In Mauritius, research monkeys are big business—and big controversy

Mauritius—Nestled here at the foot of two of the island’s tallest and greenest mountains lies Creve Coeur, a village of fewer than 3000 residents who live among sugarcane fields in modest two-story homes with unfinished cement walls. A short drive away, tourists flock to the clear waters and white-sand beaches of lavish coastal resorts. But Creve Coeur itself is home to a different treasure: monkeys.

Living on Mauritius are an untold number of cynomolgus (or long-tailed) macaques, cat-size primates that have become a precious commodity to biomedical researchers. As the supply of these animals from other countries has dried up, this small island off the coast of Madagascar has become the main exporter of monkeys used in everything from vaccine development to drug safety testing. The animals—tens of thousands of which have been exported from Mauritius over the past 5 years—are in such high demand that some are sold for as much as $20,000 to labs in the United States and Europe. So it’s no surprise that Creve Coeur is rife with monkey traps.

Seemingly everywhere in the village are metal cages with trap doors. One sits on a roof; another in a ditch by the side of a dirt road; another near a man barking through a megaphone, trying to sell a dishwasher.

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One of the villagers, who asks that we call her “Pooja” to protect her identity, says the traps are a nuisance—and that they deeply upset her. Once the monkeys are caught, she says, they howl all night, keeping her family up. Pooja says she is constantly squabbling with her neighbor, who gets paid for having the trap set up in her backyard. The first time she saw monkeys being removed from her neighbor’s property, she says, “I had a panic attack.”

Monkey traps such as this one in the yard of a Creve Coeur resident have divided the Mauritius village.Daniel Hernandez-Alonzo

Such fights have spilled well beyond Mauritius’s neighborhoods. Global demand for the island’s monkeys has pitted conservationists against each other; some worry the monkey trade could wipe out the animals; others view the primates, introduced to Mauritius centuries ago, as a harmful invasive species. Politicians have also entered the fray, clashing over whether the economic benefits of the trade outweigh ethical concerns over sending the monkeys to faraway labs.

“It is an unprecedented, vulgar business,” Arvin Boolell, Mauritius’s minister of agroindustry, food security, blue economy, and fisheries, told a radio interviewer in 2023 in the run-up to the country’s 2024 parliamentary elections. Boolell was serving as the leader of the country’s opposition party at the time; later, he advocated for phasing out the trade. “We should treat animals like our friends,” he told the interviewer. “Unfortunately we’ve lost our souls for speculative infrastructure development and wealth.”

Biomedical researchers, meanwhile, are nervously watching Mauritius. If the island were to halt exports, “we would lose new therapies, new vaccines, new treatments for diseases,” says David O’Connor, a pathologist at the University of Wisconsin–Madison whose lab has used macaques for HIV research. “It would be devastating for science.”  

The trap in the yard of Pooja’s neighbor belongs to Bioculture Group, one of Mauritius’s largest trappers, breeders, and exporters of long-tailed macaques. Located nearly 50 kilometers south of Creve Coeur in the more populated village of Riviere de Anguilles, the company’s main campus lies at the end of a dirt road that snakes through sugarcane fields. The property is surrounded by a 2-meter-tall chainlink fence topped with electrified wire.

Beyond a gate, lush green hills and a sliver of the Indian Ocean provide a backdrop to rows of fenced enclosures holding about 20 to 30 monkeys each. The animals—roughly 30,000 in all—groom themselves and their companions, dangle on swings, and scamper about on wooden beams hanging in their pens. They chatter as dozens of workers in blue jumpsuits roam the maze of cages, tossing the animals fresh melons, carrots, and apples.

An inside look into Bioculture Group’s facility, one of Mauritius’s largest exporters of long-tailed macaquesDaniel Hernandez-Alonzo; Kelly Hernandez-Alonzo

Such facilities are often reluctant to allow visits by outsiders, but Mary-Ann Griffiths is proud to show off what she and her husband, Owen Griffiths, have accomplished. Armed with bachelor’s degrees from the University of New South Wales, the duo founded Bioculture in 1984. The couple had to figure out everything largely on their own, including how to trap, feed, breed, and care for the animals. “This wasn’t written in books,” Mary-Ann says. “Everything was trial and error, learning from scratch.”

What started as a modest outfit began to blossom into a critical engine for the local economy, eventually employing hundreds of residents from villages near Bioculture’s campus. By 2001, the company was exporting a few thousand macaques each year for scientific research.

Bioculture finally became a major player in the monkey export business 20 years later, at the height of the COVID-19 pandemic. By 2021, it and a few other companies on the island were annually exporting an average of about 14,000 long-tailed macaques to labs around the world. That year, 70% of Mauritius’s macaques that went to the U.S. came from Bioculture.

The uptick was a result of geopolitics and scandal. China used to be the world leader in long-tailed macaque supply, exporting approximately 30,000 of the monkeys in 2018, mostly to the U.S. But it closed the spigot during the pandemic, redirecting the primates to its own burgeoning biomedical industry. Cambodia stepped in, largely filling the gap. In 2022, however, U.S. investigators charged several individuals with falsely labeling monkeys as captive-bred when they appeared to have been taken from the wild. Since then, Cambodian exports to the U.S. have dropped to nearly zero.

Mauritius on the rise

Once a minor player in the global trade of research monkeys, the tiny island of Mauritius has become the dominant supplier of long-tailed macaques to the United States.

(Graphic) V. Penney/Science; (Data) Centers for Disease Control and Prevention Nonhuman Primate import data

That’s left Mauritius—along with smaller suppliers such as Vietnam and Indonesia—to fill the gap. But companies like Bioculture can only breed so many monkeys; the rest—about 1500 per year—must be captured from the wild. Some are used as breeding stock; others are shipped directly to labs. Such exports are legal, as long as the monkeys are properly labeled. But the large-scale trapping has become a sore point on the island.

The same squabble Pooja is having over her neighbor’s backyard trap is playing out in villages across Mauritius. For some locals, capturing monkeys is a way to remove animals that can bite and tear up yards; villagers can also earn up to $200 for allowing Bioculture to set up a trap on their property. But others like Pooja have become close to the animals, tossing them fruit and bread from their balconies. They don’t like seeing them in cages—and they don’t want them used in biomedical research.

Arguments can grow heated, traps can be stolen and destroyed, and fights can break out. “It’s really creating a lot of tension in some of the neighborhoods,” says Mansa Daby, leader of Monkey Massacre in Mauritius, an animal rights group that aims to end the island’s macaque trade.

The monkey trade also shakes many Mauritians to their spiritual core. Nearly half the population is Hindu, whose beliefs encompass respect toward animals. Every year, thousands of locals flock to Ganga Talao, a scenic crater lake on the southern part of the island that’s overlooked by a 33-meter-tall statue of the goddess Shiva and a shrine to Hanuman, the monkey god of wisdom and courage. Many of Mauritius’s monkeys live here, where pilgrims feed them.

“Each and every monkey is sacred,” says Satish Dayal, a priest at Sviv Jyotir Lingum, one of the main temples at the site. “How is it that these atrocities and brutalities are being done to monkeys, which are the very symbol of Lord Hanuman?”

Satish Dayal, a prominent Hindu priest and advocate against the monkey trade, standing in front of the monkey deity HanumanDaniel Hernandez-Alonzo

Mauritius’s politicians have also become caught up in the debate. The monkey trade generated more than $66 million for the island in 2023, and Boolell walked back some of his earlier criticism of the exports after his party regained power in last year’s elections. Speaking to Science, he declined to say whether he still supports phasing out the trade, although he says he hopes advances in technology will eventually obviate the need for the animals in labs. Other politicians have also changed their tunes once in office.

Conservationists are split, too. Some worry continued trapping of long-tailed macaques in the wild could cause the animals to vanish locally—a catastrophe, they say, because the monkeys are an endangered species, according to a 2022 designation by the International Union for Conservation of Nature (IUCN). “Mauritius has a responsibility to protect the species, not allow its exploitation and persecution,” says Sarah Kite, co-founder of the international advocacy group Action for Primates.

But other conservationists argue the monkeys themselves are a problem. The animals are not endemic to the island; Dutch settlers introduced them from Indonesia in the 17th century, possibly as pets. They’ve been harming the environment ever since, says Vincent Florens, an ecologist at the University of Mauritius.

One of the biggest victims, he says, is the Pandanus screw pine. The monkeys rip the leaves off the tall, palmlike trees, which destroys their shoots. Roughly 14% of screw pine species have disappeared since the animals first arrived on the island, Florens says.

An echo parakeet, an endemic Mauritian bird many conservationists say is threatened by the island’s long-tailed macaquesDaniel Hernandez-Alonzo

The monkeys also eat the screw pine’s fruit before it’s ripe. That deprives the island’s native fruit bats of food, forcing them to forage elsewhere. As a result, Florens says, farmers have killed tens of thousands of bats that came to feed on their crops. Destruction of screw pines also threatens the island’s geckos, important pollinators that use the trees and shrubs as shelters. Others say the monkeys harm many of the island’s bird species by eating their eggs and destroying their nests.

But to understand just how much of a threat the primates are to Mauritius’s ecosystems, and whether they themselves are threatened by trapping, scientists need to know how many monkeys are out there. Yet those numbers are hard to pin down.

The uncertainty about long-tailed macaque numbers extends beyond Mauritius. IUCN’s conclusion that the animals are endangered was based on studies suggesting they were declining worldwide. But the surveys, camera traps, DNA analysis, and other methods that pointed to a decline have shortcomings. People can scare the animals away, and these approaches are hard to employ over large areas. The National Association for Biomedical Research, which advocates for animal research, has asked IUCN to reverse the listing, based on other studies showing the animals thriving in some regions. (So far, IUCN has maintained the status.)

The last thorough census of Mauritius’s long-tailed macaques, in 1986, used ground surveys to estimate a population of between 25,000 and 35,000 in the wild. But the scientists had difficulty following the animals through the island’s dense forests, and the surveys were limited to only certain parts of Mauritius.

“Doing population surveys of macaques on Mauritius is just extremely tricky, because of the topography,” says Raphael Reinegger, a Dutch postdoctoral researcher at the University of Bristol. “You have very limited visibility. And that’s assuming you know where the monkeys are in the first place.”

Conservationists Prishnee Bissessur (left) and Vincent Florens observing damage caused by long-tailed macaques to endemic screw pine treesDaniel Hernandez-Alonzo

So in 2022, Reinegger teamed up with Prishnee Bissessur, an ecologist at the University of Mauritius, to try a new approach: drones carrying infrared sensors to detect the animals’ body heat. The devices can see through some of the densest underbrush, but to employ them, the duo would need to understand the daily movements of the monkeys.

Fortunately, Bissessur was familiar with some of the monkey colonies and their movements, having followed them for her studies of the island’s ecology. “We would count the number of monkeys in a given population that was habituated to humans,” she says. “We would then do the drone flight to see whether we were able to detect the same number of individuals in the ground count.”  

Reinegger and Bissessur began flying drones last year. Despite the tech’s advantages, however, counting monkeys has still proved challenging. If the animals are too far beneath the forest canopy, the drones can’t spot them. And if they’re too high up in the trees, the whirring gadgets can scare them away. At first the macaques are intrigued by these strange machines, Reinegger
says. “But then at some point, their curiosity turns into panic.”

Over the course of 6 months, the duo was able to find a “sweet spot,” Reinegger says, flying the drones at just the right height to spy on the monkeys without scaring them off. To date, the team has surveyed about 1500 hectares, approximately 2% of the island’s monkey habitats.

Footage from Raphael Reinegger and Prishnee Bissessur’s drone surveys, which are being used to determine the population of long-tailed macaques in MauritiusRaphael Reinegger; Kelly Hernandez-Alonzo

Based on the data so far, Reinegger thinks his estimates are “probably going to be a lot higher” than those of the 1986 survey. That’s because the duo has found much more suitable habitat for the animals than had been previously documented. Still, because the previous census methods were less accurate, it’s difficult to know whether the macaque population really has grown since that time. Further surveys could help clarify the issue—and perhaps put some of the island’s debates to rest. 

For now, scientists who use long-tailed macaques are monitoring the strife in Mauritius with concern. They worry that—should opposition there continue to rise among politicians and animal rights activists—it could threaten the future of the Mauritian monkey business. U.S. and European reports released in 2023 concluded that the supply of monkeys for biomedical studies is shrinking and becoming increasingly unpredictable. Even with Mauritius picking up some of the slack left by China and Cambodia, many researchers worry the supply of these animals may falter.

JoAnne Flynn, a microbiologist at the University of Pittsburgh who studies tuberculosis in long-tailed macaques, used to get her monkeys from China. Now, she’s dependent on Mauritius. “Mauritius has been a really great source of animals for us,” she says. “It’s been a lifesaver.”

Still, she fears new instability in the monkey pipeline, which in the past has forced her to end some research projects. If the supply from Mauritius dwindles, she worries the animals will become so expensive—or the wait times for them so long—that it could jeopardize her remaining monkey studies.

If Mauritius were no longer an option for monkeys, she and other scientists say, vaccine development, transplant innovations, and neuroscience research would all be threatened. “The U.S. can’t breed the number of monkeys scientists are using,” Flynn says. “If Bioculture had to bring their numbers down, it would affect all of us.”

O’Connor, the University of Wisconsin–Madison pathologist, is trying to guard against one thing that could quickly cut off the supply: a scandal over undeclared wild-caught monkeys like the one that shut down the Cambodian pipeline. He has worked with Bioculture to develop a genetic test that helps distinguish captive-bred monkeys from those caught in the wild. The stakes are high, he says. “When a major supplier disappears … it discourages an entire generation of scientists from becoming experts at using these vital models.”

If Mauritius falls, Southeast Asian countries are unlikely to make up for the loss, says Francois Villinger, director of the New Iberia Research Center, a major U.S. primate facility. The U.S. has seven National Primate Research Centers, but they mostly breed rhesus macaques, which are mainly used for academic research rather than for industry labs. Funding is needed to create similar centers for long-tailed macaques, Villinger says, a process he has tried to jump-start at his facility. It is now home to 1500 long-tailed macaques, almost entirely sourced from Mauritius.

Support from the U.S. National Institutes of Health helped Villinger expand his rhesus macaque colonies from roughly 6000 to 12,000 primates throughout the pandemic. But he’s doubtful the agency will provide new funds for long-tailed macaques, especially given the dramatic cuts in research spending proposed by President Donald Trump’s administration. Without Mauritian supply or U.S. funding, Villinger says, the scarcity of monkeys for research “would be absolutely disastrous.”

Back on Mauritius itself, Pooja has become a campaigner for the island’s monkeys. She’s working with her neighbors and with residents of nearby villages to file petitions with the government denouncing the primate trade. She’s not sure how successful her efforts will be, but she hopes they will at least force others to more seriously consider the impact of Mauritius’s monkey exports—not only on the animals, but on the spirit of the island itself. “In our culture monkeys are very precious to us,” she says. “We pray to them, and we should not disrespect them.”