Species identification and measurement of activity in odontocete species of Palmyra Atoll by acoustic monitoring

Acoustic monitoring has been used to study odontocete presence at Palmyra Atoll, a remote island in the Northern Line Islands chain. Long‐term recordings of high‐frequency, broadband acoustic data have become possible with recent technological advances. A High‐frequency Autonomous Recording Package (HARP) has been developed which samples at 200 kHz with a duty cycle of 1/4 for up to seven months. This instrument has recorded since October 2006 at Palmyra Atoll. Visual and acoustic surveys were conducted around Palmyra Atoll using a four‐element towed hydrophone array sampling real‐time at 200 kHz to obtain species‐specific acoustic data. These data are used as reference for automatic detection algorithms applied on the long‐term recordings. To date, acoustically and visually detected odontocetes include bottlenose dolphins (Tursiops truncatus), spinner dolphins (Stenella longirostris), melon‐headed whales (Peponocephala electra) and beaked whales of the genus Mesoplodon. The long‐term HARP data reveal acoustic activity primarily at night time and predominantely odontocete clicks. Both the beaked as well as the melon‐headed whales are present year round and show a distinct daily acoustic activity cycle.