Estimation of von Bertalanffy Growth Curve Parameters from Recapture Data

A simple method of constructing estimating functions for parameters in the von Bertalanffy growth model E[y(t)] = L[1 - exp(-Kt)] is presented for tag-recapture data when the age of the animal is unknown. The estimating functions are unbiased under very general distributional assumptions provided K does not vary between animals. Simulations of growth in lobsters and whelks indicate that the method performs well provided the initial capture times and recapture intervals vary over reasonable ranges. Comparison is made with methods based on least squares, which have been shown to be generally inconsistent.