Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 103
B Summary from NRC [1 994) 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 con- stitute the basis for informed prediction or evaluation of the effects of intense low-frequency sounds on any marine species. 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. Certainly data on the hearing sensitivities of several Odontoceti (examples include the white whale, bottlenose dolphin, harbor por- poise, 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. But even these data are extremely limited and cannot be used to evaluate the effects of intense low-frequency sounds on all species of marine mammals. 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 103
OCR for page 103
104 APPENDIX B 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 calculating 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 ef- fects 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. 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 acquisi- tion of scientific knowledge that would benefit conservation of marine mam- mals, 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. 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 mam- mals 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. The committee considered several possible alternatives for facilitating valu- able 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
OCR for page 103
APPENDIX B 105 marine mammal interactions. Another alternative would be to establish a decen- tralized regulatory regime, possibly patterned after the Institutional Animal Care and Use Committee (IACUC) system currently used to monitor research con- ducted on nonmarine animals in scientific laboratories. 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." In order to place regulations on a more rational footing, the popula- tion 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 a blanket waiver of the require- ments for scientific research under the Marine Mammal Protection Act, the Endangered Species Act, and the National Environmental Policy Act whether 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 expe- ditious 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 com- mittee, the data from which the 120-dB criterion was derived are being overly extrapolated, largely because of the scarcity of experiments providing quantita- tive 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 detected 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 neces- sarily indicative of an adverse effect. One danger of adopting a single number, as with the 120-dB criterion, is in
OCR for page 103
106 APPENDIX B 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 concep- tually straightforward biological science, the proposed experiments should provide much of the needed information, and the cost is not enormous com- pared 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 follow- ing general areas in which more information must be developed: 1. Research on the behavior of marine mammals in the wild. 2. Research on the auditory systems of marine mammals. 3. Research on the effects of low-frequency sound on the food chain of marine mammals. 4. Development and application of measurement techniques to enhance observation and data gathering. The committee recommends that an accelerated program of scientific studies of the acoustic effects on marine mammals and their major prey be undertaken. These studies should be designed to provide information needed to direct policies that will provide long-term protection to the species.