Using a mobile hydrophone stereo system for real-time acoustic localization of killer whales (Orcinus orca)

It is usually impossible to identify the source of underwater sounds using an omnidirectional hydrophone. Traditionally, cetacean sounds are localized using hydrophone arrays, but arrays are bulky to handle and require special software. Here, we describe an easy-to-use, reliable device to localize underwater sounds by ear. It consists of two hydrophones divided by a soundproof disc, which makes them directional. The signal from each hydrophone is fed into one of the channels of a stereo-input recording system. The signal is monitored with earphones, with a signal from each hydrophone going to each ear of the operator. This mobile hydrophone stereo system was used to locate killer whale groups and to separate out the sounds of different killer whale groups when they are close to each other.