title: Effective beam pattern of the Blainville's beaked whale (Mesoplodon densirostris) and implications for passive acoustic monitoring.
abstract: The presence of beaked whales in mass-strandings coincident with navy maneuvers has prompted the development of methods to detect these cryptic animals. Blainville's beaked whales, Mesoplodon densirostris, produce distinctive echolocation clicks during long foraging dives making passive acoustic detection a possibility. However, performance of passive acoustic monitoring depends upon the source level, beam pattern, and clicking behavior of the whales. In this study, clicks recorded from Digital acoustic Tags (DTags) attached to four M. densirostris were linked to simultaneous recordings from an 82-hydrophone bottom-mounted array to derive the source level and beam pattern of the clicks, as steps towards estimating their detectability. The mean estimated on-axis apparent source level for the four whales was 201 dBrms97. The mean 3 dB beamwidth and directivity index, estimated from sequences of clicks directed towards the far-field hydrophones, were 13° and 23 dB, respectively. While searching for prey, Blainville's beaked whales scan their heads horizontally at a mean rate of 3.6°/s over an angular range of some +/-10°. Thus, while the DI indicates a narrow beam, the area of ensonification over a complete foraging dive is large given the combined effects of body and head movements associated with foraging.
authors: Naval Undersea Warfare Center Division Newport, Code 74, 1176 Howell Street, Newport, Rhode Island 02841-1708, USA. jessica.a.shaffer@navy.mil
authors: Jessica Ward
authors: JW
authors: Shaffer
authors: David
authors: D
authors: Moretti
authors: Susan
authors: S
authors: Jarvis
authors: Peter
authors: P
authors: Tyack
authors: Mark
authors: M
authors: Johnson
mesh_terms: D000162:Acoustics / Q000295:instrumentation; D000818:Animals; D004455:Echolocation; D004784:Environmental Monitoring / Q000295:instrumentation / Q000379:methods*; D005260:Female; D019416:Head Movements; D008297:Male; D011235:Predatory Behavior; D012815:Signal Processing, Computer-Assisted; D013018:Sound Spectrography; D013997:Time Factors; D014159:Transducers; D014828:Vocalization, Animal; D014907:Whales / Q000502:physiology* / Q000523:psychology