Ocean Noise and Marine Mammals (2003) / Chapter Skim
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1. Introduction
1. Introduction
Pages 12-26
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From page 12... ...
available to determine the geological structure of the seabed and to discover oil and gas reserves deep below the seafloor. Society as a whole has reaped substantial intellectual and practical benefits from these activities, including bottommapping sonars and technology leading to the discovery of substantial offshore oil reserves.
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From page 13... ...
It is in this context of parallel developments and applications in ocean acoustics, marine seismology, oil exploration, and animal bioacoustics that concerns about the effects of sound on marine life have emerged. While researchers had been aware for quite some time of the sounds produced by marine life, it was not until the Acoustic Thermometry of Ocean Climate (ATOC)
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From page 14... ...
Ears and functioning auditory systems are found in all aquatic vertebrates.] Auditory capabilities of bony fish are reasonably sophisticated, and a number of species not only detect sounds but can also determine sound source direction, detect signals in the presence of noise sources (maskers)
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From page 15... ...
Therefore, there should be concern not only about the impact of anthropogenic sounds on communication but also about the impact on general determination of information in the environment. A fundamental question is whether the impact of anthropogenic sounds on marine mammals and the marine ecosystem is sufficiently great to warrant concern by both the scientific community and the public.
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From page 16... ...
The term "ocean noise" was therefore defined by the committee as encompassing not only the usual background ambient noise but also the noise from distinguishable sources (Box 1-1~. Second, the committee agreed that, although its work would concentrate primarily on the effects of noise on marine mammals, it should consider other species as well (e.g., fish)
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From page 17... ...
INTRODUCTION 17 report, as the noise budget) to the total noise field in various parts of the worId's oceans, including seasonal differences, or about the more detailed spatial and temporal variability of the noise field.
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Probably the most widely used models of the ambient component of ocean noise continue to be the curves developed by Wenz (1962; see also Richardson et al., 1995~. These provide a summary of average ambient noise spectra from various sources, as shown in Plate 1.
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From page 19... ...
It should also be noted that marine mammals are part of a larger ecosystem upon which they depend. Included in this ecosystem are other organisms, particularly fish and possibly marine reptiles and invertebrates, which use sound in their normal behavior and that may also be impacted by anthropogenic sounds.
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From page 20... ...
, which are proportional to the logarithms of the corresponding linear values. The decibel is used largely for convenience, since the individual components of the equation may span a broad dynamic range, and furthermore, the logarithmic operation expresses multiplicative processes in terms of seemingly simpler additive operations.
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From page 21... ...
INTRODUCTION 1: 3 _100 m o A160v _ Q er120o B 40 10 21 ~ ,~.
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From page 22... ...
All of these factors combine to create a channel, or waveguide, for the sound waves that are tra~o~oed be 1 ~ 1 1 1 ~ , ~ 1 1 1 tween the surface and the bottom in shallow water or focused by the sound stored structure in deep water as they propagate outward from source to receiver. This channeling effect causes the envelope of the signal to spread cylindrically, rather than spherically, outward at ranges much greater than the waveguide thickness, D (which equals the water depth in shallow water environments)
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From page 23... ...
The complexities of sound propagation in the sea must be carefully and accurately taken into account when evaluating the contribution of a particular sound source to the overall ocean noise field and are presented in more detail in Chapter 4.
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From page 24... ...
This lower frequency limit is called the cutott frequency, and standing waves with frequencies below the cutoff cannot propagate in the horizontal direction. Therefore, at a given water depth, an absolute cutoff frequency exists that is equal to the cutoff frequency for the vertical interference pattern having the fewest number of maximum and minimum pressures in the vertical (Rogers and Cox, 1988~.
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From page 25... ...
As a result, comparisons of the density of marine mammals near sound sources and in other locations where the underwater sound levels are high may be 5Although underwater sound incident on the underside of a flat ocean surface is perfectly reflected for all intents and purposes, airborne sound that is nearly vertically incident on the sea surface can couple into ocean-borne sound, as discussed in Chapter 2.
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From page 26... ...
STRUCTURE OF THE REPORT This report describes sound origins, trends, effects on marine mammals, and current modeling efforts (Figure 1-4~. Chapter 2 provides descriptions of the natural and human sources of ambient noise in the ocean and the possible reasons and evidence for long-term trends in ocean noise.
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Key Terms
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