© Rob Perryman

These manta rays form ‘friendships’ that last longer than a summer fling

Although many sharks are solitary creatures, their manta ray relatives are surprisingly social: They copy one another’s movements, play together, and will even curiously approach nearby humans. Now, scientists have discovered they also form “friendships” with their fellow rays—loose associations that can last for weeks or months at a time.

To understand the structure of manta ray communities, researchers tracked more than 500 groups of reef manta rays (Mobula alfredi) for 5 years in the turquoise waters off the coast of northwest Indonesia (above). They photographed the rays at five gathering spots: three “cleaning stations,” where the mantas received full-body manicures from cleaner wrasse and copepods, and two popular feeding locations, where the rays slurped up shrimp and fish larvae (and sometimes their trusty cleaners, the copepods).

The researchers then identified individual rays from patterns of spots on their bodies and tracked their interactions. Females were more likely to form lasting associations with each other than males, who tended to avoid other males, the researchers report today in the journal Behavioral Ecology and Sociobiology.

But unlike other creatures with strong social bonds (for example, many species of dolphins) the rays did not form tight-knit groups. Instead, they formed two loosely associated communities, one made up mostly of female rays, and the other made up of females, juveniles, and males. The groups crossed paths at feeding areas and cleaning stations before individual members went their own way and returned hours or days later. That’s similar to chimpanzees, who “group up” differently when they are foraging or sleeping.

The rays showed a strong preference for certain spots, with females generally spending more time at cleaning stations and males typically spending more time in the feeding areas.