Planet Earth

Studying Shark Brains

Kara Yopak has amassed hundreds of shark brains. Now she's using them to better understand how the animals behave.

By David ShiffmanNov 3, 2021 12:00 AM
Yopak2
Kara Yopak has collected more than 400 shark brains. (Credit: Jeff Janowski/University of North Carolina Wilmington)

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This story was originally published in our November/December 2021 issue as "Thoughts from a Brain Collector." Click here to subscribe to read more stories like this one.


On a typical day at the beach, you might see surfers rushing out into the waves or retirees strolling through the sand with metal detectors. Then there’s Kara Yopak. She’s on the hunt for brains — shark brains, to be exact. To date, she’s collected over 400 brains from shark species all over the world. But it’s not just a hobby; Yopak, a biology professor at University of North Carolina Wilmington who leads the aptly-named ZoMBIE lab, is examining these complex organs to better understand how sharks behave.

The idea that sharks are mindless killing machines has been perpetuated for decades. In pop culture, look no further than the horror classic Jaws, where the film’s villain is a vengeful, human-chomping great white. But the misunderstood beasts are more complex than the movies might suggest. For starters, they are some of the oldest vertebrate animals alive today, and also some of the most threatened. They’re masters at adapting to new environments, and research on modern-day sharks can teach us more about the evolution of different senses. And we still have a lot to learn about protecting humans from sharks — and vice versa — which is why it’s vital for researchers like Yopak to better understand the differences between species.

Starting with their brains.

So what do you do, and how did your lab get its name?

KY: We look at differences in brains between shark species and what that can tell us about shark behavior. You can use the brain to almost predict behavior and sensory specialization, which I think is really cool. But before I can tell you what ZoMBIE stands for, first, I have to teach you a word: zootomy. It’s a fancy term that means comparative anatomy, or looking at what’s similar and different between the anatomy and biology of different animals to figure out their evolutionary relationships. The acronym [for our lab name] stands for “Zootomical Morphology of the Brain and Its Evolution,” but I’ll freely admit I had the acronym first and came up with what it stands for later. That’s because, at conferences, I’m talking with someone who’s doing some really cool work on a shark species, and I say something like, “That’s really interesting. … Do you think I could have its brain?” We’re just a bunch of zombies; all we do is look for brains!

Greenland sharks have incredibly small brains, but possess massive olfactory bulbs - meaning they likely hunt using their sense of smell. (Credit: Hemming1952/CC-By-4.0/Wikimedia Commons)

What’s it like looking at shark brains? What sights, sounds and smells do you experience when studying them in the lab?

KY: It always starts with collection. If a fisherman says, “We caught a shark,” we’ll be there to claim the specimen. And if it’s a really big shark we’re processing, the first sound you’ll hear in the lab is a bone saw. Once you get to the actual brain, it’s more of a fine-scale process. You’ll see my students in the lab hunched over a microscope, doing incredibly small, precise dissections — our kits have everything from machetes to the teeniest forceps and scissors you can imagine. We’ve gotten brains from as big as white sharks and from as small as guppies.

My favorite lab sound is a student dissecting a brain for the first time, and they shout, “Wow, that’s so cool!” It’s gross and weird to cut the brains open, but it’s incredible to see this thing that drives behavior. You can look at it and hold it in your hands and investigate it further. And the brains are totally squishy. You’d be surprised at how delicate and strong they are at the same time.

What initially drew you to this field?

KY: Most shark biologists have this same story: I was obsessed with sharks when I was 5 years old. My mom just dug up an old book of mine that I wrote when I was 5 years old, saying, “I want to be an ichthyologist who studies sharks just like Eugenie Clark!” I’ve always been fascinated by them. You don’t know where it comes from, but you know that’s your path.

That grew into an interest in sensory biology and behavior, but I didn’t get into brains until my Ph.D. My advisor said, “For your first month, just read.” And every paper I read, I realized I couldn’t understand sensory biology or behavior until I understood the brains — that’s where sensory signals go and where behavior comes from. So I asked my advisor, and he had me look into it with a sentence that started my career: “You should just go collect some brains.” I took that to heart and have since collected brains from over 130 species of sharks.

What are some common misconceptions about shark brains and shark intelligence?

KY: There’s a common misconception that sharks are these pre-programmed eating machines. Even in Jaws, Hooper, the scientist character says, all they do “is swim and eat and make little sharks.” So you have this perception that they’re primitive, simple animals. We think of birds and mammals as being these very advanced organisms that can do these very advanced things, but it turns out sharks can do some of those things, too. There are rules governing how brain size changes with body size across animals, and it turns out that many sharks have a brain size relative to their body size that’s pretty comparable to birds and mammals.

(Credit: Kara Yopak/University of North Carolina Wilmington)

You’ve addressed the question “How smart are sharks?” a little bit already, but I know you hate being asked that. Why do you feel that way?

KY: It’s the first question everybody asks me, and I hate it because “smart” is a difficult thing to quantify. Generally, we have a human-centric view on things. How do you find a way to define intelligence that’s applicable across all species? They can’t do calculus, but they’re incredibly successful in their niche and they have all these complex behaviors. So this isn’t a bad question; there are just so many more interesting questions.

What do you see when you look at a shark’s brain? Is it similar to a human brain?

KY: Most people think when they look at a shark brain they’re going to see a miniature human brain, which is kind of fist-shaped. But shark brains are long and thin and shaped almost like a spark plug. In our brain, you see the neocortex and the cerebral hemispheres, but only mammals have that. But you will see all of the major brain structures that are shared across everything; they have the vertebrate brain blueprint and they were the first to have all these structures. You can see how there were some developmental rules that have been carried through vertebrate evolution all the way to us.

This illustration approximates MRI brain scans of two different shark species. Since the two are closely related members of the same family, commonly known as “sleeper sharks,” scientists like Yopak can study these similar patterns of brain organization — the red marks the medulla oblongata, for instance, while the blue shows the cerebellum — to learn more about the animals’ shared characteristics. (Credit: Jay Smith)

But not all shark species have the same brain layout, right? What varies from species to species?

KY: They all share the same regions, and are somewhat modular — they all have the same components. But they have huge differences in brain organization, in the relative size and complexity of those components. So, when you look at a brain of a Greenland shark, they have an incredibly small brain, but a relatively enormous olfactory bulb that processes smell. You can predict from this that the shark probably hunts mostly using smell. In deep-sea sharks, you’d notice that the parts of the brain that process electrosensory input are huge, which makes sense. It’s so dark there that they probably can’t see and rely on other senses.

If I hand you a shark brain and don’t tell you what species it’s from, can you tell me about its life?

KY: I could make a pretty good prediction about it, yeah! We’ve looked at over 180 species, so if you hand me a random shark brain I could confidently predict where it lives, what it eats, how fast it swims, how it hunts, how complex its habitat is, and so on.

(Credit: Jeff Janowski/University of North Carolina Wilmington)

I’ve heard that you use this as a dissertation exam question for your students.

KY: Oh, yeah, for a defense I recently traveled to, I had a shark brain in my purse. It was a 3D-printed copy, but I’m not above bringing an actual brain with me. I handed it to the student and asked him to look at the brain and predict where it lived and how it lived — and he came really close.

One of the sadder parts of shark science is that sometimes sharks hurt people. We often hear that this is because of “mistaken identity” — like when sharks mistake surfers for seals, their normal prey. What can studying shark brains tell us about why sharks sometimes bite people?

KY: What we’ve seen from the data so far is that there’s remarkable variability in shark brains, which suggests there’s remarkable variability in how these animals perceive their environment. Sharks do things based on their sensory input, and we have to approach this problem by recognizing that each species responds differently to sensory signals.

You’ve also been involved in some research studying how sharks respond to shark repellents that target senses like sight and smell. Do those really work? What the theory behind them?

KY: The theory here is that the relative importance of different sensory systems varies, so if you’re trying to deter sharks, you need to understand the biology of the species. You need to understand how their brains work before you can even start to approach how you can keep that species away from humans. For example, of the shark species that have been identified, most are colorblind, so any visual deterrent has to be highcontrast in design, and we need to know a species’ visual acuity to know if they can even see it. There’s so many variables that go into these things. The world wants a Lord of the Rings deterrent — one shark repellent to rule them all — but that’s probably not possible given these incredible differences in species and how they perceive the world around them.

There’s been some concern about the quality of the science that’s featured on high-profile educational TV like Shark Week. You’ve appeared on Shark Week, and you’ve said that you’d like to get more good science on there. Why is that so important?

KY: I don’t produce television and there are probably some complexities to that that I don’t understand, so I understand some of the motivation to sensationalize. But it troubles me when shows are led by sensationalism or inaccuracy. There’s a danger in presenting wildly wrong information. It’s very easy for misinformation to get absorbed by the public, so it’s important to incorporate actual experts in the field who really know what they’re talking about. That way, you have a mix of something people want to watch while also teaching them real science.

What can shark brains teach us about our place in the world? We tend to think of ourselves as being the smartest thing around.

KY: Aaaaaand we’re back to the word smart. [Laughs.] What’s come out of my work that’s been so amazing is the continuity, the throughlines, the rules governing how brains change as animals grow. There are so many similarities in structure and function across all living things that I think are fascinating!

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