Steve Dawson

In a complex and inherently murky environment, toothed whales (dolphins, porpoises, beaked whales and sperm whales) rely on sound. Acoustics provides powerful tools for understanding their behaviour and ecology, and for quantifying impacts of our sounds on them. Our studies range from the largest toothed whales (sperm whales) to the smallest of all dolphins (Hector’s dolphins). Sperm whales are noisy. Not only do they make the loudest biological sounds (up to 236 dB re 1 µPa at 1m), they click almost continuously while diving. Simple directional hydrophones are invaluable tools to find and track them, and we have built a large aperture unlinked array to track their movements in 3D. At the smallest end of the size spectrum, in 1990 our studies of Hector’s dolphin, were the first to document the acoustic repertoire of any dolphin species over the full frequency range of sounds produced. Most recently, we used a four-hydrophone vertical array and a hovering drone to document details of both narrowband and broadband clicks. Narrowband clicks, centred on 130 kHz (10 dB bandwidth 29.8 kHz) are the usual echolocation signals from this species. In contrast, broadband clicks have significant energy below 100 kHz, and double the bandwidth. These signals are rare, exclusively used in social contexts, but create potential predation risks from killer whales. Lastly, we have quantified sounds generated by recent piledriving in Lyttelton, measured how they propagate in the harbour, and documented long-lasting displacement of Hector’s dolphins due to piledriving. Given the dolphins’ endemic and endangered status, effective mitigation of these effects is essential.