Studying the biosonar activities of deep diving odontocetes in Hawaii and other western Pacific locations

Ecological acoustic recorders (EARs) have been deployed at several locations in Hawaii and in other western Pacific locations to study the foraging behavior of deep-diving odontocetes. EARs have been deployed at depths greater than 400 m at five locations around the island of Kauai, one at Ni’ihau, two around the island of Okinawa, and four in the Marianas (two close to island of Guam, one close to the island of Saipan and another close to the island of Tinian). The four groups of deep-diving odontocetes were blackfish (mainly pilot whales and false killer whales), sperm whales, beaked whales (Cuvier and Bainsville beaked whales) and Risso’s dolphin. In all locations, the biosonar signals of blackfish were detected the most followed by either by sperm and beaked whales depending on specific locations with Risso’s dolphin being detected the least. There was a strong tendency for these animals to forage at night in all locations. The detection rate indicate much lower populations of these four groups of odontocetes around Okinawa and in the Marianas then off Kauai in the main Hawaiian island chain by a factor of about 4–5.