Ears Wide Open

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 stabilization 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 moderately affected even by noisy environments. They also found that two thirds of hearing specialists 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."

Moderate Noise Exposure Increases Heart Attack Risk - A major new study of heart attack risk looked at the effect of chronic exposure to moderate environmental (traffic) and workplace noise. After controlling for other more classic risk factors, researchers found a significant increase in heart attacks in men (doubled risk) and women (tripled risk) exposed to environmental noise, and in men exposed to workplace noise. The risk seemed to increase as sound increased, up to about 60-65dB, after which risk leveled out. Current workplace noise standards range from 90dB in the US to 85 in most of Europe; 60dB is a typical noise level in a busy large office while 85dB is equivalent to road construction equipment, according to the scientists. One explanation was that noise might increase psychological stress and anger, causing physical changes such as increased levels of adrenaline and noradrenaline, hormones linked to increased blood pressure. Especially interesting was that annoyance about noise was not related to risk, while the actual exposure level was. These findings may also raise questions about risks to animals exposed to human noise, where stress may also be triggered, especially if annoyance (as evidenced in animals by avoidance of noise) is not a reliable measure of impact. Sources: MedPageToday, 11/23/05 [READ ARTICLE] Reuters/Alternet, 11/24/05 [READ ARTICLE] The Australian, 11/25/05 [READ ARTICLE]

NRDC Releases Oceans of Noise Report - Increasing levels of ocean noise generated by military sonar, shipping, and oil and gas exploration are threatening dolphins and whales that rely on sound for mating, finding food and avoiding predators, according to a new report. The report released Monday by the Natural Resources Defense Council found that the effects of ocean noise on marine life range from long-term behavioral change to hearing loss to death. The report, a follow-up to a 1999 study, included details from necropsies performed on beached whales suspected of being exposed to Navy sonar. Sources: AP/Seattle Post-Intelligencer, 11/22/05 [READ ARTICLE] Virginian Post-Pilot, 11/23/05 [READ ARTICLE] ENS, 11/22/05 [READ ARTICLE(sub)]

Hospital Noise Hampers Healing - A review of 20 years of studies of hospital noise indicates that not one facility has met World Health Organization noise standards. A team from Johns Hopkins University Hospital, considered America's top hospital, began close to home; they discovered that even the newest wings, designed with acoustics in mind, routinely exceed standards. WHO standards for hospitals are undeniably stringent: 35 dB during the day, 30dB at night, about the sound level of a loud whisper. However, since the establishment of the standards, noise levels have been rising, from around 40dB in the 1960s, to about 60dB today, the level of a person talking loudly. Low frequency noise from air conditioning, the beeping of machines, and the reverberations caused by hard walls (best for sanitation), all contribute to the problem. Intensive care units are, ironically, especially noisy. "People have been complaining about hospital noise for years, but little has been done about the problem," says Johns Hopkins acoustic engineer James West. It seems the complaints have actually been going on for centuries. Florence Nightingale wrote in 1859: "Unnecessary noise is the most cruel absence of care which can be inflicted either on sick or well." It isn't just a matter of disturbing the patients' peace, the researchers say. Noise contributes to stress in hospital staff, and some studies have suggested that their memory and other mental functions can be impaired by it. And high sound levels have been found to slow down wound healing. Source: Nature News, 12/20/05 [READ ARTICLE]

Recordings Reveal Whale Dialects and Appearances in Unexpected Places - Blue whales off the Pacific Northwest coast sound different than blue whales that live in the western Pacific Ocean, and those sound different from blue whales off Antarctica. And they all sound different than the blue whales off Chile, according to scientists listening to whale sounds recorded by undersea microphones moored to the ocean floor. "The whales in the eastern Pacific have a very low-pitched pulsed sound, followed by a tone," NOAA researcher David Mellinger explained. "Other populations use different combinations of pulses, tones and pitches. The difference is really striking, but we don't know if it is tied to genetics, or some other reason." In addition, the network of hydrophones reveled a surprising concentration of sperm whales wintering in the Gulf of Alaska, and the first identification of North Pacific right whales in the Gulf of Alaska in decades. "There has been only one confirmed sighting of a right whale in the Gulf of Alaska since 1980, so discovering them is not only surprising, it is fairly significant," said Mellinger. "We picked up the sounds of one whale off Kodiak Island, and several others in deep water, which is also something of a surprise, since most right whale sightings have been near-shore." The recorders are attached to hydrophones that are held at different distances from the ocean floor and are equipped with disk drives able to store tens of gigabytes of data, she writes. This allows them to operate for months before they are recovered and the data accessed. Source: Science Daily, 1/2/06 [READ ARTICLE]
Related: Scientists Listen for Minke Whales in Antarctic - Scientists on a research voyage into the Southern Ocean are trying to discover the unheard song of the Minke Whale. The whale songs of other species have been identified and used to track animals, but the sound made by Minke Whales is yet to be determined. During the voyage, sonar buoys will be dropped every few hours in an attempt hear the Minke song. Dr Jason Gedamke says population information comes from sightings of whales and would be more accurate if whales could also be acoustically tracked. Source: ABC, 1/2/06 [READ ARTICLE]
Related: Mysterious Boing Sound Attributed to Minke Whales - One particular song, a sort of fluttering echo, or "boing," sound first heard by human listeners in the North Pacific Ocean in the 1950s (and recorded by US Navy submarines) baffled scientists. Where was it coming from? Only now have the sounds been identified as coming from minke whales. Shannon Rankin and Jay Barlow, scientists at the National Marine Fisheries Service in La Jolla, California, have gathered hydrophone data in the body of ocean between Mexico and Hawaii and combined this with visual sightings of the marine mammals. Not only has the source been traced to minke whales, but the songs seem to be somewhat different on either side of a certain longitude. Source: AIP, 11/16/05 [READ ARTICLE]