New findings: Seals’ whiskers detect vortex-ring cues in fish escapes
In a surprising twist on the predator–prey chess game beneath the waves, a team from the University of Rostock has shown that harbour seals can pick out subtle differences in the size of vortex rings generated by escaping fish. Published in the Journal of Experimental Biology (2025), the work demonstrates that the seals’ mystacial vibrissae — the sensitive whiskers along their muzzles — can resolve ring-width differences as small as 17.6 millimetres. This tactile acuity could give a seal the upper paw in predicting which way a fish will dart next, even when the water carries the telltale wakes away from sight.
How the researchers tested whisker sensing
The scientists trained a harbour seal, a young individual named Filou, to identify which side of his head produced a larger emerging vortex. In a controlled tank at the Marine Science Centre, Rostock, Filou wore a blindfold and, on cue, researchers released a spinning vortex ring from a piston positioned to one side of his head. A second ring, either larger or smaller, followed on the opposite side. Filou indicated the side with the larger ring by tapping one of two green balls placed near his head, earning a fish reward when correct.
In the initial rounds, researchers tested rings ranging from 89.9 mm to 45.8 mm in diameter, with the smallest tested difference between rings at 17.6 mm. Filou’s performance was strikingly strong, correctly choosing the larger vortex more than 80 percent of the time based on whisker cues alone. To ensure the result wasn’t a fluke, the team rearranged the side pairings so that a previously smaller ring would become the larger one; Filou still picked the larger ring. After thousands of trials over months, Krüger, Hanke, Miersch and Dehnhardt concluded that the seal could distinguish vortex rings that differed by as little as 17.6 mm using only the sensation along his mystacial vibrissae.
What this tells us about seal perception
Dr. Yvonne Krüger explains that the seal’s whiskers can sense the flow deflection caused by a larger spinning ring, a cue that helps infer the direction of a fleeing fish. “The seal will have a better chance of guessing a fish’s escape direction if it can tell the difference between the two vortex rings,” notes co-author Wolf Hanke. The discovery suggests that the whisker system is finely tuned to discriminating subtle differences in wake structures, allowing a predator to “see through” some of a prey fish’s evasive tricks.
From a sensory biology standpoint, the study strengthens the idea that mammalian whiskers do more than detect contact — they continuously sample the hydrodynamic world. The ability to differentiate minute vortex rings emphasizes how seals integrate tactile input with their existing sense of water movement, refining foraging decisions in cluttered, dynamic environments.
Why it matters for marine life interactions
Predator–prey encounters in the ocean hinge on rapid interpretation of fluid cues. Fish that release multiple jets and create opposing vortex rings may momentarily obscure their trajectory. If seals can single out the largest spinning ring, they gain a crucial clue to predict where a fish will dive next, potentially reducing the energy cost of pursuit and increasing hunting success. The finding also hints at broader ecological interactions: prey species may evolve more complex wake patterns, while predators may rely increasingly on tactile sensors to stay ahead in the chase.
Source, attribution and further reading
These results were reported in Journal of Experimental Biology (2025) by Y. Krüger, W. Hanke, L. Miersch and G. Dehnhardt, in a study titled “Sensitivity of the mystacial vibrissal system of harbour seals (Phoca vitulina) to size differences of single vortex rings.” The official DOI is 10.1242/jeb.249258. For online reporting, a link to the journal is provided: https://journals.biologists.com/jeb/article-lookup/doi/10.1242/jeb.249258. This article is posted to give advance access to authorised media with full attribution; more information is available at https://journals.biologists.com/jeb.
