Trialling an automated passive acoustic detector (T-POD) with Hector's dolphins (Cephalorhynchus hectori)

Abstract

Acoustic surveys can have several advantages over visual methods in surveys of cetaceans, although verification is required that novel techniques are effective. The T-POD is an autonomous acoustic data logger with inbuilt filters that can be set to match the click characteristics of the target species. We tested the performance of the T-POD for detecting Hector's dolphins at Flea Bay, Banks Peninsula, New Zealand. Simultaneous visual surveys were conducted from a hillside overlooking the bay, with distances between the T-POD and dolphins measured using a theodolite. Wideband sound recordings confirmed that T-POD detections were echolocation clicks made by Hector's dolphins. Detection probability and click train detection rate decreased with increasing distance, with no detections made beyond 500 m. By fitting detection functions to the probability of detection versus distance we showed that the T-POD effectively detected all dolphin groups within a radius of 198–239 m, depending on the click train categories utilized. The T-POD shows considerable promise as a tool for passive acoustic surveys of Hector's dolphins, with possible applications in studies of distribution, habitat use and echolocation behaviour.