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This page includes archived research summaries of studies released in 2005

For the most recent research studies: [GO THERE]

For archives of research studies released in 2004: [GO THERE]
For archives of research studies released in 2006: [GO THERE]
See also archives of our News Digest coverage of science results: [GO THERE]

Also, check the AEI Special Reports on the annual International Whaling Commission Scientific Committee meetings, which always include important new science results related to noise
[2004: GO THERE] [2005: GO THERE] [2006: GO THERE]

Wildlife Response to Yellowstone Snowmobiles is Modest, Yet Reveal Clear Patterns of Increased Disruption
White, Davis, Borkowski. Wildlife responses to motorized winter recreation in Yellowstone. 2005 Annual Report. National Park Service. [DOWNLOAD REPORT(pdf)]
A survey of the responses of elk, swans, and bison to the approach of snowmobiles and snowcoaches reports that in 81% of encounters, the animals either showed no apparent response, or a "look and resume" response. Bison were the least reactive, with only 9% showing any active response (defined as attention/alarm, travel, or flight). Given the small proportion of animals responding, and the relative brevity of the responses, researchers concluded that average daily increase in energy expenditure would increase be under 5%. (note: these are averages; there is no indication of whether individual animals that are more sensitive may have more cumulative impact). Researchers also noted that there has been no apparent long-term population level effects over three decades of increasing motorized use prior to the introduction of wolves. Despite these reassuring totals, however, some clear patterns emerged that will be used in developing operational recommendations. The proportion of active responses increased dramatically as the number of snow machines increased (e.g. active response doubled in bison when snowmobile group sized increased from 2 to 4; an even more dramatic increase occured with multiple snowcoaches). Increased interaction time has an even more dramatic effect; each minute of lingering increased active response by a factor of 28x. The report recommends that all vehicles and humans on foot stay 100 yards from animals, that humans do not dismount or approach, and that they maintain consistent behavior, as deviations from familiar behavior spur more reaction.

Report on Marine Mammal Observations During LDEO Yucatan Seismic Survey: Few encounters, evidence that dolphins stayed at greater distance during operations
Holst, Smuleta, Koski, Haley. Marine mammal and sea turtle monitoring during Lamont-Doherty Earth Observatory's Marine Seismic Program off the Northern Yucatan Peninsula in the Southern Gulf of Mexico, January-February 2005. LDEO and NMFS, June 2005. [READ REPORT(pdf)]
During a 6 week academic seismic survey off the north coast of the Yucatan peninsula in early 2005, marine mammal observations were made in order to reduce exposure to high levels of sound, and to monitor behavioral responses to airgun sounds. The survey included 9400km of travel, during which 3500km of visual observations and 2900km of passive acoustic monitoring took place. Results indicate that only dolphins were encountered (no whales), and that dolphins tended to be closer to the ship during times when no airguns were firing than when they were. 13 detections were made using passive acoustic monitoring (i.e., listening via hydrophones). For acoustic monitoring, the mean encounter rate during non-seismic periods was more than three times higher than during seismic periods (9.2 vs. 2.7 sightings/1000km, respectively). 19 detections were made by visual observers. Of these, the first observed movement was toward the vessel only when airguns were off (other directions of movement showed no significant difference). The mean closest observed approach was 172 meters during non-seismic periods, and 472m during seismic operations (though the report notes that the mean for seismic periods was likely more, due to avoidance at distances greater that visible by the observers--as also reflected by the fact that visual detections took place only half as often during seismic operations, relative to non-seismic periods). Aerial surveys, which took place about every two days, revealed no stranded or floating dead animals. The airgun array was shut down once and powered down four times due to the presence of dolphins in or near the safety radius, all in shallow water where the 180dB safety radius was 3500m. Results for sea turtles were largely similar, with more sightings when airguns were off, though the closest observed approach was the same with airguns on or off. Four shut-downs and three power downs took place in response to the presence of turtles.

Helicopter Surveys Cause Minimal Disturbance to Seals, Penguins
Colin Southwell. Response behavior of seals and penguins to helicopter surveys over the pack ice off East Antarctica. Antarctic Science 17 (3), 328–334 (2005) [READ PAPER(PDF)]
Helicopter surveys are often used to monitor population levels of animals. In this study, researchers examined avoidance behavior, in response to the noise of the aircraft. They found that penguins moved more often and farther than seals, but that the distance moved seemed inconsequential. At close range (under 400m from the flight path), over half the penguins moved; the farthest any moved was 20m, but 90% moved less than 12m. Seals showed a similar extreme of movement, though 90% of those moving went less than 5m and far fewer responded: only about 20% moved at all, with another 25% exibiting an alert response without movement. Both animals showed some movement out the the limits of the test, 800m. While these results suggest that using aircraft for biological surveys is likely to not cause any dramatic impacts on populations, it also suggests than areas with high levels of aircraft traffic (eg, near villages, scientific outposts, common backcountry destinations, or industrial development) deserve to be examined for chronic modest behavioral disruption.

Prairie Dogs Show Increased Reaction, Rather Than Habituation, to Repeat Human Intrusion
Magle, Zhu, Crooks. Behavioral Responses to Repeated Human Intrusion by Black-tailed Prairie Dogs. Journal of Mammalogy, 86(3):524-530, 2005.
This study took place in rural and urban areas of Boulder, Colorado, where four colonies were approached over a hundred times over seven months. Contrary to expectations, the prairie dogs did not habituate to the intrusions, but rather retreats into holes when the intruders were at greater distances as the study proceeded. The distance at which barking was initiated did not change significantly during the study, fewer intrusions triggered barking over time, perhaps because the animals retreated at a distance greater than the normal barking distance.

Dolphin Group Foraging Vocalizations Vary by Habitat Type; No Evidence of Prey Stunning
Douglas Nowacek, Acoustic ecology of foraging bottlenose dolphins (tursiops truncatus), habitat-specific use of three sound typs. Marine Mammal Science, 21(4):587-602 (October 2005)
This study analyzed the relative use of three types of dolphin vocalizations (whistles, pops, and echolocation clicks) in two habitats (sandy bottom and seagrass). Echolocation, which is often considered to be used for both navigation and foraging, was found to be apparently less important to navigation than sometimes assumed; however, the dolphins being studied were all locals, so there is a good chance that they were familiar enough with the territory to navigate with minimal echolocation cues (similar familiarization has been observed in bats). Single foraging dolphins echolocated much more than dolphins in groups (even the cumulative number of clicks generated by the group was less than the number made by single foragers); this supports earlier suggestions by Tyack that dolphins are able to make use of clicks by their compatriots in ways that are not possible for single dolphins (for example, a fish between two dolphins would alter the sound of a click passing through it to a silent dolphin). In seagrass, echolocation was less frequent, which makes sense, as seagrass could scatter the echoes; pops were more common, and the suggestion is that these are designed to startle fish into revealing themselves from their hiding places in the grass. There was no evidence that the pops caused fish to be stunned or otherwise physically debilitated, as has been suggested elsewhere.

Sloping Seabottom, Microbubbles in Turbulent Water Proposed as Cause for Whale Strandings in Australia
Chambers S., James R. N. - Sonar termination as a cause of mass cetacean strandings in Geographe Bay, south-western Australia. p.391-398, Acoustics 2005, Acoustics in a Changing Environment. Proceedings of the Annual Conference of the Australian Acoustical Society, Busselton, Western Australia. November 9 - 11, 2005 [READ PAPER(pdf)]
Geographe Bay in southwest Australia has been the site of several mass strandings of cetaceans over the past 15 years. While acknowleding that other factors may well be involved, this paper describes the bioacoustics of the particular location, and suggests that a combination of a very gentle slope and the presense of micro-bubbles in the water (caused by turbulence of high seas) could cause echolocation signals sent by the cetaceans to attenuate before returning. The bubbles, in particular, absorb sound most effectively in the 50-70kHz range, just the range used most effectively as well by the affected cetaceans. Microbubbles can persist in the water after the passage of the storm that caused them. It should be noted that this study is based on acoustic modeling (eg, assuming perfect reflectivity of the bottom, etc), and that in situ measurements of the particular stranding locations would be needed to confirm the findings.

Louder Environments Associated with Lower Frequency Dolphin Calls
Morisaka, Shinohara, Nakahara, Akamatsu. Effects of Ambient Noise on the Whistles of Indo-Pacific Bottlenose Dolphin Populations. Journal of Mammalogy, 86(3):541-546, 2005.
This study looked at three separate populations of bottlenose dolphins in Japanese waters with varying levels of ambient noise. In habitats with less ambient noise, dolphins produced whistles at varying frequencies with greater modulations; when ambient noise was greater, dolphins produced whistles of lower frequencies (which travel further) with fewer frequency modulations. The results suggest that communication signals are adaptive and are selected to avoid the masking of signals and the attenuation of higher-frequency signals. The researchers note that the results do not support the acoustic niche theory, because even the lower frequency whistles did not avoid the ambient noise frequency range, but only maximized sound propagation within the noisy environment. They also note that further study is warrented on possible effects on behavior, social patterns, and development in populations adapting in this way to noise.

Harbor Porpoises Have Less Focused Directionality in Hearing than Bottlenose Dolphins
Kastelein, Janssen, Verboom, deHaan. Receiving beam patterns in the horizontal plane of a harbor porpoise. J. Acoust. Soc. Am. 118 2, August 2005. 1172-1179.
This study, using captive harbor porpoises trained to position themselves in the midst of 16 speakers arranged in a circle, and to leave the station when they heard a signal. Porpoises hear best (have greatest hearing sensitivity) within a 30 degrees of straight ahead, with reduced sensitivity around the sides and back; this increased sensitivity to sound coming from the direction the animal is swimming is more pronounced with higher frequency sounds (which thus allows them to better hear their own higher frequency echolocation and communication signals in noisy environments). The results imply that harbor porpoises have a wider receiving beam pattern, or less focused directivity in their hearing, as compared to bottlenose dolphins. More directivity helps an animal to perceive a biologically important sound in front of the animal within a noisy environment. Thus, we may suspect that harbor porpoises will be somewhat more impacted by noise than bottlenose dolphins; that is, as they are listening for their echolocation signals, they will be also hearing noise from a wider field around their target.

Bubble Growth in Tissues Can be Caused by Sound Energy
Crum, Bailey, Guan, Hilmo, Kargl, Matula. Monitoring bubble growth in supersaturated blood and tissue ex vivo and the relevance to marine mammal bioeffects. Acoustic Research Letters Online, ARLO 6(3), July 2005, p 214-220
In recent years, much research has looked at the formation and growth of bubbles in the tissues of whales that beached after exposure to mid frequency active sonar systems. Such bubble growth causes tissue damage, which in some cases has been extreme, even fatal. Rapid surfacing ("the bends") has been one concern; there has also been a question as to whether strong sound waves could themselves trigger bubble formation or growth in the tissues of deep-diving species. This study showed that tissue that is super-saturated with nitrogen, by being pressurized as in deep dives, does show signs of bubble growth after exposure to acoustic energy. The study used cow blood, livers, and pig kidneys, and took place in laboratory settings. It appears that tissue that has gone through a cycle of compression and decompression (as would be the case in marine species) is especially susceptible; the researchers stress that the sound waves did not CREATE the bubbles, but rather seem to have disrupted a stablization mechanism that normally keeps these bubbles small (perhaps lipid layers that surround the bubbles).

Hearing in Fishes Under Noise Conditions
Wysocki and Ladich. Hearing in Fishes Under Noise Conditions. JARO 6: 28-36, 2005.
This study exposed three species of fish to white noise of 110dB and 130dB RMS (typical of ambient noise conditions of natural habitats and fish-raising facilities), and found significant masking effects (in order for fish to hear another sound in the presence of the noise, the sound needed to be louder than what is normally audible). Hearing specialists (goldfish and catfish) showed the greatest loss in sensitivity (23-44dB in the goldfish, 4-22db in the catfish), while hearing generalist (sunfish) had far less reaction, with threshold increasing only at 130dB, and only 7-11dB. Researchers conclude that "results indicate that acoustic communication and orientation of fishes, in particular of hearing specialists, are limited by noise regimes in their environment." Note: Most fresh-water fish are hearing specialists, while most marine fish are hearing generalists. Hearing specialists tend to hear a wider frequency range of sounds, and to have more sensitive hearing; their hearing also tends to center on higher frequencies (since sound propagation in shallow waters favors high frequencies).

Amoser and Ladich. Are hearing sensitivities of freshwater fish adapted to the ambient noise in their habitats? The Journal of Experimental Biology 208, 3533-3542
This related study used recordings of four different fresh-water habitats as the "noise" source in a similar masking experiment. The aim was to address the question of whether the evolution of hearing specialization is related to the predominant ambient noise conditions of a given species. Using tapes of lakes and river backwaters, slow-moving waters, a flowing stream, and a large fast-moving river, they found that hearing specialists are only moderately masked by quiet habitats, but very affected by louder habitats. By contrast, hearing generalists are only moderatly affected even by noisy environments. They also found that two thirds of hearing specialsts spend all or part of their lives in quiet habitats, while less than half of hearing generalists live in quiet environments. they conclude that "the evolution of hearing specializations was facilitated by low ambient noise levels. this evolution was most likely forced by the necessity to detect abiotic noise, avoid predators, and detect prey..."

Dolphin Behavioral Responses to Boat Traffic
Ribeiro, S., F.A. Viddi, and T.R.O. Freitas. 2005. Behavioural responses of Chilean dolphins (_Cephalorhynchus eutropia_) to boats in Yaldad Bay, southern Chile. _Aquatic Mammals_ 31(2):234-242.
In Southern Chile's Yaldad Bay, boat traffic has increased over the past 25 years due to increasing aquaculture activities. This study looked at the reactions of the Chilean dolphin to boat traffic. Boat strikes are not a significant threat, so we can assume that most of the response is noise-related. There were several behavioral responses noted, some of which varied depending on what they dolphins were doing. During foraging, swimming speed did not change, but reorientation rate (changes of direction) increased; it also took longer to re-establish the pre-boat patterns. When traveling, however, swimming speed increased, while reorientation rate did not change, and they returned to normal patterns more quickly. In all situations, the presence of a boat triggered more group cohesion. The researchers note that "these findings emphasize the need to consider boat traffic disturbance on cetaceans in coastal management plans."

River Dolphins and Boat Traffic
Kreb, Daniëlle, and Budiono. Conservation management of small core areas: key to survival of a critically endangered population of Irrawaddy river dolphins Orcaella breviorostris in Indonesia. Oryx, Vol 39 No. 2 April 2005.
This paper is largely a population survey of Irrawadday river dolphins in the Mahakam River of Borneo (the species lives in just a few river systems in southeast Asia). The emphasis is on the critical need to establish some conservation areas, especially at river confluences, to assure the survival of the species. Rivers are difficult habitats to set aside preserves in, because they are used as highways for commerce, as well as being centers of subsistence activity (fishing and farming). One section highlighted noise impacts: "Noise pollution from high-speed vessels (4.6 boats/hr) causes the dolphins to dive significantly longer than usual when within 300m. Container barges (8.4 boats/day) pass through a narrow tributary which is primary dolphin habitat. Dolphins always changed their direction (if swimming upstream) when they encountered barges and moved downsteram ahead of the boats back to the confluence area."
Note - related paper from the previous year: Kreb, D., and K.D. Rahadi. 2004. Living under an aquatic freeway: Effects of boats on Irrawaddy dolphins (Orcaella brevirostris) in a coastal and riverine environment in Indonesia. Aquatic Mammals 30(3):363-375.

Effects of Airguns on Fish
Popper, et al. Effects of exposure to seismic airgun use on hearing of three fish species. J. Acoust. Soc. Am. 117 (6), June 2005, 3958–3971.
Controlled exposure experiments on caged fish of three species, designed to mimic a worst-case exposure scenario for riverine seismic surveys (shallow water, one-time passage of seismic vessel). Three species tested for TTS (temporary reduced hearing sensitivity) after exposure to 5 and 20 airgun shots. One species showed no TTS; two species showed significant TTS, with near full recovery after 24 hours. The results seem to support a current "linear threshold theory (LINTS)" that the degree of TTS can be predicted in a linear fashion, based upon the level of the stimulus above the hearing threshold of the fish (this could allow regulators to predict the degree of TTS likely in any given situation). The observed recovery leads the researchers to conclude that these species are "not likely to be substantially impacted" by riverine seismic surveys. However, they also note that ocean-based 3D surveys, in which a ship may pass by repeatedly, could lead to exposure to more shots, and thus perhaps higher levels of TTS; they recommend further studies in which exposure to more airgun shots is examined. It is also noted that during the period of reduced hearing sensitivity, individual fish could be "impaired in their ability to survive since they would have some loss in their ability to hear biologicially significant sounds." While no gross tissue damage was immediately obvoius, the authors are conducting microscopic analysis of the ear tissue, similar to that undertaken by McCauley (2003).

Ambient Noise Monitoring and Budgets
Two papers presented at the Spring 2005 Acoustical Society of America meeting addressed topics related to acoustic monitoring in the sea.
Jeffrey Nystuen and Bruce Howe. Ambient Sound Budgets. ASA 149th Meeting, May 2005.
The Nystuen/Howe (Univeristy of Washington) paper presented data from autonomous recorders in several locations. Wind and rain tended to be the dominant sounds, with shipping and whales also signficant; there was, however a wide variation depending on location. In Haro Strait, for instance, ships were present 59% of the time, while in sections of the remote Pacific, ships were heard less than 2% of the time. In general, low frequency sounds were louder (50-60dB) than mid and high frequency sounds (varying around 40dB). Heavy rain was measured at up to 80dB, and ships were often heard at 40-60dB (though in Haro Strait ship noise was more in the 70-85dB range). The paper looks at distribution of sounds through many windows; one of interest noted that in Carr Inlet (Puget Sound) boating accounted for 4% of total sound at low frequencies, but 66% of the loudest 5%, and 88% of the loudest 1%.
David Bradley, D'Spain, Miller, Frisk. The role of ocean observatories in monitoring for potential effects of man-made sound on the marine environment. ASA 149th Meeting, May 2005.
The Bradley et al paper looked at current and potential locations for ocean-based observatories that could respond to recent calls for better monitoring of ocean noise sources. There are existing acoustic monitoring locations throughout the Atlantic, across the North Pacific, and scattered in the south Pacific, Indian Ocean, and off the coast of Africa. The authors suggest evaluating for noise that could cause physiological damage, as well as acoustic masking, habituation/sensitization, and stress; they further stress the importance of measuring multiple metrics, in order to assess a variety of impacts: RMS, SEL, rise time, spatial diffusion of sources (to assess masking), and novelty of sounds. Their calculations of the total noise power budget in the North Atlantic and North Pacific suggest that shipping accounts for about 80% of noise, with wind being close to 10%, seismic surveys about 5%, animals about 3%, and military/academic the remaining 2%. These estimates are based on military and seismic being measured based on the short duration of each pulse (eg, they assumed 3 surveys audible from 3000km, 1% of the time).

Humpback Whale Distribution Changes in Response to NPAL Transmissions
Joseph Mobley Jr. Assessing responses of humpback whales to North Pacific Acoustic Laboratory (NPAL) transmissions: Results of 2001-2003 aerial surveys north of Kauai. J. Acoust. Soc. Am. 117 (3), Pt. 2, March 2005, 1666-1673.
This study consisted of aerial surveys of an area within 40km of the Kauaii transmission station of the NPAL (North Pacific Acoustic Laboratory, formerly ATOC, a Pacific-basin-wide ocean temperature research project using long-range, low frequency sound). Surveys were done 2001, when no ATOC transmissions took place, and in the days immediately after ATOC transmissions in 2002 and 2003. Total numbers of humpbacks observed varied from year to year (75, 81, 55 respectively), but there was no statistically significant reduction during transmmission years. It did appear that humpbacks were seen slightly farther from ATOC source and shore during transmission years, but the numbers seen were not enough to provide statistically significant results (a 1998 study off California, with many more whales present, showed a more significant shift away from the ATOC source, though the shift was from a baseline of being closer to the source, and thus higher received sound levels). It is also possible that, since the survey took place after the ATOC source stopped transmissions, the results reflect a quick return to baseline behavior. Finally, it could be that the whales are habituating to the source; this may be true in the larger time scale, as there appears to be no long term avoidance of Kauaii waters due to periodic ATOC broadcasts in recent years.

Ambient Noise Levels in the Stellwagen Bank Marine Sanctuary and St. Lawrence River Estuary Marine Park
Scheifele, Peter M. and Michael Darre. 2005. Noise levels and sources in the Stellwagen Bank National Marine Sanctuary and the St. Lawrence River Estuary. Marine Conservation Series MSD-05-1. U. S. Department of Commerce, National Oceanic and Atmospheric Administration, Marine Sanctuaries Division, Silver Spring, MD. 26pp.
A study of ambient noise levels in a rich marine area that is heavily impacted by shipping noise. Near the mouth of the St. Lawrence River, ambient noise levels are generally between 133 and 147dB (rms) at low frequencies (500Hz), 124-143dB at 1kHz, 96-120dB at 10kHz, and 83-99dB at 40kHz. In the Stellwagen Bank, further offshore in the Gulf of Maine, low frequency ambient noise ranges from 72-95dB at 50Hz, 43-98dB at 100Hz, and 50-81dB at 500Hz.

Lobsters Make Harmonic, Musical Sounds
G. Latha, S. Senthilvadivu, R. Venkatesan, and V. Rajendran. Sound of shallow and deep water lobsters: Measurements, analysis, and characterization (L). J. Acoust. Soc. Am. 117 (5), May 2005, pp. 2720–2723
Analysis of sounds made by lobsters supports an earlier observation that they sound similar to musical instruments. The sounds are made by striations not those made by a bow drawn across violin strings. In shallow-water spiney lobsters, the first three harmonic components of the fundamental frequency of 5.2kHz were observed (SPL 50-70dB); in deep-sea lobsters, the first four harmonic components of the fundamental frequency of 3.7kHz were apparent (SPL 120-143dB).

Effects of Airguns on Snow Crabs
DFO, 2004. Proceedings of the Peer Review on Potential Impacts of Seismic Energy on Snow Crab, Gulf Region. DFO Can. Sci. Advis. Sec. Proceed. Ser. 2004/045 (released May 2005)
This paper, the proceedings of a meeting held by the Canadian Department of Fisheries and Oceans, presents several studies undertaken in late 2003 during a commercial seismic survey in snow crab habitat, along with rough transcripts of the peer-review questions and answers. Crabs were caged in two locations, one meant to be the control, and one meant to be exposed to the airgun noise. Unfortunately, control cages received some sound from the airguns, and the exposure cages were positioned such that they did not receive maximum exposure. Also, temperature differences between the cages confounded interpretation of results. Main results included: there was no difference in mortality or mobility between the control and exposed groups. The primary concerns raised by the results involved larval development; exposed embryos hatched slower (by 5 days) and were more apt to be not fully formed upon emergence. Also, exposed larvae were very slightly smaller (colder incubation temperature may have been the cause). Among female snow crabs, hemorrhaging and membrane detachment in the crabs' ovaries was noted, and that the condition intensified between December (when the crabs were exposed to the airguns) and May. Similarly long-lasting and worsening effects were also detected in the hepatopancreas, which functions like a liver in a crab, with abnormal cell structure, swelling and stress detected. It is not known what behavioral implications the changes may have had. Changes to hepatopancreas and ovaries suggest subtle, long-term effects, which need to be addressed in future studies. There are questions about whether unusual sediments or dragging of cages may have played a role; and, again, the temperature differences cause ambiguity in interpreting the results.

Class 1 Powerboat Races and Noise Effects on Fish
Amoser, Wysoocki, Ladich. Noise emission during the first powerboat race in an alpine lake and potential impact on fish communities. J. Acoust. Soc. Am. 116 (6), December 2004.
Class 1 powerboat racing, with top speeds of 270km/hr, has largely taken place in offshore marine environments. This race was the first in an alpine lake, in Austria. Few measurements have been made of the sound emissions of these races, and this study provides a first "listen", with consideration of the hearing capacities of local fishes. Noise levels during the races were generally 10-15dB louder than ambient lake noise levels at a distance of 300m, increasing to 60-70dB louder than ambient close to the boats; source levels were about 180dB re 1uPa at 1m. Sound energy was predominantly low frequency (400-445Hz), with significant harmonics extending up to 5kHz. Researchers calculated that hearing specialists could likely detect the noise at distances of close to 400m, while hearing generalists would hear the boats at distances ranging from 30-200m, depending on species. Since there is a solid research base that shows fish avoiding intrusive sounds, researchers conclude that "fishes near the powerboats were disturbed."

Airgun Noise in Mid-Atlantic Recordings
Nieukirk, Stafford, Mellenger, Dziak, Fox. Low-frequency whale and seismic airgun sounds recorded in the mid-Atlantic Ocean. J. Acoust. Soc. Am., Vol. 115, No. 4, April 2004. P. 1832-1843
While doing acoustics research along the mid-Atlantic ridge, airguns from surveys along the coastlines of Canada, Africa, and South America were surprisingly audible at ranges of up to 3000 kilometers. Excerpts:
Since this hydrophone array was deployed, the periodic impulses produced by seismic exploration vessels operating around the Atlantic basin were the dominant signal detected. . . The broadband frequency range and repeated firing of these guns make them a major contributor to the low-frequency sound field in the North Atlantic. . . . Sounds associated with seismic airguns were recorded routinely on all hydrophones, and trends were similar in the two years (Fig. 7). Typically airguns were heard every 10–20s (Fig. 8). Although airgun sounds tended to dominate recordings during the summer months, loud whale vocalizations could still be detected during intense airgun activity (Fig. 8). Occasionally the array recorded airguns from more than one location, masking cetacean sounds and on four occasions making the spectrogram data impossible to use.

Acoustics in Ocean Observatories
Ocean observatories are networks of data-collection units, generally envisioned as installed on the sea floor, with some free-floating elements. Initial prototypes are in the planning stages for off the coast of Monterey, California, and the Pacific Northwest (British Columbia to northern California). Cabling will link many elements, with acoustic modems transmitting data in many cases. Acoustics may be used actively (communication via acoustic modems, perhaps some fish-finder sonar units to track species abundance) and passively (listening stations used for studying ocean animals, weather and climate indicators, and human noise). Here are some recent papers looking at where this may be headed:
Science Enabled by Ocean Observatory Acoustics (Howe, Miller, IASOO), from the 2004 ORION workshop: [DOWNLOAD(pdf)]
Integrated Acoustics Systems for Ocean Observatories - A subcommittee of the ASA's Acoustical Oceanography committee. Hosts a website describing planned uses of acoustics for both communication and passive acoustic monitoring, including many papers and reports from NEPTUNE/ORION/IOOS planners. [WEBSITE]

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