Some days, they take care of their grandchildren. Other days, they prowl the bottom of the sea in search of venomous snakes.

Some days, they take care of their grandchildren. Other days, they prowl the bottom of the sea in search of venomous snakes.

“Les Fantastiques Grands-mères,” as they call themselves (“The Fantastic Grandmothers”), are a group of seven friends in Nouméa, New Caledonia who snorkel for fun and for science.

Their outings were purely recreational until two years ago, when they met a local biologist, Claire Goiran, at a popular snorkeling site, the Baie des Citrons. She mentioned that she wanted to know how big the bay’s population of greater sea snakes was but didn’t have the resources to find out. The women offered their help, and Goiran, who teaches at the University of New Caledonia, trained them to photograph the snakes and log data on their location and behavior.

“The results were astonishing,” Goiran wrote in a recent paper, “Grandmothers and deadly snakes: an unusual project in ‘citizen science.’” “As soon as the grandmothers set to work, we realized that we had massively underestimated the abundance of greater sea snakes in the bay.”

By last November, the women had documented 140 individual greater sea snakes, according to the paper. (Although the bay is a popular snorkeling site among both locals and tourists, no bites have been recorded, which Goiran regards as evidence that the snakes possess a “benevolent disposition.”) The grandmothers’ observations also suggest that Hydrophis major reproduces seasonally, with courtship occurring in winter, pregnancy in summer, and birth in autumn.

The grandmothers, who are all retired, meet every morning on the beach and swim for two to three hours. Not every woman comes every day, however. During school holidays, many of them are busy caring for their grandkids—which often means swimming and snorkeling with them—and they’re also busy with other outdoor hobbies such as biking, hiking, and birding.

Getting to know the snakes has been “amazing,” says one member of the group, Geneviève Briançon. Since they’re not aggressive, “we can swim close to them admiring how quiet and elegant they are,” she says.

Now that they know how abundant the species is, Goiran and her research partner, Rick Shine of Macquarie University in Australia, want to study it more deeply.

“Sea snakes are important apex predators in coral reef ecosystems, and their numbers are declining in many areas,” says Shine. “We urgently need to understand them better, if we are to frame sensible ways to conserve them.”

A territory of France, New Caledonia is an archipelago in the South Pacific Ocean.