Possible limitations of dolphin echolocation: a simulation study based on a cross-modal matching experiment.

Dolphins use their biosonar to discriminate objects with different features through the returning echoes. Cross-modal matching experiments were conducted with a resident bottlenose dolphin (Tursiops aduncus). Four types of objects composed of different materials (water-filled PVC pipes, air-filled PVC pipes, foam ball arrays, and PVC pipes wrapped in closed-cell foam) were used in the experiments, respectively.

Variations in received levels on a sound and movement tag on a singing humpback whale: Implications for caller identification.

Bio-logging devices are advancing the understanding of marine animal behavior, but linking sound production and behavior of individual baleen whales is still unreliable. Tag placement potentially within the near field of the sound source creates uncertainty about how tagged animal sounds will register on recorders. This study used data from a tagged singing humpback whale to evaluate this question of how sound levels present on a tag when calls are produced by a tagged animal.

Modeling of the near to far acoustic fields of an echolocating bottlenose dolphin and harbor porpoise.

Echolocation signals emitted by odontocetes can be roughly classified into three broad categories: broadband echolocation signals, narrowband high-frequency echolocation signals, and frequency modulated clicks. Previous measurements of broadband echolocation signal propagation in the bottlenose dolphin (Tursiops truncatus) did not find any evidence of focusing as the signals travel from the near-field to far-field. Finite element analysis (FEA) of high-resolution computed tomography scan data was used to examine signal propagation of broadband echolocation signals of dolphins and narrowband echolocation signals of porpoises.

Acoustic reflectivity of a harbor porpoise (Phocoena phocoena).

Acoustic backscatter measurements were conducted on a stationary harbor porpoise (Phocoena phocoena) under controlled conditions. The measurements were made with the porpoise in the broadside aspect using three different types of signals: (1) a 475 μs linear frequency-modulated (FM) pulse with a frequency range from 23 to 160 kHz; (2) a simulated bottlenose dolphin (Tursiops "truncates") click with a peak frequency of 120 kHz; and (3) a simulated killer whale (Orcinus orca) click with a peak frequency of 60 kHz. The measurement with the FM pulse indicated that the mean target strength at the broadside aspect decreased from -26 to -50 dB as the frequency increased from 23 to 120 kHz in a nearly linear fashion (on a logarithm plot).

Finite element simulation of broadband biosonar signal propagation in the near- and far-field of an echolocating Atlantic bottlenose dolphin (Tursiops truncatus).

Bottlenose dolphins project broadband echolocation signals for detecting and locating prey and predators, and for spatial orientation. There are many unknowns concerning the specifics of biosonar signal production and propagation in the head of dolphins and this manuscript represents an effort to address this topic. A two-dimensional finite element model was constructed using high resolution CT scan data.

Combining passive acoustics and imaging sonar techniques to study sperm whales' foraging strategies.

Sperm whales forage in the deep ocean, hunting for squid. An innovative approach for the study of sperm whale foraging behavior and habitat selection is reported in this letter. A DIDSON imaging sonar mounted on a profiler with a conductivity, temperature, and depth sensor was used to count and measure potential prey in the deep ocean during sperm whales' acoustical foraging encounters in Hawaii.

Application of dual frequency identification sonar for the study of deep diving odontocetes prey fields.

A dual frequency identification sonar was used to estimate density and size of potential deep diving odontocetes' prey in deep sea scattering layers in Hawaii. Size distributions data showed a bimodal pattern, with a population of data above the 50 cm of length, possibly big squids, and a population of data below 50 cm, mainly micronekton. The number of animals bigger than 50 cm was correlated with the length of the peak of the frequency distribution.

Biosonar signal propagation in the harbor porpoise's (Phocoena phocoena) head: The role of various structures in the formation of the vertical beam.

Harbor porpoises (Phocoena phocoena) use narrow band echolocation signals for detecting and locating prey and for spatial orientation. In this study, acoustic impedance values of tissues in the porpoise's head were calculated from computer tomography (CT) scan and the corresponding Hounsfield Units. A two-dimensional finite element model of the acoustic impedance was constructed based on CT scan data to simulate the acoustic propagation through the animal's head.

Measurements of humpback whale song sound levels received by a calf in association with a singer.

Male humpback whales produce loud "songs" on the wintering grounds and some sing while escorting mother-calf pairs, exposing them to near-continuous sounds at close proximity. An Acousonde acoustic and movement recording tag deployed on a calf off Maui, Hawaii captured sounds produced by a singing male escort. Root-mean-square received levels ranged from 126 to 158 dB re 1 μPa.

Temporal and spatial variation of beaked and sperm whales foraging activity in Hawai'i, as determined with passive acoustics.

Beaked and sperm whales are top predators living in the waters off the Kona coast of Hawai'i. Temporal and spatial analyses of the foraging activity of these two species were studied with passive acoustics techniques. Three passive acoustics recorders moored to the ocean floor were used to monitor the foraging activity of these whales in three locations along the Kona coast of the island of Hawaii.

Dynamics of biosonar signals in free-swimming and stationary dolphins: The role of source levels on the characteristics of the signals.

The biosonar signals of two free-swimming Atlantic bottlenose dolphins performing a complex sonar search for a bottom target in San Diego Bay were compared with the biosonar signals of a dolphin performing a target discrimination task in a net pen in the same bay. A bite-plate device carried by the free-swimming dolphins supported a hydrophone that extended directly in front of the dolphin. A biosonar measuring tool attached to the bite plate measured the outgoing biosonar signals while the dolphins conducted sonar searches.

The role of various structures in the head on the formation of the biosonar beam of the baiji (Lipotes vexillifer).

The relative role of the various structures in the head of the baiji (Lipotes vexillifer) is examined. A finite element approach was applied to numerically simulate the acoustic propagation through a dolphin's head to examine the relative role of the skull, air sacs, and melon in the formation of the biosonar beam in the vertical plane. The beam pattern obtained with the whole head in place is compared with the beam pattern when the air sac is removed and the other structures (skull and melon) are in place, with only the skull removed, and finally with only the melon removed.

Apparent source levels and active communication space of whistles of free-ranging Indo-Pacific humpback dolphins (Sousa chinensis) in the Pearl River Estuary and Beibu Gulf, China.

Background. Knowledge of species-specific vocalization characteristics and their associated active communication space, the effective range over which a communication signal can be detected by a conspecific, is critical for understanding the impacts of underwater acoustic pollution, as well as other threats. Methods.

Radiated Sound of a High-Speed Water-Jet-Propelled Transportation Vessel.

The radiated noise from a high-speed water-jet-propelled catamaran was measured for catamaran speeds of 12, 24, and 37 kn. The radiated noise increased with catamaran speed, although the shape of the noise spectrum was similar for all speeds and measuring hydrophone depth. The spectra peaked at ~200 Hz and dropped off continuously at higher frequencies.

Discrimination of frequency-modulated Baleen whale downsweep calls with overlapping frequencies.

Automatic classification of fin, sei, and blue whale frequency modulated downsweeps has been a challenging task for bioacousticians. These calls overlap in frequency range and have similar time durations. The traditional spectrogram methodology, the Short Time Fourier Transform, tends to be ineffective because of the large temporal ambiguities needed to achieve the necessary frequency resolution to study the fine time-frequency (TF) structures.

Acoustic detection of biosonar activity of deep diving odontocetes at Josephine Seamount High Seas Marine Protected Area.

The temporal occurrence of deep diving cetaceans in the Josephine Seamount High Seas Marine Protected Area (JSHSMPA), south-west Portugal, was monitored using a passive acoustic recorder. The recorder was deployed on 13 May 2010 at a depth of 814 m during the North Atlantic Treaty Organization Centre for Maritime Research and Experimentation cruise "Sirena10" and recovered on 6 June 2010. The recorder was programmed to record 40 s of data every 2 min.

Acoustic property reconstruction of a neonate Yangtze finless porpoise's (Neophocaena asiaeorientalis) head based on CT imaging.

The reconstruction of the acoustic properties of a neonate finless porpoise's head was performed using X-ray computed tomography (CT). The head of the deceased neonate porpoise was also segmented across the body axis and cut into slices. The averaged sound velocity and density were measured, and the Hounsfield units (HU) of the corresponding slices were obtained from computed tomography scanning.

Temporal signal processing of dolphin biosonar echoes from salmon prey.

Killer whales project short broadband biosonar clicks. The broadband nature of the clicks provides good temporal resolution of echo highlights and allows for the discriminations of salmon prey. The echoes contain many highlights as the signals reflect off different surfaces and parts of the fish body and swim bladder.

Simulation of ultrasound beam formation of baiji (Lipotes vexillifer) with a finite element model.

The baiji (Lipotes vexillifer) of the Yangtze River possesses a sophisticated biosonar system. In this study, a finite element approach was used to numerically investigate the propagation of acoustic waves through the head of the Yangtze River dolphin, which possesses an inhomogeneous and complex structure. The acoustic intensity distribution predicted from models with and without the melon and/or skull showed that the emitted sound beam was narrow and formed a highly directed acoustic beam, and the skull and melon significantly enhanced the directional characteristics of the emitted sound.

Dolphin biosonar target detection in noise: wrap up of a past experiment.

The target detection capability of bottlenose dolphins in the presence of artificial masking noise was first studied by Au and Penner [J. Acoust. Soc.

Presence and seasonal variation of deep diving foraging odontocetes around Kauai, Hawaii using remote autonomous acoustic recorders.

Ecological acoustic recorders (EARs) were moored off the bottom in relatively deep depths (609-710 m) at five locations around the island of Kauai. Initially, the EARs had an analog-to-digital sample rate of 64 kHz with 30-s recordings every 5 min. After the second deployment the sampling rate was increased to 80 kHz in order to better record beaked whale biosonar signals.

Nighttime foraging by deep diving echolocating odontocetes off the Hawaiian islands of Kauai and Ni'ihau as determined by passive acoustic monitors.

Remote autonomous ecological acoustic recorders (EARs) were deployed in deep waters at five locations around the island of Kauai and one in waters off Ni'ihau in the main Hawaiian island chain. The EARs were moored to the bottom at depths between 400 and 800 m. The data acquisition sampling rate was 80 kHz and acoustic signals were recorded for 30 s every 5 min to conserve battery power and disk space.

Discrimination of phase altered targets by an echolocating Atlantic bottlenose dolphin.

Sensitivity of echolocating dolphins to phase changes within echoes may be a vital piece of information when constructing echolocation models. Previous experiments have yielded ambiguous results leaving it unclear what cues might have been used by passively listening dolphins to discriminate between different phase altered signals. This study used a phantom echo generator to produce computer controlled echoes.

Automated extraction and classification of time-frequency contours in humpback vocalizations.

A time-frequency contour extraction and classification algorithm was created to analyze humpback whale vocalizations. The algorithm automatically extracted contours of whale vocalization units by searching for gray-level discontinuities in the spectrogram images. The unit-to-unit similarity was quantified by cross-correlating the contour lines.

A non-spectrogram-correlation method of automatically detecting minke whale boings.

This letter introduces an algorithm for automatic detection of minke whale boing sounds. This method searches for frequency features of boings without calculating the continuous spectrogram of the data, thereby reducing computational time. The detector has been tested on 8 h of acoustic data recorded at the Station ALOHA Cabled Observatory in March 2007.