Since 2003, FRAM's Fisheries Engineering and Acoustic Technologies (FEAT) Team has conducted joint U.S.- Canada integrated acoustic and trawl surveys of Pacific hake (Merluccius productus) off the West Coast of North America. Surveys are conducted 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-structure assessment models to estimate the current and future abundance of hake. The assessments provide advice to fishery managers on future harvests.
The surveys were initially conducted by the Alaska Fisheries Science Center (AFSC) beginning in 1977 as 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, starting in 1990. In 1995, the United States and Canada began to collaborate on the triennial hake surveys and to perform inter-vessel calibrations of the acoustic systems. The 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.
In 2012, we conducted an extra hake survey in response to stock uncertainty and recommendations of International Hake Treaty members. This survey was conducted jointly with the Southwest Fisheries Science Center's biannual sardine survey, making it the first Joint Pacific Hake and Sarine Integrated Acoustic-Trawl Survey. The joint survey will take place again in Summer 2013 and its frequency is currently under review by acousticians, stock assessors, and hake treaty committee members.
The SIMRAD EK60 Scientific Echo Sounder System is used 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. An echo-integration technique, based on the linearity principle, is used to relate 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, the FEAT Team is looking into other advanced sampling technologies like AUVs 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. The FEAT Team is also developing new sampling devices, which are non-extractive and integrate both acoustic and optic methods to provide additional information on fish distributions.