Aquatic Sciences Meeting, Albuquerque 2001

CS37 Zooplankton

Date: Wednesday, February 14, 2001, Time: 11:45:00 AM

Location: Aztec

De Robertis, A, , Scripps Institution of Oceanography, La Jolla, USA, aderobertis@ucsd.edu

SMALL-SCALE SPATIAL DISTRIBUTION OF EUPHAUSIIDS AND PLANKTIVOROUS FISH

The spatial dispersion of euphausiids and planktivorous fish in Saanich Inlet, British Columbia was characterized with a 445 kHz multibeam sonar capable of localizing individual animals in 3 dimensions. Euphausiids at this site were dominated by Euphausia pacifica and underwent diel vertical migration (DVM). Fish were only abundant at this deep-water station at night. Analyses in a volume of 4 m^3 over scales of ~100 m indicate that both euphausiids and fish are strongly aggregated in the vertical dimension, but are not detectably aggregated horizontally. Fish distribution at night was such that on average, fish overlapped with euphausiid concentrations equivalent to the horizontally integrated density, but 1.5-2 fold higher than the vertically integrated euphausiid concentrations. Analysis of interanimal distances at cm scales indicates that euphausiids are not aggregated, but rather, approximately randomly distributed. This result suggests that at this locality, euphausiids do not form subsurface social aggregations as has been documented for other species. DVM and social aggregation are both predator avoidance mechanisms that may be redundant, as species exhibiting pronounced DVM may derive little benefit from routine social aggregation.

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Aquatic Sciences Meeting, Albuquerque 2001

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