Index of content:
Volume 120, Issue 4, October 2006
- BIOACOUSTICS 
120(2006); http://dx.doi.org/10.1121/1.2258832View Description Hide Description
The Florida manatee is regularly exposed to high volumes of vessel traffic and other human-related noise because of its coastal distribution. Quantifying specific aspects of the manatee’s acoustic environment will allow for a better understanding of how these animals respond to both natural and human-induced changes in their environment. Transmission loss measurements were made in 24 sampling sites that were chosen based on the frequency of manatee presence. The Monterey-Miami Parabolic Equation model was used to relate environmental parameters to transmission loss in two extremely shallow water environments: seagrass beds and dredged habitats. Model accuracy was verified by field tests at all modeled sites. Results indicated that high-use grassbeds have higher levels of transmission loss for frequencies above compared to low-use sites of equal food species composition and density. This also happens to be the range of most efficient sound propagation inside the grassbed habitat and includes the dominant frequencies of manateevocalizations. The acoustic environment may play a more important role in manatee grassbed selection than seagrass coverage or species composition, as linear regression analysis showed no significant correlation between usage and either total grass coverage, individual species coverage, or aerial pattern.
Simulating the effect of high-intensity sound on cetaceans: Modeling approach and a case study for Cuvier’s beaked whale (Ziphius cavirostris)120(2006); http://dx.doi.org/10.1121/1.2257988View Description Hide Description
A finite element model is formulated to study the steady-state vibration response of the anatomy of a whale (Cetacea) submerged in seawater. The anatomy was reconstructed from a combination of two-dimensional (2D) computed tomography(CT) scan images, identification of Hounsfield units with tissue types, and mapping of mechanical properties. A partial differential equation model describes the motion of the tissues within a Lagrangean framework. The computational model was applied to the study of the response of the tissues within the head of a neonate Cuvier’s beaked whale Ziphius cavirostris. The characteristics of the sound stimulus was a continuous wave excitation at and re: received level, incident as a plane wave. We model the beaked whale tissues embedded within a volume of seawater. To account for the finite dimensions of the computational volume, we increased the damping for viscous shear stresses within the water volume, in an attempt to reduce the contribution of waves reflected from the boundaries of the computational box. The mechanical response of the tissues was simulated including: strain amplitude; dissipated power; and pressure. The tissues are not likely to suffer direct mechanical or thermal damage, within the range of parameters tested.
St. Lawrence blue whale vocalizations revisited: Characterization of calls detected from 1998 to 2001120(2006); http://dx.doi.org/10.1121/1.2335676View Description Hide Description
From 1998 to 2001, of acoustic recordings were made in the presence of the well-studied St. Lawrence population of blue whales, using a calibrated omnidirectional hydrophone [flat response from ] suspended at depth from a surface isolation buoy. The primary field site for this study was the estuary region of the St. Lawrence River (Québec, Canada), with most recordings made between mid-August and late October. During the recordings, detailed field notes were taken on all cetaceans within sight. Characterization of the more than 1000 blue whale calls detected during this study revealed that the St. Lawrence repertoire is much more extensive than previously reported. Three infrasonic and three audible range call types were detected, with much time/frequency variation seen within each type. Further variation is seen in the form of call segmentation, which appears (through examination of Lloyd’s Mirror interference effects) to be controlled at least partially by the whales. Although St. Lawrence blue whale call characteristics are similar to those of the North Atlantic, comparisons of phrase composition and spacing among studies suggest the possibility of population dialects within the North Atlantic.
120(2006); http://dx.doi.org/10.1121/1.2335577View Description Hide Description
A three-dimensional localization method for tracking sperm whales with as few as one sensor is demonstrated. Based on ray-trace acoustic propagationmodeling, the technique exploits multipath arrival information from recorded sperm whale clicks and can account for waveguide propagation physics like interaction with range-dependent bathymetry and ray refraction. It also does not require ray identification (i.e., direct, surface reflected) while utilizing individual ray arrival information, simplifying automation efforts. The algorithm compares the arrival pattern from a sperm whale click to range-, depth-, and azimuth-dependent modeled arrival patterns in order to estimate whale location. With sufficient knowledge of azimuthally dependent bathymetry, a three-dimensional track of whale motion can be obtained using data from a single hydrophone. Tracking is demonstrated using data from acoustic recorders attached to fishing anchor lines off southeast Alaska as part of efforts to study sperm whale depredation of fishing operations. Several tracks of whale activity using real data from one or two hydrophones have been created, and three are provided to demonstrate the method, including one simultaneous visual and acoustic localization of a sperm whale actively clicking while surfaced. The tracks also suggest that whales’ foraging is shallower in the presence of a longline haul than without.
Quantitative measures of air-gun pulses recorded on sperm whales (Physeter macrocephalus) using acoustic tags during controlled exposure experiments120(2006); http://dx.doi.org/10.1121/1.2229287View Description Hide Description
The widespread use of powerful, low-frequency air-gun pulses for seismic seabed exploration has raised concern about their potential negative effects on marine wildlife. Here, we quantify the sound exposure levels recorded on acoustic tags attached to eight sperm whales at ranges between 1.4 and from controlled air-gun array sources operated in the Gulf of Mexico. Due to multipath propagation, the animals were exposed to multiple sound pulses during each firing of the array with received levels of analyzed pulses falling between re. (pp) [ re. (rms) and re. ] after compensation for hearing sensitivity using the -weighting. Received levels varied widely with range and depth of the exposed animal precluding reliable estimation of exposure zones based on simple geometric spreading laws. When whales were close to the surface, the first arrivals of air-gun pulses contained most energy between 0.3 and , a frequency range well beyond the normal frequencies of interest in seismic exploration. Therefore air-gun arrays can generate significant sound energy at frequencies many octaves higher than the frequencies of interest for seismic exploration, which increases concern of the potential impact on odontocetes with poor low frequency hearing.