Dolphins Hush When Killer Whales Lurk

Research has suggested killer whale predation may affect cetacean vocal behavior; however, few data exist to test this hypothesis. Data collected for 19609 km of visual and acoustic shipboard surveys in the tropical Pacific Ocean were examined to determine if changes in dolphin vocal activity could be attributed to the presence of killer whales.

These surveys included 346detections of three highly vocal dolphin species (genus Stenella),whose whistles can be detected at ranges over 4.6 km. Random forest analysis was used to model vocal behavior based on sea state, visibility, fog rain, thermo cline temperature depth, mixed layer depth, chlorophyll, distance to shore, species, group size, perpendicular distance, and presence of killer whales.

The results show that the presence of killer whales significantly inhibited vocal activity in these tropical dolphins (p = 0.02). Killer whales are rare in the tropics, and this disruption in communication may not have a significant impact on interactions necessary for survival. However, in temperate climates, where increased productivity supports a greater abundance of killer whales, this interruption in communication may have a greater impact. The lower incidence of whistling dolphins in temperate waters may be related to the greater abundance of killer whales in these areas.