Tim Leighton, the lead author of the study, which was published in the latest Proceedings of the Royal Society A, found the inspiration for the research after watching an episode of the Discovery Channel series “Blue Planet” and saw how these marine mammals blow tiny bubbles around the prey when hunting.
“I immediately got hooked, because I knew that no man-made sonar would be able to operate in such bubble water,” said Leighton, who is a professor of ultrasonics and underwater acoustics at the University of Southampton.
“These dolphins were either ‘blinding’ their most spectacular sensory apparatus when hunting — which would be odd, though they still have sight to reply on — or they have a sonar that can do what human sonar cannot…Perhaps they have something amazing,” he explained.
Together with colleagues Paul White and student Gim Hwa Chua, Leighton initiated the research into determining how this behavior could be explained.
The researchers first modeled the types of echolocation pulses that dolphins emit, which they then processed using nonlinear mathematics instead of the standard way of processing sonar returns.
The technique managed to offer an explanation on how dolphins can hunt with bubbles.
The animals send out pulses that vary in amplitude. The first may have a value of 1 while the second is 1/3 that amplitude.
“So, provided the dolphin remembers what the ratios of the two pulses were, and can multiply the second echo by that and add the echoes together, it can make the fish ‘visible’ to its sonar. This is detection enhancement,” Leighton said in an interview with Discovery News.
He continued: “Bubbles cause false alarms because they scatter strongly and a dolphin cannot afford to waste its energy chasing false alarms while the real fish escape.”
In the second stage, the researchers subtracted the echoes from one another, making sure that the echo of the second pulse is first multiplied by three. What they were trying to do was making the fish visible to sonar by addition. The fish is then made invisible by subtraction to confirm it is a true target.
This sonar model can be of use for humans as it could help in detecting covert circuitry or improving detection of sea mines.
“Currently, the navy uses dolphins or divers feeling with their hands in such difficult conditions as near shore bubbly water, for example in the Gulf,” Leighton explained.
This isn’t the first study on dolphins’ math skills. Previous studies conducted by the Dolphin Research Cetner in Florida have found that these mammals can work with numerical concepts, such as recognizing and representing numerical values on an ordinal scale.
“In the wild, it would be very useful (for dolphins) to keep track of which areas were richer food sources,” Marine biologist Laela Sayigh of the Woods Hole Oceanographic Institution said.