A team of scientists took to the waters of Harrington Sound to study Bermuda’s native eagle rays and test new technology for the examination of marine life.

In a paper published in Animal Biotelemetry, researchers from the Harbour Branch Oceanographic Institute at Florida Atlantic University explained how they sought to use electronic tags to gather information about batoids, a family of fish that includes rays.

The paper noted that while marine mammals, sea turtles and large fish have been studied for years using electronic tags to collect data — or biologging — species such as rays had received less attention.

“This is disconcerting, as many batoids are facing extinction risks, yet their ecology is not well known despite being large enough to carry animal-borne sensors,” the paper said.

The researchers explained that part of the challenge was adapting electronic tags for rays as the creatures lack the prominent dorsal fins often used to apply the devices and their smooth skin is less conducive to external tagging.

As such, the scientists sought to design a new electronic tagging system for rays and test it on eagle rays both in captivity and in the wild, with Flatts Inlet and Harrington Sound selected as the test bed.

The tags included a camera and hydrophone along with a range of other sensors to record location, movement, depth and temperature.

They were attached to the animals by a series of suction cups, while some of the devices also incorporated plastic hooks designed to attach to spiracles — small openings behind the ray’s eyes used to breath.

Matt Ajemian, a senior author of the paper, said: “Our goal was to create a system that could be applied in seconds, stay on during natural behaviours and collect rich, multidimensional data.

“We’re now able to observe not just where these rays go, but how they feed, how they move through their habitats and how they interact with other species — insights that were virtually impossible to capture before.”

Between October 2022 and June 2024, the researchers tagged 13 local eagle rays and found that the tags that utilised only the suction cups remained on the animals for an average of six hours, while the spiracle hooks remained on for an average of almost 20 hours.

“While longer tag deployments are a plausible next step of this research, impacts on animal welfare are an important consideration,” the paper said.

“Indeed, suction-cup-based tagging is deemed a non-invasive technique for cetaceans. However, we noticed minor markings appear on the skin around the rim of the suction-cup attachment site from captive animals.

“Such features have been previously reported by researchers studying suction-cup attachments in cetaceans, and while markings remained evident a few months later from one individual, these were nearly healed based on visual inspection.”

Video footage recovered showed the eagle rays travelling through different marine environments, including “browsing” along the sea floor, occasionally digging into the sediment for food and, after finding food, rising and slowly gliding back down.

The researchers also discovered that they were able to detect whether the creature was swimming, browsing or feeding based solely on its movement and the sounds it produced.

While they said that the inclusion of cameras was still important as techniques develop, in the future it may be possible to remove the camera to make the tags smaller and less intrusive.

“While not the primary purpose of this tag package, the inclusion of a video camera also provided insights into species behaviours that were not foraging-related,” the paper said.

“Some of these include conspecific trailing, inter-species interactions, rapid vertical movements and manoeuvres around high-current areas.

“We suspect these observations will be of interest to scientists who study the social and reproductive behaviour of this species, which has been historically limited to direct field observations.

“However, the use of a video camera is power-intensive, and there is still a need for alternative methods for long-term behavioural monitoring, especially in circumstances where the cost of camera tags is prohibitive, or the size of the subject limits the practicality of a camera and battery large enough to support it.”