Turbulence and ichthyoplankton: influence on vertical distributions and encounter rates
Svein Sundby

Two different aspects of the effects of turbulent mixing on eggs and fish larvae are considered here. In the first topic the effects of physical processes on the vertical distribution of the eggs are considered. The physical processes which determine the vertical distribution of fish eggs, and all other immobile plankton, are the buoyancy of the plankton and the vertical mixing of the water column. Analytical models are presented to demonstrate the influence of the various terms. A numerical model is also applied to show the effects of non-stationary solutions. The model results are compared with field measurements. In the second topic the effects of turbulence on plankton encounter rates are considered. The processes are illustrated by field data on first-feeding cod larvae feeding on Calanus nauplii. These field data show that wind-induced turbulence strongly enhances the feeding rate of the larvae. For first-feeding cod larvae the feeding rate increases by a factor of about 7 when the wind speed increases from 2 m s-1 to 10 m s-1. Model simulations show how the influence of turbulence-enhanced encounter rate decreases as the larvae grow, increase their swimming speed and switch to larger prey of lower concentration. The simulations show that the turbulence-induced encounter rate decreases exponentially as cod grow, but significantly influences feeding until the stage of 2 months old juveniles.

Contents of this volume Sci. Mar. 61(Suppl.1) : 159-176 Back PDF
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