Many baleen (mysticete) whales produce high-intensity calls, the frequency content of which resides primarily in a band below 1 kHz.
Consequently, there is a reasonable probability of vocalising animals being detected on hydrophones designed to collect marine-acoustic geophysical data, such as towed and bottom-mounted seismic streamers. This represents an opportunity to collect potentially untapped data on whale distribution and behaviour over broad spatial scales. The objectives of this chapter are to present those with geophysical research backgrounds an opportunity to recognise and classify frequently encountered whale sounds in the field. The chapter provides an introduction on general classification and description of marine mammals, a brief physical description of sound, followed by the range of vocalisations produced by baleen whales on a species-by-species basis.