Transmission beam characteristics of a Risso's dolphin (Grampus griseus)

Abstract

The echolocation system of the Risso's dolphin (Grampus griseus) remains poorly studied compared to other odontocete species. In this study, echolocation signals were recorded from a stationary Risso's dolphin with an array of 16 hydrophones and the two-dimensional beam shape was explored using frequency-dependent amplitude plots. Click source parameters were similar to those already described for this species. Centroid frequency of click signals increased with increasing sound pressure level, while the beamwidth decreased with increasing center frequency. Analysis revealed primarily single-lobed, and occasionally vertically dual-lobed, beam shapes. Overall beam directivity was found to be greater than that of the harbor porpoise, bottlenose dolphin, and a false killer whale. The relationship between frequency content, beam directivity, and head size for this Risso's dolphin deviated from the trend described for other species. These are the first reported measurements of echolocation beam shape and directivity in G. griseus.

Review of Underwater and In-Air Sounds Emitted by Australian and Antarctic Marine Mammals

“…Burst-pulse sounds off NSW covered a frequency band from 1 to above 22 kHz and lasted 2-13 s [179]. Ani- [181][182][183][184][185]. Off NSW, click trains were longer, up to 24 s [179].…”

Delphinid echolocation click detection probability on near-seafloor sensors

“…Sources were assigned on-axis source levels and beam directivities drawn from distributions defined by values reported in the literature (Fish and Turl, 1976;Rasmussen et al, 2002;Au and Herzing, 2003;Rasmussen et al, 2004;Au et al, 2012a;Smith et al, 2016). Beam directivity was drawn from a uniform distribution and held constant in each simulation, but varied between simulations.…”

“…Risso's dolphins are larger, with body lengths up to 3.8 m, average dive depths less than 50 m, and maximum dive depths near 500 m (Wells et al, 2009, though the study involved a single rehabilitated animal released into the wild, and hence these data may not reflect the true dive depth distribution of the species). On-axis source levels for Risso's dolphins are expected to be higher than for shallow-divers, around 220 dB pp re 1 lPa @ 1 m (Fish and Turl, 1976;Madsen et al, 2004;Smith et al, 2016). Both species execute dives approximately 5 to 10 min long, and spend more time near the sea surface than deeper diving odontocetes, for instance sperm whales and beaked whales (Scott and Chivers, 2009;Wells et al, 2009;Hildebrand et al, 2015).…”

Transmission beam pattern and dynamics of a spinner dolphin (Stenella longirostris)

“…This arrangement resulted in an "outer" and "inner" ring of hydrophones. This configuration has successfully been utilized to investigate echolocation characteristics in a number of previous studies (e.g., Ibsen et al, 2012;Kloepper et al, 2012;Smith et al, 2016). Each hydrophone occupied an independent channel and was amplified by 20 dB with a custom-built 16 channel amplifier before being sent to two National Instruments DAQmx PCI-6133 analog to digital (A/D) boards (National Instruments, Austin, TX).…”

“…The ensonification of a larger area at close range decreases the likelihood of prey escaping perpendicular to the animal's direction of approach by falling outside the acoustic field of view (Wisniewska et al, 2015). Comparison between species indicates that some odontocetes utilize different click source characteristics that are adapted to suit specific environments (i.e., shallow, acoustically complex rivers versus the deep, open ocean), yet maintain a comparable beam directivity (Jensen et al, 2013;Ladegaard et al, 2015;Smith et al, 2016). Therefore, it is notable that despite the wide range of body sizes and click spectral characteristics across the suborder, beam directivity is similarly high and comparable in all odontocete species studied to date.…”