Partitioning the influence of physical processes on the estimation of ichthyoplankton mortality rates. 1. Theory

This paper examines the effects of natural spatial-temporal variability in ichthyoplankton concentration and in currents on the estimation of mortalit y rates. We derive expressions for the biases and variances of mortality es timates computed from the change in plankton concentration between successi ve surveys as well as estimates of the corrections due to the advection of plankton. We demonstrate that estimate bias depends primarily on how well t he mean current and mean ichthyoplankton fields are sampled whereas the var iance depends on the variability about the mean in currents and plankton co ncentration and on the time and length scales on which this variability occ urs. Simplified versions of the theoretical expressions provide an easily i mplemented framework for evaluating the quality of field sampling plans.