The ocean off the coast of Ecuador and Peru is one of the most productive in the world, due to cold, nutrient-rich water rising to the surface in a process called upwelling. Manta rays are likely drawn to the area due to availability of food, the researchers said. "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 many other manta ray populations have faced." "This work solidifies Isla de la Plata, and Ecuador more broadly, as a globally important hot spot for this endangered species," said Michel Guerrero of Proyecto Mantas Ecuador, which is a Fundación Megafauna Marina del Ecuador project. The rays tend to straddle the region around the border of southern Ecuador and Peru, though a handful were found to have traveled as far as the Galapagos Islands. The researchers' findings suggest that conditions in the region are particularly favorable for a large, healthy manta ray population, Stewart said. "This is by far the largest population that we know of." "That is significantly larger than what we've seen in oceanic manta ray populations elsewhere," said Guy Stevens, chief executive and founder of The Manta Trust. The researchers used data collected through their own observations and from recreational SCUBA diver photos between 20 to identify more than 2,800 individual rays and estimate a total population of more than 22,000. Credit: Michel Guerrero / Proyecto Mantas Ecuador FMME It is also a popular diving area, and visitors take numerous photographs of the animals, providing researchers with a trove of data. Oceanic manta rays are a challenging species to study in part because they tend to spend their time in offshore locations that are hard for researchers to access, and their visitation patterns can be unpredictable.īut in the late 1990s, researchers from Proyecto Mantas Ecuador discovered that a population of oceanic manta rays aggregate in August and September each year around Isla de la Plata off the coast of Ecuador, where they are relatively easy to locate and study. The new study was led by Proyecto Mantas Ecuador of Fundación Megafauna Marina del Ecuador, a conservation organization based in Ecuador, in collaboration with The Manta Trust, the Marine Megafauna Foundation and the Ocean Ecology Lab at OSU's Marine Mammal Institute, which is led by Stewart. The biggest threat to oceanic manta rays is commercial fishing, both as the target of some fisheries and as unintentional bycatch in many others. Endangered Species Act in 2018, and in 2019 their threat category increased from vulnerable to endangered on the International Union for the Conservation of Nature's Red List. Oceanic manta rays were listed as threatened under the U.S. They are filter feeders that eat large quantities of krill and other zooplankton and tend to live in small subpopulations in tropical, subtropical and temperate waters, spending much of their time in the open ocean. Oceanic manta rays are the largest species of ray, with wingspans that can reach more than 20 feet. In this area, we've estimated that the population is more than 22,000 mantas, which is unprecedented." In other regions, we typically have population estimates of 1,000 to 2,000 animals, which makes this species very vulnerable. "It's clear that something different is happening here," Stewart said. 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, said Joshua Stewart, an assistant professor with the Marine Mammal Institute in OSU's College of Agricultural Sciences and a co-author of the paper.
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