| Popis: |
The use of passive acoustic monitoring (PAM) is increasingly used as a monitoring tool in e.g environmental impact assessments. However, very few studies have focused on validating PAM data against independent observations which is critical in order to compare data from different studies and areas, and over time. In August 2007 we tested two types of odontocete PAM equipment: version 5 T‐PODs (Chelonia, U.K.) and PCL's (Aquatec, Lochborough, UK) by comparing acoustic detections to visual theodolite tracings of wild harbour porpoises. Eight T‐PODs with known detection thresholds and four PCLs were mounted in four clusters. Detection thresholds of the T‐PODs varied from 117 to 125dB re 1μPapp. Based on visual tracks of 28 porpoises it is shown that detection ranges correlated inversely with detection threshold. However, PAM‐detection also strongly depended on the angle between the swim track of porpoises and the line to the data logger. Some porpoises were not detected despite swimming within 20m of the nearest data logger. It was not possible to distinguish between recordings from one and more than one animal on the PAM‐recordings, despite that the number of animals was known from the corresponding tracks. All in all, the results showed good correspondence between PAM recordings and visual tracings, as well as among PAM recordings. |
