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r
Executive Summary
Sound has become a major tool for studying the ocean. Although the ocean
is relatively opaque to light, it is relatively transparent to sound. Sound having
frequencies below 1,000 Hertz (Hz) is often defined as low-frequency sound.
The speed of sound is proportional to the temperature of the water through which
it passes. Therefore, sound speed can be used to infer the average temperature of
the water volume through which sound waves have passed. The relationship
between water temperature and the speed of sound is the basis for the Acoustic
Thermometry of Ocean Climate (ATOC) experiment. The ATOC experiment is
designed to monitor the travel time of sound between sources off the coasts of
Hawaii and California and several receivers around the Pacific Ocean in order to
detect trends in ocean temperature and for other research and monitoring pur-
poses (ATOC Consortium, 1998~. The ATOC transmissions are centered at a
frequency of 75 Hz, with peak source levels of 180 decibels (dB) re 1 pPa @ lm1
at this frequency and 195 dB for its broadband source level. Based on well-tested
models of signal loss over distance in deep water, the source level should decrease
to 155 dB within 100 m from the source and to 135 dB at 1 km from the source.
Some whales, seals, and fish use low-frequency sound to communicate and
to sense their environments. For example, baleen whales and some toothed
whales are known to use and respond to low-frequency sound emitted by other
1 Decibels are used to describe the ratio between two quantities, in this case, the ratio of the sound
pressure level (SPL) of the source to the SPL of 1 microPascal (,uPa) at one meter from the source.
"re" = "with reference to." The report will henceforth omit the "re 1 pPa @ lm" notation when
referring to decibel levels measured in water. Measurements made in air are referenced to 20 pPa @
1 m and will be identified in the text.
1
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MARINE MAMMALS AND LOW-FREQUENCY SOUND
individuals of their species. Sharks are not known to produce low-frequency
sound but are attracted to pulsed low-frequency sounds. Therefore, it is possible
that human-generated low-frequency sound could interfere with the natural
behavior of whales, sharks, and some other marine animals.
In 1994 the Defense Advanced Research Projects Agency (DARPA)
requested that the National Research Council (NRC) convene a committee to
evaluate the results of ATOC's Marine Mammal Research Program (MMRP)
(see Appendix A for Committee biographies). The MMRP was designed to
monitor the effects of ATOC transmissions on marine mammals. Although
DARPA was the original sponsor, the Office of Naval Research (ONR) is now
funding the MMRP and cosponsored this study. The NRC was asked to
conduct an updated review of Low-Frequency Sound and Marine Mam-
mals: Current Knowledge and Research Needs (NRC, 1994), based on data
obtained from the MMRP and results of any other relevant research, including
ONR's research program in low-frequency sound and marine mammals;
2. compare new data with the research needs specified in the 1994 NRC
report, focusing on the strengths and weaknesses of the data for answering the
important outstanding questions about marine mammal responses to low-
frequency sound; and
3. identify areas where gaps in our knowledge continue to exist.
The Committee reviewed numerous written documents and was briefed on
the MMRP's progress at the program's midpoint (in 1996) and about 6 months
after the completion of its field observations (in 1999~. The NRC was asked to
prepare an interim report to provide midproject guidance to the MMRP as well as
this final report. Some of the recommendations in the interim report (NRC, 1996)
were implemented by 1999, but for a variety of reasons others were not.
For its update of research priorities related to marine mammals and low-
frequency sound, the Committee augmented the MMRP results with results from
the scientific literature, ONR's program on marine mammals, and observations
of the reactions of marine mammals to tests of the Navy's low-frequency active
(LFA) sonar. This report does not examine the effects of all human-generated
sound (only low-frequency sound is considered), nor does it include all marine
mammals (only whales and seals are included). This report updates all aspects of
NRC (1994), including the issue of acoustic harassment and its regulatory defini-
tion in light of the 1994 reauthorization of the Marine Mammal Protection Act
(MMPA). The publication of the report is particularly timely because the MMPA
expired on October 1, 1999 and is in the process of being reauthorized. The
Committee focused exclusively on whales and seals, because (1) they are found
near the ATOC sources, (2) the effects of low-frequency sound on whales and
seals have been studied to a greater extent than effects on other marine mammals
(in part, because they live near ATOC sources), and (3) it is thought that low-
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EXECUTIVE SUMMARY
3
frequency sound is less likely to have a significant impact on other marine
mammals, including sea and marine otters, manatees and dugongs, and polar
bears.
FINDINGS AND RECOMMENDATIONS
Some of the MMRP observations, such as movements of humpback whales
in near-coastal areas off Kauai and the abundance of some whale species near the
Pioneer Seamount source off California, showed no statistically significant effects
of ATOC transmissions. For these observations, the Committee could not distin-
guish among true lack of effect and insufficient observations, small sample sizes,
and incorrect statistical treatment of data. A somewhat clearer lack of significant
effects of the ATOC transmissions was demonstrated in observations of elephant
seals' diving behavior near the Pioneer Seamount source. Some statistically
significant differences between control and exposure conditions were found for
other species, including (1) an increase in average distance of humpback whales
from the California source and (2) increased dive duration for humpback whales
off Hawaii. The MMRP found no obvious catastrophic short-term effects as a
result of transmissions from either source, such as mass strandings or mass deser-
tions of source areas.
Statements about whether ATOC should be allowed to continue, based on
MMRP and other results, are clearly outside the Committee' s statement of task.
However, the Committee does offer suggestions about how future large-scale
acoustic tomography experiments could be designed to accomplish appropriate
monitoring for scientific purposes and mitigation measures to decrease the possi-
bility of harm to marine mammals.
Progress has been made since 1994 in answering several of the research
questions described in the 1994 NRC report. Research funded by ONR and other
agencies and the results of the MMRP and LEA tests have contributed new
knowledge regarding the effects of low-frequency sound on marine mammals.
Research and observations published since 1994 have extended our knowledge of
the hearing abilities of marine mammals at lower frequencies, at depth, in the
presence of human-generated noise, and among different individuals of the same
species. More observations of baleen whale vocalizations and responses to sound
have been collected and a greater appreciation has been gained about how the
respective locations of a baleen whale and a sound source can affect vocalizations
and other behavior. Extensive testing with conventional and new methods, such
as computational modeling of ear anatomy, auditory evoked potential techniques,
and stimulus-response experiments with trained animals have provided new
insights into normal hearing and the levels of sound required to produce shifts in
the hearing abilities of individual animals.
Most of the research directions recommended by the 1994 report are still
relevant. This continued need to answer the questions raised therein is not due to
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MARINE MAMMALS AND LOW-FREQUENCY SOUND
lack of effort but is a result of the complexities of the questions and the difficul-
ties of conducting studies on marine mammals because of the lack of adequate
research support, equipment, techniques, and facilities.
.
The 1994 amendments to the MMPA (16 U.S.C. 1361 et seq.) changed the
legal definitions of marine mammal "harassment" as applied to scientific use of
sound in the ocean. If the MMPA is to be implemented responsibly, however,
additional changes should be made to the act and to the regulations promulgated
pursuant to the act by the Office of Protected Resources of the National Marine
Fisheries Service (NMFS) in the National Oceanic and Atmospheric Administra-
tion (NOAA).
There is little disagreement that scientific use of sound in the ocean is a
minor component of human-generated sound pollution. Industry (e.g., shipping
and hydrocarbon exploration and production) are thought to be the largest sources.
Yet, uses of sound by scientists and the Navy are the most stringently regulated.
Unfortunately, few data are available to regulators regarding ambient noise levels
in the ocean and the relative importance of different sources in contributing to the
cumulative human-generated noise. Cooperative funding of research by govern-
ment and industries responsible for the noise could result in more rapid advance
of knowledge about the effects of sound on marine mammals and cooperative
solutions to noise problems.
This report includes a number of recommendations to Congress, to NOAA in
its regulatory role, and to research sponsors, as well as to the scientific commu-
nity. The recommendations directed to Congress should be implemented in the
upcoming reauthorization of the MMPA. The recommendations directed to
NOAA in its regulatory role should be implemented as it promulgates new regu-
lations based on the reauthorized MMPA. Finally, agencies that fund marine
mammal and acoustic research should begin weighing recommendations about
research, monitoring, and facilities against other budget priorities for the fiscal
year 2002 budget cycle and beyond. Some of the recommendations to research
sponsors should not require reprogramming or new money and could be imple-
mented immediately.
Recommendations for Congress
As part of the upcoming reauthorization, Congress should consider changes
to the MMPA that would allow studies of the ocean while protecting marine
mammals. In particular, Congress should consider the following actions:
· define "type B harassment" of marine mammals in terms of significant
disruption of behaviors critical to survival and reproduction.
· acknowledge the relative significance of different sources of sound in the
ocean, insofar as this is known, and provide new means to bring all commercial
sources of sound into the MMPA's legal and regulatory framework.
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EXECUTIVE SUMMARY
s
The committee believes that regulation of sound in the ocean is based
on inadequate information and that more information needs to be collected.
Congress should decide what kinds of regulations are appropriate and how much
funding should be available for marine mammal research, given the existing
inadequacy of knowledge.
Recommendations for NOAA
NOAA' s responsibilities with respect to whales and seals are set forth in the
MMPA, the Endangered Species Act, and other relevant legislation. NOAA's
responsibility has been delegated to NMFS. Although NMFS conducts and
supports some marine mammal research, it has conducted or supported very little
research aimed at determining the potential effects of anthropogenic sound on the
distributions, sizes, or productivity of marine mammal species or stocks. In
September 1998, NMFS held a workshop to seek input from the scientific com-
munity regarding guidelines or regulations that might be promulgated to guide or
govern authorization of the taking of marine mammals incidental to activities that
use or produce sound in the ocean (no publication resulted from the meeting).
The workshop participants noted a variety of uncertainties concerning the pos-
sible effects of anthropogenic sound on marine mammals. Pending resolution of
the uncertainties, NMFS should focus on developing and evaluating the effec-
tiveness of guidelines for preventing injuries and disruption of behavior that
could affect survival or reproduction. NMFS should consult further with experts
in oceanography, bioacoustics, underwater sound propagation, and animal be-
havior to (1) identify sound-producing activities that, because of their nature,
location, intensity, or duration, are likely to have biologically significant effects
on marine mammals and thus should be higher priority for enforcement of the
"taking" authorization under the MMPA or the Endangered Species Act; and
(2) for cases in which there is uncertainty or disagreement as to possible adverse
effects of underwater sound on survival or productivity, describe (a) the research
required to resolve the uncertainty, and/or (b) the monitoring that should be
required as a condition of any incidental take authorization provided by NMFS.
Further, NMFS should work cooperatively with ONR to develop technology and
programs for monitoring ambient sound levels and noise pollution in critical
marine mammal habitats and to develop and implement methods for obtaining
data on the hearing capabilities of marine mammals, including data on auditory
sensitivity, damage thresholds, and potential for behavioral disruptions of repre-
sentatives of all types of marine mammals (see Box 5.1~.
Recommendations for Research Sponsors
Developing an understanding of the effects of low-frequency sound on
marine mammals will require a more sustained and integrated approach than has
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MARINE MAMMALS AND LOW-FREQUENCY SOUND
been the case in previous research. Much research in the past was conducted by
single investigators responding to the need for specific information about the
effects of a single sound source. Multi-investigator teams of biologists, acousti-
cians, psychoacousticians, engineers, and statisticians should be funded to con-
duct a set of systematic studies of marine mammal species that represent different
potential hearing abilities, based on the need to know how sound of different
types affects characteristic species. The committee also identifies the need for
research to determine:
· now marine mammals utilize natural sound for communication and for
maintaining their normal behavioral repertoires;
.
the responses of free-ranging marine mammals to human-generated acous-
tic stimuli, including repeated exposure of the same individuals to the same
stimulus;
the response of deep-diving marine mammals to low-frequency sounds
whose characteristics duplicate or approximate those produced by acoustic ocean-
ographers and other sources of human-generated sound, such as low-frequency
military sonars and sounds used for seismic exploration;
· basic hearing capabilities of various species of marine mammals;
· hearing capabilities of larger marine mammals that are not amenable to
laboratory study;
· audiometric data on multiple animals of different sexes and ages in order
to understand variance in hearing capabilities within a given species;
· sound pressure levels that produce temporary and permanent hearing loss
. · .
In marine mammals;
· condition of a representative sample of important cochlear structures in
different species of wild marine mammals using post-mortem examinations;
· morphology and sound conduction paths of the auditory system in various
marine mammals;
.
· temporal-resolving power for various marine mammals;
· whether low-frequency sounds affect the behavior and physiology of
organisms that serve as part of the food chain for marine mammals; and
· whether low-frequency sounds affect the nonauditory physiology or struc-
tures of marine mammals.
Such research should be sponsored by the agencies that fund basic and
applied biological research and that fund ocean research using sound, including
ONR, NOAA, the National Science Foundation (NSF), the Minerals Manage-
ment Service, the Biological Resources Division of the U.S. Geological Survey,
and the National Institutes of Health (NIH). Mission-oriented agencies should
ensure that the research they sponsor will not only contribute to their immediate
missions but also answer basic questions about marine mammal bioacoustics.
Agencies that fund more fundamental science, such as NSF and NIH, should
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EXECUTIVE SUMMARY
7
consider funding marine mammal research when it has implications for under-
standing basic biology or health-related issues. Most importantly, all of these
projects should receive strict peer review and be evaluated on the quality of the
science proposed.
Other generators of sound in the ocean, such as shipping and hydrocarbon
exploration and production companies, also should participate in funding research
on the effects of sound on marine mammals. Given our ignorance about safe
exposure levels of sound, great benefit could accrue if ocean noise generators,
government agencies, and environmental groups formed a consortium to fund the
kinds of research recommended in this report. Opportunities may also exist for
cooperation between U.S. scientists and agencies and their counterparts in other
nations. Cooperation with Canada and Mexico could be particularly productive
because several species cross the exclusive economic zones of the three nations.
For example, another NRC (1999) report described research on marine mammals
that could benefit from binational research by the United States and Mexico.
Europe is also a likely source of partners for cooperative research and manage-
ment, given the shared marine mammal stocks and the existing cooperation in the
North Atlantic Treaty Organization, which shares both active and passive sonar
sources with the United States. A variety of organizations, including the Ocean
Drilling Program, provide models for the possible structure and functioning of a
multinational consortium for research on the effects of sound on marine mammals.
Research on captive marine mammals is expensive because of the need for
extended training and maintenance of animals and the added requirement of
highly specialized care (e.g., aquatic veterinarians). Funds to support marine
mammals must be provided for the long term because once an animal is in
captivity it generally must be maintained there for its lifetime. Facilities to
conduct research with marine mammals are difficult to set up, and most existing
commercial facilities are not able to provide access to animals for research.
However, without such facilities, many basic science studies on marine mammal
bioacoustics (and other aspects of marine mammal biology) such as those
described in this report cannot be conducted, and it will be difficult to develop
regulations that protect marine mammals appropriately. The lack of a specialized
marine mammal research facility available to U.S. scientists has hindered the
progress of research on marine mammal hearing. If the studies described in this
report are of sufficient priority to reduce uncertainties in the regulation of human-
generated sound in the ocean, federal agencies should consider establishing a
national facility for the study of marine mammal hearing and behavior. If estab-
lished, the proposed facility should be made available to the entire scientific
community, and the allocation of animal experimental and observation time
should be based on the scientific merit of proposals as determined by peer-
reviewed evaluation of research. Funding for research at this facility should be
coordinated with the availability of animals to ensure that once an investigator
receives funding he or she will have access to appropriate animals. The committee
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MARINE MAMMALS AND LOW-FREQUENCY SOUND
believes that such a facility could be established at relatively little incremental
cost by enhancement of an existing facility.
Our understanding of how marine mammals react to natural and human-
made sound is rudimentary. The actions recommended in this report could result
in significant advances in knowledge and better regulation of human activities
that might be harmful to marine mammals.
Representative terms from entire chapter:
marine mammal
