What Can Sharks Teach Us? with Marine Biologist Molly Gabler-Smith

HMSC Connects! Podcast Episode 10 Transcript

SPEAKERS Molly Gabler-Smith, Jennifer Berglund 

Jennifer Berglund 00:04 Welcome to HMSC Connects! where we go behind the scenes of four Harvard museums to explore the connections between us, our big, beautiful world, and even what lies beyond. My name is Jennifer Berglund, part of the exhibits team here at the Harvard Museums of Science and Culture. And I'll be your host For our second installment of the HMSC Connects! Ocean Month, I'm speaking with Molly Gabler-Smith, a Postdoctoral Fellow in George Lauder's lab at Harvard, where she studies the way sharks move through the water. I'm talking to her today about that work, as well as her work with other animals like rays and whales. At the end of the month, HMSC Connects! will be releasing a new Exhibit Spotlight online about shark locomotion, which also features her work. Stay tuned for that. Here she is. 

Molly Gabler-Smith 01:15 Unfortunately, I grew up in a landlocked state of Pennsylvania, but it didn't really inhibit me from spending a lot of time at the beach. My family vacationed many, many times in the summers on the coast of North Carolina in the Outer Banks, and I kind of grew from a young age learning to love the ocean and the water. Actually, it's interesting because my favorite animal is actually a sea turtle, and my very first trip to the Baltimore Aquarium, which was really close to where we lived, my aunt actually purchased a plastic sea turtle that I actually still have. I still have it in my apartment. It always reminds me of kind of how it started my path towards wanting to understand more about the ocean itself. I've always loved being near the water, and kind of was really intrigued about how we knew a lot about the ocean, but there was still so much to actually learn about water that makes up so much of the Earth. When I initially went to college, I was really interested in the biomedical field, but knew that I didn't want to go to medical school. After spending about a year and a half in some research labs, I realized that they really spend most of their time in the lab behind a microscope, and as much as I love microscopes, my oceanic calling was still kind of in there, and I was like, you know, I really want to step out of this lab-based research and kind of look at more environmental stuff. So, I ended up transferring from that university to a different one, where I majored in ecology and kind of looked more at the conservation side of things, and that is kind of what led me to meet my Master's advisor where I actually studied the muscles in the pectoral fin of stingrays. And that was really interesting to me because not only was I studying something from the ocean, but I also got to look at how an organism is built to live in the environment that they do. 

Jennifer Berglund 03:21 And why was that particularly interesting to you? 

Molly Gabler-Smith 03:24 So, I realized that certain animals are more equipped to live in certain parts of the ocean than others, and stingrays, in particular, some of them, perform large and long migrations like cownose rays. And it was really interesting to see how the muscle of say a cownose ray that does frequent migrations compared to a stingray, like the freshwater stingray that is a very benthic animal, and how those muscle aspects differ between the two and if we could see a difference between the ecology of how an animal exists in the ocean is related to tissues inside of the animal itself. Watching these animals swim free in the environment was really fascinating because, unfortunately for me, my research that I did on the muscles really involves specimens, and so I didn't actually get to see them swimming live. Watching these animals swim freely in the open ocean was really fascinating because I had studied the muscles behind the movement of their pectoral fins, but because the animals were just specimens, and I just collected tissues from them, they weren't actually swimming. It was really fascinating to see the muscles in action and kind of know how the muscles were moving and working together to allow that animal to perform the swimming style that it did. The stingrays that we saw were they're called undulators, and what they do is they pass multiple waves down their fins at a time. You can kind of think of it as like a ribbon kind of swimming in the water, so they pass that these multiple waves, and it just looks magical, honestly, because the way they move through the water, it's so effortless. And this is in comparison to like a cownose ray that swims almost like a bird underwater where it's more flapping. They're called oscillators, and so they'll flap through the water in, and what's interesting is that they both have different types of muscles that allow them to get these movements of their muscles and their pectoral fins. Oscillators like the cownose ray have red muscles, which they use to sustain their swimming. So, red muscles in general are used for long periods of time for more sustained movement. So, as they're flapping, they are able to not use as much energy by utilizing these red fibers and sustain their swimming. They also use them when they're migrating these long distances, whereas the undulators, more like Atlantic Stingray, they have more of like a circular disc shape. They have white muscles, and white muscles are used for more sudden movement, and because they're sedentary, or they are mostly on the ocean floor, they might need more of these white muscles in order to escape predators more easily than an animal that's kind of swimming in the pelagic region. 
Jennifer Berglund 06:18 You worked on this multi-university project on making a model of a stingray, essentially. So, like an autonomous Stingray. Can you explain that a little bit? What was that all about? 

Molly Gabler-Smith 06:32 Sure. So, the Navy is really interested in getting scientists to study animals that they deem are efficient swimmers. And so they picked the stingray for a group of scientists and engineers to study, and so what that essentially involved was a team of engineers and a team of biologists, and so the biologists would study how the sting rays swim. We did a lot of video from the Georgia Aquarium and analyzed kinematics. So, what we do is we look at how the pectoral fin is moving, how the body moves, how the tail moves, and put that into data that an engineer would then take, and then build a robot off of it. The more that the biologists studied these stingrays, the better the robot got. So initially, it started out as this kind of cumbersome mantabot that was tethered. 

Jennifer Berglund 07:24 When you say tetherd, it was it was connected. 

Molly Gabler-Smith 07:26 Connected to a string where someone else would be holding the string, and that was really the only way the robot could move, and then progressively got better, whereas it could then only be controlled by a remote control, so it was pretty much free swimming at that point. And what the engineers did was they just went through all the data we had collected from the videos of live stingrays swimming to build a robot that would mimic what an actual sting ray would do in real life. 

Jennifer Berglund 07:57 You studied the deepest diving mammals, Cuvier's Beaked Whales, which are capable of diving nearly two miles and staying at a depth like that for two hours. Can you explain that work? What were you looking at in particular? And how has that informed engineering projects. 

Molly Gabler-Smith 08:17 My PhD research was interested in looking at the physiology of air breathing, diving animals. In particular, how their fat allowed them to conduct deep diving, and perhaps how their fat allowed them to avoid getting the bends. The bends happens to any animal that is breathing air, so it can happen to humans, it happens to seals, it can happen to birds. Any animals that will breathe air at the surface. As they dive down through the water column, the pressure in the water increases, and that forces gas, so not only oxygen, but also nitrogen and carbon dioxide, to be dissolved into tissue. So, the gas will leave your lungs, travel through the blood, and as the pressure increases, it can travel into tissues like muscle and fat. And so, then, when you decide to surface, the gas will go from the tissue back into the blood, through the lungs, and then that's when you surface and you exhale. The bends happens when you ascend, or when you're coming up from that dive too quickly, and you don't allow enough time for the gas to actually come out of the tissue and into the blood. 

Jennifer Berglund 09:28 And there's some basic physics behind this too. So, when you go in a deep water, there's a lot of pressure from the water all around you. So that compresses the gas. Yes. And so, when you have less pressure as you ascend, the gas expands. Yep, yep, 

Molly Gabler-Smith 09:41 Yes. And so what happens is, sometimes that gas expands too quickly or leaves the tissue too quickly, and it can either form a bubble within the tissue itself, or it can cause bubbles to form in the bloodstream, which then is a bad thing and can either cause disease or potentialy death, if that isn't taken care of. And it was originally thought that marine animals, in particular mammals, had all of these physiological adaptations as well as morphological adaptations, like 

Jennifer Berglund 10:13 So, body shape. 

Molly Gabler-Smith 10:15 Yeah. So, things to do with anatomy and biochemistry. So, they have muscles that are built to store more oxygen to allow them to dive deeper for longer. They have collapsible lungs, which also helps them deal with the pressure effects. They also have diving behavior, which allows them to offgas properly when they come up from a dive. So, they'll spend a certain amount of time at a certain depth where they know the gas can be released from the tissue without causing any harm. So they're a very interesting study species because they have all these adaptations that humans do not. However, they are mammals, and they breathe air just like us. We work more with modelers and how they can use the data that we've collected in looking at maximum capacity or maximum dives that these animals could potentially do based on their physiology. But currently, I do know there's a project going on in California where they're actually doing research on sea lion swimming, and they're actually building a sea lion robot based on sea lion swimming because they're very streamlined, they can swim very quickly, and so that is kind of where the marine mammal world of biologists is kind of interacting with the engineering world as well too. 

Jennifer Berglund 11:40 Eventually you transitioned to working with sharks, which are physiologically very different from whales, and pretty different from rays. Why did you pivot? 

Molly Gabler-Smith 11:53 I like to think that it wasn't necessarily more of a pivot but kind of tangential line from what I was doing originally. So I like to think of myself as a researcher who looks at studying the form and function of animals. So I like to look at certain tissues within an animal and determine how it enables an animal to function in a certain environment. So for my PhD, I was looking at the fat tissue, and how it allowed these animals to dive at such great depths, and so now I'm interested in looking at shark skin and kind of how the skin and the shape of the skin allows certain species of sharks to swim at high speeds, or live in the environment that they do. 

Jennifer Berglund 12:40 You've also worked with basking sharks, which basking sharks are the second largest shark. And interestingly, they only eat these little kind of microscopic organisms called copepods mostly. How are you studying basking sharks? 

Molly Gabler-Smith 12:59 There is a research station on Grand Manan Island that is in the Bay of Fundy, and the Bay is a very diverse environment. There are everything from lots of fish, scallops, there are seals that hang out there, fin whales, minke whales, right whales, and then we also have lots of sharks. Sharks that frequent this area can range from porbeagle sharks, mako sharks, great white sharks, and then we also have basking sharks. And like you said, they're the second largest shark in the world, however they filter feed. And what's really interesting about this environment is that it's in Canada, and what Canada doesn't have that the US does are these buoys that essentially track changes in water temperature. So what we've been doing is using sharks kind of as a way to look at changes in water temperature instead of just deploying this buoy there, we're actually using the live animals. And so we're tagging them, and we can look at where they're spending time in the water column, what's the temperature range between the surface and the depth, how it changes over time. This has been a long term study that has been ongoing for about 10 years now, and what's really interesting is that we do see that temperature has been changing. There's kind of this cyclic pattern of an increase in two degrees and then decrease in two degrees, and so the bay is actually fluctuating quite a bit, and what we see is that it is actually affecting the animals that live in this environment. So, along with tagging the actual basking sharks themselves, we also deploy plankton nets. And so what we're doing is measuring the density of the copepods in the water, what types of zooplankton are there, and then what we do is we take the samples back to the lab and actually measure how much energy the animals have in them. We use the lipid, so that's fat inside the animals and we can measure how much energy about lipid has, and so that would equate to how much energy the basking shark is actually getting by consuming these animals. And so it's interesting because we also see over these changing time periods with changing temperature that the copepod population is also changing with it, and so we see that in increased temperature years, there are less copepods, they have less energy in them, and so we've also been seeing a decrease in shark sightings within the Bay. Additionally, we also see another big marine megafauna that's also present are the North Atlantic Right Whales, who also eat copepods, and what we see during the years where copepod densities are very low, we also see much less density of right whales in the Bay too. So it's really interesting to see how you can use an animal and follow how the environment is changing over the course of a time period of about 10 years.

Jennifer Berglund 15:52 Yeah, it's really interesting to see how you're using an animal like a basking shark to both monitor the environment and monitor their behavior. Yes, it's clever. 

Molly Gabler-Smith 16:05 If you can say we can use these animals to look at the environment, and how it's changing over time, maybe government agencies might be more likely to protect them and make sure that conservation efforts are happening. 

Jennifer Berglund 16:18 So you're tagging the sharks. So, what are the tags like and how do you attach them to the shark? 

Molly Gabler-Smith 16:25 Yeah, so we use a tag called a TDR, and that's a temperature depth recorder, and essentially what it is is a tag that we have programmed to stay on the fish for three days, and then it corrodes away and the tag will float to the top, and then we have to go and retrieve it to collect all the data from it. And so what it does is it collects temperature and depth data, I think every 20 seconds for that whole period of three days, and then we can kind of start to plot out where the shark was going within the water column, the location that they traveled over the course of their three days, and how we do that is that we take a boat into the Bay, we essentially just sit on the water until we find a shark fin sticking out of the water because they're basking sharks, so most of their time is spent basking on the surface. So it's really easy to spot a large dorsal fin. They can be sometimes between three and four feet tall, so you can really see them from the surface of the water. So once we find a fin, we kind of boat over to it, get as close as we can without actually touching the shark, and then someone will take a poll that has the tag deployed on it, and essentially punch it through the dorsal fin. We equate it to kind of getting your ear pierced because it is cartilage. We found that the tags don't rip through dorsal fin, so that doesn't really cause any damage to the shark, but once we tag it, the shark then just swims away and we can track our tag via satellite. 

Jennifer Berglund 17:51 Why should people care about sharks? 

Molly Gabler-Smith 17:54 I think it's really important for people to remember that this is their environment, and we're kind of the intruders to them. The sharks have been here much longer than we have, and it's obviously concerning as people are swimming in the ocean and shark attacks do happen, though very rarely, it is really important to know that you're the intruder in their environment. I also think that it's important to continue to study these sharks because who knows what information they can give us in the future? The basking sharks have been really useful in tracking the differences in temperature in the Bay of Fundy, and also looking at prey densities that have also connected the population of right whales in the area. And they're very endangered marine mammal, so who knows what they could actually be used for in the future, so I think it's really important for us to look at sharks as a way to just increase our knowledge of the ocean and see how they might be used in the future for almost anything that we can think of. 

Jennifer Berglund 18:57 Yeah, anything from studying the climate to developing a more efficient robot. 

Molly Gabler-Smith 19:03 Yeah, exactly. Exactly. 

Jennifer Berglund 19:09 Thank you so much, Molly. This has been awesome. 

Molly Gabler-Smith 19:11 Sure. It was my pleasure. 

Jennifer Berglund 19:19 Today's HMSC Connects! podcast was produced by me, Jennifer Berglund, and the Harvard Museums of Science and Culture. Special thanks to Molly Gabler-Smith, and the Harvard Department of Organismic and Evolutionary Biology for their wisdom and expertise. And thank you so much for listening. If you like today's podcast, please subscribe on Apple Podcasts, Spotify, podbean, or wherever you get your podcasts. See you next week! 

Transcribed by https://otter.ai