New Study Confirms A World-First International Migration Of Reef Manta Rays

The whooshing noise from the helicopter almost drowned out the thoughts Janneman Conradie, Marine Megafauna Foundation (MMF) pilot and field researcher, had as he looked down the lens of his camera and spotted a reef manta ray (Mobula alfredi) in what he thought was the wrong habitat for them.

Almost drowned out that surprise. But not quite.

Nothing could keep the surprise contained when he spotted the majestic predator during an aerial transect at the Sardine Run, which takes place every year along the Wild Coast of South Africa’s Eastern Cape Province. Hailed as one of the world’s most spectacular marine events, the migration of silvery sardines starts off the cool waters in the southern part of the African continent where they come together to form into hundreds of large chaotic shoals. This swirling mass then “runs” northeast to the warm waters of the Indian Ocean, the gigantic waves of this small fish accompanished by legions of predators like sharks, dolphins, Cape Gannets, cormorants, seals, and more. However, after 100 days of flying (which led to a survey time of a whopping 335 hours), he was convinced it was no coincidence: “At first it did not seem like the right habitat for them, but with increased sightings we had to concede that this area may in fact be a nursery habitat for reef mantas, with all encountered individuals being less than 2 meters in length.”

MMF’s manta ray research program in Mozambique has been monitoring this southern Mozambican population for over 20 years, making it one of the longest and most comprehensive manta ray studies globally. Recently the team has focused on better understanding where and how far this species moves in order to guide effective management solutions. The largest of the devil ray species (the Mobula genus), they’re regularly seen on coastal and oceanic reefs throughout tropical and subtropical waters of the Indian and Pacific Oceans. Previous work frok MMF has found a steep decline in manta ray sightings in Mozambique over the past two decades, highlighting it as an at-risk population. Now, long-term monitoring and photographic contributions from the public have highlighted six transboundary movements providing the first evidence of connectivity between reef manta ray aggregation sites in South Africa and southern Mozambique. This has extended the southern range of the reef manta ray in Africa, connecting the longest monitored and highly vulnerable population of reef manta rays in southern Mozambique to the UNESCO World Heritage site of iSimangaliso in South Africa.

“As highly mobile species, reef manta rays are capable of long-range movements, so it was only a matter of time until we documented international exchange between the waters of adjacent countries. We are thrilled to have finally confirmed this for the first time through rigorous, long-term research efforts along the southeastern coast of Africa,” says Dr. Andrea Marshall, one of MMF’s principal scientists who oversaw the project. Dr. Stephanie Venables, who also completed her PhD thesis on the Mozambican manta ray population, was also excited about the recent findings: “These cross-border movements are an important finding, as they demonstrate the need for cooperative species management between the neighboring countries.” Both scientists stress that this latest research supports the Convention on Migratory Species (CMS) listing for reef manta rays, suggesting transboundary management units are warranted for this wide ranging species.

What makes this discovery especially unique is that citizen science contributions from the SCUBA diving community were what helped to make it a reality! Divers constnastly uploaded photos of mantas in South Africa to MantaMatcher.org, the open-access global online database for rays. This database allows for cross-referencing of regional databases using automated pattern matching algorithms, which can lead to exciting discoveries… like this one. Anna Flam, global manager of Manta Matcher says, “Citizen science contributions were critical to this research. The fist two transboundary movements were detected with public submissions to Manta Matcher, showing how people everywhere can contribute to conservation science.” Combined with opportunistic fieldwork, the researchers were able uncover the longest the secret lives of these elegant filter-feeders. Notable discoveries include an individual making a return trip between Zavora in Southern Mozambique and Sodwana Bay (a total distance of at least 540 miles or 870 kilometers) and the (one-way) movement captured in another individual which traveled between Tofo Beach, Mozambique and Sodwana Bay, South Africa in less than 301 days – a straight-line distance of 313 miles (505 kilometers). And can’t forget the reef manta rays that were seen during aerial surveys and in-water encounters at the annual Sardine Run, with their small size of indicating a potential nursery habitat in the region.

“South Africa has been a missing piece of the puzzle for some time and there is still a lot of work needed to understand manta ray habitat use here,” says Michelle Carpenter, PhD candidate at the University of Cape Town. Dalhousie University PhD student Nakia Cullain, who is also manager of MMF’s southernmost field station for manta rays at Zavora, agrees: “Although we are just beginning to brush the surface of these movements, these findings are a huge step forward in helping us to inform the management and conservation of the species within southern Africa.”

The study, entitled “Southward range extension and transboundary movements of reef manta rays Mobula alfredi along the east African coastline” was published in the Journal of Fish Biology in December 2022 and can be accessed here.