Wet-season effects on the distribution of juvenile pigeye sharks, Carcharhinus amboinensis, in tropical nearshore waters

Tropical nearshore environments are highly dynamic systems owing to extreme freshwater flow and flooding episodes that occur in wet-season months. We hypothesised that juvenile sharks in tropical nearshore waters respond to seasonal freshwater inflow by moving away from areas of strong flow. An array of fifty-eight acoustic receivers deployed in Cleveland Bay, north Queensland, Australia, passively tracked thirty-two juvenile pigeye sharks, Carcharhinus amboinensis, throughout two wet seasons from 2008 to 2010. Influences associated with wet seasons appeared to play a role in habitat use by juvenile C. amboinensis in this region. Home ranges and distribution of individuals showed distinct changes, with individuals moving north away from sources of freshwater inflow during high flows. The location of individuals within the bay was strongly influenced by freshwater inflow in both years. Although juvenile C. amboinensis moved in response to freshwater inflow, home-range sizes remained stable, and the amount of space individuals used did not change in relation to freshwater inflow. By defining the response of juvenile sharks to highly variable freshwater flow events, this research provides useful information for understanding species behaviour in a dynamic and changing climate, and contributes towards effective management of tropical river systems.