Like many of the world’s most majestic animals, manta rays regularly suffer from the encroachment of humans on their habitat, leaving them constantly teetering on the brink of becoming an endangered species. By tracking their seasonal movements, researchers have now uncovered some crucial facts about how global manta ray populations connect with one another, providing some surprising findings that could help conservationists refine their strategies in order to better protect these amazing creatures.
Lovingly renamed “majestic sea flap flaps” by the Internet, manta rays can grow to a wingspan of up to 7 meters (23 feet), enabling them to effortlessly glide through the water like kites in an updraft. As such, they are perfectly capable of swimming long distances, with some having been recorded migrating over 1,400 kilometers (870 miles) from mainland Ecuador to the Galapagos Islands.
It has therefore been largely assumed that manta rays are highly migratory creatures, leading to a perceived need for international-scale conservation efforts. However, somewhat surprisingly, the results of the new study – which appears in the journal Biological Conservation – indicate that the rays in fact “exhibit a high degree of residency,” mainly staying put in a single region throughout their lives.
Because of this, they tend to form “well-structured sub-populations”, which are highly vulnerable to large-scale human activities such as fishing in their small corner of the ocean. Indeed, the study authors report that overfishing in Baja California in the 1980s and '90s led to the virtual disappearance of manta rays in what had previously been one of the world’s prime scuba dive spots for encountering rays.
In a statement, lead researcher Joshua Stewart explained that he and his team were somewhat surprised with the results of their investigation, saying “these animals are showing a remarkable degree of residency behavior compared to the migrations we were expecting.”
“While mantas do make the occasional long-distance movement, it appears that the norm is to stay put. This means that any one population of mantas is highly susceptible to fisheries and other human impacts, but that local populations are also more easily protected," he added.
Image in text: A majestic sea flap flap. Isabelle Kuehn/Shutterstock
In order to achieve this, however, the researchers are now urging conservationists to consider a change of tack, claiming that “oceanic manta rays can benefit from local management initiatives,” rather than large-scale, global programs.
To conduct their research, the team used satellites to track the movement of manta rays in four of the world’s most significant ray habitats, ranging from Mexico to Indonesia. They also took muscle samples from rays in each location in order to conduct genetic and stable isotope analyses – the results of which revealed that populations at each site are indeed all closely related, suggesting that these geographical subpopulations remain stable from generation to generation.
While some long-range journeys were recorded, the majority of the rays’ migratory movements tended to be on a vertical level, as they dive to different depths at different times of the year in order to feed on plankton populations, which fluctuate in vertical location from season to season.
A giant manta ray swims gracefully in the Revillagigedo Archipelago, about 300 miles off Baja California, Mexico. Scripps Oceanography/Joshua Stewart