European and US scientists believe they have discovered a revolutionary way of understanding the effects of high-intensity sounds on marine mammals including whales and dolphins. Increased shipping, petroleum exploration and production, and military exercises have amplified noise levels in the ocean in recent years, according to the researchers. As much of their work focused on the use of sonar, they hope that naval forces will use their software in the future in order to decide when and where it is safe to use sonar. The findings were recently published in the Public Library of Sciences (PLoS) ONE journal.
The researchers from the University of California, San Diego (UCSD) in the US and Kolmården Zoo in Sweden have developed a method of monitoring the effects of sound on marine mammals that integrates advanced computing, X-ray CT (computerised tomography) scanners, and modern computational methods.
This technology allows scientists to simulate sounds propagated through the virtual specimen and reveal the interactions between the sound and the mammal. It also offers them the opportunity to study a three-dimensional (3D) picture of the inside of the head of those mammals, such as Cuvier's beaked whale, which is known to be affected by noise pollution such as sonar.
'Our numerical analysis software can be used to conduct basic research into the mechanism of sound production and hearing in these whales, simulate exposure at sound pressure levels that would be impossible on live animals, or assess various mitigation strategies,' explained Professor Petr Krysl, a UC San Diego structural engineer who developed the computational methods for this research. 'We believe that our research can enable us to understand, and eventually reduce, the potential negative effects of high intensity sound on marine organisms,' he added.
'Humans introduce considerable amounts of sound and noise into the oceans of the world' and this can cause serious problems as 'many marine organisms make acute use of sound for their primary sensory modality because light penetrates so poorly into water', Dr Krysl explained. He pointed out that the researchers focused their work on the Cuvier's beaked whale because 'some have stranded and died in the presence of navy sonar' and 'the discoveries we made with regard to the mechanisms of hearing in the beaked whale also apply to the bottlenose dolphin and, we suspect, to all types of toothed whales and perhaps other marine mammals.'
Dr Krysl insisted that the project 'significantly advances our knowledge of the basic biology of marine mammals' since 'hearing is an essential sensory ability for life under water where sound is used for hunting, navigating, and social interaction'. However, he added that the team's research had particular significance concerning the navy's need to use sonar.
According to the UCSD researcher, the navy needed to be able to answer questions such as 'is sonar safe to use and under what conditions' and 'can we minimise the impact on marine life and how'. He insisted that this was 'not possible without a basic understanding of biology and acoustics of the ocean inhabitants' and hence the importance of his research.
The study was partly sponsored by the US Chief of Naval Operations (CNO) and Dr Krysl said his team would continue its 'current line of research on the beaked whale and conduct validation experiments with the bottlenose dolphin'. He added that it also planed 'additional modeling refinements that will allow us to investigate the entire sound pathway from the sea water to the entrance to the cochlea' and said that these projects 'address several primary objectives in the navy's plan to understand demographics, acoustic exposure thresholds, and mitigation strategies for living marine resources'.
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