Short Wave - One Key To Healthy Oceans? Sharks

Episode Date: March 9, 2021

Shark scientist Melissa Christina Marquez explains just how important sharks are to keeping the oceans healthy, including their role in mitigating climate change. Plus, there may be some talk about shark poop.Email the show at [e-mail] pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shortwave from NPR. Melissa Christina Marquez has been obsessed with sharks since the very first time she saw one as a little kid on TV during... You guessed it. She was watching a show called, and this is real, Air Jaws. Which essentially is just showing the power of Great White sharks breaching or flinging themselves out of the water up into the air to kind of catch their prey. You're twisting and turning as if it is trying to dismember its prey.

You know, I think for any person, but especially a child, who's never seen a shark like that before, it's really awe-inspiring. You kind of just sit there with your jaw on the ground, being like, wait, what? It kind of cemented for me as a kid being like, yeah, this is what I want to study. This is what I want to dedicate my life to.

And she does. Melissa's a shark scientist, a PhD candidate living in Western Australia. And what Melissa wants us to know is that sharks are not only these fierce and amazing creatures, like how she first saw them on TV as a kid, they also play this incredibly important ecological role, too. The saying is, a healthy ocean needs healthy sharks, and that is very, very true. So today in the show, we dive into the importance of sharks with shark scientists, Melissa Christina Marquez, including their role in mitigating climate change. And, you know, there may or may not also be some talk about shark poop. I'm Maddie Safaya, and you're listening to Shark Wave from NPR.

All right, Melissa, let's get into it. Let's talk about something people might not think about when they think of sharks, and that's the role that they play in the health of the oceans. Yeah, so let's start with kind of a generalized shark. Many of them kind of start their life out in a nursery, so in a secluded kind of area, such as, say, a mangrove. And so they use the protection of those roots to kind of learn how to become a shark to be able to hunt while not being hunted by their own species sometimes. Once this animal kind of grows up, some of them do go to coral reefs. And coral reefs need sharks.

Just a shark being there actually kind of chile. changes the dynamics of that coral reef. For example, in Fiji, there are some fish that are herbivorous that eat kind of like algae and seaweed that's in the coral reefs. They'll actually avoid areas that are patrolled by reef sharks. So that means that the seaweeds have a chance to have kind of like a refuge in that area because they're not being eaten by any fish there. So it allows for that dynamic to exist. Oh, I didn't. So they're actually, I'm not thinking of them like protecting like plant species, but just them being there is doing that. Definitely, it is.

It's one of the things of just a shark being there changes what a habitat looks like because it influences the behavior of the fish that they eat. Right, right. And I know that they also kind of feed on the dominant prey in that area and that that can cause changes in those species. Tell me a little bit about that. Quite a lot of people when they think about why do we need sharks, they think of them keeping the ocean system balanced. And they do keep prey numbers balanced. So for example, say you have a big predator fish and you have multiple of them because you've taken out the sharks that prey on them, that means that that vegetation or any of those herbivorous fish that have kind of been protected or kept in check, suddenly that whole entire system goes out of whack because you've got nothing. keeping those other predatory fish in line. So they're kind of like, right, it's a smorgasborg,

I can eat whatever I want. And really, it just leads to a ruined ecosystem. Mm-hmm. Mm-hmm. So sharks play this role at coral reefs. And then they kind of, you know, start to migrate, start to move. What role do they play while they're actually migrating? So the really cool thing about sharks is quite a lot of them are migratory. So they're not always in one location for their entire lives. Many of them, such as, whale sharks take really long migration. So they pop up in various parts around the world. And so it helps kind of transfer nutrients from different parts of the ocean via, well, poop. If you think about it, it kind of makes sense because their poop sort of acts like a fertilizer of sort for any

respective habitat. And a great example of this, there's actually gray reef sharks that are in the Central Pacific. And they forage offshore of their habitat at night and then they return to kind of rest in this atoll during the day. And so they're constantly kind of shuffling nutrients from that outer open ocean area into a more densely kind of populated coral reef area. So researchers actually estimate this day-to-day offshore water, insure water migration actually brings in about 95 kilograms of nitrogen daily onto a coral reef, which is usually nutrient limited, which means that it keeps this ecosystem pretty healthy. So yeah, I don't think we're going to be seeing poop,

like shark poop fertilizer anytime soon in our store. But it's good fertilizer. I mean, it's wild that, like, how much nutrients that is actually introducing from, you know, its original location to the new location that might not have that. I mean, that's, that's huge. I had no idea. I mean, poop's important always, but... Yeah, 95 kilograms of nitrogen. That's, it's bananas. Okay, so do sharks have any role in mitigating climate change? Because I'm thinking, you know, I'm thinking about coral reefs. I'm thinking about the changing oceans right now. Are sharks going to help us out with that? Yeah, definitely. There's actually a really great example of it here

in Western Australia. So we've got a few. tiger shark species, which is my favorite species of shark. And they patrol the seagrass beds here in Western Australia. And it seems to cause two specific animals to limit how much seagrass they eat. So sea turtles, which many people know, but dugongs, which are kind of like a relative of the manatee. So you're probably wondering why the diet of these two animals has anything to do with climate change. But essentially, them not being able to eat seagrass increases primary production, which is CO2 uptake, which maintains carbon sediment stocks. And marine sediments are one of the most expansive and critical carbon reservoirs on the planet.

So they're key for regulating climate change. Wow. So it's really, again, them just playing that role of creating a balance, right? When you think of sharks, the first thing you think of your mind isn't really like, ah, they help balance this ecosystem. Yeah, you know, it's one of those things when a lot of people think of sharks. They think of, oh, they just eat fish and they keep that food web balance. And it's true, they do do that. But they do so much more than a lot of people don't realize.

It's not until you kind of lay everything out on the table that they're like, holy crap, these animals do a lot. Yeah, we need to protect them. Yeah. I mean, yeah, that's my kind of leads to me to my next question, Melissa, which is, you know, with all of this in mind, what is this, you know, the general state of sharks. You have convinced me they are super important for all different types of reasons. You know, are they okay, I guess, is what I'm asking. I mean, it really depends the specific shark you are talking about

because there are over 500 different species of sharks out there, which is really cool. And, you know, they've been around for over 400 million years. They've survived multiple mass extinctions. But it seems that they're not really. surviving the most formidable opponent, which is us. A recent study that just came out is probably one of the most largest collaborative projects that I've seen yet was looking at the impact that threats such as overfishing and bycatch, habitat destruction and degradation, climate change, plastic pollution, and of course, illegal shark finning, what those kind of

threats have on our global shark populations. So it's bad. It was a bit. It's sobering. And I did have a little bit of a cry because, you know, as a shark scientist, I love these animals. I love learning about them. I love protecting them. But it does kind of get you a reality check of I'm not going to be able to save them all. We're not going to be able to save them all if this continues. So that's why I'm a really big advocate of get rid of the jargon of their man-eaters, that they're monsters, that they're mindless killers. Because if anything, if we're looking at the numbers, on average, they fatally bite six people per year, and we're killing millions of them a year.

So really, if we want to label someone a monster, I think we're labeling the wrong animal. So they definitely need a PR manager. Add that to my business card. Okay, Melissa, I want to end on a note of straight-up shark appreciation. So don't think too hard about this. Really quick. Give me your top three sharks. Go.

Oh, okay. Tiger shark, hands down, favorite, black tip reef sharks, and Caribbean rough shark. So if people Google that, it is a weird-looking animal. Okay, Melissa, this was super fun. I learned a lot. I appreciate you and I appreciate sharks. Thank you so much. Thanks for having me.

This episode was produced by Britt Hansen, fact-checked by Ariela Zabidi, and edited by Viet Le. I'm Maddie Safai. Thanks for listening to Shortwave from NPR. On NPR's, consider this podcast. We help you make sense of one big story in the news every day, like how to combat disinformation and conspiracy theories, which pose a real threat to democracy, and what life looks like after you're vaccinated, the next phase of do's and don'ts. All that in 15 minutes every weekday. Listen now to consider this from NPR.