- For more than four years, marine biologist Madalena Pereira Cabral has been dedicated to investigating and understanding the movements of giant manta rays (Mobula birostris) in Revillagigedo National Park in the Mexican Pacific.
- Using satellite tags, the expert aims to describe these animals’ routes through the ocean and the reasons behind the fact that almost all the individual manta rays she has been studying end up leaving the marine protected area. Leaving this area exposes them to fishing pressure, which puts them at risk.
- One of the scientist’s most important findings is that giant manta rays’ movements and the groups they form are influenced by the El Niño phenomenon. This information is crucial for the conservation of this little-understood species.
Swimming with giant manta rays (Mobula birostris) feels like an underwater dance. Their slow, rhythmic movements are astonishing to Madalena Pereira Cabral. She describes her dives alongside manta rays, which she says she believes are among the most elegant, graceful and intelligent animals in the ocean.
“It is also a very mysterious and interesting species because there is a lot to understand about its behavior,” the marine biologist says.
This is why, ever since she began working with giant manta rays in Revillagigedo National Park in the Mexican Pacific, she has dedicated herself to understanding the mysteries surrounding the species. This site is North America’s largest marine protected area. It is a bastion of protection and conservation for the giant manta ray, which is categorized as endangered by the International Union for Conservation of Nature (IUCN).
“They’re very curious about divers. It is fascinating to dive with them because they get so close. They are interested in us, and they like our bubbles. It is a very beautiful species to work with because they let me get close — without any problems and without stress — so I can take a photo, measure it and put on a satellite tag. They let you spend time with them to study them,” the expert says.
Pereira Cabral is a marine biologist and doctor of marine and coastal sciences from the Autonomous University of Baja California Sur (UABCS). For more than four years, the Portuguese scientist has worked at Revillagigedo National Park, where her work on her doctoral thesis began. There, she began to study the movements of giant manta rays not only inside the marine protected area, but also outside of it, since she has found that the manta rays continually leave the area. Why do they do this? That is one of the expert’s main questions.
“Satellite tags, along with the environmental data that we gather, will allow us to have a more complete picture of their behavior. Only when we have the big picture will we be able to protect them and carry out the necessary management to be effective,” Pereira Cabral says.
Mongabay Latam spoke with Madalena Pereira Cabral about the risks facing giant manta rays and the most recent results of her studies in Mexican waters.
Mongabay: What are giant manta rays like?
Madalena Pereira Cabral: Manta rays are fish, but they have different anatomy: They are like pancakes. They also move with so much grace, as if they are flying underwater. At times, the currents are very strong, and they swim effortlessly. They are truly breathtaking: A giant manta ray, 40 years old or older, can measure 7 meters [23 feet] from the end of one fin to the other. The giant manta ray has its endangered status worldwide, because there is a global decline.
Mongabay: What are the characteristics of the manta ray population in Revillagigedo?
Madalena Pereira Cabral: Because these animals spend more time in the open water and at islands that are very remote and far away, there was not much information. So I understood that there was a lot to do, and it was when I proposed a project that did not exist to the Autonomous University of Baja California Sur that I began to work with them.
The first publication that we did was to estimate the size of the population. We estimated approximately 1,200 manta rays there, and we also saw that 25% of that population is made up of melanistic, or black, manta rays. That is the largest proportion for this species in the world. We also saw that there are more females than males and that most of them are adults; we did not see many juveniles or their offspring. That is what we know about this population. That is the baseline.
Mongabay: What is Revillagigedo National Park like? What makes it important for manta rays?
Madalena Pereira Cabral: The park is very important for many species, such as sharks and manta rays. It has oceanographic conditions that facilitate water movements that bring nutrients from the bottom [of the ocean], so there is food available for these animals. Another important aspect is that there are cleaning stations, with Clarion angelfish [Holacanthus clarionensis] present, which are endemic and have a mutualistic symbiotic relationship with manta rays, so both species benefit. Clarions are like “doctors” or “nurses” for manta rays, because they clean parasite infections off of them and, if the manta rays have wounds, they help heal them. They play a very important role in the general health of manta rays. Also, Revillagigedo is a marine protected area, so there is no fishing. In other words, everything for manta rays is all right there: food, cleaning stations and protection. Revillagigedo is also a very special place because its islands have no hotels or developments, which makes it perfect for studying manta rays without those impacts.
Mongabay: Although there is no fishing within the area, are there any pressures or threats around Revillagigedo that could impact the manta rays?
Madalena Pereira Cabral: That is what we are realizing. Manta rays don’t migrate together; each one moves independently. They only gather in places where food is available, at cleaning stations or at sites where they mate and reproduce. I tagged about 15 specimens, and we now know that almost all of them leave the marine protected area, and there is a lot of fishing pressure outside of it.
The problem with this is that the manta rays become caught in nets. Manta rays are not the target of this fishing; they are bycatch. In order to breathe, manta rays need to be able to move, so if they become tangled, they will not be able to tolerate it very long, and although the fishers return them to the water, they will not survive.
In Revillagigedo, we see that there are manta rays with very clear signs that they were tangled [in nets]. This bycatch is what I believe we are underestimating. Revillagigedo is the largest marine protected area in North America. That is a very big achievement for Mexico, but these animals, which can migrate more than 1,500 kilometers [930 miles] and do not take into account the artificial borders that we humans create, are really in danger, because they have very low resilience. They only have one offspring at a time, their sexual maturity is very late and all of their reproduction is very slow.
When there are impacts, even if it is only a few individuals per year, in the long term it can be very serious, as we are seeing in other areas of the world. Around Cocos Island, in the eastern Pacific, which is relatively close, the decline in manta rays was up to 89%. In Mozambique, Africa, it was 90% in only two decades. In other words, in 20 years, a population can almost disappear. That is the risk. However, fishing pressure is something that can be managed, limited, regulated and agreed upon between countries.
Mongabay: What methods are used to study the manta rays’ movements? What findings have been obtained?
Madalena Pereira Cabral: What we do is put satellite tags on them to follow them and find out where they go. After that, we use environmental and oceanographic data, such as temperature, chlorophyll concentration, food availability and bathymetry, which is the depth of the ocean. All of these environmental variables, along with their data movement, allow us to have an idea of what drives the manta rays: where they go, why they go, and how much time they spend outside of the marine protected area.
Another thing we can see is that their movements are different in El Niño years, in neutral years and in La Niña years. In our earlier publication we saw that during El Niño years, there are more manta rays and that perhaps they are more concentrated in Revillagigedo because there is not as much food availability around the Pacific.
During La Niña years, when more food is available throughout that area of the Mexican Pacific, the manta rays disperse more. Their distribution range contracts and expands. Understanding those patterns and understanding their movements, whether there is connectivity or not with other places where we know there are manta rays, is very important to inform the decision-making [process] for the management of this population. That way, we can propose ‘migravías’ [ underwater biological corridors that connect marine protected areas] that can be protected so that these animals can move around.
For that reason, we are putting on two types of satellite tags. One gives us horizontal data: We have points on a map that tell us where the manta ray is. The other type of tag gives us a vertical profile, and using that, we can view the depth at which the manta ray is located. Other things we do not know are: how much time they spend in the deep [water], what depths they can reach and what they are doing when they are there. We have manta rays that went 150 meters — what for?
We are very interested in that information to understand them better, because we mostly see the manta rays at the cleaning stations, but that is a very small part of their lives. It is a very small percentage of their total lifetime, because all the rest is a mystery. We don’t know where the young are or where the pregnant manta rays have their offspring — if they have them in the deep [water], if they have them on the surface, in protected bays or in the open water.
Mongabay: How does one work with a protected and endangered species? What special precautions must be taken?
Madalena Pereira Cabral: The method that we use is invasive. We put on satellite tags that have an anchor that goes underneath the skin. The tag stays on for between four and six months, but it is not a stressful method: Manta rays do not become stressed after being tagged. Instead, they stay there with me and I can take more photos and videos of them.
For example, manta rays have natural predators — sharks — and there are manta rays that have bites from which they can recover. So this tagging method does not hurt or sicken the manta rays, but we do need a permit to work with an endangered species and in a marine protected area. The Mexican Secretariat of Environmental and Natural Resources, the National Commission of Protected Natural Areas and Revillagigedo National Park are providing us with that permit to work with this population.
I work with a local non-governmental organization called Pelagios Kakunjá, and it is they who receive the permit in collaboration with the UABCS. We are always seeking donations, and we also have many organizations that support the project because the tags are very expensive, and so are the trips to Revillagigedo: the Marine Megafauna Foundation, Manta Trust and Mares de México are helping. This is all possible thanks to the collaboration of several Mexican and international organizations, in addition to universities, such as the University of Lisbon, for which I feel very fortunate.
Mongabay: What contributions has your research generated? Have you managed to solve any of the mysteries surrounding manta rays?
Madalena Pereira Cabral: That first publication was very important to have a baseline; we didn’t know how many manta rays we had. They cannot be protected if you don’t know how many there are. The important part of this scientific paper was the influence of El Niño on [manta rays’] movements. For that reason, we characterized Revillagigedo as a refuge for this population. We still have not published [anything] about the [satellite] tags. Because each manta ray is independent, we have to put on a lot of tags to find these patterns.
Now, I’m dedicated to putting on more [satellite] tags [and] to raising more funds, because the more tags, the better. That publication, which I hope will come out next year, I believe will be very important, because we are creating —all of us who study sharks and manta rays— these areas and important migravías for the species, and [I hope] that a management proposal can be presented from all over Latin America.
The United Nations has several countries that have signed to protect — by 2030 — 30% of the territory, which also includes 30% of the oceans. We hope that, when they go to create these protected areas, that it be done with information, so that the most important areas for these species are truly protected, and so that effective management and conservation can be carried out.
Mongabay: What is it that most inspires you about your work? What has given you the most satisfaction during this research?
Madalena Pereira Cabral: I love diving. Giant manta rays and whale sharks are the largest animals that you can get close to in their natural habitat, without putting yourself or the animal in danger, using good practices. I feel very fortunate to be able to work with these animals.
Manta rays are curious about us divers, so you can dance underwater with them. If you do it well, you aren’t going to change their natural behavior. These animals transmit a type of magic to you. There are even people who, after their first dives with manta rays, come out of the water crying, because visually, it is so pretty. They are very calm experiences; manta rays do everything with so much grace.
We are now trying to take virtual reality images so that people can experience what it’s like to be with these animals in their natural habitat, without having to see them in aquariums, but instead through virtual goggles. It is a very up-close experience, and you feel as though you are underwater. It is very important that Mexicans know what they have in their country. Virtual reality is a way of sharing that with children and with people who live in cities, so that they can become interested in these animals that little is known about, and so that they can contribute in some way to their protection and conservation.
Mongabay: Why should what happens in places like Revillagigedo matter to those of us in cities?
Madalena Pereira Cabral: Everything that happens in the oceans affects everyone. Everything is connected. Manta rays are part of an entire cascading ecological system. There are many more studies about sharks, and now we know that when there are problems with one of these species, the entire balance of the ocean is affected. That impacts us all. Imbalances in the ocean affect the climate, ocean productivity [and] the abundance of fish. Wherever you live, what happens in the oceans is going to affect you. Having healthy, balanced oceans and ecosystems is very important — more than we can imagine.
Mongabay: Is that why you began your @manta__lena project on Instagram?
Madalena Pereira Cabral: Exactly. I didn’t have an Instagram, but I began it because I realized that it is a way of reaching people, [such as] visitors to the park, to talk about my work and let them know what is happening. They can follow any manta ray that we tag and they can also “meet” each one of them, because they all have a unique pattern of spots on their belly, with which they can be identified. This account has also served to invite [people] to make donations. I’m currently fundraising to be able to continue with this project.
These days, a scientist is more than just a scientist. Scientists need to have many sides: they need to be on social media, they need to apply for funding, they need to work with statistics, they need to dive [and] sometimes they need to write in a language other than their native language.
In other words, a scientist is so many things. This is why it’s important that science does not just stay between scientists and that it also reaches politicians, the general public and the people who visit the park. Producing and publishing information — and [ensuring] that it reaches everyone — is what could make a difference.
Mongabay: What are your hopes for the future of manta ray conservation in Revillagigedo?
Madalena Pereira Cabral: We should have more information. We can’t protect manta rays if we don’t know how they behave and how they will [behave] with the changes we are already experiencing in terms of increasing temperatures. Because I am a scientist, for me, information is the basis. After obtaining information, we want it to reach all the decision-makers and the general public so that we can manage to do something really visible, with social, scientific and political impact.
What I would love to see is, in 20 years, that we will still be there diving with the manta rays, and that this is because effective management, protection and conservation decisions were made. [I would like] what happens in Revillagigedo to be distinct from what happens in other places around the world, where we see that animals are in decline and that every day, there are fewer and fewer. We still have time to conserve and protect this population of Mexican manta rays.
Banner image: The belly of a giant manta ray allows for the identification of each individual because each one has its own pattern, just like a fingerprint. Image by Andrea Marshall.
This story was reported by Mongabay’s Latam team and first published here on our Latam site on Jun. 27, 2024.
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