Differences in growth rates between habitats of South-east Australian snapper (Chrysophrys auratus)

Abstract

Data on recaptured fish from two tagging experiments on south-east Australian snapper, Chrysophrys auratus, were analysed: 198 fish released in several Victorian locations between 1956 and 1962, and 118 fish released in Port Phillip Bay in 1971 and 1972. Movement data from both experiments were used to classify the fish into habitats (oceanic and bay) and stocks (western and eastern). Length increment data from the earlier experiment indicate that the major growth-rate differences in south-east Australian snapper lie within the western stock (between oceanic and bay habitats) rather than between stocks as suggested by an earlier analysis of the same data. The annual growth rates of 20-30-cm snapper in Port Phillip Bay and Western Port are 17-20% higher than for fish in the ocean. Oceanic growth rates in the western stock appear to be lower than those in the eastern stock. Procedural differences in length measurements at tagging and recapture can introduce a net bias in the length increment that, if ignored (as is conventional in tagging growth models), will bias growth rate estimates. In the earlier tagging experiment, this is shown to have caused a 10% positive bias in growth rate estimates.