Evaluation of Evidence for Altered Behavior and Auditory Deficits in Fishes Due to Human-Generated Noise Sources

Approved for public release; distribution is unlimited. In this study, we have evaluated peer-reviewed publications and contracted reports to provide an overview of what is known about auditory processing by fishes and the behavioral and physiological effects of various noise stimuli as documented by the best and most appropriate studies. We include reviews of work on both cartilaginous (sharks, skates, and rays) and teleost fishes (modern bony fishes) and provide recommendations for research to address remaining issues. Clear responses to human-generated noise have been documented in several marine species of interest. Sharks may be attracted to low-frequency pulsed sounds, which can change their normal distributions and could increase agonistic interactions between individuals and/or species. However, sharks also learn to ignore sounds that are not associated with food, so that any change in distribution or local density should return to normal levels eventually. There are no studies that show long-term avoidance of an ensonified area, even though a shark may exhibit a startle response at the onset of a sudden loud noise. Teleost fishes also have specific behavioral responses to some human-generated noise, in particular to seismic surveys and ship noise. The responses range from brief interruptions in normal behavior, such as a startle response or alarm swimming, to changes in distribution that may last days due to departure from an area of continuing noise (avoidance). Physiological responses to noise include increased levels of stress hormones that can affect the overall health of the individual and changes in hearing. Changes in hearing (threshold shifts) that have been measured to date have been temporary. Fishes have the advantage of being able to produce new sensory cells in the ear, thus being capable of repairing damage induced by loud noises. Unfortunately, the majority of the studies showing temporary threshold shifts have been conducted on hearing-specialist species. The auditory systems of hearing-specialist species respond to the pressure wave of sound due to an accessory air-filled structure that transduces pressure to particle motion, an indirect source of stimulation. Most marine species are not hearing specialists, and their auditory systems are believed to respond best to the direct particle motion of a sound, with little or no sensitivity to the pressure component. Historically, these fish species have been lumped together as " hearing generalists. " The experiments using a hearing generalist have not quantified the particle motion at the fish nor controlled for consistent sound fields …