Liebsch, Nikolai (2002) Measurement of feeding activity in air-breathing marine vertebrates using the Hall effect. (Diploma thesis), Christian-Albrechts-Universität, Kiel, Germany, III, 73 pp.

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Abstract

A new technology is presented in this study that offers insight into assessing movement and feeding activity in a variety of airbreathing marine vertebrates. It consists of an archival unit logging data from a Hall sensor, sensing magnetic field strength produced by a rare-earth magnet, at frequencies of up to 30 Hz. Perceived magnetic field strength varies with changing distance between magnet and sensor. A magnet attached to a limb or appendage of an animal with the Hall sensor placed adjacent on the body, produces variations in the magnetic field strength perceived by the sensor during changes of limb position. Originally developed on penguins, this work tests the potential use of the device on captive hawksbill turtles (Eretmochelys imbricata), harbour seals (Phoca vitulina), Australian sea lions (Neophoca cinerea) and bottlenose dolphins (Tursiops truncatus aduncus). During these trials, work was focused on the positioning of the Hall sensor and on the shape and strength of the magnet with respect to the animal so as to optimise perception of limb movement. The aim was to separate feeding events from other mouth movements in the recorded data and to assess flipper stroke frequency and amplitude during locomotion. Even though the positioning on the jaws of the study animals was not always optimal, feeding events produced distinguishable signatures in the recorded data. It was found that limb movements associated with locomotion could be well quantified (frequency), however, the study also showed that qualitative (amplitude) assessment seems to depend on very precise positioning of the device and careful calibration. Therefore, in certain cases the whole range of the movement could not be resolved. Accuracy, limitations and field use are discussed as well as the potential for system applications for uses other than assessing feeding or movement.

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