Highly Directional Sonar Beam of Narwhals (Monodon monoceros) Measured with a Vertical 16 Hydrophone Array

Abstract

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° 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 μPa, with a mean apparent source level of 215 dB pp re 1 μPa. 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.

Spatial and temporal patterns of sound production in East Greenland narwhals

“…Click trains from other (non-tagged) narwhals on the Acousonde record were generally short (a few seconds) and often included rapid changes in amplitude between successive clicks. Both of these factors can be explained by the random movements of whales with respect to the tagged whale, combined with the highly directional echolocation beam of narwhals [ 8 ].…”

“…e ., clicks, burst pulses, and whistles. Technological improvements, such as the ability to record at higher sampling rates, later led to more accurate or complete descriptions of these sounds [ 7 , 8 ]. A few other studies have investigated behavioral aspects of the vocal repertoire, such as the possible use of “signature” calls [ 9 ], the vocal repertoire during the winter [ 10 ], and the possible relationship between call use and behavioral state [ 11 ].…”

tacost: Testing and simulating the performance of acoustic tracking systems

“…Another important aspect affecting all tracking systems is the directionality of the sensors (microphones) and emitted signals (animal vocalisations, calibration speakers). A common problem in acoustic tracking with bats and cetaceans is not being able to track animals because their echolocation calls can be very directional (Matsuta et al 2013;Surlykke, Pedersen, and Jakobsen 2012;Koblitz et al 2016). Implementing sensor and source sound directionality will help assessing how many microphones might be required to successfully track animals in their surroundings, and which array geometries are best able to do so.…”

A multi-year study of narwhal occurrence in the western Fram Strait—detected via passive acoustic monitoring

“…However, because the current study included all narwhal sounds and because the sampling rate of the AURAL was not high enough to capture the highest frequencies used by narwhal (e.g., Møhl et al 1990;Miller et al 1995;Rasmussen et al 2015), it was not possible to confirm specific feeding events. Given the highly directional nature of narwhal echolocation, and high sample rates required to capture such sound (Koblitz et al 2016), it is not clear whether PAM could be used to determine feeding behaviour over annual scales. However, short-term deployments of high-frequency vertical arrays (e.g., Miller et al 1995;Koblitz et al 2016) or joint acoustic and satellite tracking studies (Blackwell et al 2018) in the future might help elucidate narwhal feeding patterns in this offshore habitat.…”

“…Given the highly directional nature of narwhal echolocation, and high sample rates required to capture such sound (Koblitz et al 2016), it is not clear whether PAM could be used to determine feeding behaviour over annual scales. However, short-term deployments of high-frequency vertical arrays (e.g., Miller et al 1995;Koblitz et al 2016) or joint acoustic and satellite tracking studies (Blackwell et al 2018) in the future might help elucidate narwhal feeding patterns in this offshore habitat.…”