Up-beat motion in swimming limbs: New insights into assessing movement of free-living marine vertebrates..

Wilson, Rory P. and Liebsch, Nikolai (2003) Up-beat motion in swimming limbs: New insights into assessing movement of free-living marine vertebrates.. Marine Biology, 142 . pp. 537-547. DOI 10.1007/s00227-002-0964-9.

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Abstract

A new system is presented for assessing the movement of animal limbs including, after suitable calibration, quantification of limb stroke frequency and amplitude, which may be used to derive limb angular velocity and acceleration. The system is based on use of an archival unit logging data from a Hall sensor, itself set to sense magnetic-field strength at frequencies of up to 30 Hz. Typically, the Hall sensor is placed on the animal body adjacent to the limb being monitored, while a small magnet is glued to the limb. Changes in limb position result in variation of the magnetic-field strength perceived by the sensor. Captive trials were successfully performed on a harbour seal (Phoca vitulina), an Australian sea lion (Neophoca cinerea) and a hawksbill turtle (Eretmochelys imbricata), as well as on 18 free-living Magellanic penguins (Spheniscus magellanicus). The unit performed well in almost all cases, illustrating that stroke frequency was relatively invariant in any species tending, however, to be higher in smaller animals and showing that the primary variance was manifest in stroke amplitude. As an example of the utility of the system, the importance of buoyancy was demonstrated in the penguins, which had longer glide phases and lower flipper beat amplitudes at greater depths, because body air was compressed, which reduced upthrust. The small size of the system (ca. 25 g in air) makes it suitable for a wide range of marine vertebrates. Potential problems of system sensitivity, the suitability of particular recording frequencies and the value of appropriate calibration are discussed.

Document Type: Article
Keywords: Harbour Seal, Hall Sensor, Aquatic Vertebrate, Magellanic Penguin, Stroke Frequency
Research affiliation: OceanRep > GEOMAR > FB3 Marine Ecology > FB3-EV Marine Evolutionary Ecology
Refereed: Yes
Open Access Journal?: No
Publisher: Springer
Date Deposited: 18 Feb 2008 17:26
Last Modified: 07 Jun 2018 09:58
URI: https://oceanrep.geomar.de/id/eprint/7979

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