Once thought solitary creatures, a new study of manta rays finds the reef-dwelling cartilaginous fish form social relationships and choose social partners.
Scientists studied more than 500 social groups of reef manta rays over the course of five years in Indonesia’s Raja Amput Marine Park, one of the most biodiverse marine habitats on Earth, to analyze social networks in order to show how manta rays interact with one another. Identification photos of all rays were taken and researchers monitored which mantas were seen with others and at what times and locations. Their findings are published in the journal Behavioral Ecology and Sociobiology.
"Mantas have active social preferences, which means they are actively choosing to socialize with other individuals that they know, and they remember their social contact with those individuals (they have friends – to put it in quite an anthropomorphic way)," lead author Rob Perryman told IFLScience.
They found that reef manta rays (Mobula alfredi) have several “socially mediated behaviors” observed within two different groups: one made up of mostly mature female rays and another being a mix of males, females, and juveniles. Though they do not live in tight-knit social groups, females tend to make long-term bonds with other females. Males, on the other hand, do not form strong connections, possibly due to reproductive strategies.
"While we found that many of the rays had social preferences that lasted several weeks or months, there were not so many relationships that remained strong between years in the study," explained Perryman, adding that this suggests social relationships in mantas may be temporary alliances aligned with seasonal movements that allow rays at a similar life or reproductive stage to group together, perhaps to protect from predators or unwanted mating attempts by males.
Location also played a role in how manta rays form social bonds. Even though the animals are wide-ranging, they tended to return to their preferred “cleaning” sites with the same groups where cleaner wrasse and other small fish can clean them. Certain groups were regularly observed at the same site together, suggesting these locales may serve as meeting points or that some mantas have strong connections to certain cleaning stations. However, Perryman is quick to note that his study only provided "snapshots" in time and space, allowing for large gaps of time that may have not been observed.
Though manta rays were protected in Indonesia in 2014, they remain internationally threatened as populations decline due to the demand for their gill plates, which are used in traditional Chinese medicine, along with other human-caused threats like pollution, habitat destruction, and ghost fishing gear. Understanding how mantas live could help inform how best to protect the species.
“Knowing how mantas interact is important, particularly in areas where they are susceptible to increasing dive tourism,” said study co-author Andrea Marshall in an emailed statement. “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 researchers hope their work helps people to empathize with these animals and raises awareness to protect them from the many threats they face.
"The more we learn about sharks and rays, the more we are discovering that they are not so dissimilar from ourselves. They have individual personalities and are social animals with complex feelings and emotions," said Perryman.