Ultra-Rare Manta Ray Nursery on the Coast of South Florida

Written By Sofia Perez

In the murky coastal waters of urban South Florida lie a diamond-shaped mystery. Related to sharks, these graceful creatures glide like shadows close to shore in the clear two-meter-deep beaches. It’s true they are beautiful, but unlike the iconic manatees and leatherback turtles emblematic of the state, these batoidea remain largely in the shadow of our admiration.

            We call these enigmas manta rays, ‘manta’, meaning blanket or coat in Spanish. With fleshly wing-like pectoral fins, they glide through the water almost like birds, but upon closer inspection, the extension of their cephalic fins from the front of their heads gives them the appearance of the devil, hence their title as ‘devil ray.’

            Unlike other fish, their lives can span up to fifty years of gliding across warm coastal shores and somersaulting out of the water, but not only are mantas the picture of aquatic elegance; they are also the mysteries of coastal ecosystems as well. Only recently in 2008 did researchers even discover that two distinct species existed: the reef manta, which lives along coastlines in the Indo-Pacific, and the giant ocean manta, which lives in major oceans, spending most of its life far from land.

Marine science has made another step towards understanding manta ray behavior. With only two previously known large manta ray nurseries in the world- one in the Gulf of Mexico, the other in Indonesia- scientists believe they have found a third right under the nose of the busy metropolis of South Florida. In fact, the genetics of these Florida mantas are even unique enough to be considered a third distinct species.

The project leading to this discovery, the Florida Manta Project(FMP), was led by Jessica Pate, who surveyed a 58-mile stretch of coast from the St. Lucie Inlet to Boynton Beach from 2016 to 2019, identifying 59 individuals, mostly juveniles, in the process.

This discovery not only aids research into manta behaviour, but also conservation. The International Union for Conservation of Nature considers both manta species as ‘vulnerable to extinction’, and the U.S. Endangered Species Act in 2018 listed them as an endangered species. This emphasises the requirement for critical habitat conservation designations. However, with insufficient data on manta ray populations, any productive conservation efforts are difficult.

Moreover, this newfound nursery lies in a more precarious location than most. With mantas frequenting areas with high levels of boat traffic or popular fishing piers, it’s easy to imagine why FMP observed such high rates of entanglement and vessel strike injury. Almost half of the 59 individuals identified showed signs of entanglement, and it’s believed that 27% of the local manta population experience a similar fate: the fishing line cutting into the ray’s body, preventing normal swimming, and sometimes leading to death. In addition to this, many local rays are in danger of boat strikes, with FMP finding ten of the 59 individuals with scars from a propeller.

The human population of Florida has increased 262% from 1960 to 2008, with intensive human development occurring along the coast. However the threats to mantas stretch far beyond the densely populated coast of Florida. Worldwide, manta and mobula rays have been targeted for their gill plates, which are transported and sold in Asia as health tonics, as well as facing the dangers of habitat destruction, ingestion of microplastics, unsustainable tourism, and climate change.

Since 2011, manta rays have been protected in international waters by the Convention on Migratory Species and fishing bans have been placed on them in Ecuador, Peru, Mexico, the Philippines and New Zealand, but this is not enough. “My ultimate goal is that someday the Florida manta ray will be as iconic and recognizable as the sea turtle and manatee,” says Pate. Fortunately though, with her discovery of a new urban nursery, more research can be done into the ecology and life history of the species, which will propel conservation efforts. She has also begun a collaborative satellite tagging study with a team from NOAA to better understand where the boundaries of the South Florida nursery lie.

Recently, the FMP has also partnered with the local female-led Field School to interview hundreds of fishers to better understand how mantas become entangled in fishing line. They found that most times, entanglement was unintentional, but occasionally was used as a tactic to target gamefish. Now the team is producing outreach materials to incentivize fishers to reel in their lines whenever mantas are sighted.

“Humans are central to both the causing and solving of all environmental problems,” says Dr. Julia Wester, the Director of Program Development for the Field School. Hopefully, this means that with enough determination, not only can we discover more about these cloaked enigmas, but we can also watch them thrive.

Bibliography

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