Frightened bat rays produce a chemical cue to warn other rays of danger, a well-known anti-predator strategy for bony fish that has not been documented in cartilaginous fish until now.
Oregon State University researchers found the behavior of bat rays changed when they received water flow from a tank where another bat ray was frightened by a mock predator, suggesting a chemical disturbance cue was passed from one tank to the other.
"The animals could not see each other, and they were acoustically isolated, so our work shows the response was induced by a chemical alert from the frightened ray," said Joshua Bowman, the study's lead author.
Bowman completed the research as part of his master's degree thesis at OSU's Big Fish Lab and is now a faculty research assistant with the Cooperative Institute for Marine Ecosystem and Resources Studies at OSU's Hatfield Marine Science Center in Newport.
The findings were just published in the Journal of Experimental Zoology Part A: Ecological and Integrative Physiology.
Rays are part of a subspecies of cartilaginous fish called elasmobranchs, which includes rays, sharks and skates. Bowman took on the experiment as a first step to better understanding flight response observed in white sharks.
"People don't necessarily think of sharks as prey, but even white sharks - the largest predatory sharks in the ocean - can be prey to orcas," Bowman said. "Past research has documented sharks fleeing when orcas are present, and they're probably not all seeing an orca and saying 'ok, time to leave.' That suggests there's probably some other signal they are responding to."
Bat rays are easier to study than white sharks, Bowman noted - they are smaller and more accessible to researchers, who borrowed the rays in this study from the Oregon Coast Aquarium in Newport.
"Rays are closely related to sharks, so studying their communication pathways can provide insights into sharks as well," said study co-author Taylor Chapple, an associate professor and co-director of OSU's Big Fish Lab.
"Disturbance cues have never been described in sharks or rays, so these findings provide new insights into the communication pathways and behavioral complexities of these critically important marine species."
For the experiment, Bowman set up three tanks, each with an individual bat ray - one signaler tank that flowed to two receiver tanks. These tanks were visually and acoustically isolated from one another.
After the rays had an opportunity to settle in and adjust to their environment, Bowman simulated a predator in the signaler tank by chasing - but not harming - the ray in that tank.
Overhead cameras monitored the behavior of the rays in the receiver tanks before and after the signaler was chased. Within seconds of the water from the signaler tank flowing into the receiver tanks, the receiver rays exhibited obvious behavioral changes, including swimming at higher velocity, that are characteristics of an evasion or flight response.
The findings support a chemical cue being passed through the water from the chased individual to two unaware animals. Previous research has documented this kind of chemical cue in bony fish, but this is the first documentation of chemical disturbances in cartilaginous fish, the researchers said.
The nature of the chemical remains unclear but could be the focus of future research, Bowman said.
"This behavior evolved to help the animals survive in the wild," he said. "But it also serves as a reminder to people that if they disturb these animals, in the wild or in controlled settings, that they may be impacting more animals than just the one in front of them."
Additional coauthors of the study are Jamie Cornelius, associate professor in OSU's College of Science; and Mauricio Cantor, assistant professor with OSU's Marine Mammal Institute.
The Big Fish Lab, the largest dedicated shark research lab on the West Coast of the United States, is part of the OSU College of Agricultural Sciences' Coastal Oregon Marine Experiment Station and is based at the Hatfield Marine Science Center.
