Estimating growth and mortality in stage-structured populations

This paper presents a practical numerical method for separating and estimating growth and mortality coefficients in stage- or size-structured populations using only observations of the relative or absolute abundance of each stage. The method involves writing a system of linear ordinary differ- ential equations (ODEs) modelling the rate of change of abundance. The solution of the differential system can be numerically approximated using standard (e.g. sixth-order Runge-Kutta-Felhberg) methods. An optimization problem whose solutions yield 'optimal' coefficients for a given model is formulated. The ODE numerical integration technique can then be employed to furnish required function and gradient information to the optimization algorithm. The data-fitting software package ODRPACK is then successfully employed to estimate optimal coefficients for the ODE population model. Simulation experiments with four- and eight-stage model populations illustrate that the method results in the successful estimation of coefficients of mortality and growth from abundance data.

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