Harbor Seals Use Whiskers to Decode Fish Escape Trails, Study Finds

A new study demonstrates that harbor seals can use their whiskers to detect and interpret hydrodynamic trails left by fish, enabling them to track prey even when visual cues are absent. The research, involving a single trained seal, suggests this sensory ability may allow seals to overcome complex evasion tactics used by fish like rainbow trout.

Sensory Capability and Research Objective

Harbor seals possess approximately one hundred whiskers that function as sensory hairs capable of detecting minute water movements. These movements are generated by swimming fish and create underwater trails, which the seals can follow.

The research, led by biologist Yvonne Krüger of the University of Rostock, aimed to test whether seals use their whiskers to interpret the hydrodynamic signals created by specific fish escape maneuvers.

Experimental Design and Findings

The study focused on an adult male harbor seal named Filou. Researchers investigated the seal's ability to sense the hydrodynamic disturbance created by rainbow trout, a common prey species.

When evading predators, rainbow trout bend into a C-shape, which generates two underwater vortex rings that move in opposite directions. Only the slightly smaller of the two rings moves in the fish's actual swimming direction, a tactic that could potentially confuse a pursuing predator.

Filou was trained over nearly two years to select the larger of two artificially generated vortex rings presented to him. The seal successfully distinguished between the rings even when the size difference was minimal—described in one source as less than the width of a human thumb.

A key control experiment involved covering Filou's whiskers with a nylon stocking. Under this condition, the seal could no longer complete the discrimination task, indicating that his whiskers were essential for gathering the necessary sensory information.

Researcher Statements and Interpretations

Yvonne Krüger stated that the findings suggest harbor seals can determine where a fish has been and where it is going based on whisker information. She noted this ability could enable seals to hunt successfully in murky water or at night without relying on visual cues.

"The researchers suggest this sensory capability is likely shared by harbor seals generally and may be deployed in natural hunting situations."

Sensory biologist Robyn Grant of Manchester Metropolitan University, who was not involved in the research, described the work as "a really important step in working out how the seals [use] their whiskers to extract tiny bits of information from these hydrodynamic trails."

Broader Implications and Potential Applications

The research has prompted discussion about several broader implications:

• Environmental Impact: Robyn Grant noted that understanding this sensory capability may help assess how environmental changes, including extreme weather events, could affect seals by potentially masking these critical hydrodynamic stimuli.
• Technological Inspiration: Grant and other sources observed that the findings could inform the development of sensitive sensors for aquatic robots, with potential applications in fields such as underwater archaeology, mining, or biological surveys.
• Future Research: Grant suggested that additional research on the precise movements of seal whiskers during detection would provide further insight into this sensory mechanism.

Research Context: The study's conclusions are based on experiments with a single animal. The researchers involved have stated they believe the ability is common to harbor seals.