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Conservation scientist Dr. Lesley de Souza is working with the people of Guyana to establish a new protected area. Their goal is to safeguard a watershed for animals like the arapaima, one of the largest freshwater fish in the world.

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Producer, Writer, Creator, Host:
Emily Graslie

Producer, Editor, Graphics:
Sheheryar Ahsan

Producer, Camera:
Brandon Brungard

Interview with:
Dr. Lesley de Souza

This episode is filmed at and supported by The Field Museum in Chicago, Illinois.

EMILY: This is Dr. Lesley de Souza. She's a conservation scientist and an ichthyologist, which means she studies fish, primarily those in South America, and one group in particular, the arapaima. A genus of freshwater fish that can get up to nearly 10 feet, or 3 meters in length.

When she's not here at the Field Museum, she's conducting fieldwork in Guyana along alongside the indigenous people in the region. Their goal is to create a protected area to ensure a healthy future for the land, water, and people in the country. So we met up with Lesley to talk about her work and geek out about these incredible fish.

EMILY: I think it's really interesting that when we think a lot about, like, rainforests, conservation, most people think about saving the trees but what you're really advocating for is saving these watersheds and saving these, these, ahm, aquatic environments.

LESLEY: Essentially a watershed is a whole river system that's connected to the forest, and to the people, and every aspect of that natural environment. If you have a headwater system that is flooding a savannah or a forest, anything that's upstream is gonna affect anything that's downstream. What fish are doing, especially in these Amazonian systems, is that, they migrate into this flooded forest during the rainy season, and so not only do you have to protect the waterways that they use to reproduce, but you have to protect the forest that becomes flooded that are connected to those river systems.

EMILY: Why arapam-arapaima? I mean, there are so many different, diverse, species of fishes in the Amazon, and why just focus on one?

LESLEY: The arapaima in that particular region is endemic, which means it's found there-no where else in the world.


LESLEY: And their populations were declining; the local people wanted to protect this species. And so, together with the local, indigenous, communities, we started studying their movement patterns. And so, as the rainy season comes on, the river floods, and a lot of fish are moving upriver and going to the flooded forests to spawn, and have babies, and eat food. The main question that we were trying to get after is where do they go, and what is the extent of this river drainage are they utilizing?

EMILY: How do you track that kind of movement?

LESLEY: Oh my goodness. I mean, it was something that had not been ever been done for arapaima, yet. Using radio telemetry, which is a technique to track and follow fish using a radio transmitter that has a certain frequency and that's connected to a receiver. And essentially, what you do is you have an antenna and you could have a radio transmitter inside a fish.

You are riding down the river and you're just looking for this fish. And you're looking for this signal of that fish based on the frequency.

EMILY: Are you putting radio collars on these fish? Or what is, what is, that whole process?

LESLEY: That's a great question. And what we did on this particular study, radio telemetry study with the arapaima, is that we inserted radio transmitters into the inter-ceolom, so, which is the stomach cavity of the arapaima. So, here is a very, very, small arapaima. Very different than, uhm, what I'm dealing with in the field.

If you look in this bottom area--which there is already an incision-- there's a large space, because it's a large fish, that's essentially at empty. It's like a huuuge cavity.

EMILY: Okay.

LESLEY: And then that's where the radio would sit. So we used nets to, kind of, corral them into a shallow space. We essentially had to wrangle them and hold them. Then we turned over the fish, took out scales, inserted this radio transmitter, sewed 'em up and then we monitored that fish for about 24 hours before we left the site.

EMILY: So y-the radio-inserting the radio transmitter doesn't like, severely harm the fish in any kind of way?

LESLEY: I actually had a couple of arapaima, that, when I was tracking, were actually breeding.


LESLEY: And that had babies. So--


LESLEY: To me, that was a very strong indication that they recovered really well from the surgery.

EMILY: That they're good.

LESLEY: They're all right. [LAUGHTER]

EMILY: They're doing okay. When you go to work and do research in these areas, you mention you work with the indigenous communities a lot. And how does that relationship come together? Like, is there a certain skepticism or hesitancy, like, who is this scientist who is not from here and why and why does she want to collect all of our fish?

LESLEY: Yeah. My crews, a lot of times, were made up of the local indigenous communities. For them, it was like, "I want to learn how to use a GPS!" (overlapping)

EMILY: Yeah!

LESLEY: I mean that was really cool. They were like, "Oh, I want to GPS my farm." But that exchange of knowledge over time lead to increased trust, it became a "we" thing, it was our project. We have an obligation and a responsibility as scientists working in other communities, to, you know, bring an understanding of what it is that we're trying to do whether it's anthropological research, or whether it's fish work, or or turtle work, or snake work, or whatever! The most important thing I learned over my time there, is that these are the local people that understand this environment better than anybody else in the world.

It doesn't matter what I read in a book. It doesn't matter what I understand from here in Chicago. We're in the water with piranhas, with eels, with stingrays.

EMILY: You're not--not your everyday fishing trip. [LAUGHING]

LESLEY: No! It's not! Like, you know, having a team that is very familiar with the ecosystem--the behavior of these fish, was critical.

EMILY: You're now involved in trying to creat this protected area in Guyana but what does that actually involve? Do you just, like, write a letter to somebody? [LAUGHTER] You're like, "You should protect this because, um, doctor fish scientist." I don't know.

LESLEY: We have been meeting with government officials, NGOs, protected areas commissions, ministers, the president and really making a case for why this area should be protected. And not just for the biodiversity, but from a cultural standpoint and the livelihood of the people that depend on this ecosystem for every aspect of their lives.

EMILY: That's huuuge!

LESLEY: So huge. (overlapping)

EMILY: That's huge! [LAUGHTER]

EMILY: That's so huge!

LESLEY: It's so huge. You know, I've always been into the work that I've been doing. I've just--just geeking out on, "Oh, there's a new species," or, "This fish is related to this one," and, "This--like first originated here and now it's here." And I think that there was just another level that I reached, that there could be an application for the science that I'm doing. We can only, like, inform them.

That's all we can do. But they're the ones that have the power to do it. And it's like, we have to keep fighting for it.

EMILY: I think it's great to have fish nerds like you out there fighting the good fight. Thanks, Lesley.

LESLEY: Thank you.

EMILY: Yeah.

LESLEY: Thank you so much.

EMILY: I'm teary-eyed a little bit.

LESLEY: Hmmmm. (overlapping)

EMILY: It gets really emotional on this show sometimes thinking about fish. [LAUGHTER]

EMILY: I can't help it. [MUSIC]

EMILY: It still has brains on it.