Reef Manta Rays Found to Frequent Marine Protected Areas

Reef manta ray, Mobula alfredi (Credit: Amelia J. Armstrong and colleagues)

(CN) — Scientists announced Wednesday they had tracked the movements of reef manta rays between two UNESCO World Heritage areas along Australia’s west coast using satellites and a set of decades-old photographs, giving them unique insights into their little-known behaviors.

Researchers tracked a group of 22 rays across the western coast of Australia, a notoriously difficult feat, according to a study published in the journal Frontiers in Marine Science

The authors attached satellite tracking tags to the rays and compared their movements with data gleaned from a photo database to gain a better understanding of the species’ visitation patterns and use of space.

Reef manta rays, among the largest ray species on Earth, are an integral part of Australia’s swim-with-megafauna tourism industry and bring in thousands of visitors annually hoping to catch a glimpse of these sleek sea creatures in the wild. 

They’re also listed as a vulnerable species on the International Union for Conservation of Nature’s Red List. Despite their importance, little was previously known about their movements, migratory patterns or behavior.

Scientists found the rays revisited several the same locations over a 15-year timespan, including two UNESCO World Heritage areas. The rays seemed to prefer coastal shelf waters, mostly remaining in relatively shallow depths of less than 60 feet. 

They tended to venture between the Ningaloo and Shark Bay World Heritage areas, two ecologically protected areas that could provide authorities a fortunate opportunity to safeguard the species.

“This is a great discovery for the reef manta rays on this coastline, because these protected areas provide the legislative framework needed to underpin further management action,” said Amelia J. Armstrong, lead author of the new paper and a doctoral student in biomedical sciences at the University of Queensland in Australia, in a statement.

Researchers found reef manta rays can travel vast distances when their local habitat is contentious, covering around 430 miles, yet exhibit a remarkable long-term affinity for their favored locations. 

Protecting such a far-ranging species is especially challenging, as it’s often impractical to establish safe areas over such a vast distance. That makes understanding their movements and behavior even more critical to their continued survival.

The tags used by researchers to track the animals only collect location data when the rays come to the surface, so they store depth, temperature and light-level readings as the rays move through their environment. The authors then used sophisticated models to extrapolate their locations over time.

“Satellite tags allow us a short peek into the secret lives of these animals to understand where else they frequent outside of key tourism locations, while photographic identification helps us track visitation over longer periods,” Armstrong said.

The underside of reef manta rays displays a Rorschach-like pattern of spots that researchers used to identify and track individuals. They compared these unique patterns with a database of photos dating back to the early 2000s taken by local tourism operators and citizen scientists. 

These images allowed the researchers to identify more than 1,100 individuals out of 5,000 sightings.

Reef manta rays are the second largest recognized species of ray on the planet (an unrecognized species from the Caribbean also appears to be larger). They can live to be 50 years old, reproduce slowly and measure 11 feet in width on average, but can grow to a maximum size of 18 feet. 

They were only confirmed to be a distinct species back in 2009, and lack the spiked tail found on some of their more notorious cousins.

“Unfortunately for manta rays, a slow growth rate and few offspring means that populations can take a long time to recover from disturbance,” Armstrong said.

Manta ray populations have been steadily declining over the past 20 years due to the international trade in manta ray body parts driven by their popularity in traditional Chinese medicine. Specifically, the rays’ gill plates are highly prized by practitioners.

The species prefers the tropical and subtropical waters of the Indo-Pacific. In addition to Australia, they can also be found swimming off the shores of Hawaii, Fiji, French Polynesia, Micronesia, Bali, Mozambique and the Philippines. They’re relatively sedentary animals, and this research confirms they prefer to stay around their favored locations once they’ve found them.

“Further investigation into population size and trends is an urgent research priority to ensure this manta ray population is robust and resilient in the face of future change,” Armstrong said.

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