ABSTRACT: Modelling encounter rates between planktonic predators and prey in turbulent waters requires an estimate of a spatial scale. One spatial scale proposed in the literature based on prey concentration is shown to be systematically inconsistent and its use is shown to imply that plankton sampling methodology can bias encounter rate estimates in turbulent situations. We show that a scale based on the predator's reactive distance is more appropriate, as it has clear theoretical support, and is consistent with other mathematical treatments of encounter problems. Applying the reactive distance as the length scale produces encounter rates for small (e.g. 4 to 10 mm) fish larvae 2- to 3-fold lower than those using prey separation distance.

KEY WORDS: Turbulence · Plankton · Predation · Encounter rate · Turbulent velocity scale · Spatial scale

Published in MEPS Vol. 166 (1998) on May 28
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1998