In August 2007, Australia Zoo, the University of Queensland and Queensland Parks and Wildlife undertook a project to monitor the movements and behaviour of estuarine crocodiles in Lakefield National Park. The aim of the study was to provide better information on how adult estuarine crocodiles interact within a river system, enabling informed decisions on how to better manage crocodile populations.
Crocodiles are cryptic, secretive and easily disturbed by human presence. In order to monitor their movements in the wild, a novel technology using implanted transmitters and remote listening stations was used. A total of 27 adult estuarine crocodiles between 2.1 and 4.86 metres in length were captured along the Kennedy River and in adjacent tributaries. Miniature electronic devices were implanted under the skin, which later transmitted a sonic pulse containing information about the animals’ identification, body temperature and diving habits. Listening receivers were deployed underwater along the length of the Kennedy River, and these continually listened out for the devices carried by the crocodile. The receivers had a limited range and would only collect the data when the crocodile swam within a few 100 metres.
The transmitters implanted inside the crocodiles had a battery life of one year, and vast amounts of data were generated from our 27 tagged crocodiles. From the 19 males that were tagged, some maintained a small home range of only few kilometres of river, while others would travel back and forth along the full stretch of the river. They could travel over 60km in a single night, and remain out at sea for a few weeks before returning to the river. Female crocodiles generally moved less distance than the males, and two of our tagged females remained in the same small water hole throughout most of the year. These data sets were very complex and are still undergoing analysis, to look at interactions between individual animals and seasonal differences in movement patterns. We anticipate that many more interesting facts about the private life of estuarine crocodiles will be revealed over the coming months.