122 devil rays joined in a wild mating ritual that lasted for hours
Scientists captured rare footage of the animals in a stunning “courtship vortex” that raises concerns about their survival. Splashes at the surface give an indication of the commotion below. Beneath the waves, a tornado of hundreds of devil rays swirl in a dizzying dance that goes on for hours.
This is a “courtship vortex”: a previously undescribed behavior among munk’s devil rays (Mobula munkiana) that has now been captured on film in a study conducted by the conservation nonprofit Manta Trust. New drone footage shows 122 individuals taking part in this five-hour display in Mexico’s Baja California, with different mating groups joining and leaving the main formation over time.
"It's amazing to see a vortex of mobulas," says Marta D. Palacios, co-founder of Mobula Conservation, whose study examines courtship and mating behaviors in three mobula species: spinetail, bentfin, and munk’s devil rays. Mobulas are known to create vortex formations when feeding or resting, but this is the first time vortexes have been reported in a mating context. The circling motion was more relaxed: the rays were touching each other, and they weren't unfurling their cephalic fins—the horn-like appendages in front of their face—to eat. The researchers also saw courtship trains—when male mobula rays chase a female to try to mate with her—weaving in and out of the larger vortex.
(See a rare view of a manta ray courtship train deep in the sea.)
This behavior gives the rays a faster way to select a mate, explains Palacios: "If you're in a courtship train, you need to chase the same female for hours or even days"—but in the vortex males can choose their best match from 30 or 40 females. “We know so little about mobula rays,” says Stephanie Venables, senior scientist from Marine Megafauna Foundation, who was not involved in the study: “Reproductive behavior is one of the most important aspects of their life history to understand so these findings will be really important for protection.”
In this study, 122 individuals were observed circling in a "courtship vortex"—the first time this behavior has ever been seen during mating. For five hours, this vortex of animals swirled as courtship groups joined and exited the formation.
Video at link: https://www.nationalgeographic.com/animals/article/devil-ray-courtship-vortex-behavior-mobulas
= new reply since forum marked as read
Don't think I'd want to swim there for a while..... 
