NOAA scientists launch survey from American Samoa to assess the distribution and abundance of cetaceans in the Pacific Islands Region

March 5, 2006
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Rough-toothed dolphins off the east side of Tutuila, American Samoa

On March 5, having completed several weeks of fisheries oceanography research in local waters, the NOAA Ship Oscar Elton Sette departed Pago Pago, American Samoa, for a 24-day return voyage to Honolulu, Hawaii, the ship's home port. With a fresh scientific crew on board, the Sette's return trip will focus on a different research objective – understanding the distribution and abundance of whales and other cetaceans in the vast oceanic region between American Samoa and Hawaii. The expedition by the NOAA Pacific Islands Fisheries Science Center (PIFSC), based in Honolulu, is assisted by funding from the Joint Institute for Marine and Atmospheric Research, University of Hawaii. Marine mammal specialists led by Chief Scientist David Johnston of the PIFSC's Protected Species Division will identify, count, and sample cetaceans encountered during the transit to Hawaii and during occasional fishery research operations along the way. The ship will spend several days working in American Samoa waters off Swains Island before heading north. Waters around Johnston Atoll will also be visited en route.

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Sperm whale north of Tutuila, American Samoa

The Pacific Islands Region, the largest management jurisdiction for the NOAA Fisheries Service, is home to more than 20 species of cetaceans, many of which are poorly understood or virtually unstudied. Some species, such as the false killer whale, are listed as strategic stocks under the U.S. Marine Mammal Protection Act because of their interactions with pelagic longline fisheries. Other species, such as the humpback whale, are listed as endangered under the Endangered Species Act. Although humpback whales are known to make extensive seasonal migrations from feeding grounds in the northern Pacific to mating grounds in the waters of the central Pacific, the distribution, abundance, and behavior of humpbacks and other cetaceans within most of the Pacific Islands Region have yet to be studied. Very little is known about the cetacean community in the waters of Johnston Atoll or other U.S. islands and territories in the central Pacific, especially outside Hawaii. In particular, the abundance and stock identity of humpbacks wintering in the waters of Johnston Atoll are unknown. The Sette surveys will provide valuable new information about the winter populations of cetaceans around American Samoa and Johnston Atoll.

During the voyage scientists will use line-transect survey methods. In this approach, observers stationed on the Sette's flying bridge use special binoculars to search for cetaceans along pre-determined tracklines. As the ship travels through the water at a fixed speed, a pair of observers monitors the area off the port and starboard sides of the ship and a third observer occupies a central data recording station. The observers work in 2-hour rotations, spending 40 minutes at each station. Observers identify the species of cetaceans seen, estimate their number, and determine the distance and angle of the animals from the ship. The recording scientist logs all observations and keeps an accurate account of the survey time along the trackline ("effort-time"). Occasionally, the ship must take time out and divert from the trackline (go "off-effort") to confirm a species identification. An "independent observer" may keep a separate watch of animals sighted during the cetacean survey operations, to be compared later with the observer team's data. During the line-transect surveys, the scientists will tow a "hydroacoustic array" of sonar instruments behind the Sette to record sounds emitted by cetaceans in the vicinity of the ship. The sonar information assists observers trying to sight cetaceans and can detect animals too far away to be observed directly.

The survey information will help scientists assess the status of cetaceans and other marine mammal populations in the Pacific Islands Region and answer many key questions about their biology, including how far the animals range in their movements. For example, do the dolphins seen near American Samoa travel to Hawaii? The best way to determine this is to analyze DNA samples from animals in various locations. During the Sette cruise, skin samples will be collected from cetaceans using harmless biopsy darts fired from the ship or a smaller, mobile boat launched from the Sette. Analysis of DNA from the skin samples will show if the animals come from the same or different populations.

Although the primary mission of the survey is to study cetaceans, as time and conditions permit Fishery Biologist Mike Musyl of the Fishery Biology and Stock Assessment Division will be able to study the movements of marlin, another important component of the Pacific pelagic ecosystem. Pop-up Satellite Archival Tags (PSATs) will be attached to large marlin caught by longline gear and then returned alive to the sea. The PSATs will measure water temperature, depth, and light levels where the fish are swimming and record these data on the tag's memory chip. Days or months later, the tags will release from the fish. The tags will rise to the sea surface and transmit their archived information to an orbiting satellite which will relay the information to a scientist's computer. Analysis of the PSAT data will lead to a better understanding of the range and movements of marlin in their habitat, both laterally and vertically.