Acceleration as a measure for movement in selected vertebrates

• Main Author: Ruth, Lena
• Format: Thesis
• Language: English
• Published: 2006
• Subjects: harbour seal; Phalacrocorax atriceps; Phoca vitulina
• Online Access: https://oceanrep.geomar.de/id/eprint/54446/; https://oceanrep.geomar.de/id/eprint/54446/1/Dipl.%202006%20Ruth,%20L.pdf

Although cognisance of swim speed is fundamental to understanding the broad context of marine animal behaviour (impacting on dive duration, dive depth, foraging range, foraging success, breeding success and energy expenditure ), numerical determination of speed has proved problematic. Many different methods for assessment of swim speed are known to be problematic to some extent. This study investigates the potential of newly-developed tri-axial acceleration-measuring data-loggers for assessing the movement, and determining the swim speed, of selected marine vertebrates. Three different methods were used to calculate swim speed of a Harbour seal (Phoca vitulina) and Imperial cormorants (Phalacrocorax atriceps). Acceleration data recorded from a captive seal were used 1) to determine flipper stroke frequency and amplitude as a measure of swim speed and 2) to calculate velocity from acceleration using pure physics. In addition, 3) static acceleration due to body angle and the change of <live depth was used to calculate swim speed from free-ranging cormorants during descent and ascent phases of dives to the seabed. Although acceleration is clearly a useful tool to assess animal activity, it seems generally to be a poor indicator of speed. Dynamic acceleration accurately allowed determination of flipper stroke frequency and amplitude but the derivation of speed could only be used for horizontal swimming and even here was inappropriate during glide phases. U se of a pure physics approach and dynamic acceleration led to unrealistically high calculated speed values of up to 40 m/s, primarily due to cumulative errors, problems in separating static from dynamic acceleration and errors due to difficulties in determining the longitudinal axis measured by the accelerometer with respect to the longitudinal axis of the animal. The best results for speed were gained using simple trigonometry to calculate speed from static acceleration due to body angle and vertical change in depth. Thus, although measurement of triaxial ...