Manta rays are social creatures who are choosy about their friends

It turns out that manta rays might be as picky about their friends as you or me.

Researchers have found evidence of structured social relationships among wild, free-ranging reef manta rays. The rays appear to actively choose other individuals to socialize with, according to a study published in the journal Behavioral Ecology and Sociobiology last week.

In order to examine manta ray social networks, a team of scientists with the US-based Marine Megafauna Foundation, Australia’s Macquarie University, Indonesia’s University of Papua, and the UK’s University of York spent five years collecting data on more than 500 groups of reef manta rays (Mobula alfredi) in Indonesia’s Raja Ampat Marine Park.

Many shark and ray species lead generally solitary lives, but reef manta rays are known to congregate at feeding and cleaning sites in shallow waters. The researchers took photos of all rays present in each group studied, which allowed them to monitor which individuals were most likely to be socializing with each other at different times and in different locations and determine whether these interactions occurred more frequently than could be expected if the encounters were purely random. After studying the structure of more than 500 groups in Raja Ampat Marine Park, the researchers discovered two distinct communities of rays living together.

“Like dolphins, manta rays are intelligent and perform collective behaviors such as foraging and playing,” the study’s lead author, Rob Perryman, a researcher with the Marine Megafauna Foundation and a PhD student at Macquarie University, said in a statement. “They are curious, often approaching humans, and individuals appear to have different personalities.”

Perryman and co-authors write in the study that “Associations were the result of more than just similarities in habitat use, gregariousness, or overlaps in time, indicating that individuals actively chose to group with preferred social partners.”

One of the manta ray communities discovered by Perryman and team was composed primarily of mature female rays, while a mix of males, females, and juveniles belonged to the other. These communities are mainly constituted by a web of what the researchers describe as “weak acquaintances,” but more durable relationships were also discovered, especially among female mantas, which tend to make long-term bonds with each other. Males, by contrast, were not found to make many strong social connections, which the researchers theorize could be due to different reproductive strategies or dispersal patterns.

The researchers say that certain social groups were regularly seen together at specific cleaning stations, where the rays are cleaned by cleaner wrasse and other small fish, suggesting that they may be using those sites as meet-up points. Some rays were observed returning frequently to certain cleaning stations despite the close proximity of several other sites.

“We still understand very little of how mantas live their lives, but we know they are socially interactive, and these interactions seem important to the structure of their populations,” Perryman said. “Understanding social relationships can help predict manta ray movements, mating patterns and responses to human impacts. That’s essential for conservation and ecotourism efforts.”

Reef manta rays are listed as Vulnerable to extinction on the IUCN Red List, which reports that the ray’s numbers are believed to have declined by as much as 30 percent globally over the last 75 years. Manta rays are hunted for their gill plates, which are used in traditional Chinese medicine. Entanglement or injury due to discarded fishing gear, pollution, and habitat destruction are also threats to the species.

Manta rays have been protected in Indonesia since 2014, but artisanal fishing is still an issue. There’s also concern that ecotourism could be disruptive to the social structures of manta rays in popular diving spots like those in Raja Ampat Marine Park. Perryman and team hope that by revealing the social lives of manta rays, they can help build public support for protection measures around the world. “Collecting more information about their social relationships and structures will be needed to develop sustainable ecotourism and conservation initiatives that allow mantas to coexist with humans in their natural habitats,” Perryman said.

Study co-author Andrea Marshall, co-founder and principal scientist of the Marine Megafauna Foundation, noted that a careful balance must be struck between wildlife ecotourism that will bring economic benefits to local communities and conservation measures aimed at preserving manta ray populations. “Knowing how mantas interact is important, particularly in areas where they are susceptible to increasing dive tourism,” Marshall said. “The increasing number of boats and scuba divers around reef mantas in Raja Ampat, particularly at cleaning stations, could break apart their social structures and have impacts on their reproduction.”

The research team say their results show the importance of understanding social relationships in manta rays when designing measures to protect manta ray populations from the impacts of human activities.

“Our results suggest that fine-scale conservation measures will be useful in protecting social groups of M. alfredi in their natural habitats and that a more complete understanding of the social nature of manta rays will help predict population responses to anthropogenic pressures, such as increasing disturbance from dive tourism,” the authors write.

CITATION

• Perryman, R. J., Venables, S. K., Tapilatu, R. F., Marshall, A. D., Brown, C., & Franks, D. W. (2019). Social preferences and network structure in a population of reef manta rays. Behavioral Ecology and Sociobiology, 73(8), 114. doi:10.1007/s00265-019-2720-x

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