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Wind Farm Noise Can Mask Dolphin Calls at Very Close Range
Lucke, Lepper, Hoeve, Everaarts, van Elk, Siebert. Perception of Low-Frequency Acoustic Signals by a Harbour Porpoise (Phocoena phocoena) in the Presence of Simulated Offshore Wind Turbine Noise. Aquatic Mammals 2007, 33(1), 55-68, DOI 10.1578/AM.33.1.2007.55
In this study, a 7 year old captive (formerly stranded) male harbour porpoise was trained to accept Auditory Evoked Potential monitors and to remain relatively motionless in a pool while being presented with both pulsed and amplitude-modulated signals, both with and without the presence of a masking signal modeled on the sounds of wind turbines (the masking tone had a frequency spectrum from 16 Hz up to > 1 kHz, with strong tonal components at 200 Hz and 500 Hz). The results showed a modest masking effect (4.8-7.3dB) when the masking sound was received at 128dB re1uPa, at frequencies of .7, 1.0, and 2.0 kHz; there was no significant masking when the masking sound was received at 115dB re 1uPa. Due to a number of complex issues related to the study conditions, frequencies targeted compared to the broader spectrum of noise created by turbines, and the technologies used to make measurements, the researchers suspect that "the actual masking effect...could be larger....hence, a narrower test signal would be very likely to reveal a more pronounced masking effect." However, the likely range of this masking effect is rather small, in the order of tens of meters. Since turbines are spaced further than this apart, the masking zone of neighboring turbines would not overlap. Thus, any masking effect would only be noticed in the immediate vicinity of turbines. Researcher note, thought, that measurements of displacement indicate that harbour porpoises avoid turbines over slightly larger distances than the masking takes place in. The researchers note that actual sound measurements have been carried out only on relatively small turbines; new and larger turbine designs currently being constructed have been modeled for sound, but should be measured in the field once complete.
Listening: A More Accurate Way to Take the Blue Whale Census?
McDonald, Mark A. et al. “Biogeographic characterization of blue whale song worldwide: using song to identify populations.” Journal of Cetacean Resource Management 8.1 (2006): 55-65.
Listening for regional differences in blue whale song may be the quickest way to ascertain their group distribution and dynamics for the purpose of population-scale management, propose McDonald et al. Researchers here identified specific regional dialects that suggest the extent of sub-populations of blue whales. Some populations, such as along the east coast of North America, are fairly concentrated in one area, while others, including one that ranges across much of the North Pacific, are more wide-spread. The paper suggests that the stock structures of blue whales, traditionally based on International Whaling Commission boundaries, should instead be reconstructed based on song, which would more accurately represent their true population distributions. In addition, current methods of census-taking, which include taking of tissue samples and photographs, stand to be bolstered by the addition of an audio record. The authors looked into decades-old blue whale recordings and have found that blue whale song can be divided into nine stabile and distinguishable dialects worldwide. These dialects can be more broadly grouped into three categories. Songs containing only simple tonal elements are evident in the North Atlantic, North Pacific, and Southern Oceans. Songs that also include complex pulsed units are sung off the west coast of the Americas and around New Zealand. Finally, the longest and most complex songs can be found in the Indian Ocean. More song types may be found as the poorly studied Indian and South Atlantic oceanic regions are given more attention. Critics of this paper point to songbird studies: ornithologists put ecological and social factors above genetics in importance for birdsong variation, invalidating it as a source of population structure data. McDonald et al. admit the need for a larger body of corresponding genetic data before they can effectively determine whether or not song reflects heredity in the case of blue whales. If it is validated, however, audial monitoring seems the most cost-effective method and the one most potentially able to detect short-term changes in populations. The authors anticipate further refinement of the ability to quantify populations based on recordings.
Nearby Ship Likely Masks Beaked Whale Calls, Dive Cut Short
Soto, Johnson, Madsen, Tyack, Bocconcelli, Baorsani. Does intense ship noise disrupt foraging in deep-diving Cuvier's beaked whales (Ziphius cavirostris)? MARINE MAMMAL SCIENCE, 22(3): 690–699 (July 2006)
This paper reports on a single observation that suggests the need for further investigation: an acoustic digital tag was attached to a Cuvier's beaked whale, which then exhibited an unusual foraging dive pattern when a large ship passed nearby. The tag was attached for over 15 hours, during which the whale made eight deep dives, with typical click and buzz vocalizations recorded on all dives. During the fourth dive, a single large ship passed nearby, and the dive was seemingly cut short (42 minutes; the mean of the other 7 dives was 57 minutes). A key finding was that the ship noise included frequency components close to beaked whale clicks; the 15dB increase in ambient noise levels caused by the ship would decrease the maximum effective range of echolocation by more than half, and the maximum range of communication between whales by a factor of five (it is assumed that foraging at depth involves coordinated behavior among several whales, so that this vocalizing is important). The results presented here came from a Z. cavirostris tagged some 25 km south of the busy ports of Savona and Genoa. Dense vessel traffic in the area includes ferries (conventional and high speed), tankers, cargo ships, and recreational boats. While beaked whales in the area may well be habituated to moderate noise levels from ship traffic, the apparent response to a close ship approach reported here suggests that they may not habituate to the elevated noise levels from such a close approach, which may be less common.
Wind Farms Show Little Effect on Fish, Modest Effects on Porpoises
DONG Energy, the Danish Energy Authority, and the Danish Forest and Nature Agency. Danish Offshore Wind–Key Environmental Issues. November 2006.
[DOWNLOAD REPORT (pdf)] [MAIN AGENCY WIND FARM SITE]
A Danish government report on the environmental effects of ocean-based windfarms showed some interesting findings. Fish abundance was not significantly affected by either construction (pile-driving) or operations at the two wind farms studied; there was some expectation that the turbine structures might create an attractive "artificial reef' habitat that would attract fish. At one windfarm site, dolphin abundance was only slightly affected by construction, and no effect was seen during operations, while at the other windfarm, a clear decrease in porpoises occurred during construction, and persisted during the first two years of operation, with possible signs of a slow recovery. Birds tended to avoid the vicinity of the turbines, and there was considerable movement along the periphery of both windfarms.
Weddell Seals Hear Aircraft More Clearly Than Oversnow Transport
van Polanen Petel, terhune, Hindell, Giese. An assessment of the audibility of sound from human transport by breeding Weddell seals (Leptonychotes weddellii). Wildlife Research, 2006, 33, 275–291
After making underwater recordings of carefully controlled passages of a variety of human transport vehicles (walking with crampons, four wheeled ATVs, tracked ATVs, helicopter, Twin Otter airplane, and Zodiac boat), the researchers created sound profiles for each type of vehicle, and modeled the likely received levels against Weddell seal hearing sensitivity. Results suggest that the ground vehicles were most commonly inaudible or barely audible, while the air and water vehicles were likely barely to clearly audible (20dB above Weddell seal threshold of hearing). More specifically, the tracked oversnow vehicle would be clearly audible when closer than 32 meters, and barely audible when closer than 156 meters; helicopters in flight would be barely audible at altitudes of up to 2500 feet, 250 meters lateral from the animal; airplane takeoffs at 500m would be barely audible, and Zodiac travelling at 35km/h would be clearly audible at 3000m. The study also included making recordings of Weddell seal vocalizations, to observe any changes observed during low-amplitude over-snow vehicle noise; call types did not change, but the seals did decrease their calling rate.
Nerves May Use Sound, Rather Than Electricity - A new study by Danish scientists suggests that communication between nerves may take place via sound or vibratory waves, rather than electrical impulses, as long believed. The lack of evidence for heat given off by nerves, as would be expected if electricity were involved, led to the new inquiries. The researchers propose that the lipid fats in the membranes of nerve cells could transmit vibrations efficiently. Their suggested mechanism could also explain how anesthesia works; changes in the temperature of the lipids would diminish their ability to transmit information between nerves. Source: CBC, 3/9/07 [READ ARTICLE] Press Release (with picture), 3/7/07 [READ PRESS RELEASE]
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