The metrics that regulators use for assessing seismic exploration and marine life have been reviewed. In particular, the airgun source levels and what they really mean have been clarified, and common pitfalls and misunderstandings of the acoustics have been explained.

The scientific background of basic bioacoustics has been reviewed, including the definitions of the various established metrics. The thresholds for injury and disturbance are explained along with how to calculate them, for example, sound exposure level (SEL) and root mean square (RMS) levels.

The important (and often misunderstood) conceptual difference between the source level, which the airgun array emits, and the received level, which the animal experiences, has been clarified to provide a clear understanding of the acoustics and relationships of the sound levels to avoid further confusion and misunderstanding among the public and the news media.

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