Waves and the perception power of seals

May 16, 2011
Waves and the perception power of seals

If you ever thought that murky waters would stop seals in their (hunting) tracks, think again. Harbour seals (Phoca vitulina) extend their vibration-sensitive whiskers to find food when their vision is obstructed. But can these mammals differentiate objects that pass them? Scientists from the University of Rostock in Germany shed new light on the ability of harbour seals to distinguish between the wakes (the trails of water disturbance) generated by objects that differ in both size and shape. The findings of the study are presented in the Journal of Experimental Biology.

The Rostock scientists had already identified the seals' ability to perceive and follow fish wakes, around half a minute after the passes. In this latest study, they found that harbour use only their to make distinctions in wakes produced by different objects.

The researchers evaluated a called Henry. They tested the seal's ability to distinguish between the wakes of differently sized paddles. Blindfolding Henry's eyes and covering his ears, the investigators swept a paddle through a big box in the seal's enclosure. After an interval of just three seconds, Henry was allowed to enter the area, where he was tested.

Already trained to press a target outside the enclosure when he recognised the wake of a standard paddle, Henry was also trained to press a different target when he recognised the wake of a bigger or smaller paddle. Henry, according to the researchers, could differentiate between paddles that had a tiny difference between them, as little as 2.8 centimetres in width. Following this, they tested which aspects of the wake Henry detected.

'We randomised the speeds of the paddles so that the maximum flow velocity wasn't a distinguishing cue for the widest paddles, but the structure of the wake had to be recognised by the seal and he could do that too, but with slightly less accuracy,' says Professor Wolf Hanke of the University of Rostock.

Henry was also tested on his ability to distinguish between the wakes of triangular, cylindrical, flat and undulating paddles. His responses were spot on when he distinguished between cylindrical and flat, flat and undulating, and cylindrical and undulating paddles.

Henry didn't pass muster when it came to distinguishing between the triangular paddle from the cylindrical or undulating shapes, though.

Using digital particle image velocimetry to measure Henry's successful attempts at distinguishing between the wakes of passing objects that vary in size and shapes, Professor Hanke says it is not easy to determine which 'part of the wake serves the animal most and which aided only a little'.

The Rostock researcher plans to test the seal's responses to single vortices in order to identify the wake components that could give a fish's size and shape away. The seal's hunting efficiency would be hugely boosted if it could differentiate between various differently sized fish, particularly thin ones which force them to waste a lot of energy in order to reach their target.

Explore further: 'Divide and rule'—raven politics

More information: Wieskotten, S., et al. (2011) Hydrodynamic discrimination of wakes caused by objects of different size or shape in a harbor seal (Phoca vitulina). J Exp Biol 214: 1922-1930. DOI:10.1242/​jeb.053926

add to favorites email to friend print save as pdf

Related Stories

Seals sense shapes using their whiskers to feel wakes

May 12, 2011

Hunting in the North Sea, harbour seals often encounter murky water that impedes their vision; but it doesn't affect their ability to chase prey. Extending their vibration-sensitive whiskers, the mammals are almost as efficient ...

Mercury pollution causes immune damage to harbor seals

Oct 21, 2008

Methylmercury (MeHg), the predominant form of mercury found in the blood of marine mammals and fish-eating communities, could be more damaging to seals than has previously been thought. Research published in BioMed Central's ...

European coastal pollution is harmful to seals

Mar 22, 2011

The bodies of harbour seals (Phoca vitulina), which live in estuaries or along coastlines where industrial activities take place, are highly contaminated. This is the result of a European study, involving Spanis ...

Seals like it hot

Sep 10, 2009

(PhysOrg.com) -- Using innovative thermal imaging techniques and CCTV recording, a St Andrews academic has shed new light on previously unseen aspects of the life of seals.

Recommended for you

'Divide and rule'—raven politics

1 hour ago

Mythology has attributed many supernatural features to ravens. Studies on the cognitive abilities of ravens have indeed revealed that they are exceptionally intelligent. Ravens live in complex social groups ...

Science casts light on sex in the orchard

20 hours ago

Persimmons are among the small club of plants with separate sexes—individual trees are either male or female. Now scientists at the University of California, Davis, and Kyoto University in Japan have discovered ...

Four new dragon millipedes found in China

22 hours ago

A team of speleobiologists from the South China Agriculture University and the Russian Academy of Sciences have described four new species of the dragon millipedes from southern China, two of which seem to ...

Scientist creates automatic birdsong recognition app

Oct 30, 2014

Dr Dan Stowell, an EPSRC Research Fellow in QMUL's School of Electrical Engineering and Computer Science, has used a grant from Queen Mary Innovation to develop a prototype for an app that turns his research ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.