Diving deep in a foraging hotspot: acoustic insights into bottlenose dolphin dive depths and feeding behaviour
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To exploit resources in their environment, odontocete cetaceans have evolved sophisticated diving abilities to allow effective foraging. However, data on the diving behaviour and underwater foraging behaviour remains limited. This study made use of echolocation clicks and other calls to study the diving behaviour of bottlenose dolphins. Dolphins used the full water column and consistently dived to depths of around 50 m, close to the seabed. However, the majority of their time appeared to be spent within the surface layers of the water column. In addition, by localising calls that have been associated with prey capture events (Janik, Proc R Soc Lond Ser B 267:923–927, 2000a), it appeared that certain forms of feeding behaviour occurred primarily at depths of between 20 and 30 m. Furthermore, data on the depth of clicks made before and after these feeding calls suggested that during the minute before the calls, dolphins were consistently diving from the surface to depths close to the seabed, and were subsequently returning to the surface after the calls. This passive acoustic technique proved an accurate method for studying the depth distribution of dolphin vocalisations. By exploiting the natural sounds made by these wild odontocetes, this investigation provided a previously unavailable perspective on the the 3D nature of bottlenose dolphins foraging behaviour. It confirmed that while the dolphins spent the majority of time close to the surface, the full water column was exploited during foraging events.
KeywordsAtlantic Salmon Depth Distribution Hydrophone Bottlenose Dolphin Prey Capture
This work was supported by Talisman Energy (UK) Ltd., the Cromarty Firth Port Authority, Ross and Cromarty Enterprise, the Whale and Dolphin Conservation Society and the Caledonian Society of Sheffield. We thank all those who spent long hours in the field assisting with data collection, in particular Lindsay Tufft, Stuart Middlemas and Tim Barton. Thanks also to Vincent Janik for advice and guidance throughout the study.
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