Current research is aiming to verify a process known as sonar termination. It may be that sonar termination is the main cause of dysfunction of cetacean echolocation during a mass stranding of apparently healthy toothed cetaceans (odontoceti). Sonar termination occurs when a pod of cetaceans emits an echolocation signal toward a coast with a gently sloping shoreline and under certain meteorological conditions a reflection will not be detected. The reflection contains important information about the location and features of the shoreline. The lack of reflections received from the coast would appear to be a ‘deaf spot’ to the cetaceans, analogous to the human ‘blind spot’. The coast may appear as thick 'fog' to the pod of cetaceans and may induce a navigational error.

The research is in part collaboration with the Acoustic Research Laboratory, National University of Singapore.

In establishing a cause an effect mechanism the research can be divide into four areas: Cetacean Dynamic Range, Coastal Shallow Water Acoustics, Bubble Acoustics and Acoustic Spread Spectrum Signalling

Cetacean Dynamic Range
The research is establishing dynamic range responses of a variety of stranding species. The cetacean dynamic range is the difference between the hearing threshold and the emission thresholds. A cetacean’s hearing and emission thresholds are variable with frequency. It will then hear the constituent frequencies in its echoes differently. The establishment of a cetacean dynamic range will then give a good indicator of how much an echo can attenuate in seawater before it is no longer detectable by the cetacean.
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Coastal shallow water acoustics
Past studies concerning the incidence of mass cetacean strandings suggest that cetaceans are vulnerable to stranding in the presence of gently sloping shore of low angle. These shorelines are often of an angle less than 0.50. An echolocation signal will then suffer many reflections off the sea surface and sea bottom before returning to the cetacean . In a coastal environment a signal suffers a loss of energy for each reflection and accumulates a loss of energy over the total propagation distance resulting in sonar termination. The research being conducted is currently examining the propagation of sound in very shallow water sloping costal environments.
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Bubble Acoustics
The presence of small bubbles (microbubbles) spread throughout the water column and surface layer can affect cetacean echolocation. Bubbles are created at the water surface by rain impact and surface waves. The bubbles are then spread throughout the water column by tidal and wave motion. Microbubbles will take a long time to rise to the surface of the water because of their size. This can lead to the presence of bubbles long after the onset of rain or rough weather. Each bubble within the water column will absorb acoustic energy from an incident whale or dolphin echolocation signal. This process is known as resonant bubble absorption, , where the size of a bubble determines which frequency within an echolocation signal it will absorb. The combination of scattering and absorption of an acoustic wave’s energy by an ensemble of microbubbles can have a drastic effect on cetacean echolocation over a long distance and is a major contributor to sonar termination.
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Western Australian Mass Cetacean Stranding Database
Additional to the research establishing a bioacoustic mechanism for mass cetacean strandings, a Western Australian cetacean stranding database is being collated. The definition of a mass stranding for this database is when 4 or more cetaceans strand.
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