Harbour porpoise (Phocoena phocoena) static acoustic monitoring: laboratory detection thresholds of T-PODs are reflected in field sensitivity

Abstract

The T-POD (Timing POrpoise Detector) is a self-contained acoustic data logger used for detecting and monitoring the presence of echolocation clicks of small cetaceans. It has become a standard tool in environmental impact assessments and monitoring programmes. Yet, little is known about the variability in sensitivity and detection range of T-PODs. In this study the field performance of ten v3 T-PODs was compared to detection thresholds measured in a tank. The T-POD thresholds ranged from 123 to 132 dB re 1μPa (pp). The detection thresholds of the ten individual T-PODs were different and the differences increased over time. The more sensitive a T-POD was in the laboratory (i.e. the lower the threshold) the more clicks were recorded by it in the field. Threshold correlated differently to the five analysed T-POD parameters (encounters, encounter duration, waiting time, porpoise positive minutes, clicks per porpoise positive minute). This study demonstrates that individual threshold calibrations of T-PODs are necessary to obtain comparable results when monitoring odontocetes with this tool. Regression equations for relationships between T-POD detection thresholds and study parameters obtained during field trials may allow comparisons of T-PODs with different detection thresholds.

Using Static Acoustic Monitoring to Describe Echolocation Behaviour of Heaviside’s Dolphins (Cephalorhynchus heavisidii) in Namibia

“…The T-POD is a SAM tool which has been used extensively to monitor odontocetes (Leeney & Tregenza, 2006;Leeney et al, 2007;Philpott et al, 2007;Verfuß et al, 2007;Kyhn et al, 2008;Todd et al, 2009), including Hector's dolphins of New Zealand (Rayment et al, 2009a(Rayment et al, , 2009b, a species closely related to Heaviside's dolphins. The T-POD is a self-contained, submersible hydrophone and digital processor which recognizes and logs the echolocation clicks made by odontocetes.…”

“…The T-POD is a self-contained, submersible hydrophone and digital processor which recognizes and logs the echolocation clicks made by odontocetes. Todd et al (2009) provide a description of the T-POD hardware and of the processes of data collection and classification, while numerous studies have reviewed settings and T-POD functionality (e.g., Thomsen et al, 2005;Philpott et al, 2007;Kyhn et al, 2008;Simon et al, 2010). The onboard data logging nature of the T-POD makes it particularly suited to the study of odontocetes, which use narrow-band high frequency (NBHF) echolocation clicks, such as the Phocoenids (for which the instrument was initially designed; Goodson & Sturtivant, 1996) and members of the Cephalorhynchus genus, as the sampling rate required for real-time recording (> 250 kHz) makes long-term recordings unfeasible.…”

Study of the Acoustic Effects of Hydrokinetic Tidal Turbines in Admiralty Inlet, Puget Sound

“…DPM specifically refer to narrow-band high frequency (NBHF, porpoise) detections in the context of this study. DPM are a commonly used unit for measuring cetacean echolocation (e.g., Kyhn et al, 2008). Counting intervals of time with confirmed detections reduces the chance for bias created by particularly vocal animals (Mellinger, et al, 2007).…”

“…Figure 13 shows a comparison of porpoise detection positive minutes per day (medium or high quality detections) for a one year period from May 2010 -May 2011. For the four underlying deployments, the same C-POD and T-POD units were used (prior research by Kyhn et al (2008) indicates that relative sensitivity differences between T-POD instruments exist) and the instrumentation package (SS #02) was deployed at approximately the same geographic coordinates. Comparisons are shown between version 1 of the C-POD classifier, version 2 of the C-POD classifier, and the T-POD classifier.…”

“…SMRU, Ltd. and Acadia University have had the same experience in C-PODs used for studies in the Bay of Fundy. While Chelonia, Ltd. maintains that sensitivity is calibrated in their laboratory and there is not a difference between instruments, prior research has demonstrated inter-instrument variability for T-PODs (Kyhn et al, 2008). We suspect that similar variability may exist for C-PODs and recommend that procedures be developed for field calibration of instrument sensitivity.…”