Snorkelling grandmothers uncover large population of venomous sea snakes in Noumea

A group of snorkelling grandmothers who swim up to 3km five days a week have uncovered a large population of venomous sea snakes in a bay in Noumea where scientists once believed they were rare.

Dr Claire Goiran from the University of New Caledonia and Professor Rick Shine from Australia’s Macquarie

University were studying a small harmless species known as the turtle‐headed sea snake located in the Baie des Citrons, but would occasionally encounter the 1.5 metre-long venomous greater sea snake, also known as the olive-headed sea snake.

Goiran and Shine believed the greater sea snake was an anomaly in the popular swimming bay as it had only been spotted about six times over 15 years. From 2013, they decided to take a closer look at the greater sea snake to better understand its importance to the bay’s ecosystem.

“The study zone is in the most touristic bay in Noumea, so I often meet people when I am doing field work on sea snakes,” Goiran said. “When I was snorkelling on my own studying sea snakes, I used to meet a friend of mine called Aline that was snorkelling and taking photos on the same reef. In order to help me, she started taking photos of sea snakes and would send them to me by mail.

“I was very happy, so she asked her neighbour and friend Monique to help me too. Monique asked another friend, and soon there were seven grandmothers helping me.” The group named themselves “the fantastic grandmothers” and range in age from 60 to 75.

As the grandmothers sent photos through to Goiran and Shine, they realised they had vastly underestimated the population of greater sea snakes. Goiran and Shine have now published a paper in the journal Ecosphere revealing there are more than 250 greater sea snakes in the bay. Greater sea snakes have distinctive markings, allowing individuals to be easily identified from photographs.

“Even when I am stuck at university

with teaching, I know what is going on in the study zone because the grandmas survey the zone for me and send me the photos,” Goiran said.

“Remarkably,” Shine added, “the grandmothers found a large number of lethally toxic sea snakes in a small bay that is occupied every day by hordes of local residents and cruise‐ship passengers – yet no bites by the species have ever been recorded at Baie des Citrons, testifying to their benevolent disposition.”

They said the findings mean the role the snakes play in the functioning of the ecosystem is more important than previously thought. Scientists believe the snakes likely play a role in nutrient cycling through coral reefs, but there is little research available.

Would this work have been possible without help from the citizen scientist grandmas?

“Of course not,” Goiran said. However it was hard to get all seven in the group going out at the same time, she said, because “there is always at least one away hiking, biking, sailing, taking yoga class or taking care of the grandkids”. One of the grandmothers, Aline Guémas, said she was not scared of the greater sea snakes despite their potential deadly bite. The grandmothers always keep their distance and never touch them. “That’s the job of the boss,” Guémas said.

Her job was just to take videos and photos. Other members of the group helped with identifying the snakes and documenting their characteristics. The sea snakes could move quickly, making taking photographs difficult at times. But Guémas said “they are very slow in their movements when they forage for food”, making those times ideal for photography.

Her friend in the group, Sylvie Shebert, said she was afraid of the snakes at first but has grown to appreciate them. “It has been interesting to learn about and discover their lifestyle and to work with the group,” she said. “It allows us to integrate our swimming with the scientific world by sharing the results of what we find with the researchers, such as the area where the snake is located, it’s condition such as if it is pregnant or not, that kind of thing.”

Monique Mazière said “the snakes are not aggressive, just curious”.

“Of course, we will never touch them.”