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Free Content Acoustic observations of vertical and horizontal swimming velocities of a diel migrator

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Abstract:

A strong sound scattering layer which underwent diel vertical migration was observed over 176 days using a bottom-mounted 600 kHz ADCP at a depth of approximately 285 m on the upper continental slope. Average observed descent times of the scatterers were within 12 minutes of sunrise and average ascent times were within 13 minutes of sunset. Average ascent speeds progressively increased away from the bed and approached 6 cm/s. Average descent speeds similarly reached a maximum of ∼6 cm/s. Horizontal velocities of the scatterers during vertical migration were found to be smaller than ambient velocities (by up to 3 cm/s), and it is inferred that the migrators were swimming horizontally against the flow. Horizontal velocities of the scatterers during time intervals when the layer was near the seafloor were found to be southwest (up to 3 cm/s), and onshelf (up to 1.7 cm/s) relative to the flow above the layer. Swimming velocities were independent of alongshelf flow direction, counter to the hypothesis that the scatterers sought to maintain their position by swimming against the flow.

Document Type: Research Article

DOI: http://dx.doi.org/10.1357/002224006779367258

Publication date: September 1, 2006

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  • The Journal of Marine Research publishes peer-reviewed research articles covering a broad array of topics in physical, biological and chemical oceanography. Articles that deal with processes, as well as those that report significant observations, are welcome. In the area of biology, studies involving coupling between ecological and physical processes are preferred over those that report systematics. Authors benefit from thorough reviews of their manuscripts, where an attempt is made to maximize clarity. The time between submission and publication is kept to a minimum; there is no page charge.
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