Marine Mammals and Low-Frequency Sound Progress Since 1994 (2000) / Chapter Skim
Currently Skimming:
1 Introduction
1 Introduction
Pages 9-20
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 9... ...
Because of the wave properties of sound and propagation conditions, waves from different sources or refracted and reflected waves from a single source can converge and either add to or cancel each other, so that simple geometric models of spreading do not always predict actual sound fields in the ocean. This is especially true in shallow water.
|
From page 10... ...
The decrease in sound transmission distance with increasing frequency also has implications for marine mammal communication because only low-frequency vocalizations can travel long distances. Because of property 2, sound speed can be used to infer the average temperature of the water volume through which the sound waves have passed.
|
From page 11... ...
m 1 55 d] Source Level ~ 95 dB \ \ \ / FIGURE 1.1 Calculated received levels at various distances from the ATOC source, based on spherical spreading, assuming no reflections from the sea surface or bottom.
|
From page 12... ...
Serious misunderstandings of the potential effects of sound of various intensities on marine mammals have occurred because the levels of sound intensity in water and in air have not been consistently (or in some cases, correctly)
|
From page 13... ...
The issue of global warming is of major significance to scientists, policymakers, and citizens worldwide, yet it has been difficult to determine the extent of atmospheric and oceanic warming based on observations of global air and sea surface temperatures.4 The advantages of long-distance sound transmissions in the ocean are that (1) low-frequency sound waves pass through and thus sample a wide range of ocean depths between the source and the receivers, (2)
|
From page 14... ...
Combinations of the GCM, altimeter, and ATOC data show that the GCM alone underestimates the magnitude of the seasonal sea surface heat flux cycle. However, despite the usefulness of acoustic tomography programs like ATOC and other research uses of low-frequency sound in the ocean, concern exists that adding more sound to the ocean could harm marine mammals, sea turtles, and other organisms, as the following section will describe.
|
From page 15... ...
Table 1.2 shows the frequency range and dominant frequencies of the vocalizations of a sample of baleen whales, toothed whales, and seals. The geographic extent of the use of low-frequency sounds by baleen whales is being monitored on an experimental basis in the Atlantic and Pacific oceans using a novel source of data the Integrated Undersea Surveillance System (IUSS)
|
From page 16... ...
b Selected Baleen Whales Gray Whale adults 20-2,000 20- 1,200 calf clicks 100-20,000 3,400-4,000 Humpback Whale 30-8,000 120-4,000 Finback Whale 14-750 20-40C Minke Whale 40-2,000 60-140d Southern Right Whalee 30-2,200 50-500 Bowhead Whale 20-3,500 100-400 Blue Whale Atlanticf — 1 0-20h Pacificg 10-390 16-24 Selected Toothed Whales Sperm Whale (clicks) 100-30,000 2,000-16,000 White Whalei whistles 260-20,000 2,000-5,900 clicks 40,000-120,000 Killer Whale whistles 1,500-18,000 6,000-12,000 clicks 1,200-25,000 Bottlenose Dolphin whistle 800-24,000 3,500- 14,500 clicks)
|
From page 17... ...
Subsequent to HIFT, the ATOC program was proposed with a mission to make regular measurements of the travel times of low-frequency sound throughout the Pacific Ocean (Figure 1.2~. As a result of concerns about the effects of low-frequency sound added to the ocean by ATOC, the ATOC program conducted the first several years of transmissions under a permit to test the effects of ATOC sound sources on marine mammals through a Marine Mammal Research Program (MMRP)
|
From page 18... ...
Underwater Audiograms of Eared Seals C Sea LionlS C Sea LioniK N Fur Seal/hA N Fur Seal/B 1 1 T I ~ I T '-i I ~ r- I t~ I - T I I I I T 1 1 ) O 1,000 1O,OOO 10O,000 1,00O,OOO Frequency (Hz)
|
From page 19... ...
~1 I -I I I I 111' -- -' - l~~-l~T r-rll' - I I I ~ 11~1. 10 100 1,000 1 O'OOO Frequency (Hz)
|
From page 20... ...
Chapter 4 discusses regulatory issues, such as how permits for acoustic and marine mammal research are issued. Chapter 5 draws together the Committee's findings and provides recommendations based on these findings.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.