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  • 1
    Online Resource
    Online Resource
    Hydrodynamic perception in true seals (Phocidae) and eared seals (Otariidae)
    Springer Science and Business Media LLC ; 2013
    In:  Journal of Comparative Physiology A Vol. 199, No. 6 ( 2013-6), p. 421-440
    Details
    In: Journal of Comparative Physiology A, Springer Science and Business Media LLC, Vol. 199, No. 6 ( 2013-6), p. 421-440
    Type of Medium: Online Resource
    ISSN: 0340-7594 , 1432-1351
    URL: Article
    DOI: 10.1007/s00359-012-0778-2
    RVK:
    WA 15000
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2013
    detail.hit.zdb_id: 1459295-2
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  • 2
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    Online Resource
    Passive electroreception in aquatic mammals
    Springer Science and Business Media LLC ; 2013
    In:  Journal of Comparative Physiology A Vol. 199, No. 6 ( 2013-6), p. 555-563
    Details
    In: Journal of Comparative Physiology A, Springer Science and Business Media LLC, Vol. 199, No. 6 ( 2013-6), p. 555-563
    Type of Medium: Online Resource
    ISSN: 0340-7594 , 1432-1351
    URL: Article
    DOI: 10.1007/s00359-012-0780-8
    RVK:
    WA 15000
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2013
    detail.hit.zdb_id: 1459295-2
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  • 3
    Online Resource
    Online Resource
    Unique fur and skin structure in harbour seals ( Phoca vitulina )—thermal insulation, drag reduction, or both?
    The Royal Society ; 2015
    In:  Journal of The Royal Society Interface Vol. 12, No. 104 ( 2015-03), p. 20141206-
    Details
    In: Journal of The Royal Society Interface, The Royal Society, Vol. 12, No. 104 ( 2015-03), p. 20141206-
    Abstract: Vertebrate surface structures, including mammalian skin and hair structures, have undergone various modifications during evolution in accordance with functional specializations. Harbour seals rely on their vibrissal system for orientation and foraging. To maintain tactile sensitivity even at low temperatures, the vibrissal follicles are heated up intensely, which could cause severe heat loss to the environment. We analysed skin samples of different body parts of harbour seals, and expected to see higher hair densities at the vibrissal pads as a way to reduce heat loss. In addition to significantly higher hair densities around the vibrissae than on the rest of the body, we show a unique fur structure of hair bundles consisting of broad guard hairs along with hairs of a new type, smaller than guard hairs but broader than underhairs, which we defined as ‘intermediate hairs’. This fur composition has not been reported for any mammal so far and may serve for thermal insulation as well as drag reduction. Furthermore, we describe a scale-like skin structure that also presumably plays a role in drag reduction.
    Type of Medium: Online Resource
    ISSN: 1742-5689 , 1742-5662
    URL: Article
    DOI: 10.1098/rsif.2014.1206
    Language: English
    Publisher: The Royal Society
    Publication Date: 2015
    detail.hit.zdb_id: 2156283-0
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  • 4
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    Online Resource
    Detection and direction discrimination of single vortex rings by harbour seals ( Phoca vitulina )
    The Company of Biologists ; 2018
    In:  Journal of Experimental Biology
    Details
    In: Journal of Experimental Biology, The Company of Biologists
    Abstract: Harbour seals possess highly sensitive vibrissae that enable them to track hydrodynamic trails left behind by a swimming fish. Most of these trails contain vortex rings as a main hydrodynamic component. They may reveal information about their generator as the trails differ depending on the fish species, the fish's body shape, size, and swimming style. Additionally, fish generate single vortex rings in diverse natural situations. In this study, the ability of blindfolded stationary harbour seals to detect and analyse single vortex rings regarding directional information has been investigated. In three different behavioural experiments, the animals were trained to respond to single artificially generated vortex rings. The results show that harbour seals are able to respond to a variety of different vortex rings upon vibrissal stimulation. The investigation of the minimum hydrodynamically perceivable angle revealed that it is at least as small as 5.7°, which was the smallest adjustable angle. Moreover, harbour seals are capable of analysing the travel direction of a vortex ring perceived by the mystacial pads irrespective of whether the vibrissae were stimulated ipsilaterally or contralaterally. In situations in which no complex hydrodynamic trail is available, it is advantageous for a hunting seal to be able to extract information from a single vortex ring.
    Type of Medium: Online Resource
    ISSN: 1477-9145 , 0022-0949
    URL: Article
    DOI: 10.1242/jeb.170753
    Language: English
    Publisher: The Company of Biologists
    Publication Date: 2018
    detail.hit.zdb_id: 1482461-9
    SSG: 12
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  • 5
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    Multifocal lenses in a monochromat: the harbour seal
    The Company of Biologists ; 2008
    In:  Journal of Experimental Biology Vol. 211, No. 20 ( 2008-10-15), p. 3315-3322
    Details
    In: Journal of Experimental Biology, The Company of Biologists, Vol. 211, No. 20 ( 2008-10-15), p. 3315-3322
    Abstract: Previous photorefractive results from harbour seals indicated the presence of a multifocal lens. This was surprising because the evolution of multifocal lenses has served to compensate for chromatic aberration in animals with colour vision, which harbour seals as monochromats should not be capable of. To gain insight into the lens optics of these animals, we extended our photorefractive measurements in live seals under water and in air and,additionally, analyzed eight extracted juvenile harbour seal lenses with schlieren photography and a laser scanning technique. The results from all methods applied support the presence of multifocal lenses in harbour seals. However, the functional significance of multiple focal lengths in harbour seal lenses remains speculative. Interestingly, the slit pupils of harbour seals cannot be considered to be an adaptation to the multifocal optical system of the eye.
    Type of Medium: Online Resource
    ISSN: 1477-9145 , 0022-0949
    URL: Article
    DOI: 10.1242/jeb.018747
    Language: English
    Publisher: The Company of Biologists
    Publication Date: 2008
    detail.hit.zdb_id: 1482461-9
    SSG: 12
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  • 6
    Online Resource
    Online Resource
    Hydrodynamic discrimination of wakes caused by objects of different size or shape in a harbour seal ( Phoca vitulina )
    The Company of Biologists ; 2011
    In:  Journal of Experimental Biology Vol. 214, No. 11 ( 2011-06-01), p. 1922-1930
    Details
    In: Journal of Experimental Biology, The Company of Biologists, Vol. 214, No. 11 ( 2011-06-01), p. 1922-1930
    Abstract: Harbour seals can use their mystacial vibrissae to detect and track hydrodynamic wakes. We investigated the ability of a harbour seal to discriminate objects of different size or shape by their hydrodynamic signature and used particle image velocimetry to identify the hydrodynamic parameters that a seal may be using to do so. Hydrodynamic trails were generated by different sized or shaped paddles that were moved in the calm water of an experimental box to produce a characteristic signal. In a two-alternative forced-choice procedure the blindfolded subject was able to discriminate size differences of down to 3.6 cm (Weber fraction 0.6) when paddles were moved at the same speed. Furthermore the subject distinguished hydrodynamic signals generated by flat, cylindrical, triangular or undulated paddles of the same width. Particle image velocimetry measurements demonstrated that the seal could have used the highest velocities and the steepness of the gradients within the wake to discriminate object size, beside the size of counter-rotating vortices and the spatial extension of a wake. For shape discrimination the subject could have used the spatial extension of the whole wake, in addition to the arrangement of the vortices. We tested whether the seal used highest velocities, the steepness of the gradients and the spatial extension of the wake in a second set of experiments by varying moving speed and paddle size, respectively. The subject was still able to discriminate between the respective object sizes, but the minimum detectable size difference increased to 4.4 cm (Weber fraction 3.6). For the shape discrimination task, the seal was only able to distinguish flat from triangular paddles. Our results indicate that the seal's discrimination abilities depend on more than one hydrodynamic parameter.
    Type of Medium: Online Resource
    ISSN: 1477-9145 , 0022-0949
    URL: Article
    DOI: 10.1242/jeb.053926
    Language: English
    Publisher: The Company of Biologists
    Publication Date: 2011
    detail.hit.zdb_id: 1482461-9
    SSG: 12
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  • 7
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    Online Resource
    How harbor seals (Phoca vitulina) pursue schooling herring
    Springer Science and Business Media LLC ; 2015
    In:  Mammalian Biology Vol. 80, No. 5 ( 2015-09), p. 385-389
    Details
    In: Mammalian Biology, Springer Science and Business Media LLC, Vol. 80, No. 5 ( 2015-09), p. 385-389
    Type of Medium: Online Resource
    ISSN: 1616-5047
    URL: Article
    DOI: 10.1016/j.mambio.2015.04.004
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2015
    detail.hit.zdb_id: 2785152-7
    detail.hit.zdb_id: 2072973-X
    SSG: 12
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  • 8
    Online Resource
    Online Resource
    Optokinetic nystagmus in harbor seals (Phoca vitulina)
    Elsevier BV ; 2008
    In:  Vision Research Vol. 48, No. 2 ( 2008-01), p. 304-315
    Details
    In: Vision Research, Elsevier BV, Vol. 48, No. 2 ( 2008-01), p. 304-315
    Type of Medium: Online Resource
    ISSN: 0042-6989
    URL: Article
    DOI: 10.1016/j.visres.2007.11.012
    RVK:
    WW 1780
    RVK:
    WA 15000
    RVK:
    CP 2500
    Language: English
    Publisher: Elsevier BV
    Publication Date: 2008
    detail.hit.zdb_id: 2011974-4
    SSG: 12
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  • 9
    Online Resource
    Online Resource
    Underwater auditory localization by a swimming harbor seal ( Phoca vitulina )
    Acoustical Society of America (ASA) ; 2006
    In:  The Journal of the Acoustical Society of America Vol. 120, No. 3 ( 2006-09-01), p. 1550-1557
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 120, No. 3 ( 2006-09-01), p. 1550-1557
    Abstract: The underwater sound localization acuity of a swimming harbor seal (Phoca vitulina) was measured in the horizontal plane at 13 different positions. The stimulus was either a double sound (two 6-kHz pure tones lasting 0.5s separated by an interval of 0.2s) or a single continuous sound of 1.2s. Testing was conducted in a 10-m-diam underwater half circle arena with hidden loudspeakers installed at the exterior perimeter. The animal was trained to swim along the diameter of the half circle and to change its course towards the sound source as soon as the signal was given. The seal indicated the sound source by touching its assumed position at the board of the half circle. The deviation of the seals choice from the actual sound source was measured by means of video analysis. In trials with the double sound the seal localized the sound sources with a mean deviation of 2.8° and in trials with the single sound with a mean deviation of 4.5°. In a second experiment minimum audible angles of the stationary animal were found to be 9.8° in front and 9.7° in the back of the seal’s head.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.2221532
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2006
    detail.hit.zdb_id: 1461063-2
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  • 10
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    Online Resource
    Underwater sound localization of pure tones in the median plane by harbor seals ( Phoca vitulina )
    Acoustical Society of America (ASA) ; 2016
    In:  The Journal of the Acoustical Society of America Vol. 140, No. 6 ( 2016-12-01), p. 4490-4495
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 140, No. 6 ( 2016-12-01), p. 4490-4495
    Abstract: In an underwater environment the physical characteristics of sound propagation differ considerably from those in air. For this reason, sound localization underwater is associated with difficulties, especially in the median plane. It was the approach of the present study to investigate whether harbor seals (Phoca vitulina) are able to determine the direction of a tonal signal form above or below in the underwater environment. Minimum audible angles (MAAs) or the angular range in which the animals could localize a pure tone stimulus in the vertical plane were obtained for frequencies from 0.35 up to 16 kHz. Testing was conducted with four male harbor seals in a semi-circle area of 6 m in diameter in about 2.5 m depth, by using a two alternative forced choice method. The results show that harbor seals are able to localize a pure tone in the median plane under water with a high performance for low frequency stimuli between 350 Hz and 2 kHz with MAAs ranging from below 2.5° up to about 25°. For higher frequencies the animals show strong individual differences.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.4972531
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2016
    detail.hit.zdb_id: 1461063-2
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