Sound-Scattering Layers in the Northeastern Pacific

• Published in: Journal of the Fisheries Research Board of Canada
• Main Authors: Donaldson, Henry A., Pearcy, William G.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1972
• Subjects: General Medicine; Pacific; Adak; Subarctic; Alaska
• Online Access: http://dx.doi.org/10.1139/f72-220; http://www.nrcresearchpress.com/doi/pdf/10.1139/f72-220

Temporal and spatial variations in the depth, thickness, and vertical movement of scattering layers were studied using a 38.5 kHz echosounder in waters off Oregon and between Hawaii and Adak, Alaska.Off Oregon one or two layers migrated toward the surface at dusk and descended into deeper water at dawn. Although individual scattering layers migrated at a fairly constant rate during a twilight period, rates of ascent and descent varied from day to day. Average rates were 2–3 m/min. During the night the depth of the top of the scattering layer averaged 40 m, and it varied between 50–245 m during the day. The bottom of the deepest recorded layer was 450 m deep.Regardless of intensity, the thickness of the scattering layers in the water column was usually greater during night than day. It was greater over the continental slope than abyssal depth, and in some years it was greater during the summer than during other seasons.Between Hawaii and Adak, Alaska, central waters had large amounts of scattering but low midwater trawl catches, transitional waters had high-intensity scattering layers and high biomass, and subarctic waters had very reduced scattering layers but high biomass.