Research Cruise Tests Methods for Fishery-independent Bottomfish Assessment, Studies Key Pelagic Habitat
Leg 2 Oceanographic Survey Progress Reports
Leg 1 Bottomfish Assessment Progress Reports
The NOAA Ship Oscar Elton Sette is facilitating research by oceanographers and biologists from the Pacific Islands Fisheries Science Center (PIFSC) on a 30-day cruise in the main Hawaiian Islands (MHI) and the central North Pacific. The research vessel departed Ford Island, Pearl Harbor on February 25, 2011, for a 12-day study in the MHI surveying bottomfish abundance and investigating fishery-independent stock assessment methods. The Sette will then sail northward and spend 18 days investigating the physical and biological oceanography of the Hawaii-based longline fleet's fishing grounds. The expedition is a cooperative venture between PIFSC, the University of Hawaii (UH), and Hawaii's commercial bottomfish fishermen. The scientific field party includes staff from PIFSC, UH, the Joint Institute for Marine and Atmospheric Research (JIMAR), and the American Museum of Natural History.
On the first leg of the cruise, Chief Scientist Dr. Don Kobayashi will conduct and coordinate research into fishery independent methods to assess stocks of economically important bottomfish. The research involves a host of cooperating vessels, including the Sette, the vessel Hukipono chartered by the University of Hawaii at Manoa, and several commercial bottomfish vessels chartered by PIFSC. On the Sette, active sonar will be used to assess biomass density of bottomfish in several study areas of the MHI. The sonar instrument sends sound waves from the ship toward the seafloor in short bursts at three different frequencies. When the sound waves encounter organisms or the seafloor, echoes are reflected back to the ship where they are recorded and analyzed. The acoustics data will be compared to video footage captured by an array of baited underwater video cameras (BotCams) simultaneously operated from the Hukipono by UH scientists. Each BotCam will be moored to weights on the ocean floor, release bait fish into the water to attract bottomfish, and capture stereo video of bottomfish swimming within range of the camera. Video data help scientists identify the bottomfish species in the area and estimate their abundance and size. While the acoustics and BotCam studies are being carried out, handline fishing for bottomfish will be conducted in the same areas by the commercial fishermen. The combination of acoustics data, BotCam video footage, and fishermen's catch and effort data will provide several measures of bottomfish abundance and help the Center determine the effectiveness of acoustics as a fishery-independent method for stock assessment of bottomfish. Scientists from the University of Miami are assisting with the cruise survey design.
On the second leg of the cruise, led by Chief Scientist Phoebe Woodworth, the Sette will move north of the main Hawaiian Islands and investigate fishing grounds of the Hawaii-based longline fleet. This area of the North Pacific is marked by distinct, migrating thermal and chlorophyll fronts. Fish species such as swordfish and bigeye tuna are found along these fronts and are targeted by longline fishermen. Loggerhead sea turtles are also associated with these fronts. To better understand the ecology of these species and their habitats, physical and biological characteristics of the ocean will be assessed along a single survey transect extending northward from Oahu almost 1,000 nm. Active sonar will be used to determine the relative biomass density of the sound scattering layers - fish and other marine organisms in the water column that are prey for targeted commercial species. By determining how deep these layers are in the ocean, researchers learn where swordfish and bigeye tuna forage. Another acoustic instrument, the Acoustic Doppler Current Profiler (ADCP) will be used to measure the speed and direction of ocean currents. A CTD instrument will be deployed from the Sette every 15 nm along the survey transect to measure the conductivity/salinity, temperature, fluorescence, and dissolved oxygen of the water to a depth of 1000m. Water samples will also be collected at several depths during each cast and analyzed for chlorophyll and nutrient content.
The data gathered on this scientific expedition will give researchers a better understanding of several ecologically and economically important fish species. The methods studied on the first cruise leg will lead to improved assessments of bottomfish species in the MHI. The survey on the second leg will lead to better understanding of physical and biological oceanographic features that define habitat for bigeye tuna, swordfish, and loggerhead turtles.
