Electric rays and stingrays can be used to map the seabed

Mapping the seabed.

Many of the natural resources are on the ocean floor in places we have yet to find. For that purpose, ocean exploration is necessary.

Currently, automated vehicles, sonar, and satellites, with varying advantages and disadvantages, are being used for ocean exploration.

Now, scientists at RIKEN are developing a completely different system that relies on electric rays’ natural swimming behavior and sting rays.

What’s fascinating is, scientists even have completed a feasibility study indicating that electric rays and sting rays equipped with pingers will be able to map the seabed through natural exploration.

Yo Tanaka, a lead author of the study, said, “Electric rays and stingrays are benthic animals, meaning that they spend most of their time swimming around the ocean floor in deep places. By combining simple pinger technology and digital cameras with this natural behavior, we think we can use rays to map the ocean floor, and at the same time collect meaningful data about ocean wildlife, biota, and resources.”

“This method could be much more cost-effective as Tanaka and his team have already shown that electric rays can use their electricity to power the small pingers.”

The pinger device emits an ultrasonic sound. When several receivers pick up a pinger’s sound, the receivers’ position and the time when the sound is detected can be used to calculate the pinger’s position. By placing cameras on rays and linking the recorded video’s timing to the timing and locations determined by the pingers, the scientists believe they can create accurate maps of the ocean floor. In their proof-of-concept study, the team conducted two experiments that showed that their idea to use rays is feasible.

Scientists conducted the first trial in a large water tank. They set up cameras in three planes–front, side, and top–verified that both types of rays swam near the tank’s bottom. The images taken by the camera allowed the 3-D reconstruction of movements over time. They also verified that a camera could be attached to the rays to record video of their exploration.

Seeing these positive results, scientists were ready to test their system out in the real world–an area off Okinawa’s coast in Japan. As this was a proof-of-concept experiment, they chose a room with a relatively flat seabed.

Scientists attached pingers to both sting rays and electric rays. They then lowered them into the ocean from a large boat along with four ultrasound receivers. The ocean’s depth was about 20 m (60 ft), and the rays were allowed to swim about 40 m (120 ft) out from the boat.

Scientists recorded the pinger-derived positions as the rays swam near the boat for about two hours. Afterward, they compared the data with a seabed map of the area that already exists.

They confirmed rays’ positions were within about 10 cm of those on the public map. 

Tanaka said, “In our ocean experiment, in addition to the pinger positioning, we were able to confirm that electric rays move around the seabed. Shortly, we will test the system for long-term monitoring. Long-term monitoring will require pingers that the electric rays can self-charge and wearable battery packs for the stingrays. The next test will also monitor an area with a more varied seabed with complex geometry.”

Journal Reference:
  1. Furano, Si., Tanaka, N., Amaya, S. et al. Movement tracing and analysis of benthic sting ray (Dasyatis akajei) and electric ray (Narke japonica) toward seabed exploration. SN Appl. Sci. 2, 2142 (2020). DOI: 10.1007/s42452-020-03967-6

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