Electric rays have been observed using a unique defense mechanism to fend off large predators like sharks, according to a new study by researchers at Florida International University. The findings, published in the journal Ethology, reveal that these rays emit electric discharges to deter potential threats in their natural habitats.
Yannis Papastamatiou, a researcher at the Florida International University Institute of Environment, explained that while traditional defense methods such as camouflage and venom are often ineffective against large predators, electric rays have developed a bold strategy. “We had an idea that there was something special about the rays because they are very bold,” he said. “In Guadalupe Island, Mexico, our cameras on white sharks showed these rays up in the water column, one of the most dangerous places to be. They must be pretty confident.”
Understanding Electric Organ Discharge
Electric rays, encompassing 69 species across four families, have the ability to produce electric organ discharge (EOD). Some of the larger species can generate EODs with a maximum voltage of 50 volts, using their muscles to create these electric discharges. While this behavior has been documented in captivity, its use in the wild was previously unknown.
The study involved deploying six Customized Animal Tracking Solutions (CATS) biologgers on white sharks off the Pacific coast of Mexico at Guadalupe Island. One particular instance recorded a shark at a depth of 164 feet approaching an electric ray. As the shark neared, the ray cupped its pectoral fins, prompting a sudden increase in the shark’s movement as it rapidly ascended to nearly 100 feet. The shark later returned but avoided the ray, which continued its path undisturbed.
Field Observations and Comparisons
Further observations were made during a baited shark dive in Fuvahmulah, Maldives, where a Gulf torpedo ray was seen buried in the sand. As it began to swim away, it was approached by a tiger shark. However, as the shark came within inches of the ray, it rolled its nictitating membrane—a protective third eyelid—and quickly retreated.
Researchers also analyzed EOD characteristics from field experiments conducted off Palos Verdes, California, between 1989 and 1991. The study compared predatory and defensive behaviors, noting that while the maximum voltage did not vary, the initial trains for predatory discharges were longer and more frequent. In defense, the rays moved into the water column and performed stationary spinning.
“This study adds important insight into the evolution of defensive traits in marine animals,” Papastamatiou stated.
Implications for Future Research
The findings highlight the potential for further studies into the foraging and defensive behaviors of electric rays, particularly with the increasing use of animal biologging technology. Understanding these behaviors could provide deeper insights into the evolutionary adaptations of marine species.
As researchers continue to explore the capabilities of electric rays, the study underscores the complex interactions between predators and prey in the ocean. The ability of these rays to deter large sharks using electric discharges represents a fascinating example of nature’s ingenuity in survival strategies.
For more information, refer to the study by Yannis P. Papastamatiou et al., titled “Electric Rays Defend Themselves From Large Sharks Using Electric Discharge,” published in Ethology (2025). DOI: 10.1111/eth.70005.