Survey of Cetaceans Completed in Waters of Palmyra Atoll

PIFSC researchers, in collaboration with colleagues from the NOAA Southwest Fisheries Science Center in La Jolla, California, are making strides in understanding the distribution and abundance of cetaceans in the scattered parts of the Pacific U.S. Exclusive Economic Zone (EEZ) and the adjoining high seas. From April 23 to May 17, 2012, researchers on the NOAA Ship Oscar Elton Sette conducted a multidisciplinary survey of whales and dolphins in the U.S EEZ around Palmyra Atoll, located about 950 nmi south of Hawaii. This was the second leg of a 2-part Palmyra Cetacean and Ecosystem Assessment Survey (PICEAS); the first leg was completed in October-November 2011. PICEAS is a large-scale visual and acoustic line-transect survey intended to assess cetacean abundance. The last full survey in the Palmyra EEZ was in 2005.

The main goal of PICEAS Leg-2 was to collect the data needed to calculate new estimates of abundance for each species of cetaceans in Palmyra waters. The survey lines were designed to cover the waters within the 200 nm EEZ around Palmyra Atoll uniformly. Cetaceans were encountered in 2 ways: acoustically, using passive sonar; and visually, by sighting animals at the sea surface from the ship. Despite poor weather conditions, cetaceans were encountered at rates much higher than during the Leg-1 survey; altogether, 48 visual sightings and over 150 acoustic detections were recorded. There were 6 encounters with false killer whales. During these encounters, researchers successfully used a new field protocol aimed at understanding and accurately accounting for false killer whale subgroup structure.

Survey effort was also conducted in the nearshore waters around Palmyra and Kingman Reef, resulting in several sightings of island-associated melon-headed whales, bottlenose dolphins, and spinner dolphins. The inshore surveys also recorded, in 4 separate sightings, what is tentatively thought to be the beaked whale Mesoplodon hotaula. This newly discovered species has been recorded elsewhere in the tropical Indo-Pacific. During the 4 sightings, very close to Palmyra and Kingman, it wasn't possible to obtain photos or biopsies that would help identify the animals encountered. However, acoustic recordings may eventually confirm the species' identities.

At Kingman Reef, the scientific team recovered a High-Frequency Acoustic Recording Package (HARP) from the seafloor; it had been deployed there during another cetacean expedition in 2011. The broadband acoustic data collected by the HARP will be used to assess the connectivity and seasonality of island-associated cetacean populations at Kingman and Palmyra.