Use of age- and time-dependent seasonal growth models in analysis of tag/recapture data on the western king prawn Penaeus latisulcatus in the Gulf St. Vincent, Australia

Abstract

Most growth models describe a relation between an animal’s size and its age and are independent of time and time-dependent factors. However, some factors that vary with time (e.g., ambient temperature and food availability) also affect the growth of animals. Consequently, many attempts have been made to incorporate time and time-dependent factors, implicitly, in age-dependent growth models, to consider seasonal growth, biphasic growth, and the effects of tagging. But, time-dependency can render them dependent on the start of time and hence practically useless. This is because when time started is still unknown. Under what conditions are age- and time-dependent growth models independent of the start of time for them to be useful? How should their estimates of parameters be adjusted to make them useful? In this paper, we use age- and time-dependent seasonal growth models to analyse tag/recapture data on the western king prawn Penaeus latisulcatus in the Gulf St. Vincent, Australia, examine conditions under which age- and time-dependent growth models are independent of the start of time for them to be useful, and demonstrate how they should be adjusted for subsequent applications. Such analyses suggest that P. latisulcatus exhibits a strong seasonality in growth, with males’ growth cycle lagging 2 weeks behind females’. The carapace length of males grows fastest 2 weeks after the start of autumn, grows less until a full stop 2 weeks before the start of spring, shrinks until the middle spring, and resumes its positive growth for another cycle, whereas that of females grows continuously throughout the year but at a slower rate in certain months.