Danger in the ocean isn’t always visible on the surface. Sometimes it spreads as an invisible chemical signal, drifting through the water and warning nearby animals of approaching trouble.
Bony fish have relied on this signal for a long time. A frightened individual releases a warning substance into the water, and nearby fish pick up the message and respond accordingly.
Previously, it was believed that sharks, rays, and their relatives were left out of this communication network. But new research has shown that rays use chemical signals to warn others about approaching predators. The study’s findings were published in the Journal of Experimental Zoology.
Researchers from Oregon State University demonstrated that a frightened bat ray (Myliobatis californica) releases a chemical substance that alerts other rays to potential danger. The signal traveled from one tank to another, altering the behavior of the animals that received it.
This predator defense strategy was well-documented among bony fish. Until now, it had never been recorded in cartilaginous fish.
“The animals couldn’t see each other and were acoustically isolated, so our work shows that the reaction was triggered by a chemical alarm signal from a frightened ray,” said Joshua Bowman, the lead author of the study.
Bowman started with a bigger question about great white sharks. These ocean giants sometimes leave their hunting grounds, and no one was sure how this warning spread.
“People don’t always see sharks as prey, but even great white sharks—the largest predatory sharks in the ocean—can become prey for killer whales,” Bowman said. “Previous studies have shown that sharks flee when killer whales are present, and it’s unlikely that every single one of them sees a killer whale and thinks, ‘Okay, time to go.’ This suggests they’re likely responding to some other signal.”
Keeping and studying great white sharks is challenging. Bat rays were chosen as a practical alternative because they are smaller and easier to maintain in a lab.
The team borrowed young rays from the Oregon Coast Aquarium in Newport. Rays and sharks belong to the same evolutionary branch, so knowledge gained from studying one can be useful for understanding the other.
Co-author Taylor Chapple, from the Big Fish Lab at Oregon State University, explained the connection.
“Rays are closely related to sharks, so studying their communication pathways can give us insights into sharks as well,” Chapple said. “Disturbance signals have not been described before in sharks or rays, so these results provide new understanding into the communication pathways and behavioral complexity of these critically important marine species.”
The setup was simple. One signal tank delivered water to two downstream receiving tanks, each containing a single ray.
Thick foam, opaque barriers, and falling water blocked sound, visibility, and vibration between the tanks. Anything the receivers detected had to arrive dissolved in the water itself.
Once the rays were settled, Bowman chased the signal animal with a stick for 30 seconds. He never touched or harmed the animal, keeping the stick clean of blood or damaged tissue.
Cameras above the water recorded each ray for 15 minutes before and after the chase. The receivers reacted within seconds of the disturbed water reaching their tanks.
The receiving rays sped up, while control rays in a parallel setup showed no change in speed. They also shifted from resting on the bottom to moving along the walls of their tanks.
The average speed of rays receiving the water increased by about three centimeters per second, a jump of roughly 21 percent. The control animals, which received water from an empty tank, showed no significant changes.
These faster movements, hugging the walls, match a classic avoidance response. In the wild, extra speed helps prey increase the distance between themselves and a hunter.
One might expect that an animal involved in such a chase would show signs of physical stress. Researchers tested blood for glucose, lactate, pH, and a ketone called 3-HB.
None of these markers differed between the alarmed subjects and the calm control groups. Behavior changed, but the body’s chemistry stayed stable.
This stable chemistry suggests that the rays handled the sudden burst of activity easily. Bat rays process oxygen well and recover quickly, so a short sprint fits within their aerobic limits.
Daily feeding might have also smoothed out any metabolic signals. The animals had enough fuel, so they didn’t need to tap into deeper energy reserves.
These signals matter far beyond just scaring one animal. When a predator like a great white shark leaves a certain area, its prey can multiply and alter the local food chain. So, the chemical alarm could move predators in ways that affect entire ecosystems.
This work hints that such chemical risk assessment might be far more common among sharks and rays than anyone assumed. The chemical itself remains a mystery. Bowman hopes future research will pinpoint exactly what these rays release.
“This behavior evolved in animals to help them survive in the wild,” Bowman said. “But it also serves as a reminder to people that if they disturb these animals, whether in the wild or in controlled settings, they might be affecting more than just the animal right in front of them.”
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