Temporary Threshold Shift as a Measure of Anthropogenic Sound Effect on Fishes

Vertebrates exposed to intense or long-duration loud sounds often show a temporary loss of hearing (temporary threshold shift, TTS). TTS has been examined in a number of fish species after exposure to white noise, pure tones, and impulsive sources, leading to the concern that TTS has the potential to impact fitness and survival of fishes exposed to anthropogenic sound. This chapter focuses on whether TTS is of real concern with regard to developing criteria for sound exposure for fishes. It starts with a review of the literature on TTS and ear damage as a result of exposure to various sounds and shows that the data are highly variable and that most of the significant TTS occurs in species that are defined as having specializations to enhance hearing sensitivity. The chapter then argues that TTS is not likely for free-swimming fishes since they can leave the areas of the most intense sounds and that most fish in a population exposed to such sounds will receive levels that are well below those that could produce TTS. At the same time, since data are limited, it is proposed that further studies using approaches that allow comparison between species and sounds be conducted.