A new MIT study has delved into harbor seals' ability to sense and follow prey with impressive accuracy. The research involved building a large-scale version of the little antennas, and the results could prove useful for man-made sensors.
Harbor seals' ability to sense their prey is certainly impressive. Tests have shown that if an object moves past one of the creatures while it's blindfolded, it can still follow its exact route, even after as much as 30 second has passed. It's been thought that the ability was due to the seals' whiskers, but the new MIT study reveals just how impressive those little antenna-like structures really are.
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So what makes the harbor seals' whiskers so interesting? Well, it's all in their unique shape. The whiskers might appear to be straight, simple structures from afar, but viewing them up close, under a magnifying glass, reveals a wavy structure with an elliptical cross section, and asymmetrical elements.
In order to confirm that the intricate structure of the whiskers is linked to the tracking ability, the team turned to 3D printing, creating a large-scale plastic version of a whisker (seen above, at left). They then submerged it in a 30 m (98 ft)-long tank, passing it through the water by means of a moving track suspended from above.
The following tests found that when the whisker was moved through the tank on its own, it created much smaller eddies, or vortices, than are produced by normal rods. It moved through the water silently, and with very little vibration. This ability to move through the ocean without disturbing water around the whiskers allows the seal to block out its own disturbance of the water, allowing it to sense prey much more clearly.
The second half of the testing involved moving a long circular cylinder in front of the whisker. This created very large eddies, mimicking the passage of fish through the ocean. When moving behind the cylinder, the artificial whisker moved in a slaloming pattern, vibrated significantly.
When the speed of the movement was adjusted, the whisker reacted, vibrating at the same frequency as the vortices created by the cylinder. It's thought that this may allow the seals to determine the size of the object it's following.
Not only does the study shed light on how the harbor seals are able to detect accurately movement in the water and follow their prey with such precision, but it could also lead to some practical uses down the line.
"We already have a few sensors that can detect velocity, but now that we know better what they can do, we can use them to track sources of pollution and the like," says Michael Triantafyllou of MIT's Department of Mechanical Engineering. "By having several whiskers on a vehicle, like the seal, you can, for example, detect a faraway plume, and track it all the way to the end."
The findings of the study were published in the Journal of Fluid Dynamics. For more on the study, you can take a look at the video below.