Sensing the Splash: whiskers as a directional sensor
New research shows that harbour seals may read a fleeing fish’s evasive maneuvers not just by tracking wakes, but by sensing the size of spinning vortex rings generated by the fish’s jets. When a fish darts away, it can produce two jets in opposite directions, often creating a pair of vortex rings that differ in size. If the seals’ whiskers—also known as mystacial vibrissae—can pick up these minute size differences, they could glean the fish’s escape direction even before the last gulp of water settles in. The study, led by researchers from the University of Rostock, suggests that these quiet cues could help seals anticipate where the fish is headed next.
The experiment: teaching a seal to discriminate ring size
In a controlled setup at a marine science centre in Rostock, a harbour seal living at the facility was trained to submerge its head while blindfolded. The researchers released a spinning vortex ring on one side of the seal using a piston, sometimes highlighting the ring with a dye to confirm its path. A second ring, either larger or smaller, was released on the opposite side. The seal indicated which side produced the larger ring by tapping green indicators placed on either side of its head and earned a fish reward when correct. This training gradually established whether the seal could rely solely on tactile information from its whiskers to discern ring size.
Results: discrimination down to tiny differences
Early tests varied vortex rings in sizes from 89.9 mm to 45.8 mm, with the smallest perceptible gap at 17.6 mm. The seal performed remarkably well—consistently choosing the side associated with the larger ring in this range, using nothing but its whiskers. To confirm true discrimination, researchers swapped the ring pairings so that a previously smaller ring became the larger one, yet the animal still selected correctly. After thousands of trials over months, the team concluded that harbour seals can distinguish vortex rings that differ by as little as 17.6 mm with their whiskers alone.
Implications for predator-prey dynamics
The finding matters because a fish’s escape involves a second jet in the opposite direction of travel, typically accompanied by a larger vortex ring. If a seal can detect even small size differences in these rings, it could identify the dominant ring and infer the fish’s intended direction. By tuning in to the most prominent spinning cue, the seal could effectively anticipate where the fish plans to dive next, increasing its chances of a successful catch. In short, the whiskers may provide a fine-tuned sensory edge in the ongoing arms race beneath the waves.
Source and further reading
This story is based on a study published in the Journal of Experimental Biology. For full details and data, consult the original article: Krüger, Y., Hanke, W., Miersch, L. and Dehnhardt, G. (2025). Sensitivity of the mystacial vibrissal system of harbour seals (Phoca vitulina) to size differences of single vortex rings. J. Exp. Biol. 228, jeb249258. doi:10.1242/jeb.249258. If reporting online, please include a link to the Journal of Experimental Biology: https://journals.biologists.com/jeb/article-lookup/doi/10.1242/jeb.249258. This embargoed press information is provided to advance media reporting with proper attribution to the source.
About the study
The work was conducted by researchers from the University of Rostock, with all experiments performed under controlled conditions to isolate sensory input from whisker-based perception. The findings shed light on the sophisticated ways marine mammals use their tactile sense to interpret complex water movements, offering a fresh perspective on predator-prey interactions in coastal ecosystems.
