Anthropogenic Noise Sources Research Articles

Navy sonar, cetaceans and the US Supreme Court: A review of cetacean mitigation and litigation in the US

One source of anthropogenic noise in the oceans which has attracted much concern is naval sonar. As a result of possible impacts of such sonar, several environmental NGOs have pursued legal cases in the United States criticizing environmental assessments conducted prior to exercises and proposed mitigation measures. Cases have been brought using the US National Environmental Protection Act, Marine Mammal Protection Act, Endangered Species Act, Coastal Zone Management Act and other statutes. This paper reviews the chronology and results of these various cases. During the G.W. Bush presidential administration, the legal battle went to the US Supreme Court in the case Winter vs. Natural Resources Defense Council. This case however, did not address the potential impacts of sonar on cetaceans or the effectiveness of mitigation measures. During the Obama administration, mitigation measures for naval exercises have been revised, and working groups planned, in an attempt to resolve conflict between parties.

Impacts of Anthropogenic Noise on Wildlife: Research Priorities for the Development of Standards and Mitigation

Human development introduces anthropogenic noise sources into the environment across many elements of the modern terrestrial landscape, including roads, airports, military bases, and cities. The im...

Anthropogenic noise: Is this an issue for elasmobranch fishes?

Underwater anthropogenic noise has developed into a major national and international issue since it is becoming more apparent that human activities can have an adverse effect on the survival of fish stocks. It is unclear, however, whether human‐generated noise in the aquatic environment could have an effect on the health and behavior of elasmobranch fishes (sharks, skates, and rays), a group already being threatened worldwide due to overfishing. Many sources of anthropogenic noise produce sounds in the frequency range detectable by these fishes; however, elasmobranchs are not considered to have sensitive hearing and therefore we do not know if they could be affected by these sounds. A review will be presented of what is known and unknown in regard to elasmobranch hearing abilities as well as behavioral studies in which sharks were exposed to or attracted by auditory stimuli. With these in mind, the goal will be to address whether anthropogenic environmental noise could be having deleterious effects on elasmobranch fishes.

Characterizing and Locating Very Weak (−2.2 ≥ M L ≥ −3.4) Induced Seismicity in Unstable Sandstone Cliffs by Nanoseismic Monitoring

Unloaded natural rock masses are known to generate seismic signals (Green et al., 2006; Hainzl et al., 2006; Husen et al., 2007; Kraft et al., 2006). Following a 1,000 m3 mass failure into the Mediterranean Sea, centimeter-wide tensile cracks were observed to have developed on top of an unstable segment of the coastal cliff. Nanoseismic monitoring techniques (Wust-Bloch and Joswig, 2006; Joswig, 2008), which function as a seismic microscope for extremely weak seismic events, were applied to verify whether brittle failure is still generated within this unconsolidated sandstone mass and to determine whether it can be detected. Sixteen days after the initial mass failure, three small-aperture sparse arrays (Seismic Navigation Systems-SNS) were deployed on top of this 40-m high shoreline cliff. This paper analyzes dozens of spiky nanoseismic (−2.2 ≥ M L ≥ −3.4) signals recorded over one night in continuous mode (at 200 Hz) at very short slant distances (3–67 m). Waveform characterization by sonogram analysis (Joswig, 2008) shows that these spiky signals are all short in duration (>0.5 s). Most of their signal energy is concentrated in the 10–75 Hz frequency range and the waveforms display high signal similarity. The detection threshold of the data set reaches M L −3.4 at 15 m and M L −2.7 at 67 m. The spatial distribution of source signals shows 3-D clustering within 10 m from the cliff edge. The time distribution of M L magnitude does not display any decay pattern of M L over time. This corroborates an unusual event decay over time (modified Omori’s law), whereby an initial quiet period is followed by regained activity, which then fades again. The polarization of maximal waveform amplitude was used to estimate spatial stress distribution. The orientation of ellipses displaying maximal signal energy is consistent with that of tensile cracks observed in the field and agrees with rock mechanics predictions. The M L– surface rupture length relationship displayed by our data fits a constant-slope extrapolation of empirical data collected by Wells and Coppersmith (1994) for normal fault features at much larger scale. Signal characterization and location as well as the absence of direct anthropogenic noise sources near the monitoring site, all indicate that these nanoseismic signals are generated by brittle failure within the top section of the cliff. The atypical event decay over time that was observed suggests that the cliff material is undergoing post-collapse bulk strain accommodation. This feasibility study demonstrates the potential of nanoseismic monitoring in rapidly detecting, locating and analyzing brittle failure generated within unconsolidated material before total collapse occurs.

Anthropogenic and natural sources of ambient noise in the ocean

Ocean ambient noise results from both anthropogenic and natural sources. Different noise sources are dominant in each of 3 frequency bands: low (10 to 500 Hz), medium (500 Hz to 25 kHz) and high (>25 kHz). The low-frequency band is dominated by anthropogenic sources: pri- marily, commercial shipping and, secondarily, seismic exploration. Shipping and seismic sources con- tribute to ambient noise across ocean basins, since low-frequency sound experiences little attenua- tion, allowing for long-range propagation. Over the past few decades the shipping contribution to ambient noise has increased by as much as 12 dB, coincident with a significant increase in the num- ber and size of vessels comprising the world's commercial shipping fleet. During this time, oil explo- ration and construction activities along continental margins have moved into deeper water, and the long-range propagation of seismic signals has increased. Medium frequency sound cannot propagate over long ranges, owing to greater attenuation, and only local or regional (10s of km distant) sound sources contribute to the ambient noise field. Ambient noise in the mid-frequency band is primarily due to sea-surface agitation: breaking waves, spray, bubble formation and collapse, and rainfall. Var- ious sonars (e.g. military and mapping), as well as small vessels, contribute anthropogenic noise at mid-frequencies. At high frequencies, acoustic attenuation becomes extreme so that all noise sources are confined to an area close to the receiver. Thermal noise, the result of Brownian motion of water molecules near the hydrophone, is the dominant noise source above about 60 kHz.

Acoustic sampling for marine mammals in the Beaufort Sea July 2007–March 2008.

As climate change is driving rapid, unprecedented warming of the Arctic, there is increasing interest in how such change will impact Arctic marine mammals. Impacts are anticipated from from habitat alteration, including increasing ambient noise levels from shipping, seismic exploration for oil and gas and geophysical research, and (potentially) commercial fishing. In order to monitor natural and anthropogenic sources of noise, four autonomous recorders were deployed along the 100‐m isobath between Cape Halkett and Barrow and recorded data from July 2007–March 2008. The instruments sampled at 8192 Hz on a schedule of 10 min on, 20 min off. Marine mammal sounds recorded included pinnipeds (walrus and bearded seals) and cetaceans (bowhead and beluga whales), while anthropogenic sources included shipping and air gun sounds. Seasonal and geographic patterns for these sounds will be presented. These data form part of a broader‐scale international, year‐round monitoring program in the Arctic that we hope will ev...

Metrics for characterizing the sources of ocean anthropogenic noise.

Decibels are the standard shorthand for describing acoustic intensity and sound pressure level, but may lead to misunderstanding when applied as bioacoustic metrics. Acoustic power and source transmission energy are alternate metrics with intuitive appeal. Acoustic power, calculated from the acoustic intensity multiplied by the emitted solid angle, yields units of watts. Likewise, the energy per source transmission, given by multiplying acoustic power by the duration of the transmission, yields units of joules. For continuous (or quasicontinuous) signals, the standard procedure is to measure the root‐mean‐square (rms) of the signal. However, this presents problems for short duration signals where the duration of the signal being measured is an important parameter. In these cases it may be more appropriate to measure the peak‐to‐peak signal, rather than rms. Bandwidth is another important component of how the signal is described, typically in a narrow‐band for ambient noise and broad‐band for discrete sources. The characteristics of ocean anthropogenic noise sources in terms of these metrics will be discussed.

Underwater detection of tonal signals between 0.125 and 100kHz by harbor seals (Phoca vitulina)

The underwater hearing sensitivities of two 1-year-old female harbor seals were quantified in a pool built for acoustic research, using a behavioral psychoacoustic technique. The animals were trained to respond when they detected an acoustic signal and not to respond when they did not (go/no-go response). Pure tones (0.125-0.25 kHz) and narrowband frequency modulated (tonal) signals (center frequencies 0.5-100 kHz) of 900 ms duration were tested. Thresholds at each frequency were measured using the up-down staircase method and defined as the stimulus level resulting in a 50% detection rate. The audiograms of the two seals did not differ statistically: both plots showed the typical mammalian U-shape, but with a wide and flat bottom. Maximum sensitivity (54 dB re 1 microPa, rms) occurred at 1 kHz. The frequency range of best hearing (within 10 dB of maximum sensitivity) was from 0.5 to 40 kHz (6(1/3) octaves). Higher hearing thresholds (indicating poorer sensitivity) were observed below 1 and above 40 kHz. Thresholds below 4 kHz were lower than those previously described for harbor seals, which demonstrates the importance of using quiet facilities, built specifically for acoustic research, for hearing studies in marine mammals. The results suggest that under unmasked conditions many anthropogenic noise sources and sounds from conspecifics are audible to harbor seals at greater ranges than formerly believed.

Chronic Anthropogenic Noise Exposure and Songbird Hearing

As human populations have increased, our impact can now be felt even in the deepest remnants of wilderness (Vitousek et al. 1997). The resource demands of the ever-increasing human enterprise are creating substantial amplification of man-made pollution, including noise production. The dominant sources of anthropogenic noise are transportation networks, development (including energy, urban and industrial) and recreational activities. These activities are increasing faster than population growth. Between 1970 and 2007 the US population increased by approximately one third whereas (http://www.census.gov/compendia/statabO traffic on US roads nearly tripled, to almost 5 trillion vehicle kilometers per year, (http://www.thwa.dot.gov /ohim.tutw/tvpage.cfm.) Similar trends in shipping noise have also been observed in marine ecosystems, as discussed in reviews of noise impacts on marine animals (e.g., Nowacek et al. 2007).

Auditory masking of anuran advertisement calls by road traffic noise

There is growing concern that anthropogenic noise could interfere with animal behaviours by masking the perception of acoustic communication signals. To date, however, few experimental studies have tested this general hypothesis. One common source of anthropogenic noise is the sound of roadway traffic. We tested the hypothesis that road traffic noise can mask a female's perception of male signals in the grey treefrog, Hyla chrysoscelis, by comparing the effects of traffic noise and the background noise of a breeding chorus on female responses to advertisement calls. In this species, advertisement calls are necessary and sufficient to attract females for breeding. Using a phonotaxis assay, we presented females with an advertisement call broadcast at one of nine signal levels (37–85 dB, 6-dB steps) in one of three masking conditions: (1) no masking noise, (2) a noise simulating a moderately dense breeding chorus, or (3) a noise modelled after road traffic noise recorded in two wetlands near major roads. Females showed similar increases in response latency and decreases in orientation towards the target signal in the presence of both the chorus noise and the traffic noise maskers. Moreover, response thresholds were elevated by about 20–25 dB in the presence of both noise maskers compared to the unmasked condition. Our results suggest that realistic levels of traffic noise could place constraints on the active space of the acoustic signals of some animals.

The impacts of anthropogenic ocean noise on cetaceans and implications for management

Ocean noise pollution is of special concern for cetaceans, as they are highly dependent on sound as their principal sense. Sound travels very efficiently underwater, so the potential area impacted can be thousands of square kilometres or more. The principal anthropogenic noise sources are underwater explosions (nuclear and otherwise), shipping, seismic exploration by mainly the oil and gas industries, and naval sonar operations. Strandings and mortalities of especially beaked whales (family Ziphiidae) have in many cases been conclusively linked to noise events such as naval maneuvers involving tactical sonars or seismic surveys, though other cetacean species may also be involved. The mechanisms behind this mortality are still unknown, but are most likely related to gas and fat emboli at least partially mediated by a behavioral response, such as a change in diving pattern. Estimated received sound levels in these events are typically not high enough to cause hearing damage, implying that the auditory system may not always be the best indicator for noise impacts. Beaked whales are found in small, possibly genetically isolated, local populations that are resident year-round. Thus, even transient and localized acoustic impacts can have prolonged and serious population consequences, as may have occurred following at least one stranding. Populations may also be threatened by noise through reactions such as increased stress levels, abandonment of important habitat, and “masking” or the obscuring of natural sounds. Documented changes in vocal behavior may lead to reductions in foraging efficiency or mating opportunities. Responses are highly variable between species, age classes, behavioral states, etc., making extrapolations problematic. Also, short-term responses may not be good proxies of long-term population-level impacts. There are many examples of apparent tolerance of noise by cetaceans, however. Noise can also affect cetaceans indirectly through their prey. Fish show permanent and temporary hearing loss, reduced catch rates, stress, and behavioral reactions to noise. Management implications of noise impacts include difficulties in establishing “safe” exposure levels, shortcomings of some mitigation tools, the need for precaution in the form of reducing noise levels and distancing noise from biologically important areas, and the role of marine protected areas and monitoring in safeguarding cetaceans especially from cumulative and synergistic effects.

Recreational boating traffic: A chronic source of anthropogenic noise in the Wilmington, North Carolina Intracoastal Waterway

The majority of attention on the impact of anthropogenic noise on marine mammals has focused on low-frequency episodic activities. Persistent sources of mid-frequency noise pollution are less well studied. To address this data gap, the contribution of 25 physical, biological and anthropogenic factors to the ambient noise levels in the Wilmington, North Carolina Intracoastal Waterway were analyzed using a principal components analysis and least squares regression. The total number of recreational vessels passing through the waterway per hour is the factor that had the single greatest influence on environmental noise levels. During times of high boat traffic, anthropogenic noise is continuous rather than episodic, and occurs at frequencies that are biologically relevant to bottlenose dolphins. As a daily part of resident bottlenose dolphins' acoustic environment, recreational boating traffic may represent a chronic source of acoustic harassment.

Evaluation of the auditory capabilities of marine mammals using a portable auditory-evoked potential system

There is growing concern about the increasing amounts of acoustic pollution in our oceans. Anthropogenic noise sources span a large range of frequencies and amplitudes. The extents to which these noise sources adversely impact marine mammals is poorly understood yet they are of particular significance given that the acoustic environment is crucial for many aspects of marine mammal life. Past and present experiments have addressed the effects of different sounds on the hearing capabilities of captive dolphins. However, only a few individuals from a small number of species have been tested. Our research group has created a portable system that is capable of measuring the hearing thresholds of marine mammals using auditory-evoked potential (AEP) techniques. This portable system has enabled us to obtain audiograms of otherwise inaccessible marine mammal species. This system will also allow us to measure the hearing of stranded animals as well as begin to quantify the normal variations in hearing between different ages and genders of animals in captivity.

EFFECTS OF WATERCRAFT NOISE ON THE ACOUSTIC BEHAVIOR OF BOTTLENOSE DOLPHINS,TURSIOPS TRUNCATUS, IN SARASOTA BAY, FLORIDA

AbstractWatercraft may provide the greatest source of anthropogenic noise for bottlenose dolphins living in coastal waters. A resident community of about 140 individuals near Sarasota, Florida, are exposed to a vessel passing within 100 m approximately every six minutes during daylight hours. I investigated the circumstances under which watercraft traffic may impact the acoustic behavior of this community, specifically looking for short‐term changes in whistle frequency range, duration, and rate of production. To analyze whistles and received watercraft noise levels, acoustic recordings were made using two hydrophones towed from an observation vessel during focal animal follows of 14 individual dolphins. The duration and frequency range of signature whistles did not change significantly relative to vessel approaches. However, dolphins whistled significantly more often at the onset of approaches compared to during and after vessel approaches. Whistle rate was also significantly greater at the onset of a vessel approach than when no vessels were present. Increased whistle repetition as watercraft approach may simply reflect heightened arousal, an increased motivation for animals to come closer together, with whistles functioning to promote reunions. It may also be an effective way to compensate for signal masking, maintaining communication in a noisy environment.

Report provides roadmap for improving understanding of impacts of ocean noise on marine mammals

Several recent U.S. federal courts' injunctions against marine acoustical research have caused some scientists to worry about the very future of this research. They say it provides the most useful and important remote sensing tool available for learning about the geological structure of the seabed and discovering sub‐sea floor oil and gas reserves.In addition, they question why the research community is being targeted by some environmental and other groups who filed for these injunctions in the courts, rather than marine based industries, which are a far greater source of anthropogenic noise in marine environments.

Fish, mollusks and other sea animals’ use of sound, and the impact of anthropogenic noise in the marine acoustic environment

Many marine animals use sound and acoustic energy sensors to adapt to their environment. Most biological studies closely examine a particular species’ relationship to a specific stimulus. This report examines the fields of research on marine biological adaptations to sound since 1950, assembling an overview of the biological importance of sound in the ocean. It also examines the various sources of anthropogenic noise in the sea with a focus on the potential impacts of that noise on the marine acoustic environment. [Work sponsored by Earth Island Institute.]

Interpreting research results: Government regulation of anthropogenic noise sources

The Precautionary Principle, which advocates taking anticipatory management action in the absence of complete proof of harm, is embedded in several U.S. environmental laws, including the Marine Mammal Protection Act and the Endangered Species Act. However, in practice it is often ignored. Recent U.S. regulatory actions addressing the following anthropogenic noise sources are evaluated as cases in point: the North Pacific Acoustic Laboratory (NPAL), the U.S.S. Winston S. Churchill ship shock trials, and the Surveillance Towed Array Sensor System (SURTASS) Low Frequency Active (LFA) sonar. The impact of anthropogenic noise on marine mammals is poorly understood. Therefore, establishing adequate mitigation measures for noise sources is difficult. In an effort to increase knowledge and build toward certainty regarding the impacts of anthropogenic noise on the marine environment, recent research on low-frequency noise has focused on behavioral responses of large whales. These studies address limited hypotheses, but their results have been broadly interpreted to justify regulatory decisions. The pursuit of carefully designed research on the impacts of noise on the marine environment and the refinement of noise source mitigation is important, but interpreting research results is subject to political and economic pressures, casting doubt on the research conservation value.

Masking in three pinnipeds: underwater, low-frequency critical ratios.

Behavioral techniques were used to determine underwater masked hearing thresholds for a northern elephant seal (Mirounga angustirostris), a harbor seal (Phoca vitulina), and a California sea lion (Zalophus californianus). Octave-band white noise maskers were centered at five test frequencies ranging from 200 to 2500 Hz; a slightly wider noise band was used for testing at 100 Hz. Critical ratios were calculated at one masking noise level for each test frequency. Above 200 Hz, critical ratios increased with frequency. This pattern is similar to that observed in most animals tested, and indicates that these pinnipeds lack specializations for detecting low-frequency tonal sounds in noise. However, the individual pinnipeds in this study, particularly the northern elephant seal, detected signals at relatively low signal-to-noise ratios. These results provide a means of estimating zones of auditory masking for pinnipeds exposed to anthropogenic noise sources.

The detection of conspecific and heterospecific calls in noise by birds

Little is known about the effects of noise on the ability of birds to detect vocal communication signals. To address this question, an operant conditioning procedure was used to test two species of birds, budgerigars (Melopsittacus undulatus) and zebra finches (Taeniopygia guttata), for their ability to detect conspecific and heterospecific calls in noise. Calls from three species, budgerigars, zebra finches, and canaries (Serinus canaria), served as test stimuli. In general, budgerigars showed lower thresholds (better detection abilities) across all call types than zebra finches. Both zebra finches and budgerigars showed a similar pattern of threshold changes for call types from different species. Calls of budgerigars were the easiest to detect, followed by canary calls, and finally zebra finch calls. Call bandwidth, which increases across species from budgerigars, to canaries, to zebra finches, may influence the pattern observed in thresholds. Low-frequency, band-passed noise simulating anthropogenic noise sources resulted in considerably less masking than broadband white noise. Generally, these results conform to the power spectrum model of auditory function. [Work supported in part by the Comparative and Evolutionary Biology of Hearing at the University of Maryland, NIDCD Grant No. DC00198 to R.J.D., the SERDP program, and the U.S. Army Construction Engineering Research Laboratories.]