Scientists at Oregon State University have found that threatened bat rays (Myliobatis californica) produce a chemical cue that triggers an escape response in nearby rays.
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Published in the Journal of Experimental Zoology Part A: Ecological and Integrative Physiology, the study marks the first documented evidence of a "disturbance cue" using chemical communication in cartilaginous fish – a group that includes sharks, rays and skates.
Bony fish are known for releasing chemical signals when threatened to warn other fish in the area of potential danger but no such behaviour had previously been confirmed in elasmobranchs: the ancient lineage that includes sharks and rays.
The researchers set up the experiment as a first step to better understand the flight response observed in white sharks, with the bat rays being easier to study.
"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," says lead author Joshua Bowman, who conducted the research as part of his master's degree at Oregon State University.
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"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."
Using bat rays provided by the Oregon Coast Aquarium, researchers set up three tanks, each with an individual bat ray with one signaller tank that flowed to two receiver tanks. These tanks were visually and acoustically isolated from one another.
A predator attack was then stimulated by chasing the signaller ray without causing it harm. Within seconds of water from the signaller tank reaching the receiver tanks, the previously-unaware rays altered their behaviour by swimming faster and showing movements consistent with an escape (or flight) response.
"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," Bowman explains.
From rays to sharks
According to co-author Taylor Chapple, associate professor and co-director of Oregon State University's Big Fish Lab, the findings offer an important glimpse into the behavioural complexity of these often misunderstood animals.
"Rays are closely related to sharks, so studying their communication pathways can provide insights into sharks as well," says Chapple.
"Disturbance cues have never been described in sharks or rays, so these findings provide new insights into the communication pathways and behavioural complexities of these critically important marine species."
Future research will aim to identify the chemical substance released and determine whether similar warning signals occur across other species of sharks and rays.
The discovery could also help explain large-scale behavioural responses observed in the wild. For example, researchers have long noted that sharks sometimes rapidly abandon an area following the arrival of killer whales – even when individual sharks may not have directly encountered the predators.
Understanding these communication systems may have practical conservation implications too. Human activities that disturb marine wildlife could inadvertently affect far more animals than those immediately visible.
"This behaviour evolved to help the animals survive in the wild," Bowman said.
"But it also serves as a reminder that if people disturb these animals, whether in the wild or in controlled settings, they may be impacting more animals than just the one in front of them."
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