Moon Phases May Drive Mantas To Congregate And Feed
February 19, 2014

Manta Rays Found Congregating During Moon Phase

April Flowers for - Your Universe Online

Julia Hartup is the Mariana Islands Program Leader for the Manta Trust, a non-profit organization dedicated to research and conservation of mantas and their environment. When several of her paddler and free-diving friends reported seeing mantas congregating in a purposeful manner in an area where surgeonfish were spawning, Hartup was intrigued. Even more so when they were able to give her a specific date, which allowed her to calculate the moon phase. This is important data because many fish species synchronize their spawning with the moon.

Hartup used this data to predict when the spawning event would occur in the upcoming year, and her friends' observations told her where to look. Hartup was therefore able to witness a shoal of spawning surgeonfish accompanied by a fever of mantas.

The findings of Hartup's study not only highlight important data about mantas, but they also reveal predictable spawning aggregations (SPAGs) for three important reef species, as well—Acanthurus triostegus, Acanthurus gutattus, Acanthurus lineatus. All three species try to evade the mantas in their spawning area.

These findings bring up further questions for Hartup and other marine biologists. "The mantas come in patterns. Are they herding the spawning fish? Is there cooperative behavior? How do the mantas know to come? Mantas are thought to be singular except for feeding or visiting [a] cleaning station. Are they really singular or more social than we know? These are some of the questions I really want to investigate," said Hartup in a recent statement from the University of Guam.

Mantas — which grow between 18 and 23 feet in width, depending on the species — mature late and live between 40 and 50 years. A manta female generally has only one pup every 2 to 5 years, which takes 13 months to develop. The pup emerges into the world rolled up like a burrito, then must fend for itself, as there is no parental care. Where the mantas go to have their young is unknown at this time.

"I believe mantas must have a remarkable sensory system. Their cerebellum and frontal lobes are quite large so they are naturally curious and will check out humans in their vicinity," explained Hartup. She used direct observation, photographs and videos to document 41 individuals on Guam, but there is a massive lack of information about the lives of mantas in Micronesia.

Yap, an island state in the Federated States of Micronesia, enacted Law No. 7-36 in 2008, which designates "...all the internal and territorial waters of the State of Yap are hereby established as an official sanctuary for manta rays." The Yap government has tapped Hartup's research to help in developing an effective management plan for the protection of the mantas in Yap. Yap is made up of three islands in the Caroline Islands chain: Yap proper, Maap, and Rumung.

"By understanding the lives of Micronesia's mantas, we'll know where to start protecting them," said Hartup, who wants to document the mantas before they are lost due to human encroachment or habitat degradation.