Journal Article

Acoustic observations of the swimming behavior of the euphausiid <i>Euphausia pacifica</i> Hansen

Alex De Robertis, Chad Schell and Jules S Jaffe

in ICES Journal of Marine Science

Published on behalf of ICES/CIEM

Volume 60, issue 4, pages 885-898
Published in print January 2003 | ISSN: 1054-3139
Published online January 2003 | e-ISSN: 1095-9289 | DOI: http://dx.doi.org/10.1016/S1054-3139(03)00070-5
Acoustic observations of the swimming behavior of the euphausiid Euphausia pacifica Hansen

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A high-resolution, 445 kHz, multi-beam sonar and new data-processing techniques were used to characterize the swimming behavior of the euphausiid Euphausia pacifica Hansen, in Saanich Inlet, British Columbia. The instrument was deployed when the euphausiids were at depth during the day and during dusk periods of population ascent. Three-dimensional swimming paths of individual euphausiids were reconstructed by linking successive, acoustically determined positions. Median swimming speeds were 1.8 cm s−1 during the day and 2.2–3.5 cm s−1 during dusk periods of vertical ascent. The presence of a fish at distances of 20–300 cm did not affect the swimming speed or turning of the euphausiids, suggesting that they did not respond to the presence of a potential predator at these distances. Euphausiids moved primarily obliquely in the vertical plane, with few individuals moving directly up or down, even during periods of vertical migration at dusk. We hypothesize that oblique swimming trajectories of euphausiids may reduce vulnerability to visual predators by allowing them to maintain bioluminescent counter-illumination during vertical migration.

Keywords: acoustic tracking; bioluminescence; euphausiid; krill; swimming behavior

Journal Article.  7152 words.  Illustrated.

Subjects: Environmental Science ; Marine and Estuarine Biology

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