Tracking endangered rays: A new chapter in marine conservation

Up to now, scientists have followed sharks, turtles, and even albatrosses by strapping recorders to their bodies, yet most rays have slipped through that technological net.

Biologging – attaching tiny sensors that record movement, sound, and surroundings – has thrived in other species, but rays’ smooth skin and fin-like bodies limited most attempts to just a few hours.

The whitespotted eagle ray, a six and a half foot wide coastal predator, is listed as Endangered by the International Union for Conservation of Nature (IUCN).

Dr. Matt Ajemian of Florida Atlantic University’s Harbor Branch Oceanographic Institute led a team that finally built a tag that can track rays for up to 60 hours.

Why eagle rays are hard to track

Studying rays in the wild is tougher than tracking sharks. Their flat bodies lack a sturdy dorsal fin for clamps, and their skin feels almost velvety, so adhesives and darts fail fast.

Many species migrate across reefs, lagoons, and shipping lanes, meaning any tag must survive swift turns and strong cross currents.

Fieldwork is further hampered by conservation rules that limit handling time, leaving researchers mere seconds to attach equipment.

Because of these hurdles, less than ten published studies have reported fine scale behavior of pelagic rays, compared with hundreds of sharks.

How the new tag works

The Harbor Branch team nested a camera, motion sensors, hydrophone, satellite pinger, and acoustic beacon inside a package smaller than a paperback and lighter than one pound.

Silicone suction cups hold the tag to the ray’s head, but the breakthrough was a soft strap that loops through the animal’s spiracles, the small breathing holes behind each eye, adding grip without piercing skin.

“Our goal was to create a system that could be applied in seconds, stay on during natural behaviors, and collect rich, multi dimensional data,” said Ajemian. Attachment now takes about eight seconds on a gently restrained ray. 

In sea trials off Bermuda, ten tagged rays kept their devices for an average of 21 hours, and one individual carried it 59.2 hours, three times longer than previous ray tags.

What eagle rays do underwater

Video showed the fish cruising over seagrass, coral rubble, sand flats, and reef ledges – dives that matched depth readings down to 72 feet.

“We’ve shown that complex behaviors, like the crunching of clams, can be identified using sound and movement data alone, even without video,” noted doctoral researcher Cecilia Hampton.

Audio captured the distinct crack of crushed clams, confirming feeding bouts even when the camera switched off to save battery. Motion logs revealed rhythmic wingbeats while swimming and chaotic bursts during bottom digging before prey capture.

The tag also filmed brief meetings with other eagle rays and a curious barracuda, hinting at social and predator prey links that surface observers rarely see.

AI reads ray movements

Every second, the tag’s accelerometer and gyroscope, parts of an Inertial Measurement Unit (IMU), recorded 50 data points per axis.

A supervised Random Forest model trained on one ray’s footage correctly labeled “swimming” 99.6 percent of the time and picked out “browsing” and “digging” behaviors with useful accuracy.

Similar machine learning approaches already classify accelerometer data in cattle and narwhals, showing the method scales across species.

As training libraries grow, future tags may drop the camera entirely, extending battery life while still logging every clam crunch.

Saving endangered eagle rays

Eagle rays help control conch and clam populations, yet bycatch, coastal construction, and targeted fisheries have pushed numbers down 50 to 79 percent in three decades.

Knowing where and when rays feed lets managers draw smarter no take zones and adjust dredging schedules to avoid peak foraging periods.

The new tags revealed long stays around inlet passes, data that could guide boat speed limits in those hotspots.

They also showed night time visits to shellfish farms, backing earlier acoustic surveys that hinted at after dark foraging on cultured clams.

What’s next for tracking eagle rays

Slimmer sensor suites and longer life releases could turn rays into mobile habitat monitors, sampling noise, temperature, and water quality across coastal grids.

Other smooth skinned species, such as cownose rays and manta rays, share similar spiracle shapes, so minor tweaks may spread the method throughout the family and even to small sandbar skates.

Biologging on bluefin tuna recently recorded a dramatic orca attack, proving that tags can chronicle entire food web interactions.

Combining these broader community insights with the new ray data could finally reveal how predators, prey, and habitats interact along tropical coastlines.

The study is published in the journal Animal Biotelemetry.

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