Splashes on the surface give an indication of the commotion below. Beneath the waves, a tornado of hundreds of demonic lightning spins in a dizzying dance that lasts for hours.
This is a “courting vortex”: a previously undescribed behavior among the demonic rays of munk (Munkian mobula) which has now been captured on film in a study conducted by conservation nonprofit Manta Trust. New drone footage shows 122 individuals participating in this five-hour display in Baja California, Mexico, with different mating groups moving in and out of 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 species of mobula: spinetails, curved fin and devil rays. munk.
Mobulas are known to create vortex formations when they feed or rest, but this is the first time vortices have been reported in the context of mating. The circular movement was more relaxed: the rays touched each other and did not unfurl their cephalic fins – the horn-shaped appendages in front of the face – to eat. The researchers also observed courtship trains – when male mobula rays chase a female to try to mate with her – moving in and out of the larger vortex.
(See a rare view of a manta ray procession train in the depths of the sea.)
This behavior gives rays a faster way to select a mate, explains Palacios: “If you’re on a courtship train, you have to chase the same female for hours or even days” – but in the vortex, males can choose their best mate. . of 30 or 40 women.
“We know so little about mobula rays,” says Stephanie Venables, senior scientist at the 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.”
Jumping on the back
The study also describes another new behavior, called back jumping, when the male leading the chase in a courtship train jumps on top of the female, raises his tail and begins rapidly thrusting her clasper, or reproductive organ.
This happened to one woman more than 135 times. “Imagine you’re swimming at the surface and someone jumps at you from behind again, and again, and again,” says Palacios.
(Do you think dating is difficult? Try to be one of these animals.)
Previously, it was believed that males needed to bite the female’s pectoral fin before attempting to copulate, but this was not seen here.
The jump on the back leaves a rash on the female’s back, Palacios says — a finding that future researchers could use to determine whether a female is sexually mature.
First, though, Venables stresses that researchers must be able to distinguish these rashes from other abrasions — and understand how long they last on the body — before they can be effectively used as a sign of maturity.
Devil rays, which are incredibly shy, typically do not tend to approach humans and can be easily frightened.
But, during this encounter, “the animals didn’t care [the researchers’] presence, they would even bump into them,” says Palacios. The mating frenzy “makes them almost blind to the outside world,” she adds, making them vulnerable to threats such as tourism, fishing and boat traffic.
When rays come together in large groups like this, they are all more vulnerable, says Palacios, because a threat won’t affect just one ray: “There will be 10 or even hundreds of devil rays that will be caught in the same net or on the same trawler.”
“Think about how easy it would be for a fisherman to put a net around that little cyclone and catch them all,” says Venables.
The study also found that these waters off the southwestern Gulf of California are breeding grounds for three species of mobula, all of which are threatened: The International Union for Conservation of Nature categorizes munk devil rays as vulnerable to extinction, while the spinaltail (mobile mobula) and folded fin (Mobula thurstoni) the devil’s rays are both threatened.
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“When you put a net around the mature mating population, you are not only taking out the animals, but also the animals that are raising babies,” says Venables, adding that these findings highlight why it is important to regulate fishing. in these areas, particularly during the mating season.
Local success story
This area was once one of the main fishing spots for manta rays and devil rays, and Palacios remembers the days when you could see “hundreds, thousands of [dead] mobulas lying on the beach.”
(This Marine Protected Area in the Maldives offers hope for reef mantas.)
After the introduction of a new law banning fishing, the area became a tourist hub. Instead of trying to capture stingrays, communities now take tourists to swim with them.
However, without adequate regulation, this tourism can also pose a threat. Conservationists are teaching guides best practices so that tourists can see these animals in a responsible way, without influencing their natural activities – especially their reproductive behaviors.
“Disrupting reproduction directly impacts the health of the population,” says Venables. “Dating is the worst thing to upset.”