There is a distinct population of manta rays that is 10 times larger than the rest of the population.
The findings, just reported in the journal Marine Ecology Progress Series, indicate that while other populations of oceanic manta rays are typically small and vulnerable to human impacts, this population is large and potentially quite healthy.
Stewart said something different is happening here. It's a rare story of ocean optimism. The population estimates of 1,000 to 2,000 animals make this species very vulnerable. We estimate that the population in this area is more than 22,000.
The largest species of ray is the ocean manta rays. They are filter feeders that eat a lot of zooplankton and spend a lot of their time in the ocean.
The International Union for the Protection of Nature's Red List increased the threat category for the ocean manta rays in 2019. Commercial fishing is one of the biggest threats to the manta rays.
The new study was led by Proyecto Mantas Ecuador of Fundacin Megafauna Marina del Ecuador, in collaboration with The Manta Trust, the Marine Megafauna Foundation and the Ecology Ocean Lab at the Marine Mammal Institute.
It's difficult to study the ocean manta rays because they tend to spend their time in offshore locations that are hard for researchers to get to.
In the late 1990s, researchers from Proyecto Mantas Ecuador discovered that a population of manta rays aggregate in August and September off the coast of Ecuador. Visitors take many pictures of the animals at the diving area, which provides researchers with a lot of data.
The study's lead author said that many of the photos used in the study were contributed by recreational divers who became citizen scientists. The photographs give us a lot of information about the animals.
Each manta ray has a unique spot pattern on its belly, similar to a human fingerprints, which allow researchers to identify individual animals and track their movements and locations over time. There are photos of individual rays that can be used to document things.
The researchers used data from their own observations and recreational SCUBA diver photos to estimate a total population of more than 22,000.
"That is larger than what we've seen in other parts of the world," said Guy Stevens. This is the largest population we have.
Stewart said that conditions in the region are favorable for a large, healthy manta ray population. Some rays have traveled as far as the Galapagos Islands, but the rays tend to straddle the region around the border of South America.
"This work has solidified Isla de la Plata as a globally important hot spot for this species, and it is a Fundacin Megafauna Marina del Ecuador project," saidMichel Guerrero of Proyecto-Mantas-Ecuador, which is a Fundacin While this population may be healthy thanks in part to its large size, it is essential that we take the necessary steps to protect and prevent the declines that other manta ray populations have faced.
The researchers said that the availability of food is likely to be the reason for the drawn-to nature of the area. The ocean off the coast of South America is one of the most productive in the world due to cold water rising to the surface.
Stewart said that the region is able to support large populations of animals.
In 2010 and 2016 it has been illegal to catch manta rays in the waters of the two countries. More than half of the manta rays identified in the study were either entangled in fishing gear or had scars from fishing.
Stewart said that continued monitoring of the population is needed to understand how climate change may affect food availability, distribution and overall population health.
There is good news about this population. Changes to ocean temperatures and food availability seem to be sensitive to environmental disruptions. If upwelling strength and the abundance of food changes alongside ocean temperatures, they will be impacted.
The Fundacion Megafauna Marina del Ecuador and the Marine Megafauna Foundation have additional co- authors.
The world's largest known population of oceanic manta rays Mobula birostris can be found in coastal Ecuador. It's called 10.3354/meps14189.
Journal information: Marine Ecology Progress Series
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