Aversive Conditioning of Larger Estuarine Crocodiles (Crocodylus porosus) and the Remote Deployment of Transmitters

Aversive conditioning has been used with terrestrial predators to reduce conflict with humans by changing predator behavior or moving them away. Proving the effectiveness of this management tool for cryptic animals, however, can be challenging. In this study, we assessed the interaction between presence and sightability in Estuarine Crocodiles (Crocodylus porosus) after a period of aversive conditioning. Crocodiles > 2 m in length were subjected to aversive conditioning using two non-lethal beanbags fired from a 12-gauge shotgun. Traditional night-time surveys were conducted prior to and after aversive conditioning to determine any changes in crocodile sightability. To detect crocodiles underwater and their movement, we attached acoustic transmitters with a hand-held pole harpoon, which were monitored with an acoustic receiver array. This technique allowed for transmitter attachment without the need for capture. Immediately after aversive conditioning, there was a significant reduction in the sightability of larger Estuarine Crocodiles (> 2 m) using traditional spotlight survey, and a detectable change in the movement patterns of two of the three tagged individuals. The two tagged crocodiles resumed normal movement patterns soon after (42 h, 15 d) and no crocodiles left the area in response to the treatment. Aversive conditioning has limited use in moving crocodiles away from a discrete area; however, it did have a short-term impact on crocodile behavior and crocodiles became more challenging to detect by traditional spotlight survey. The reduced sightability may indicate an increased wariness of people, which in some circumstances may be an acceptable outcome for management.