In American Samoa, scientists aboard the NOAA Ship Oscar Elton Sette are learning how oceanographic processes affect the distribution and abundance of albacore tuna

February 15, 2006
Scientists deploy a CTD rosette with Niskin bottles during the 2004 American Samoa cruise.

On February 15, the NOAA Ship Oscar Elton Sette will set out from Pago Pago, American Samoa, to embark on an 18-day scientific investigation of the surrounding waters. The expedition by the NOAA Fisheries' Pacific Islands Fisheries Science Center (PIFSC), based in Honolulu, Hawaii, will study the local fishing grounds for albacore tuna, the primary species supporting the American Samoa longline fishery. The research project is being conducted by PIFSC's Ecosystems and Oceanography Division and aided by funding from the Pelagic Fisheries Research Program of the Joint Institute for Marine and Atmospheric Research, University of Hawaii. Led by Chief Scientist Dr. Reka Domokos, a team of investigators on the Sette will collect physical, chemical, and biological information to help identify and understand oceanographic processes that affect the abundance and distribution of albacore in the area.

The South Pacific albacore resource is important to the American Samoa economy. Albacore caught by local vessels and by U.S. troll vessels and foreign longline fleets operating in more distant waters are processed by tuna canneries in American Samoa. Local longline fishermen earn over $5 million annually for their albacore catch and the canneries provide jobs for local citizens. Identifying oceanographic factors that affect the movements and abundance of albacore will help scientists provide sound advice to fishery managers responsible for maintaining a healthy albacore stock and sustainable fisheries for this commercially important species.

An acoustics transect shows a dense layer of organisms (shown in red) migrating from shallow to deep waters during dawn (North of American Samoa, 2004).
Click here for high resolution version.

The scientists will study the local current system, identified in a 2004 survey as likely having a critical influence on the abundance and distribution of both albacore and its prey species in the area. Using a variety of survey methods and equipment, NOAA scientists and collaborators from the University of Hawaii and Lund University (Sweden) will collect data to assess the physical and biological environment. The ocean's temperature, salinity, and concentrations of dissolved oxygen and chloropigments will be measured from the sea surface down to a depth of 1000 m (3300 feet) by deploying sensors on a "CTD rosette" that will be lowered into the ocean from the ship. Niskin bottles attached to the rosette will collect water samples at certain depths during its descent. The speed and direction of the current down to a depth of 500 m (1640 ft) will be continuously monitored by a shipboard acoustics instrument. The composition, density, and spatial distribution of tuna prey species in the upper 1000 m of water will be assessed by a hull-mounted, dual-frequency bioacoustics instrument. In areas and depths where the bioacoustic survey shows a high density of organisms, trawl nets will be used to collect samples of prey and determine their species composition.

American Samoa longline vessel engaged in cooperative research with the NOAA Ship Oscar Elton Sette (background).

Some of the Sette's oceanographic work will be conducted in an area where commercial longline vessels are fishing for albacore. PIFSC Biologist Don Hawn will work aboard one of the cooperating longline vessels to study their catch and carry out several ancillary research projects. In one project, Hawn will attach Time-Depth-Temperature Recorders (TDRs) and electronic timing devices (hook timers) to the longline gear as it is being deployed. Information collected by the TDR instruments will reveal the depth and temperature conditions where the baited longline hooks were fishing and, together with the hook timer data, show at what depths fish were caught.

In another project, Hawn will attach electronic Pop-up Satellite Archival Tags (PSATs) to several albacore and other species of fish caught by the vessel and then return the tagged fish alive to the sea. The PSATs will measure water temperature, depth, and light levels where the fish are swimming and record the data on the tag's memory chip. Days or months later, the tags will release from the fish and transmit their archived information to an orbiting satellite which relays the information to a scientist's computer. The PSAT data will allow scientists to map the movements of albacore and other species of fish in the ocean and, combined with the oceanographic data, will help reveal the influence of oceanographic factors on movement patterns.

By combining and analyzing the various sources of data collected on the Sette cruise and catch data from the longline fleet, scientists will be able to assess how both the physical and biological environment affect the distribution, abundance, and catch of albacore.

Although the primary objective of the Sette cruise is to conduct scientific research, there will also be an educational component. While the oceanographic surveys are underway, Lucas Moxey of NOAA's OceanWatch-Central Pacific will be conducting a real-time outreach project with middle school students on the Hawaiian island of Oahu. From the deck of the Sette, Moxey will communicate with the students and their teacher by e-mail and share bits of oceanographic data for use in classroom mathematics exercises. The outreach project is part of the OceanWatch-Central Pacific Algebra@Sea initiative. The program seeks to link NOAA PIFSC scientists at work in the field with Hawaii middle and high school students. With guidance from their teachers, students learn how math skills can be applied not only to their textbook exercises but to real world problems in marine science and discovery.