Highly directional sonar beam of narwhals (Monodon monoceros) measured with a vertical 16 hydrophone array

• Published in: PLOS ONE
• Main Authors: Koblitz, J., Stilz, P., Rasmussen, M., Laidre, K.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: 2016
• Subjects: Arctic; Baffin Bay; Greenland; Baffin; Monodon monoceros; narwhal*; Sea ice; toothed whales
• Online Access: http://hdl.handle.net/21.11116/0000-0005-A4EA-A

Recordings of narwhal (Monodon monoceros) echolocation signals were made using a linear 16 hydrophone array in the pack ice of Baffin Bay, West Greenland in 2013 at eleven sites. An average-3 dB beam width of 5.0 degrees makes the narwhal click the most directional biosonar signal reported for any species to date. The beam shows a dorsal-ventral asymmetry with a narrower beam above the beam axis. This may be an evolutionary advantage for toothed whales to reduce echoes from the water surface or sea ice surface. Source level measurements show narwhal click intensities of up to 222 dB pp re 1 mu Pa, with a mean apparent source level of 215 dB pp re 1 mu Pa. During ascents and descents the narwhals perform scanning in the vertical plane with their sonar beam. This study provides valuable information for reference sonar parameters of narwhals and for the use of acoustic monitoring in the Arctic.