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Marine mammals intensively use underwater acoustics to communicate, navigate, and detect prey and predators. Like birds, many species and sub-groups can be identified by their specific calls. Recording these signature calls then reveals the presence of the species in the monitored area. As sound propagates very efficiently in water, the detection area can be quite large, exceeding 100 kilometres in favourable conditions for low-frequency vocalizations. This surpasses visual detection ranges by a large factor. Thus, marine mammal scientists from various disciplines have worked for several decades to harness this acoustic potential to non-intrusively detect and monitor whales in their environment. With the rapid development of knowledge and technology in this field a new methodology, named PAM (Passive Acoustic Monitoring), is emerging (Fig. 5).
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