Northwest Fisheries Science Center

Acoustics

Acoustics help estimate Pacific hake biomass

Since 2003, The NWFSC's Fisheries Engineering and Acoustic Technologies (FEAT) Team has conducted joint U.S.–Canada integrated acoustic and trawl surveys of Pacific hake, an economically important fish species found off the West Coast of North America. Scientists conduct these surveys during the summer months, when Pacific hake are feeding in aggregations along the continental shelf break from northern California to Queen Charlotte Sound.

This survey is the primary source of data for the U.S.–Canada Pacific hake stock assessment, which uses age–structured assessment models to estimate the current and future abundance of hake. The assessments provide advice to fishery managers on future harvests.

Scientists use the SIMRAD EK60 Scientific Echo Sounder System to collect acoustics data for 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, 70, 120, and 200 kHz. The acoustic transducers are mounted on a retractable centerboard at the bottom of the ship. A special echo–integration technique is then used to relate the acoustic intensity with the number of fish in the sample volume.

In addition to using the conventional narrow–band, split–beam technology in the acoustic survey, we are also looking into other advanced sampling technologies like Autonomous Underwater Vehicles and 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. We are also developing new sampling devices which are non–extractive and integrate both acoustic and optic methods to provide additional information on fish distributions.

Integrated Wave Glider-Echosounder

As part of the NWFSC's Fisheries Engineering and Acoustics Technologies Team, Larry Hufnagle and Dezhang Chu develop and use acoustic technology to research marine life. They recently collaborated with a robotics group to combine an acoustic tool used in fishery surveys, called an echosounder, with a solar-powered Wave Glider to develop a new tool to survey fish populations.