Categorizing the Effects of Anthropogenic Noise on Aquatic Life

Categorizing the effects of anthropogenic noise on aquatic life according to the mechanisms of effects could help regulators with their decision-making. This chapter proposes categorizing effects into those that likely scale directly with sound level and those that are influenced by many other factors and thus may scale inconsistently with sound level. The first proposed category of mechanisms is physical (direct effects of sound waves on biological tissues or interference of sound during detection). Physical mechanisms could lead to injuries, temporary hearing loss, and masking. The severity of responses with physical mechanisms is likely to scale with received sound level. The second proposed category of mechanisms is perceptual (following sensory experience of sound waves). Perceptual mechanisms, such as stress and distraction, could lead to changes in physiology, cognition, and behavior. The severity of responses with perceptual mechanisms depends on the receiver’s external context (e.g., other environmental stressors), current behavioral context (e.g., feeding or breeding), and internal state (e.g., hungry, distressed), as well as the received sound level. Threshold values for noise criteria where effects are driven by perceptual mechanisms will be challenging to establish due to the large number of interacting factors. However, regulating noise is an urgent priority as mortality can arise from effects with perceptual mechanisms, for example from a failure to exhibit a normal anti-predator response. Pragmatic policymaking for anthropogenic noise could consider area-based and time-based limits until sufficient information for effective level-based limits is available.