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Acoustics - FRAM
Acoustics
| Since 2003 FRAM’s Acoustics Team has been conducting the joint U.S.–Canada integrated acoustic and trawl surveys of Pacific Hake (Merluccius productus) off the west coast of North America. These time series of surveys are the primary data source for the U.S.–Canada Pacific hake stock assessment, which uses age–structured assessment models to estimate current and future hake abundance. The assessments provide advice to fishery management on future harvests. |
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| Initially, the surveys were conducted by the Alaska Fisheries Science Center (AFSC) beginning in 1977. These were triennial surveys along the U.S. and Canadian Pacific Coast. Canadian scientists from the Department of Fisheries and Oceans (DFO) did their own annual survey of hake along the Canadian west coast since 1990. Beginning in 1995, the two agencies began to collaborate on the triennial hake surveys and to perform inter–vessel calibrations of the acoustic systems. The Northwest Fisheries Science Center (NWFSC) assumed responsibility for the U.S. portion of the survey, conducting biennial surveys of hake beginning in 2003 in an ongoing partnership with DFO. The next survey will take place in 2009 and, as in the previous surveys, during the summer months when Pacific hake are feeding in aggregations along the continental shelf break from northern California to Queen Charlotte Sound. |
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| The acoustics system is used to collect acoustics data on hake biomass estimates, which are then verified by trawl catches. The acoustics data are recorded with a number of discrete narrow–band, split–beam acoustic echo sounders, typically at 18, 38, 120, and 200 kHz. The acoustic transducers are mounted on a retractable centerboard at the bottom of the ship. An echo–integration technique, based on the linearity principle, is used to relate acoustic intensity with the number of fish in the sample volume. |
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| In addition to using the conventional narrow–band, split–beam technology in the acoustic survey, the Acoustics Team is looking into other advanced sampling technologies like multi–beam technology that provides a larger sample volume, and broadband technology that provides a much wider spectrum, higher spatial and temporal resolutions, and significantly improved signal–to–noise ratio. At the same time, the Acoustic Team is developing new sampling devices, which are non–extractive and integrate both acoustic and optic methods to provide additional information on fish distributions. |
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last modified
12/05/2008
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