Static acoustic monitoring (SAM) is one major technology for observing small cetacean species. Automatic click loggers deployed for long time periods (>2 months) with a single hydrophone are a standard solution. Acoustic properties, like detection thresholds of these instruments, are essential for interpretation of results, but have nevertheless received little attention. A methodology for calibrating tonal click detectors in small tanks consisting of the determination of the horizontal directivity pattern and detection thresholds including a transfer function is presented. Two approaches were tested to determine detection thresholds by (a) determining the 50% detection threshold and (b) fitting a linear regression model to the recorded relative amplitudes. The tests were carried out on C-PODs (Cetacean PODs, tonal click detectors), the most commonly used instrument for SAM in Europe. Directivity and threshold were tested between 60 and 150 kHz. Directivity showed a maximum variation of 8.5 dB in the horizontal plane. Sensitivity is highest between 80 and 130 kHz and linear (±3 dB) in this frequency range for most of the instruments tested. C-PODs have a detection threshold (calculated with the linear model) of 114.5 ± 1.2 (standard deviation) dB re 1 μPa peak–peak at 130 kHz.
Methodology and results of calibration of tonal click detectors for small odontocetes (C-PODs)a)
Author to whom correspondence should be addressed. Current address: Institute for Terrestrial and Aquatic Wildlife Research (ITAW), University of Veterinary Medicine Hannover, Foundation, Werftstr. 6, 25761 Büsum, Germany. Electronic mail: michael.daehne@tiho-hannover.de
Current address: SMRU Marine Limited, Scottish Oceans Institute, St. Andrews KY16 9SR, Scotland, United Kingdom.
Current address: Coastal and Marine Research Centre, University College Cork, Irish Naval Base, Haulbowline, Cobh, County Cork, Ireland.
Parts of this work were presented as a poster at the annual meeting of the European Cetacean Society in Istanbul 2009.
Michael Dähne, Ursula Katharina Verfuß, Anja Brandecker, Ursula Siebert, Harald Benke; Methodology and results of calibration of tonal click detectors for small odontocetes (C-PODs). J. Acoust. Soc. Am. 1 September 2013; 134 (3): 2514–2522. https://doi.org/10.1121/1.4816578
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