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

The whistling noise of the helicopter almost drowned out the thoughts of Jahneman Konrady, pilot and field researcher for the Marine Megafauna Foundation (MMF), as he looked down his camera lens and spotted a reef manta ray (Mobula Alfredi) in what he believes is the wrong habitat for them.

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It almost drowned out that surprise. But not quite.

Nothing could contain the surprise when he spotted the majestic carnivore during an aerial transect of the Sardine Run, which takes place every year along the Wild Coast of South Africa’s Eastern Cape province. Hailed as one of the most spectacular marine events in the world, the silver sardine migration begins in the cool waters of the southern part of the African continent, where they gather to form hundreds of large, chaotic shoals. This rotating mass then “runs” northeast to the warm waters of the Indian Ocean, the giant waves of this small fish accompanied by legions of predators such as sharks, dolphins, Cape Gannets, cormorants, seals and others. However, after 100 days of flight (resulting in a total of 335 hours of survey time), he was convinced that this was no coincidence: “At first it didn’t look like the right habitat for them, but with increased observations they had to admit that this area may actually be a habitat for reef manta rays, with all individuals encountered being less than 2 meters in length.

MMF’s Manta Ray Research Program in Mozambique has monitored this southern Mozambican population for more than 20 years, making it one of the longest and most comprehensive studies of manta rays worldwide. Recently, the team has focused on better understanding where and how far this species is moving to guide effective management solutions. The largest of the devil ray species (the Mobula genus), they occur regularly on coastal and oceanic reefs in the tropical and subtropical waters of the Indian and Pacific oceans. Previous work by the MMF found a sharp decline in manta ray sightings in Mozambique over the past two decades, highlighting it as a population at risk. Now, long-term monitoring and photographic input from the public has highlighted six transboundary movements, providing the first evidence of connectivity between reef manta aggregation sites in southern Africa and southern Mozambique. This extended the reef manta’s southern distribution range in Africa, linking the longest-monitored and highly vulnerable population of the reef manta in southern Mozambique with the iSimangaliso UNESCO World Heritage Site in South Africa.

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

What makes this discovery particularly unique is that citizen science input from the SCUBA diving community helped make it a reality! Divers are constantly uploading photos of manta rays in South Africa to MantaMatcher.org, the global open access online database of stingrays. This database allows cross-referencing of regional databases using automated pattern-matching algorithms, which can lead to exciting discoveries… like this. Anna Flamm, global manager of Manta Matcher, says: “The input of citizen science was critical to this research. The first two transboundary movements were detected with Manta Matcher public statements, showing how people everywhere can contribute to conservation science.” Combined with opportunistic fieldwork, the researchers were able to uncover the longest secret life of these elegant filtering devices. 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 traveling between Tofo Beach, Mozambique and Sodwana Bay, South Africa in less than 301 days – a straight-line distance of 313 miles (505 kilometers). And I can’t forget the reef manta rays that were seen during aerial surveys and in-water encounters during the annual Sardine Run, with their small size indicating potential nursery habitat in the region.

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

The study, titled “Southern range expansion and transboundary movements of reef manta rays Mobula Alfredi along the East African coast’ was published in the Journal of Fish Biology in December 2022 and can be accessed here.

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