Partitioning the influence of physical processes on the estimation of ichthyoplankton mortality rates. II. Application to simulated and field data

Helbig and Pepin (1998. Can. J. Fish. Aquat. Sci. 55: 2189-2205) developed a theory partitioning the bias and variance of a number of population and m ortality measures in terms of the space and time scales of natural variabil ity of the underlying current and plankton fields. This study verifies that theory through a series of numerical simulations and by comparing predicte d variances in estimated fluxes with those observed in an earlier field stu dy. In the simulations, errors in estimated mortality rates were clearly do minated by errors in estimated flues due to transport, and estimates of var iance and bias were all in good agreement with theoretical predictions. For the field data, the theory predicted a distribution of values slightly low er than that observed, but of the correct order. That the model performed w ell for both simulated and field data suggests that it can be applied in pr actice with reasonable confidence. We also briefly explore the role of the model in survey design and analysis for ichthyoplankton studies in which tr ansport might be important.