A Nonparametric Von Bertalany Model for Estimating Growth Curves Of Atlantic Cod

No abstracts are to be cited without prior reference to the author.

A nonparametric model is developed for estimating growth of Atlantic cod in NAFO Subdivision 3Ps and Divisions 3KL during 1997-2000 based on Þshery tag-returns. The tag-returns provide information on lengths at release and capture, and time to capture. One use of the growth curves is to account for Þshing gear length selectionwhenestimatingÞshery exploitation rates using tagging information. We use a simple version of the Von Bertalanffy growth model, modiÞed to accommodate seasonal variations in growth rates. The growth rates are modelled using spline methods, which leads to a growth curve model that includes a monotone spline component. A measurement bias component is also incorporated in the model because the tag-return data suggest that there is some bias in the lengths-at-capture reported by Þshermen. The interesting implications of intra-population variability in growth rates are also considered. We use the estimated model to predict cod growth for times-at-liberty ranging from 0-4 years; for example, we estimate that a 40 cm Þsh will grow 28 cm during 1997-2000, but in the same period a 90 cm Þsh will grow only 9 cm.