ORIENTATION OF BLACKTIP SHARKS (CARCHARHINUS LIMBATUS) TO UNDERWATER SOUND

Sharks respond to low frequency pulsed sounds but are documented to lack the capacity to detect these sounds beyond the acoustic near field. The purpose of my study was to quantify the distance blacktip sharks (Carcharhinus limbatus) oriented to sound stimuli, and determine if responses occurred in the far field. Using an aerial drone and underwater speaker, C. limbatus were filmed responding to sound stimuli (100 – 200 Hz; 200 – 400 Hz; and 400 – 800 Hz). Upon detection, C. limbatus elicited a 20 – 160° turn from the speaker, and rapidly swam away. Sharks responded to all frequencies from at least 62 m, and 71.6% of all responses (n = 209) occurred in the far field. This indicates that blacktip sharks can detect and orient away from a sound stimulus at distances that extend beyond the acoustic near field, which suggests that they are not detecting sound using the inner ear otoconia.