One of the most tenacious challenges in establishing mitigation guidelines for marine animal noise exposure is the lack of a clear numeric threshold that regulators can unambiguously use. There is no “55 miles per hour” in marine bioacoustics because the physical environment of the ocean and the biological adaptations to habitat are extremely complex.
There is a well known need for a marine “Noise Exposure Criteria” such as is used in contemporary architectural practice. But architectural noise criteria have been established over the years through empirical assessment of how humans use and inhabit built environments, and are predicated on our priorities of speech intelligibility, annoyance, and physiological damage. And while noise criteria for animal enclosures are beginning to appear, these criteria are for domesticated animals with behaviors that we know and understand.
The range of species and adaptations in the ocean are much more complex. Some animals live in extremely noisy environments – such as intertidal zones and Arctic ice flows. Some animals need to perceive highly detailed sound characteristics, others only need to hear rudimentary thuds and bumps; some animals use sound to see and navigate, others only to threaten or court.
Given the vast repertoire of bioacoustic adaptations found in the ocean, trying to find one number or one measurement that expresses conflicting or compromising noise exposures would be impossible. But as our understanding of animal interactions with their habitat unfolds we can begin to find ways to express these interactions in well defined terms and quantitative expressions.