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MEPS 480:39-56 (2013)  -  DOI: https://doi.org/10.3354/meps10215

Second-order seasonal variability in diel vertical migration timing of euphausiids in a coastal inlet

Mei Sato1,*, John F. Dower2,1, Eric Kunze3, Richard Dewey1

1School of Earth and Ocean Sciences, University of Victoria, Victoria, British Columbia V8P 5C2, Canada
2Department of Biology, University of Victoria, Victoria, British Columbia V8P 5C2, Canada
3Applied Physics Laboratory, University of Washington, Seattle, Washington 98105-6698, USA

ABSTRACT: Variability in the diel vertical migration timing of euphausiids in Saanich Inlet, British Columbia, Canada, is quantified using 2 yr of echosounder data from a cabled observatory. The continuous and high-resolution nature of the observations allows examination of second-order seasonal variability in migration timing relative to civil twilight times. Early dusk ascent and late dawn descent occur during spring–fall, while late dusk ascent and early dawn descent occur during winter. Ascent timing appears to be regulated by (1) light availability at the daytime depth of the euphausiids, which is modulated by phytoplankton bloom shadowing, and (2) euphausiid size-dependent visual predation risk. Because (1) does not apply at dawn, descent timing appears to be regulated by (2). During the pre-spawning period, higher energy demand for reproduction may cause earlier dusk ascent and later dawn descent to maximize energy gain, even with larger body size. Instead of the traditional view of diel vertical migration timing, correlated solely with civil twilight, our data suggest that euphausiids also adapt their migration timing to accommodate changes in environmental cues as well as their growth.


KEY WORDS: Diel vertical migration · Euphausiids · Variability · Echosounder · Time-series


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Cite this article as: Sato M, Dower JF, Kunze E, Dewey R (2013) Second-order seasonal variability in diel vertical migration timing of euphausiids in a coastal inlet. Mar Ecol Prog Ser 480:39-56. https://doi.org/10.3354/meps10215

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