Seasonality and site fidelity of the zebra shark, Stegostoma fasciatum, in southeast Queensland, Australia

Abstract

Site fidelity and migratory movements of vertebrate animals occur at many spatial and temporal scales. Larger migratory movements tend to occur in species that live in seasonal environments in which food supplies vary markedly, while species found in thermally stable environments are more site-attached. In the marine environment, seasonal migrations are often associated with predictable temporary aggregations that have largely been targeted for exploitation. We employed passive acoustic telemetry to investigate inter- and intraseasonal site fidelity of zebra sharks to an aggregation site in southeast Queensland, Australia, close to the southern latitudinal extent of this species' range. We tracked 10 zebra sharks over two aggregation seasons (21 months). We applied a generalized linear mixed-effects model to investigate the presence/absence of these zebra sharks with respect to several environmental variables. We found that different environmental factors were associated with site fidelity of zebra sharks at different temporal levels and that these may be indicative of the mechanisms driving the movements. Seasonal patterns may be driven by endogenous systems, and cues such as photoperiod and water temperature are likely to be important. Intraseasonal patterns are more likely to be indicative of direct behavioural responses to changes in environmental conditions such as increased wave heights, as well as foraging bouts away from a core refuge. Understanding the relative contributions of these environmental parameters, as well as biological factors, will be important for making predictions of site fidelity and movements of migratory marine vertebrates under differing future scenarios such as increases in sea temperature.