Sonar based enrichment and detection of hidden fish by bottlenose dolphins (Tursiops truncatus)

Abstract: Dolphins at Kolmården dolphinarium were given a set of 20 floating fish hides, in order to simulate aforaging situation. The idea was to motivate the dolphins to use echolocation, in order to differentiatebetween hides which contained fish and hides that were empty. The dolphins would access the fish hidesfor 20-minute sessions five days per week, during a total period of five weeks. The results indicated thattheir interest in the fish hides was maintained over the entire study period for all individuals, and thisinterest did not correlate with age. However, older dolphins seemed more prone to solely inspect, possiblyby using echolocation aimed towards the fish hides than to physically interact with them. Neither was theirinterest affected by the dolphins’ pre-session activities. However, not all dolphins seemed interested in fishunless given to them by care takers. Thus, some dolphins were likely less motivated in solving theecholocation task. As a pod, the dolphins’ interest in this innovative enrichment was maintained over time,and the plasticity of these fish hides would suggest a range of different setups for the future. However,when analysing the potential use of echolocation cues, theoretical calculations of the target strengthdifferences between filled and empty fish hides, together with data on the physical interactions with them,suggested that the dolphins did not use sonar cues, but resorted to more or less random manipulation of thefish hides in order to eject the fish.