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Fig. 1. Summary of bottlenose dolphin and white whale temporary threshold shift (TTS) experimental data showing relationship between level and duration of expo- sures that produce measurable TTS adapted from Fig. 9 of Finneran et al. (2005). Data are from Finneran et al. (2000 and 2002) (triangles–explosion simulator and watergun sources), Schlundt et al. (2000) (squares–pure tones), Nachtigall et al. (2003 and 2004) (diamonds–band-limited white noise), and Finneran et al. (2005) (circles–3 kHz pure tones). Closed symbols represent exposures where TTS was observed and open symbols indicate exposures that did not produce a measurable TTS. Solid lines represent an equal-energy condition.
the latest reports published by the NRC (2003, 2005). These reports were researched and written by balanced study panels of scientific experts and anonymously peer-reviewed prior to publication. The proceedings of an International Conference on the Effects of Noise on Aquatic Life, held August 2007 in Nyborg, Denmark—the first to include both marine mammals and fish—will soon be published in the journal, Bioacoustics. So the following provides only a brief summary of past find- ings and an update on research activity since 2005.
Probably the most progress in any area during the last 15 years has been achieved in quantifying the effects of sound exposure on hearing in dolphins, white whales, seals, sea lions, and several species of fish. Exposure to excessive sound energy may reduce hearing sensitivity by producing an ele- vated hearing threshold, also known as a threshold shift. If the hearing threshold returns to the pre-exposure level after a period of time, the shift is a temporary threshold shift or TTS. If the threshold does not return to the pre-exposure
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level, then it becomes a permanent threshold shift (PTS). Through TTS experiments, scientists at SSC San Diego, HIMB and UCSC have greatly advanced our understanding of the effects of sound on hearing in odontocetes and pin- nipeds (Kastak and Schusterman, 1995; Ridgway et al., 1997; Kastak and Schusterman, 1999; Kastak et al., 1999; Schlundt et al., 2000; Finneran et al., 2000; Kastak and Schusterman, 2002; Finneran et al., 2002; Nachtigall et al., 2003; Finneran et al., 2003; Nachtigall et al., 2004; Kastak et al., 2005; Finneran et al., 2005; Yuen et al., 2005; Kastak et al., 2007). One outcome of this research indicates that TTS in dolphins and white whales depends on the duration as well as SPL, and onset of TTS correlates with sound exposure level (SEL) for several different types of sound sources.
Finneran et al. (2005) concluded that collectively these data indicate an SEL of 195 dB re 1 μPa2-s as a reasonable threshold for the onset of TTS in dolphins and white whales. But in the absence of data for other species, these findings (Fig. 1) have provided a useful baseline to estimate effects of sound on hearing in other odontocetes. Current hearing research efforts are focused on understanding the effects of lengthy continuous exposures, and of intermittent exposure and recovery to multiple pulses such as those transmitted by active sonar or a seismic air gun.
Several workshops and research studies have also addressed effects of sound exposure on hearing and tissue injury in fish. In 2004 Caltrans supported a comprehensive literature review complete with recommendations for noise exposure criteria (based on available data at that time) and research needed to understand the effects of pile driving sound on fish (Hastings and Popper, 2005). These recom- mendations for research have provided a framework for proj- ects to be supported through the Transportation Pooled Fund Program. The federal courts directed the U.S. Navy to look at the effects of LFA transmissions on fish after accept- ance of the final Overseas Environmental Impact Statement and final Environmental Impact Statement for SURTASS LFA (DoN, 2001). In response, the Navy funded a controlled exposure experiment (CEE) on caged fish at Seneca Lake (see Fig. 2) to prepare for a supplemental environmental impact
progress has been made in several areas during the last two decades. Research activity is evident by the increase in number of scientific publications and special conferences, workshops and symposia over the last 10 years. The state of scientific knowledge and recommendations for future research on marine mammals and noise through 2005 are summarized in
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