Environmental Engineering Reference
In-Depth Information
Nowacek et al. (2007) reviewed the literature on the behavioral, acoustic, and
physiological effects of anthropogenic noise on cetaceans and concluded that the
noise sources of primary concern are ships, seismic exploration, sonars, and some
acoustic harassment devices (AHDs) that are employed to reduce the by-catch of
small cetaceans and seals by commercial fishing gear.
Two marine mammals whose hearing and susceptibility to noise have been studied
are the harbor porpoise (
Phocoena phocoena
) and the harbor seal (
Phoca vitulina
).
Both species inhabit shallow coastal waters in the north Atlantic and North Pacific.
Harbor porpoises are found as far south as Central California on the West Coast. The
hearing of the harbor porpoise ranges from below 1 kHz to around 140 kHz. In the
United States, harbor seals range from Alaska to Southern California on the West
Coast, and as far south as South Carolina on the East Coast. Harbor seal hearing
ranges from less than 0.1 kHz to around 100 kHz (Thomsen et al., 2006). Sounds
produced by marine energy devices that are outside of these frequency ranges would
not be detected by these species.
Thomsen et al. (2006) compared the underwater noise associated with pile driv-
ing to the audiograms of harbor porpoises and harbor seals and concluded that pile-
driving noise would likely be detectable at least 80 km away from the source. The
zone of masking (the area within which the noise is strong enough to interfere with
the detection of other sounds) may differ between the two species. Because the echo-
location (sonar) used by harbor porpoises is in a frequency range (120 to 150 kHz)
where pile-driving noises have little or no energy, they considered masking of echo-
location to be unlikely. On the other hand, harbor seals communicate at frequencies
ranging from 0.2 to 3.5 kHz, which is within the range of the highest pile-driving
sound pressure levels; thus, harbor seals may have their communications masked at
considerable distances by pile-driving activities.
The responses of green turtles (
Chelonia mydas
) and loggerhead turtles (
Caretta
caretta
) to the sounds of air guns used for marine seismic surveys were studied by
McCauley et al. (2000a,b). They found that above a noise level of 166 dB re 1 µPa
rms the turtles noticeably increased their swimming activity, and above 175 dB re
1 µPa rms their behavior became more erratic, possibly indicating that the turtles
were in an agitated state. On the other hand, Weir (2007) was not able to detect an
impact on turtles of the sounds produced by air guns in geophysical seismic surveys.
Caged squid (
Sepioteuthis australis
) showed a strong startle response to an air gun at
a received level of 174 dB re 1 µPa rms. When sound levels were ramped up (rather
than a sudden nearby startup), the squid showed behavioral responses (e.g., rapid
swimming) at sound levels as low as approximately 156 dB re 1 µPa rms but did not
display the startle response seen in the other tests.
Hastings and Popper (2005) reviewed the literature on the effects of underwater
sounds on fish, particularly noises associated with pile driving. The limited number
of quantitative studies found evidence of changes in the hearing capabilities of some
fish, damage to the sensory structure of the inner ear, or, for fish close to the sources,
mortality. They concluded that the body of scientific and commercial data is inad-
equate to develop more than the most preliminary criteria to protect fish from pile-
driving sounds and suggested the types of studies that could be conducted to address
the information gaps. Similarly, Viada et al. (2008) found very little information on the
