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The U.S. Navy’s response to public outcry in the 1990’s was twofold. First was initiation of environmental risk assess- ments and preparation of documents and requests for per- mits needed for HIFT and SURTASS LFA in compliance with national environmental laws. Second was funding for scien- tific research to understand the interactions between marine animals and sound. ONR funded the National Research Council (NRC) in 1992 to establish a Committee on Low- Frequency Sound and Marine Mammals, and produce a report on the state-of-knowledge and recommendations for changes in the regulatory process4 to facilitate scientific stud- ies as well as research needed to evaluate effects of low-fre- quency sounds on marine mammals and their major prey (NRC, 1994). ONR also began to sponsor research on the effects of low frequency sound on marine mammals and fish. Initially the primary concern was hearing and communica- tion. So experimental studies to determine the effects of underwater sound on hearing in odontocetes (toothed whales) and pinnipeds (seals, sea lions and walrus) were ini- tiated with captive animals—and continue today—at the Space and Naval Warfare Systems Center San Diego (SSC San Diego), the Hawaii Institute of Marine Biology (HIMB) at the University of Hawaii, and Long Marine Laboratory at the University of California, Santa Cruz (UCSC). In addition a SURTASS LFA Scientific Research Program (SRP) began in 1997 to quantify the reactions of large whales to low fre- quency broadcasts (Croll et al., 2001).
The debate continued as plans were made for the off- spring of the HIFT—a long term monitoring project, acoustic thermometry of the ocean climate (ATOC), using a lower power source operating at 75 Hz over a smaller region of the Pacific Ocean. Even though the ATOC sound projectors had lower source levels than those used for the HIFT (195 dB vs. 221 dB re 1 μPa at 1 m), public outcry caused the final proj- ect to be significantly delayed and scaled back. The final environmental impact statement set aside about $3 million of funding to study the effects of ATOC sound transmissions on marine mammals—the first two years of the project—so that it could be stopped if any adverse effects were observed. This ATOC Marine Mammal Research Program (MMRP) was reviewed by a new NRC study panel to update the 1994 NRC report with MMRP data and results of any other relevant research, and to identify continuing knowledge gaps. The review (NRC, 2000) indicated that results of the MMRP were inconclusive as to whether or not ATOC sound transmis- sions had any effect on marine mammals (Au et al., 1997; Frankel and Clark, 2000; Frankel and Clark, 2002).
Attention turns to mid-frequency sonar, seismic air guns, and impact pile driving
Mid-frequency active sonar has been in operation since the 1940’s and is the standard modality for localizing sub- marines. But in 1996 exposure to military sonar during a North Atlantic Treaty Organization (NATO) Undersea Research Centre exercise was postulated as the cause of a mass
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stranding of 12 beaked whales in Greece (Frantzis, 1998). Similar mass stranding events during military exercises in the Bahamas and Madeira in 2000 (Evans and England, 2001; Cox
et al., 2006), and the Canary Islands in 2002 (Evans and Miller, 2004), each involving between 4 and 18 whales within two days, confirmed that beaked whales, and in particular Cuvier’s beaked whale (Ziphius cavirostris), are sensitive to mid-fre- quency sonar, which operates in the 1 – 10 kHz bandwidth with source levels as high as 235 dB re 1 μPa at 1 m (Evans and England, 2001). In these four events about half of the stranded animals died, but the mechanisms that caused the animals to strand and contributed to pathological traumas revealed dur- ing necropsies are unknown (Ketten, 2005).
Subsequent mass stranding events coincident with the use of mid-frequency sonar in the Haro Strait near the state of Washington in 2003 (Norman et al., 2004; National Marine Fisheries Service, 2005), and off the coasts of Hawaii in 2004 (Southall et al., 2006) and North Carolina in 2005 (Hohn et al., 2006) involved other species, including harbor porpoises, melon-headed whales and short-finned pilot whales, respec- tively. Medical examinations and necropsies of animals affected in these events, however, indicated that beaked whales are most susceptible to acoustic trauma when exposed to mid-frequency sonar transmissions (Freitas, 2004; Ketten, 2005; Fernández et al., 2005).
Seismic air gun surveys for hydrocarbon exploration or oceanographic research are similar to active sonar opera- tions. An air gun array towed by a vessel emits acoustic puls- es directed vertically downward that penetrate the seabed. Refracted and/or reflected waves from different sediment layers are recorded by sensors on streamers towed behind the air gun array and used to reconstruct a picture of the sub- strate below the seafloor. Most all the acoustic energy in an air gun pulse is below 1000 Hz; however, sound pressure level (SPL) and spectral content vary spatially depending on the local undersea environment. Peak-to-peak source levels of emissions from air gun arrays can exceed 250 dB re 1 μPa at 1 m. Although the Department of Fisheries and Oceans (DFO) Canada, the U.S. Department of the Interior Minerals Management Service (MMS), as well as oil and gas compa- nies worldwide had investigated the effects of noise on marine life from offshore industrial activities and seismic exploration for many years (e.g., Falk and Lawrence, 1973; Pearson et al., 1987 and 1992; Richardson et al., 1990, Richardson et al., 1995), two beaked whales stranded September 2002 in the Gulf of California in association with seismic air gun use (Cox et al., 2006). This stranding occurred coincidentally with a seismic air gun survey by the NSF-supported oceanographic research vessel, Maurice Ewing; however, the Ewing was also operating mid-frequency active sonar at the time. Since 2003, legal challenges and risk assessments for documentation of environmental impact statements have significantly hampered oceanographic research funded by NSF.
In the autumn of 2000 while the U.S. Navy was still try- ing to understand conditions that contributed to the March 2000 stranding of beaked whales in the Bahamas, the California Department of Transportation (Caltrans) was responding to a fish kill that occurred during a pile installa- tion demonstration project (PIDP) for the San Francisco- Oakland Bay Bridge (SFOBB) East Span Seismic Safety
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