deep Dive with the World’s Most Misunderstood Predator. Welcome to Science Friday, David.

DAVID SHIFFMAN: Thanks for having me, John.

JOHN DANKOSKY: Well, we’re going to get to why sharks are misunderstood in just a moment, but first, let’s spend some time just marveling at them a bit. What’s your favorite shark fact?

DAVID SHIFFMAN: Oh, man. There are so many fascinating facts about these animals, and like many kids, I had a shark thing when I was little that I never grew out of. Ask the eight-year-old in your life, and they probably know some amazing facts of their own. But the one that I used when I just have one fact to blow people’s mind, it’s Greenland sharks, which are a deep sea Arctic species. They can live to be over 400 years old. They’re the longest-lived vertebrate animal in the world, and they have been found with polar bears and reindeer in their stomachs.

JOHN DANKOSKY: Oh my–

DAVID SHIFFMAN: Isn’t that incredible? It’s probably scavenging of animals that are swimming from ice floe to ice floe and drown, but I like to think that a polar bear swimming from ice floe to ice floe is pretty vulnerable to getting slurped up from below.

JOHN DANKOSKY: My goodness. 400 years, how does that even happen?

DAVID SHIFFMAN: Isn’t that wild? And they’re not considered reproductively mature adults until they’re in their 160s, which means that a Greenland shark born on the day that Canada was confederated as a modern nation is still a teenager

JOHN DANKOSKY: Oh my goodness. Well, we’re going to have lots more shark facts, and I’m sure people will want to hear more of them. One of the things I want to talk about for a second is shark skin. Now, I’ve never gotten to pet a shark myself, but I just assumed that the skin was smooth. And you write that it is kind of. Tell us about sharkskin.

DAVID SHIFFMAN: Yeah, so sharks are covered in these amazing scale like features called dermal denticles, which means skin teeth, and they are pointed backwards. So if you do touch a shark from nose to tail, it’s incredibly smooth. But if you go the other way, it’s incredibly rough, rough enough to cut your skin. Many marine biologists I know I have experienced something called shark burn, which is because of this.

One time I was helping to work up a lemon shark for some of my PhD research. And I looked down, and the back of the lemon shark was covered in hair. And I thought, that’s weird. Fish don’t have hair. And then I looked, and my leg was bleeding.

So just from the skin, the shark did not bite me. It was safely restrained, but it just moved just a fraction of an inch. And that was enough to just shear a whole bunch of skin and hair right off me.

JOHN DANKOSKY: My goodness. And you talk about how diverse a group of animals these are, these animals that we call sharks. Maybe you can explain a little bit about that diversity because there’s not just one thing. As you say over and over again in your book, the great white from Jaws is not the only shark out there.

DAVID SHIFFMAN: Absolutely. There are actually over 500 known species of sharks, and there’s a new species of shark, skate, ray, or chimera discovered on average about every two weeks somewhere in the world. And they come in just about every shape, and size, and color that you can imagine. The smallest is smaller than your forearm. The largest as larger than a school bus.

Some are striped. Some are spotted. Some have crazy long tails. Some have weird faces or weird snouts. One is bubblegum pink in color.

So just about any place that you can imagine, there’s sharks that live there. The US Navy SEALs have a saying that, if you want to test if there’s a shark near you, you dip your finger in the water and taste it. And if it’s salty, that means you’re in the ocean, and therefore, there’s probably a shark near you. And that’s true. But it’s also incomplete because some sharks live in rivers.

JOHN DANKOSKY: And among all these various types of sharks, David, you say there’s even one that glows.

DAVID SHIFFMAN: Yeah, there’s a whole group of sharks that can glow in the dark that are called the lantern sharks. There’s a lot of deep sea organisms that are able to bioluminescence or biofluorescence in some ways because, if you live in the deep sea, it’s so dark there because the sunlight never reaches. So sometimes that’s for signaling other members of your own species. Sometimes it’s for attracting prey to come investigate what the weird light is sometimes. It’s for scaring away predators. So yeah, there are glow-in-the-dark sharks.

JOHN DANKOSKY: So sharks are, of course, fish, but maybe you could help me place them on the evolutionary tree.

DAVID SHIFFMAN: Sure. That’s a question I get a lot actually, that, are sharks fish? And the answer is, yes, but they’re a different group of fish from something like a tuna, or a goldfish, or a bass. Those are the bony fishes. They have skeletons that are made of bone just like ours. But if you crinkle your nose or crinkle your ears, you can feel that that’s more flexible.

That’s cartilage, and sharks, skates, rays, and chimeras are the cartilaginous fishes. Their skeletons are made out of cartilage just like that. And it is more flexible than bone. It’s lighter than bone. It heals faster than bone.

JOHN DANKOSKY: Is there something in the way that sharks are made that have allowed them to live so long, to be on this planet for such a very long time, and thrive, and survive?

DAVID SHIFFMAN: Sharks are just extraordinarily well adapted to their environments. There were animals recognizable as shark swimming in the ocean not only before there were dinosaurs on land but before there were trees on land and long before they were rings around Saturn. So this is a really ancient group of fish, which makes their modern-day conservation crises all the more tragic.

JOHN DANKOSKY: Your message in the book is that sharks do matter. Explain why they matter so much ecologically.

DAVID SHIFFMAN: Predators help keep the food web in balance. It’s really that simple. And when you lose predators, it can unravel the whole food web with wide-ranging and unpredictable effects that can be really, really ecologically disruptive. And for organisms, including humans that depend on those ecosystems, that can be unbelievably bad.

And when we’re talking about the ocean, that is a series of ecosystems that billions of humans depend on for food and for employment. We very much want the oceans to be healthy, and for there to be healthy oceans, we need there to be, among other things, healthy populations of predators.

JOHN DANKOSKY: But not all sharks are just predators. Some are food as well and not just for humans.

DAVID SHIFFMAN: Absolutely. Some are the apex predators at the top of the food chain that you may visualize when you hear about sharks, but some are small. And there are sharks that have been eaten by birds. There are sharks that are eaten by bony fish. There are sharks that are eaten by seals and sea lions. One of my favorite photos from a few years ago was a bull shark that got taken out by a saltwater crocodile. So these animals can be fulfilling all sorts of important ecological roles.

JOHN DANKOSKY: Could you explain how threatened sharks are?

DAVID SHIFFMAN: Sharks are some of the most threatened animals in the world. According to the IUCN Red List, which is an international group of conservation science experts, about one-third of all known species of sharks and their relatives are considered threatened with extinction. Frogs are in worse shape than that because of the Chytrid fungus disease that’s spreading through rainforests. One type of hard corals is in worse shape than that. And that’s it.

JOHN DANKOSKY: When people hear about sharks in the media, there’s this tone of danger and threat. I know that the numbers of people who are attacked by sharks, whether it’s in the US or globally, is nowhere near as much as the hype. But maybe you could put in some context the threat that sharks pose to humans.

DAVID SHIFFMAN: The threat that sharks pose to humans is astronomically low. In a typical year, hundreds of millions of humans go in the ocean, and 50 to 70 are bitten by sharks, not 50 to 70 million, 50 to 70. Many of those bites are so minor that they require a Band-Aid, not even stitches.

In a typical year, more Americans are killed by flowerpots falling on their heads from above as they walk down the street than are killed by sharks. And as a social media guy, my favorite one of those statistics is that more people in the world are killed not paying attention while taking a selfie of the beautiful scenery and falling off cliffs than are killed by sharks.

JOHN DANKOSKY: So why do you think it is that we have such a preoccupation with shark safety, with worries about swimmers being eaten by a shark? Is it just that movie Jaws? Or is there something else to it?

DAVID SHIFFMAN: Jaws is a big part of it. Jaws really changed the world and how people think about sharks in that a lot of people didn’t really think about sharks that much before that movie and the associated book. When my parents saw Jaws, they said they didn’t even want to go swimming in their community pool that summer. It absolutely terrified people, and when most people– when I say shark, what you picture is the shark from Jaws, even though we know that’s not really how they behave or really what they look like.

The same is true of dinosaurs. If I ask you to picture a T-Rex, you picture the T-Rex from Jurassic Park, even though we know that’s not what they look like or a lot of how they behave. So Jaws played a major role. But there’s also this inflammatory and fear-mongering media coverage that, whenever anyone is bitten by a shark anywhere in the world, it’s front page news everywhere.

My favorite analysis of this was done by my colleagues Dr. Christopher Neff and Bob Hueter. And they found that, in Australia, things that were reported as shark attacks– for instance, this is audio. I’m doing very sarcastic air quotes when I say shark attacks– about a third of what was reported as a shark attack, the shark did not physically touch the human at all. It swam near the human in a way that the person interpreted as threatening.

JOHN DANKOSKY: All this being said, you make it clear in your book that some shark attacks do happen and that you don’t want to minimize the fear that people have. You don’t want to minimize the fact that some people have been maimed or killed. Are there things that we can do to minimize the risk that does exist?

DAVID SHIFFMAN: Yeah, the risk is very small, but it is real. And I don’t want to take away from anyone suffering. Tragedies do happen. But it’s important to keep in mind these relative risks when we plan policy responses to a particular issue. Some things that you can do to minimize your risk, if you are concerned about this, is stay relatively close to shore around other people in the middle of the day, not at dawn or dusk when some species of sharks are more active.

What I just said is notably the exact opposite of what most surfers do. They go far from shore by themselves either before or after work, and what that leads to is surfing being still relatively safe but relatively less safe than just a typical beachgoer.

JOHN DANKOSKY: You’ve talked about how threatened shark species are. Let’s talk through some of the major threats that they’re facing, and I will say that almost every time that we do an interview on this program about threats to sea life, two things come up– climate change and commercial fishing practices. And you say both of those things can play a role, but those aren’t necessarily the biggest threats to sharks.

DAVID SHIFFMAN: Yeah, the biggest threat by far to sharks is unsustainable overfishing, which is different from fishing in general. There is sustainable fishing, both for marine life in general and for sharks specifically.

Climate change is something of an emerging threat to sharks. We don’t know exactly what it’s going to do, but thus far, it’s considered a much, much, much, much less major threat to sharks than unsustainable overfishing by which I mean, if we totally solve climate change, which we should do– it’s a major threat to other things. But if we totally solve climate change but don’t fix overfishing, many species of sharks are still in trouble. If we fix overfishing but don’t fix climate change, many species of sharks will have their trajectories improved significantly.

JOHN DANKOSKY: Explain how unsustainable overfishing harms sharks.

DAVID SHIFFMAN: We talked earlier about how sharks are so well adapted to their environment and have been around for hundreds of millions of years, but the problem is they’re really well adapted to environmental conditions that don’t really exist anymore. Sharks life history is not designed for large numbers of their species being killed. They have relatively few babies relatively late in life relatively infrequently, and every one of those babies is better able to survive than a larval tuna or something like that.

But it means that their populations take a really, really long time to bounce back from being hit by something like overfishing, and that means they’re especially vulnerable to overfishing. And also sharks are– in addition to targeted fisheries for sharks, both for their fins and for their meat, sharks are also commonly victims of what’s called bycatch, which is accidentally catching a fish that’s swimming near what you were trying to catch, which is unavoidable with large-scale commercial fishing gear. You fish for tuna with these long lines that have tens of thousands of baited hooks on them, you’re also going to catch sea turtles, and seabirds, and sharks.

JOHN DANKOSKY: I’m John Dankosky, and this is Science Friday from WNYC Studios. I’m talking with Dr. David Shiffman, who’s the author of the new book Why Sharks Matter– a Deep Dive with the World’s Most Misunderstood Predator. You can read an excerpt at sciencefriday.com/sharks. People want to help protect sharks. What are some things they can do?

DAVID SHIFFMAN: The single most effective thing that one person can do to help the ocean in general, including but not limited to sharks, is to not eat unsustainable seafood. Notice I did not say we all have to give up seafood and all become vegans immediately as has been claimed by some. If you want to do that, that’s certainly a valid choice, but we’re absolutely not at the point where the science says we all have to do that or the ocean is doomed.

So you can eat sustainable seafood if, like me, you love seafood or if it’s culturally important to you. It’s also can be very nutritious. So don’t eat unsustainable seafood is the biggest thing that people can do to help the ocean, including sharks. There are also some great environmental nonprofits that could sure use your support. I introduce readers to many of them in the book. But also I want to stress that there are some problematic nonprofits that do not actually do a whole lot to help, and the book also talks about ways that people are trying to help that are perhaps not especially helpful.

JOHN DANKOSKY: Without getting into too many of those details, are there things that people are doing to try to help the oceans as a whole that maybe, in the end, can harm a species like sharks?

DAVID SHIFFMAN: There are some problematic practices done by some wildlife tourism operators. These are people who operate businesses where you can pay to go swimming with sharks, scuba diving, or snorkeling, or something. And that absolutely can be done in a way that is safe for humans and sharks, but it’s increasingly done in such a way that it is bad for sharks and can be quite dangerous for humans.

There are people who have swung the pendulum of shark misunderstanding too far in the wrong direction. It used to be this belief that the only good shark is a dead shark. And if you dip your toe in the bathtub, a shark is going to eat your whole family, so we should kill them all. And we don’t have that as a problem so much anymore.

But now we have people who go too far in the other direction and say sharks are actually cute, innocent, adorable puppy dogs who just need love, and hugs, and kisses. And there are people who hug, and kiss, and ride large free-swimming sharks. And they say they’re doing conservation by doing this. I don’t know what the heck that is, but it’s not conservation.

JOHN DANKOSKY: I can’t leave this conversation without asking you, what’s your favorite shark, David?

DAVID SHIFFMAN: My favorite shark is the sandbar shark. Follow #bestshark on Twitter and Instagram, and you will see years of me talking about how much I love my sandbar sharks.

JOHN DANKOSKY: Why do you love the sandbar shark so?

DAVID SHIFFMAN: Sandbar sharks are sort of the classic model shark. If I ask you to visualize a shark, it’s going to look at an awful lot like a sandbar shark. If you’ve ever been to an aquarium, you’ve probably seen one. They’re very common aquarium animals, which means that, for millions of children around the world, a sandbar shark is the first shark they ever see in their whole life, and that can lead to a life of wanting to protect the ocean.

JOHN DANKOSKY: Dr. David Shiffman is a faculty research associate at Arizona State University, and he’s the author of Why Sharks Matter– A Deep Dive with the World’s Most Misunderstood Predator. David, thanks so much for being with us.

DAVID SHIFFMAN: Thanks for having me.

JOHN DANKOSKY: That’s all the time we have this hour. Here’s Kyle Marian Viterbo with some of the folks who helped to make this show. possible.

KYLE MARIAN VITERBO: Annie Nero is our individual giving manager. Nahima Ahmed is our manager of impact strategy. D Peterschmidt is our digital producer, and I’m community manager Kyle Marian Viterbo. Thanks for listening.

JOHN DANKOSKY: Thanks, Kyle. BJ Leiderman composed our theme music. Ira’s back next week I’m John Dankosky.

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