Ontogenetic movement patterns of the bull shark, Carcharhinus leucas, in the Gold Coast canal system.
The bull shark is one of a small number of elasmobranchs that can live and breed in marine and freshwater. The juveniles often utilise upper estuarine areas (of reduced salinity) as nurseries prior to moving towards the seaward (more saline) estuarine areas and then migrating offshore as adults. Determining the value of urbanised coastal habitats to bull sharks is therefore crucial in understanding the potential use of man-made habitats such canals and also for managing the possible interactions between humans and this dangerous species. This study used acoustic tracking to determine the value of different coastal habitats to neonate, juvenile and sub-adult bull sharks. The sharks were tagged with coded acoustic tags that were detected by a network of acoustic listening stations strategically placed within the Gold Coast canal system and the Nerang River. The data showed that the neonate and juvenile bull sharks spent the majority of their time in the upper tidal reaches of the Nerang River where salinity is greatly reduced. However, neonate and juvenile bull sharks also made small excursions into the canals. Sub-adult sharks moved over larger areas of the river and canals. They also moved out of the study site and returned on occasions. These results suggested that the neonate and juvenile, bull sharks used the Nerang River and adjacent canals as a nursery area. The man-made canals, while occasionally utilised by the sub-adults, were not the preferred habitat of adults of this species.