Researchers from the Riken Center for Biosystems Dynamic Research conducted a study to find if stingrays and electric rays could be used to map out the largely unexplored ocean floor. The team believed that by equipping the rays with pingers, they would be able to map out the ocean floor with natural exploration.
The new system relies on the natural swimming behavior of electric rays and stingrays. These rays are benthic animals, which means they spend most of their time swimming on the ocean floor in deep places.
The team’s new mapping method is cost-effective. The electric rays' electricity could be used to power their small pingers. Pingers are devices that emit an ultrasonic sound, which is picked up by receivers. The position of the receivers and the time when the sound was detected can be used to calculate the position of the pinger. Cameras attached to the rays capture video of the rays exploring. The timing of the recorded video could be linked to the timing and location of the ray pings to create accurate maps of the ocean floor.
The first study was conducted in a large tank. Three cameras were placed on three planes of the tank, front, side and top. This study verified that both types of rays swim near the bottom of the tank. Images taken by a camera allowed the team to create a 3D reconstruction of movements over time. It also confirmed that a camera could be attached to rays to record video of their exploration.
Once the team was confident in their initial findings, they conducted a second study in a natural environment. Their proof of concept experiment happened in an area off of Okinawa in Japan. The team chose this area because it is a relatively flat seabed. The seabed depth was 20 m. The team attached pingers to stingrays and electric rays and lowered them into the ocean from a large boat with four ultrasound receivers. The rays were allowed to swim about 40 m out from the boat. While the rays were swimming for about two hours, the team recorded the pinger derived positions.
After the study, the team compared data with a seabed map of the area that already existed. They confirmed that the ray positions were within 10 cm of what the map showed. The results were similar in both kinds of rays, which is important because rays are seasonal animals.
The ocean experiment allowed the team to confirm that electronic rays move around the seabed. The team plans to test their system for long term monitoring. Long term monitoring would require pingers that electric rays can self-charge and wearable battery packs for stingrays. They also plan more testing in an area with more varied seabed with complex geometry.
The study was published in SN Applied Sciences.