Acoustic behavior of beaked whales, with implications for acoustic monitoring

Beaked whales (Cetacea: Ziphiidea) of the genera Ziphius and Mesoplodon have been reported to mass strand during naval sonar exercises, and the ability to mitigate such negative effects is of increasing importance. Beaked whales dive for long periods and are difficult to sight at the surface. We discuss new results suggesting that passive acoustic monitoring for beaked whales holds promise for detecting their presence. A new non-invasive acoustic recording tag was attached to beaked whales of two species, 3 Mesoplodon densirostris and 7 Ziphius cavirostris. High-frequency clicks were recorded for about 30 min every 2-4 hours during deep dives of all tagged whales. These data can be used to estimate the probability of detecting the presence of beaked whales by listening. Critical parameters include the density of sensors and the listening time needed to achieve adequate detection probability. The greatest problem for beaked whale detectors is likely to be false alarms from biological and physical acoustic transients (such as dolphin clicks), and monitoring efforts will need to trade off probability of false alarm against maximizing detection probability. While results may be somewhat poorer in realistic noise conditions and with practical detectors, there appears to be considerable potential for the acoustic detection of beaked whales