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Underwater gliders for acoustic monitoring

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Quiet Autonomous Gliders Promise “New Era” in Acoustic Monitoring – A major step forward in acoustic monitoring has passed its first test. “We are entering a new era of underwater sensing,” says Jim Theriault of Defence Research and Development Canada, in Dartmouth, Nova Scotia, who ran the first trial of small torpedo-shaped “gliders” as a platform for acoustic monitoring. Unlike other systems, which require a boat nearby to monitor either the tagging of whales or other autonomous vehicles, the gliders can use a satellite phone connection to return data to distant research bases. Also, the new system has enough data capability to detect not only low-frequency baleen whale calls, but also the high-frequency calls of sperm and beaked whales,  Read the rest of this entry »

Beaked whale controlled exposure study

Science, Sonar No Comments »

Initial Cruise Report From First Controlled Exposure Studies of Beaked WhalesIan Boyd, Diane Claridge, Christopher Clark, Brandon Southall, Peter Tyack. Behavioral Response Study-2007, Cruise Report, Phase 1    A summary of the project, and the preliminary cruise report are available: [WEBSITE]During August and September, 2007, the first controlled exposure experiments aimed at learning more about the ways that beaked and pilot whales respond to exposure to mid-frequency active sonar took place in the Bahamas.  Read the rest of this entry »

Beaked whales fleeing near surface at risk for bends?

Science, Sonar No Comments »

Extended Near-surface Dives May Be Cause of Beaked Whale BendsWalter, M.X. Simmer, Peter L. Tyack. Repetitive shallow dives pose decompression risk in deep-diving beaked whales. Marine Mammal Science, Volume 23 Issue 4 Page 888-925, October 2007.  ScienceNow summary of paper: [WEBSITE]It is apparent that beaked whales are especially sensitive to mid-frequency sonar, but the reasons have remained elusive. This study explores a new idea about how the whales’ dive patterns may be disrupted enough to cause decompression sickness (DCS, ie “the bends”). Some have suspected that exposure to sonar may cause the whales to surface more quickly than usual, but since the whales’ lungs are collapsed in dives deeper than 70m (thus preventing nitrogen from entering the bloodstream and infiltrating into tissues where it could cause damage), it is not readily apparent how faster surfacing would cause DCS. Instead, this study looks at the “recovery” period observed in beaked whales, during which they make a series of near-surface dives before embarking on a new deep foraging dive. The researchers modeled the possible physiological effects of having this recovery period extended longer than usual. The team incorporated known physiological data into a model that charts how the bubble size might increase in the circulatory system, brain, muscles, and fat tissues when a whale dives repeatedly to between 30 and 80 meters for as long as 3 hours. The team’s model predicts that if the whales’ lungs do not collapse during a long series of shallow dives, the increased pressure can cause nitrogen bubbles to diffuse into tissues, increasing the risk of bubble formation on ascent. Such behavior may result if the whales perceive sonar transmissions as a predator:  Read the rest of this entry »

Boat traffic creates daily noise for dolphins

Ocean, Science No Comments »

Boat Traffic Noise High Enough in Intracoastal Waterways to Raise Concerns About Hearing Damage and Making; Dolphins Seem to Avoid Weekends
Haviland-Howell, Frankel, Powel, Bocconcelli, Herman, Sayigh. Recreational boating traffic: A chronic source of anthropogenic noise in Wilmington, North Carolina Intracoastal Waterway. J. Acoust. Soc. Am. 122 (1), July 2007, p.151-160.
 This study analyzed recordings of ocean noise during the summer season (June 21-September 1) in a 100m-wide intracoastal waterway off North Carolina. The mean received sound levels (measured as RMS re 1uPa, at frequencies averaged in steps over 0-37.5kHz) ranged from 109dB at 6am to 118dB in early afternoon and back down to 111dB by 10pm. Not surprisingly, weekends and holidays were 1-3dB louder than weekdays. The frequency spectrum shows that low frequencies (below 1kHz) dominate, with significant energy remaining up to 5kHz, and lesser but still perceptible noise up to the 37.5kHz limit of the study. Dolphin observations showed a clear reduction in numbers of dolphins observed on weekends and holidays, relative to weekdays; less than half as many dolphins were observed on weekends. Noise levels in the range of 5-25kHz, the primary range of dolphin social whistles, was of particular concern.
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LFAS effects on fish hearing

Science, Sonar No Comments »

Low Frequency Active Sonar Shows Less Impact on Fish than Airguns  

Popper, Halvorsen, Kane, Miller, Smith, Song, Stein, Wysocki. The effects of high-intensity, low-frequency active sonar on rainbow trout. J. Acoust. Soc. Am. 122 1 , July 2007. p. 623-635.
This study extended a previous line of research that had measured physiological impacts of seismic survey air guns on fish kept confined in a cage and exposed to the noise. This time, the research team exposed trout (which share hearing mechanisms with salmon, which are of special concern due to their endangered status) to sounds produced by low-frequency active sonar. LFA sonar uses frequencies (100-500Hz) that many fish can detect, often the range of most sensitive hearing. Fish were tested for hearing sensitivity using Auditory Brainstem Response (ABR), and some were sacrificed to check for physiological damage, including swim bladder or ear hair damage. Results indicate that fish had reduced hearing sensitivity after exposure to LFA sonar, ranging from 17-25dB at particular frequencies (i.e., sounds needed to be that much louder in order to be heard), and that the effects lasted at least 48 hours (the longest followup the study included). 

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