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5 Findings and Recommendations This report is the third in a series by the National Research Council examining the potential effects of ocean noise on marine mammals. Although these reports evolved from very different charges and were generated by separate committees, similar research needs became evident during each study. The recommendations in this report expand on rather than replace those from earlier efforts (Appendix D; NRC, 1994, 2000). Recommendations of all three reports should be examined to better comprehend the full spectrum of research required to understand the effects of human-generated noise on the marine ecosystem. It should also be noted that while some of the research needs from past reports, particularly from the first report (NRC, 1994), have been met, some of the new information has led to additional research questions that must now be answered. SOURCES OF NOISE IN THE MARINE ENVIRONMENT The recommendations made here are intended to improve our understanding of the effects of noise on marine mammals. To this end, any efforts to implement these recommendations should be planned and structured to facilitate use in conjunction with data on marine mammal physiology and behavior. Currently, data regarding noise produced by shipping, seismic surveying, oil and gas production, marine and coastal construction, and other marine activities are either not known or are difficult to analyze because they are maintained by separate organizations such as industry database companies, shipping industry groups, and military organizations. It would
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be advantageous to have all data in a single database in order to improve the ability of interested parties to access the data sets and use them in research, for scientific publications, in education, and for management and regulatory purposes. This database could be a distributed network of linked databases, using a standardized series of units of measure. International cooperation in this database development effort, as well as international access to the information, should be encouraged since the marine mammal and ocean noise issue is global. Recommendation: Existing data on marine noise from anthropogenic sources should be collected, centralized, organized, and analyzed to provide a reference database, to establish the limitations of research to date, and to better understand noise in the ocean. Each characteristic of noise from anthropogenic sources may differentially impact each species of marine mammals. The complex interactions of sound with marine life are not sufficiently understood to specify which features of the acoustic signal are important for specific impacts. Therefore as many as characteristics as possible should be measured and reported. Recommendation: Acoustic signal characteristics of anthropogenic sources (such as frequency content, rise time, pressure and particle velocity time series, zero-to-peak and peak-to-peak amplitude, mean squared amplitude, duration, integral of mean squared amplitude over duration, repetition rate) should be fully reported. For transients, publication of actual acoustic pressure time series would be useful. Experiments should be conducted that expose marine mammals to variations in these characteristics in order to determine the physiological and behavioral responses to different characteristics. Particular attention should be paid to the sources that are likely to be the large contributors to ocean noise in particularly significant geographical areas and to sources suspected of having significant impacts on marine life. Little is known about long-term trends in ocean noise levels. Although evidence is limited concerning long-term trends in ocean noise, and few observations concerning the effects of ocean noise on marine life exist, the current data are sufficient to warrant increased research and attention to trends in ocean noise. Recommendation: A long-term ocean noise monitoring program over a broad frequency range (1 Hz to 200 kHz) should be initiated. Monitoring and data analysis should include average or steady-state ambient noise as well as identifiable sounds such as seismic surveying sources, sonars, and explosive noise that are not identified in classical ambient noise data sets. Acoustic data collection should be incorporated into global ocean observing systems initiated and under discussion in the United States and elsewhere. A research program should be initiated that develops a predictive
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model of long-term noise trends. Data from monitoring systems should be available in a timely manner to facilitate informed decision making by interested industry, military, and marine researchers, operators, and regulatory agencies. Efforts must be made to measure ocean noise in marine mammal habitats. Until these habitats are fully known and described, it is reasonable to begin a long-term monitoring program in coastal areas and areas close to known marine mammal foraging, migration, and breeding areas. Recommendation: Efforts to measure ocean noise should be targeted toward important marine mammal habitats. As new marine mammal habitats are identified, these should be added to the acoustic surveys in order to provide a complete picture of the acoustic environment in important marine mammal ecosystems. Identifying reliable indicators for anthropogenic sources will provide an additional modeling tool and predictive capability that will be particularly useful in areas where long-term monitoring may be difficult or impossible. For instance, although the global shipping fleet increased from 30,000 commercial vessels in 1950 to 87,000 vessels in 1998, consequent noise changes cannot be determined because noise data were not collected in a systematic way to allow scientific comparisons, nor are they being systematically collected at this time. Similar needs exist for every facet of human activity in the oceans. Recommendation: Research to determine quantitative relationships between levels of anthropogenic activity and noise should be conducted. For example, if there is a robust relationship between vessel type and noise, vessel traffic data could be used to predict shipping noise. MARINE MAMMALS AND OCEAN NOISE Although it is difficult to obtain direct evidence of impacts of human activity on marine mammals, it is even more difficult to determine long-term impacts on individuals or impacts on populations. Although the few documented cases of direct impact on individuals have raised awareness of potential population impacts, no measures exist of marine mammal population effects from ocean noise. Recommendation: Whenever possible, all research conducted on marine mammals should be structured to allow predictions of whether responses observed indicate population-level effects. Despite the large body of marine mammal research to date, including what was recommended in previous reports (NRC, 1994), there is a sur-
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prising lack of information regarding the global distribution of marine mammals. Migration routes, breeding grounds, and feeding areas are known for relatively few species. In order to predict the importance of noise effects on marine mammal behavior, the seasonal and geographic distribution of the mammals must be better known both through survey data and through the use of predictive oceanographic variables, such as topography, bottom type, and water column variables. This enormous task will require the development of new sampling and extrapolation techniques in order to be practically achievable. Recommendation: Research should be conducted beyond locales already known and studied to globally characterize marine mammal distributions and populations. While good progress has been made in describing marine mammal acoustic repertoires, much less is known about the details of natural patterns of sound production, including the means of production and context in which different vocalizations are produced, as well as how they vary diurnally, seasonally, and geographically. Marine mammals themselves may be significant sources of ocean noise, although possibly in localized areas over limited time periods. Recommendation: Research should be undertaken to describe the distribution and characteristics of sounds generated by marine mammals and other marine organisms seasonally, geographically, and within behavioral contexts. These studies will also shed light on the contribution which marine organisms make to the global ocean noise budget. Efforts to improve marine mammal tagging technology should continue to receive support. Two technological improvements of current tags are needed: (1) increase the duration of long-term data-gathering tags from months to multiple years to observe annual behavior cycles and migration patterns, and (2) extend the duration of high-resolution tags from hours to days to gather more data on daily behavior and environmental cues. Current tagging technology allows individual marine mammals to be tracked up to months. Tags capable of higher-resolution data collection, including animal orientation, acceleration, and produced or received sounds, can generally collect data for less than one day. These data have proven very valuable in determining behavioral patterns in a variety of cetaceans and pinnipeds and correlating their behavior with environmental cues. The technology should continue to be developed to allow longer studies using both the high- and low-resolution tags. Recommendation: Marine mammal tagging studies should be continued to observe behavioral changes in response to acoustic cues and to provide important data for simulation models.
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Short-term responses of marine mammals to anthropogenic noise sources have been documented to a limited degree; however, long-term effects of marine noise on the behavior of marine mammals have received less attention. Impacts due to increases in background ambient noise have not been documented. Recommendation: Research should be conducted to determine subtle changes in marine mammal behavior, as well as failure to detect calls from other animals or echoes from their own echolocation, that might result from masking of biologically important acoustic information by anthropogenic sounds. Stress indicators may be one useful marker for long-term effects of anthropogenic noise on marine mammals. Recommendation: Research efforts should seek to determine if reliable long-term stress indicators exist and if they can be used to differentiate between noise-induced stress and other sources of stress in representative marine mammal species. Fish use sound in many ways that are comparable to the ways marine mammals communicate and sense their environment. The effects of anthropogenic noise on fishes and other nonmammalian species, including their eggs and larvae, are largely unknown. As cohabitants of the marine ecosystem and as members of the same food web, noise impacts on marine fish could, in turn, affect marine mammals. Recommendation: The impact of noise on nonmammalian organisms in the marine ecosystem should be examined. OCEAN NOISE MODELS Simulation models that predict the characteristics of the noise (frequency content, mean squared level, peak level, pressure time series, etc.) and their effects on marine mammals may assist in understanding and mitigating harmful effects of marine noise on mammals. At least one such effort is underway: the Effects of Sound on the Marine Environment model sponsored by the Office of Naval Research. Modeling some direct physiologic effects on hearing (e.g., temporary or permanent threshold shift) is relatively straightforward, although limited by the small data sets available from a limited number of species. These integrative tools should be expanded to include the effects of sources of noise that may change their distribution over time such as shipping, wind-induced breaking waves, and distributed biologic noise. More effort should be placed on modeling, both explicit marine species hearing models and behavioral effects models for all types of ocean noise. Recommendation: Modeling efforts that integrate acoustic sources,
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propagation, and marine mammals should be continued and fully supported. The conventional approach that utilizes an average pressure spectrum budget is limited in its application to the marine mammal problem. A more comprehensive approach that encompasses contributions of both transient events and continuous sources to ocean noise should be pursued. Many of this committee’s recommendations, particularly those concerning information on distribution and source signatures of man-made sources, must be addressed in order to have the capability to develop a marine-mammal-relevant global ocean noise model. In addition, since model validation is a critical part of the model development process, the committee’s recommendations pertaining to the collection of high-quality, well-documented ocean noise data sets must be pursued in tandem. Recommendation: A model of global ocean noise that properly reflects the impact of both ambient noise and noise from identified sources on marine mammals should be developed and verified. OVERARCHING RECOMMENDATIONS Federal leadership is needed to (1) monitor ocean noise, especially in areas with resident marine mammal populations; (2) collect and analyze existing databases of marine activity; and (3) coordinate research efforts to determine long-term trends in marine noise and the possible consequences for marine life. Recommendation: A federal agency should be mandated to investigate and monitor marine noise and the possible long-term effects on marine life by serving as a sponsor for research on ocean noise, the effects of noise on marine mammals, and long-term trends in ocean noise. Recent reports both in the press and from federal and scientific sources indicate that there is an association between the use of high-energy mid-range sonars and some mass strandings of beaked whales. Recent mass strandings of beaked whales have occurred in close association, both in terms of timing and location, with military exercises employing multiple high-energy, mid-frequency (1-10 kHz) sonars. In addition, a review of earlier beaked whale strandings further reinforced the expectation that there is at least an indirect relationship between strandings and the use of multiple mid-range sonars in military exercises in some nearshore beaked whale habitats. Several press reports about the recent incidents appeared while this report was in preparation attributing the strandings to “acoustic trauma.” Acoustic trauma is a very explicit form of injury. In the beaked whale cases to date, the traumas that were observed can result from many causes, both directly and indirectly associated with sound, but similar trau-
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mas have been observed in terrestrial mammals under circumstances having no relation to sound exposure. Careful sampling and analysis of whole animals have rarely been possible in the beaked whale cases to date, which has made definitive diagnoses problematic. To date, eight specimens in relatively fresh condition have been rigorously analyzed. Because of the repeated associations in time and location of the strandings and sonar in military exercises, the correlation between sonars and the strandings is compelling, but that association is not synonymous with a causal mechanism for the deaths of the stranded animals. The cause of death in all cases was attributed to hyperthermia, but a precise cause for the unusual traumas that were also seen in the cases examined has not yet been determined. The NATO/SACLANT Undersea Research Center report (D’Amico and Verboom, 1998) and the joint NOAA-Navy interim report (Evans and England, 2001) have not been discussed in detail in this document because of the preliminary nature of the findings. However, this is clearly a subject to which much additional research needs to be directed. Recommendation: A program should be instituted to investigate carefully the causal mechanisms that may explain the traumas observed in beaked whales, whether this is a species-specific or broader issue, and how the acoustics of high-energy, mid-range sonars may directly or indirectly relate to mass stranding events. The research program outlined in Evans and England (2001) represents a good initial effort. Addressing the challenge of both short- and long-term effects of ocean noise on marine mammals is a difficult problem and will require a multidisciplinary effort between biologists and acousticians to establish a rigorous observational, theoretical, and modeling program. An initial significant focus of this work should be the examination of the possible relationship between the acoustics of identifiable high-energy, mid-frequency sonars, marine mammal trauma, and mass stranding events. In addition, a study of the potential influence of ambient noise on long-term animal behavior should be vigorously pursued. Recommendation: A research program should be instituted to investigate the possible causal relationships between the ambient and identifiable source components of ocean noise and their short- and long-term effects on marine organisms. The public, including environmental advocates, are very interested in anthropogenic noise in the ocean and its effect on marine animals. Recently there has been a communication gap between users of sound in the ocean, including scientists, and the public. Much of the gap in understanding between the ocean science community and the public arises from the public’s lack of understanding of fundamental acoustic concepts and the scientific community’s failure to communicate those concepts effectively. Source and
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received levels, propagation loss, air-water physical acoustic differences, and the term “decibel” are examples of concepts that have been misunderstood by the media, environmental organizations, and the general public. Recommendation: The committee encourages the acoustical oceanography community, marine mammal biologists, marine bioacousticians, and other users of sound in the ocean, such as the military and oil industry, to make greater efforts to raise public awareness of fundamental acoustic concepts in marine biology and ocean science so that they are better able to understand the problems, the need for research, and the considerable potential for solving noise problems.
Representative terms from entire chapter: