On comparison of growth curves: How do we test whether growth rates differ?

Comparisons of growth rates of populations and species are important in fi sheries science for a range of reasons that vary with the context of each study. Most studies of fi sh growth have focused on the practical issues of the most appropriate way of comparing growth rather than on recognizing that there are several methods for making these comparisons and that the conclusions will differ depending on the method chosen. Francis (1996) discussed the problem of how to compare different growth rates or growth curves. He suggested six plausible ways of making a comparison and suggested that the rate at which the asymptotic size is approached was the most natural method of comparing growth (his method 6). He illustrated the differences between the methods by comparing von Bertalanffy growth equations that are based on fi xed growth parameters and that assumed that growth parameters are known and there are no associated uncertainties. However, in practice, the growth parameters are often estimated, and therefore are random variables. Consequently, the corresponding growth curves are also subject to variations. For comparison with Francis’s work, we will assume that growth for a speOn comparison of growth curves: How do we test whether growth rates differ?