Executive Summary

In 1992, the Committee on Low-Frequency Sound and Marine Mammals was established under the auspices of the Ocean Studies Board of the National Research Council. The committee's charges were to review the current state of knowledge and ongoing research on the effects of low-frequency [1 to 1,000 hertz (Hz)] sound on marine mammals and to advise the sponsors of the report about the effects of low-frequency sound on marine mammals. In addition, the committee was asked to consider the trade-offs between the benefits of underwater sound as a research tool and the possibility of its having harmful effects on marine mammals.

Limitations of Current Knowledge

Data on the effects of low-frequency sounds on marine mammals are scarce. Although we do have some knowledge about the behavior and reactions of certain marine mammals in response to sound, as well as about the hearing capabilities of a few species, the data are extremely limited and cannot constitute the basis for informed prediction or evaluation of the effects of intense low-frequency sounds on any marine species.



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--> Executive Summary In 1992, the Committee on Low-Frequency Sound and Marine Mammals was established under the auspices of the Ocean Studies Board of the National Research Council. The committee's charges were to review the current state of knowledge and ongoing research on the effects of low-frequency [1 to 1,000 hertz (Hz)] sound on marine mammals and to advise the sponsors of the report about the effects of low-frequency sound on marine mammals. In addition, the committee was asked to consider the trade-offs between the benefits of underwater sound as a research tool and the possibility of its having harmful effects on marine mammals. Limitations of Current Knowledge Data on the effects of low-frequency sounds on marine mammals are scarce. Although we do have some knowledge about the behavior and reactions of certain marine mammals in response to sound, as well as about the hearing capabilities of a few species, the data are extremely limited and cannot constitute the basis for informed prediction or evaluation of the effects of intense low-frequency sounds on any marine species.

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--> As discussed in Chapter 1 of this report, marine mammals1 use sound to sense their environment and to communicate among themselves. Dolphins and other toothed whales use echoes from the high-frequency sound pulses they produce in order to navigate and to locate prey. They use lower-frequency sounds for communication among individuals. Baleen whales are known to produce low-frequency sounds that can propagate over long distances. Although the exact functions of most of these sounds are not yet known, they clearly play an important role in the life of the species. The ocean is a noisy place. There are many sources of sound, and sound travels efficiently in water. Natural ocean sounds are produced by wind, waves, precipitation, cracking ice, seismic events, and marine organisms. The hearing abilities of marine mammals undoubtedly evolved to deal with these natural sounds—the ambient noise levels of the ocean. Since the advent of the industrial age, sounds made by human beings have combined with natural ocean sounds, resulting in elevated noise levels, primarily in the frequency region below 1,000 Hz. Some of the more intense human-made sounds come from ocean-going vessels, especially larger ships such as super-tankers. Other human-made sources include (1) explosive and nonexplosive seismic sounds used in geological exploration for oil and gas; (2) dredging, drilling, and marine construction; (3) surface vessels (for example, commercial, military, and pleasure boats) and submarines that use sonar to locate targets; and (4) the sound sources used by acoustical oceanographers. The committee could find almost no quantitative information with which to assess the impact of low-frequency noise on marine mammals. For those few marine mammals on which data are available about their hearing sensitivity, it appears that low-frequency sound, even at very high levels, is barely audible to them. In addition, the range of frequencies by which these animals are affected appears to vary among, as well as within, the three different orders of Mammalia to which they belong (see Appendix B for the classification of marine mammals in the three orders). Certainly data on the hearing sensitivities of several Odontoceti (examples include the white whale, bottlenose dolphin, harbor porpoise, and false killer whale) and Pinnipedia (for example, several seals and the California sea lion) suggest that sounds below about 100 Hz are practically inaudible to these mammals (see the subsection on Acoustic Characteristics of Marine Mammal Hearing Organs, and Figure 2, in Chapter 1). But even these data are 1    This report concentrates on cetaceans (whales, dolphins, and porpoises) and pinnipeds (seals, sea lions, and walruses) and only briefly mentions manatees, polar bears, and sea otters.

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--> extremely limited and cannot be used to evaluate the effects of intense low-frequency sounds on all species of marine mammals. There are literally no data available on the auditory sensitivity of any baleen whales (examples of baleens are the gray whale, right whale, fin whale, and humpback whale), although evidence from several sources suggests that members of this suborder are much more sensitive to low-frequency sounds than are members of the toothed whale suborder. The implications of this paucity of audiometric information include profound uncertainty about the interfering effect of any potential sound source on baleen whales. For example, depending on these animal's auditory sensitivity, the effect of loud low-frequency sound could conceivably range between potential hearing damage and gradual deafness for the entire species—and eventual extinction—or practically no discernible impact. Such uncertainty prevents the committee from reaching any but the most general conclusions in this regard. There have been some observational or experimental studies and numerous anecdotal reports about the responses of marine mammals to certain sounds. Rather than summarize the existing reviews, the committee decided that its efforts could be more usefully directed to a discussion of the implications of the existing information. The committee noted, for example, that missing in most of these anecdotal accounts is information on the level of the sound exposure experienced by individual animals. Typically, neither the source level nor the received level was measured. Even when the approximate level at the source was known, the received level near the animal was usually not measured, and if it was, there were often uncertainties associated with estimating that level. This dearth of scientific evidence makes it virtually impossible to predict the effects of low-frequency sound on marine mammals, especially on baleen whales. In the absence of such an impact assessment, the committee finds itself unable to fulfill the second part of its charge, namely, to balance the costs and the benefits of "underwater sound as a research tool" versus "the possibility of harmful effects to marine mammals." Rigorous experimental research on marine mammals and their major prey is required to resolve the issue of how low-frequency sound affects these species. The committee recommends that future experiments be conducted in such a manner that the received level of the sound and the behavior of the animal can be studied together. Such investigations may be logistically complex and may require permits, which are sometimes difficult to obtain. Chapter 2 discusses the permit issue, and Chapter 3 describes the types of studies needed.

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--> Changes Proposed in Regulatory Structure It is the committee's judgment that the regulatory system governing marine mammal "taking" by research actively discourages and delays the acquisition of scientific knowledge that would benefit conservation of marine mammals, their food sources, and their ecosystems. The committee thus proposes several alternatives for reducing unnecessary regulatory barriers and facilitating valuable research while maintaining all necessary protection for marine mammals. Although the committee strongly agrees with and supports the objective of marine mammal conservation, it believes that the present regulation of research is unnecessarily cumbersome and restrictive.2 Not only is research hampered, but the process of training and employing scientists with suitable research skills is impeded by this system. Better and more humane management of marine mammals depends on understanding them better. Well-trained researchers are the ultimate source of our knowledge about marine mammals. The present system, in effect, impedes acquisition of the information and understanding needed to pursue a more effective conservation policy. At present, one of two types of regulatory approval is necessary to pursue any scientific research that might "take" marine mammals. "Take" is defined in the Marine Mammal Protection Act of 1972 as harass, hunt, capture, or kill. The two types of approval are (1) a scientific research permit, which currently is available only for research on or benefiting marine mammals, or (2) a small incidental take (SIT) authorization.3 Harassment has been interpreted as any action "that results in an observable change in the behavior of a marine mammal." This interpretation of harassment seems to the committee to be inappropriately broad. Although a scientific research permit may be granted a few months after application, the SIT authorization can take up to two years and may require public hearings. Any general biological investigations of nonmarine mammals, as well as 2    Under the Marine Mammal Protection Act of 1972 and the Endangered Species Act of 1973, the National Marine Fisheries Service of the U.S. Department of Commerce has responsibility for all cetaceans and all pinnipeds except walruses. The U.S. Fish and Wildlife Service in the Department of the Interior has responsibility for walruses, sea otters, manatees, and polar bears. 3    A small incidental take authorization refers to the provision in the Marine Mammal Protection Act of 1972 (Sect. 101(a)(5)) that allows for the incidental, but not intentional, taking of a small number of marine mammals within a specified geographical region by U.S. citizens engaged in a specified activity other than commercial fishing.

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--> general physical investigations of the ocean and planet, when carried out in the ocean, may disturb marine mammals to some degree. Such investigations presently require, at least in theory, SIT authorizations. Neither general biological nor physical research is eligible for the scientific research permit, unless it can be shown that the investigations might benefit conservation of marine mammals by providing useful information concerning their habitats or the food chains. The committee compared the effects of scientific research on marine mammals with the effects from commercial fishing and shipping. Commercial fisheries have had a blanket exemption4 under the Marine Mammal Protection Act of 1972 from the prohibition on taking marine mammals, and can kill marine mammals even from depleted populations. Furthermore, the noise from passing marine traffic, including supertankers, is not regulated as harassment or as a "take." Scientific research, especially oceanographic surveys, seldom results in any fatalities among marine mammals, although the sound levels produced in these investigations are intense and could potentially affect large populations. The shipping industry, especially super-tankers, produces much more total noise than scientific research does, if measured on a yearly basis. Making an exact comparison is difficult, because the dominant sound frequencies produced by super-tankers are much lower than those produced by oceanographic experiments, and the hearing sensitivity of the affected animals is not known. Given these facts, it is illogical to regulate scientific sources, some of which have the potential to produce answers about the impact of noise on marine mammals, while ignoring other significant sound sources that are far more common, such as supertankers. To regulate intelligently, we need more information about the auditory systems of marine mammals and the impact of all noise sources. The committee considered several possible alternatives for facilitating valuable research while maintaining all necessary protection for marine mammals. One alternative would be to incorporate scientific researchers as "other users" in the regulatory regime recently proposed by the National Marine Fisheries Service (NMFS) of the U.S. Department of Commerce to govern commercial fishing and marine mammal interactions. Another alternative would be to establish a decentralized regulatory regime, possibly patterned after the Institutional Animal Care and Use Committee (IACUC) system currently used to monitor research conducted on nonmarine animals in scientific laboratories. 4   This exemption under the Marine Mammal Protection Act of 1972 expires May 1, 1994.

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--> If the existing system of regulations is maintained, the committee urges that steps be taken to expedite the small incidental take authorization process for all scientific activities involving nonlethal takes, and to further simplify the process for nonlethal takes producing only negligible impact. The committee suggests rewording those provisions to delete references to effects on "small" numbers of marine mammals, provided that the effects are negligible. It would also be beneficial to broaden the definition of research for which scientific permits can be issued to include activities beyond those directly "on or benefiting marine mammals."5 In order to place regulations on a more rational footing, the population status of each species should determine the number and types of allowable takes, and the same regulations should apply equally to all activities, scientific and otherwise. The committee notes that some of these recommendations would require congressional action to change the Marine Mammal Protection Act and perhaps other laws. However, other recommendations could be implemented under existing laws through changes in regulations. The committee is by no means recommending that scientific research be afforded a blanket waiver of the provisions of the Marine Mammal Protection Act, the Endangered Species Act, and the National Environmental Policy Act that relate to taking of marine mammals, either during research on marine mammals or on other topics where experiments might incidentally affect marine mammals. Rather, the committee urges a more logical balance between the regulation of research and other human activities, and a more expeditious permitting process. Appropriate scientific research might identify the sources of human-made noise that actually endanger marine mammals, and may suggest regulation of certain sound sources that are presently unregulated. This research could provide information that would benefit all marine mammals. Finally, the committee considered the "120-decibel (dB) criterion" that is regarded in some contexts as a noise level above which potentially harmful acoustic effects on marine mammals might occur. In the opinion of the committee, the data from which the 120-dB criterion was derived are being overly extrapolated, largely because of the scarcity of experiments providing quantitative information about the behavior of marine mammals in relation to sound exposure. It is possible that this level is simply the one at which the animals de- 5   It is the committee's view that the recent proposed rule changes make it clear that NMFS intends to make regulations on general scientific research even more restrictive (58 Fed. Reg. 53,320–53,364 (1993)).

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--> tected the presence of a sound. If this is true, then there is no scientific evidence to indicate that the relatively minor and short-term behavioral reactions observed indicate any significant or long-term effects on the animals. Marine mammals, like other animals, respond to many stimuli, natural and human-made. These reactions are part of their normal behavioral repertoire and are not necessarily indicative of an adverse effect. One danger of adopting a single number, as with the 120-dB criterion, is in applying it to all species of marine mammals and to all sounds and situations, regardless of the frequency spectrum, regardless of the temporal pattern of the sound, and regardless of differences in the auditory sensitivity of the different groups of marine mammals. There is general agreement that these variables are important in determining whether the 120-dB figure is appropriate in any given situation. Recommended Research The research that would provide some of the missing information is conceptually straightforward biological science, the proposed experiments should provide much of the needed information, and the cost is not enormous compared with that of other scientific efforts of comparable magnitude. The committee's aim was to identify general research needs that are crucial to a full evaluation of the effects of intense low-frequency sounds on a variety of marine mammals and their major prey. The committee has identified the following general areas in which more information must be developed: Research on the behavior of marine mammals in the wild. Research on the auditory systems of marine mammals. Research on the effects of low-frequency sound on the food chain of marine mammals. Development and application of measurement techniques to enhance observation and data gathering. Chapter 3 presents the committee's recommendations for specific types of studies that are needed in each of these general areas. The committee recommends that an accelerated program of scientific studies of the acoustic effects on marine mammals and their major prey (including the studies described in Chapter 3) be undertaken. These studies should be designed to provide information needed to direct policies that will provide long-term protection to the species.