Extended Near-surface Dives May Be Cause of Beaked Whale Bends
Walter, 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: repeated dives travelling horizontally to escape the percieved predator could put the animals at risk. When fleeing an orca (their primary predator), such avoidance would like be short duration, and not dangerous; however, if the sonar transmissions continued to be audible for long periods of time, the whales might continue the avoidance dives to the point where they begin to sustain injury. This could also explain the relatively unusual appearance of beaked whales close enought to shore to end up beaching: they might be chased far from their normal habitat by continuing sonar sounds (ed. note: it also begs the question of whether many other animals are similarly injured, but happened to be fleeing in other directions). The team concludes that limiting the duration of sonar testing may prevent the animals from diving in these harmful patterns.
Related Paper: Analysis of Beaked Whale Dive Patterns With Consideration of Proposed Behavioral Risks in Response to Mid-Frequency Sonar
Tyack, Johnson, Soto, Sturlese, Madsen. Extreme diving if beaked whales. Journal of Experimental Biology 209, 4238-4253 (2006) [READ PAPER ONLINE]
This detailed report examines 44 dive sequences by 10 individual beaked whales. Deep foraging dives, during which the whales attempt to eat about 30 prey fish, last 45 minutes to an hour; between deep dives, they perform a series of dives closer to the surface. It appears that the surface dives become progressively shallower over the course of the hour to hour and a half spent between deep dives. The authors examine several proposed changes in dive behavior or possible physiological responses to observed dive patterns, and conclude that the evidence does not clearly support most of the proposals, noting that "aspects of the diving behavior of beaked whales remain enigmatic." They propose the theory explored in the physiological modeling paper above: that extending or altering the near-surface dive behavior could place the animals at risk for decompression sickness, triggering gas and fat embolic syndrome and stranding deaths.
Living in a Stethoscope: Low Frequencies Amplified in Burowing Mammal Tunnels
Simone Lange, Hynek Burda, Regina E. Wegner, Philip Dammann, Sabine Begall and Mathias Kawalika. Living in a “stethoscope”: burrow-acoustics promote auditory specializations in subterranean rodents. Naturwissenschaften, Volume 94, Number 2 / February, 2007, pp 134 - 138.
This very interesting study examined the observed decreased hearing sensitivity at a narrow range of low frequencies in subterranean mammals. While some researchers considered this to be due to lack of stimulation due to these frequencies being dampened in the tunnels, while other studies discovered a rich vocal repertoire at low frequencies. This study aimed to see whether the acoustic environment in burrows of subterranean mammals was similar, and so measured acoustic attenuation in the burrows of two different-sized species of mole rats. The researchers found that not only were frequencies between 200 and 800Hz not attenuated, but were actually amplified, up to 2x over three meters. Thus, the authors suggest that the decreased hearing sensitivity may have evolved to avoid over-stimulation of the ear in their natural environment. Ed. Note: These results spur questions related to elevated levels of low-frequency noise in tunnels, due to nearby roadway noise; such road noise amplification has been observed in unpublished studies by David Dunn.
Initial Cruise Report From First Controlled Exposure Studies of Beaked Whales
Ian 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]
Good article in Woods Hole magazine, Oceanus, on the research: [READ ARTICLE]
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. For the past decade or more, much emphasis has been placed on discovering what sound levels cause TTS (temporary threshold shifts, or short-term hearing impairment), with the thought that these levels could serve as a benchmark of exposure levels that we should be concerned about; however, it appears that in some cases, beaked whales that ended up stranding were exposed to much lower sound levels. Hence, the need to learn more about how they change their dive patterns and other behaviors in response to moderate sound exposure. D-tags, which have been successfully used in studies of sperm whales for several years, provide an opportunity to safely measure received sound levels and dive patterns simultaneously. The tags are applied with a long pole when the whales are at the surface, remain attached via suction cups, and fall off within 10 or 15 hours. The researchers noted that, in the absence of a clear sense of when and why some beaked whales are affected to such a strong degree that they beach and die, the result has been a highly precautionary and sometimes arbitrary approaches to management of sound, leading to debates between interested parties that have at times been difficult and ultimately unproductive. In planning for these experiments, the researchers worked with a wide range of parties, including environmental NGOs; while some NGOs had strong reservations about controlled exposure studies, the researchers note that "a constructive spirit of dialogue contributed to the success of the study." Goals of this study: to establish protocols for tagging and careful controlled exposures, to discern exposure parameters that cause a behavioral response (change in behavior), and to compare any responses to sonar signals and orca sounds, to begin to explore whether they respond to sonar as a possible predator. Ten animals were successfully tagged; 6 Blainsvilles beaked whales and 4 pilot whales. Seven provided control/baseline measurements, and 3 tagged animals were exposed to playbacks of MFA and/or orca sounds (1 beaked, 2 pilot). The researchers provide rather detailed descriptions of the responses of the one beaked whale that was tagged during controlled exposure; of course, with only one sample, and few controls, all results are very tentative.
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). However, the researchers note that there was quite a lot of variability in results, with some study groups showing little shift in hearing thresholds even with longer exposure to the LFA sounds, and some frequencies of hearing being little affected; also, the fish, being captive in a cage, were exposed to constant high sound levels that are unlikely in the wild, making this a probable worst-case scenario (the levels these fish were exposed to would occur only within 100m of the sonar transmission, which would be on a moving vessel). Unlike some earlier pile-driving and explosives studies, the fish exposed to LFA sounds did not show any acute tissue or organ damage. And, unlike earlier airgun studies, there was no apparent damage to ear hair cells; such injury would likely cause a permanent reduction in hearing sensitivity. The fish did respond to the onset of the sound with a rapid burst of swimming; this will be examined in another paper.
Right Whales Change Call Frequencies in Noisy Conditions
Parks, Clark, Tyack. Short- and long-term changes in right whale calling behavior: The potential effects of noise on acoustic communication. J. Acoust. Soc. Am., Vol. 122, No. 6, December 2007
This study looked at the ways that Right whale calls are altered by anthropogenic noise, primarily shipping. The authors used three approaches: listening to any changes that occur during transient nearby passage of a ship, comparing recordings from the 1950s with recordings made in recent years, and comparing right whale calls in quiter South Atlantic location with ones made off New England, where background noise from accumulated distant shipping is significantly higher. They found that during times of increased transient noise, the whales seemed to avoid using lower frequecies in their calls, call duration increased, and they made fewer attempts to communicate; this study did not measure whether the calls were louder in noisy conditions. Similarly, the longer time-scale studies observed an increase it the average frequency of calls in noisy conditions: average call frequency was 2/3 of an octave higher in 2000 than in 1956, and also sigificantly higher average frequencies in New England than Argentina. The authors note that it is possible that the measured differences could be attributed to other factors, including differences among individuals who chanced to be recorded, a predominance of young whales in modern studies, or slight speciation shifts between whale stocks; however, the clear pattern in the three distinct studies lends credence to the explanations that they are responding to high noise conditions. The paper concludes with this thought: "This is a significant result because
it indicates there could be a species-wide behavioral change in response to gradual but chronic increases in ambient noise over time. Given the observed behavioral response, the impacts on right whale communication need to be considered to determine what, if any, role increased noise may have on limiting reproduction and recovery of the species."
Deep Ocean Vents "Sing" With Tones
Crone TJ, Wilcock WS, Barclay AH, Parsons JD (2006) The Sound Generated by Mid-Ocean Ridge Black Smoker Hydrothermal Vents. PLoS ONE 1(1): e133 doi:10.1371/journal.pone.0000133 [READ PAPER(PLOS)]
Hydrothermal vents along deep ocean ridges, over 2000m below the surface, have been recorded for the first time. The vents increase the ambient noise level by 10-30dB, and include both broad-band noise and tones that are unique to each vent, perhaps indicating resonant frequencies of the cavities. The authors speculate that such sounds coudl be used by fish and other organisms living near the "black smokers" in order to avoid the scorching water, or to seek out prey living nearby. [UNIVERSITY PRESS RELEASE, WITH VIDEO AND AUDIO]
Noise Weakens Pair Bonding in Zebra Finches
Swaddle, John and Page, Laura. High levels of environmental noise erode pair preferences in zebra finches: implications for noise pollution. Animal Behavior, 2007, 74, 363-368.
Zebra finches are a model species often used in studies of pair-bonding in birds; in the wild, only 3% of offspring are illegitimate (sorry, got unscientific there for a second, I meant to say, are the result of "extrapair preference," or EPP); in noisy and dense captive conditions, these rates can rise to 11-30%. For this study, the researchers worked with captive zebra finches, who were of the first generation of a captive breeding program. They exposed females who had already bonded with a male (having already built a nest and raised a brood), to recorded white noise of various intensities, while giving the females access to two males. In a series of tests involving 20 pairs of birds, exposed in these conditions to three levels of white noise (45dB, 75dB, 90dB), there was little change from baseline in low noise conditions, moderate EPP in moderate noise conditions, and a high level of EPP, approaching equality with preference for original mates, in high noise conditions. The researchers propose two possible explanations: masking of the paired males' gentle bond-maintaining call, or inability to distinguish the pair-bonded male's calls from the other male under noise conditions.
Using Fixed Hydrophones to Listen for Whales: An Review of Current Techniques
Mellinger, D.K., K.M. Stafford, S.E. Moore, R.P. Dziak, and H. Matsumoto. 2007. An overview of fixed passive acoustic observation methods for cetaceans. Oceanography 20(4):36-45. [DOWNLOAD PAPER(pdf)]
This is a good overview of the state of technology and procedures used in using passive acoustics (listening to hydrophone recordings) in studying whale and dolphin populations. The focus here is population assessment, but the information is relevant to other uses of passive acoustics as well. The paper also features two very clear charts showing the frequency ranges used by several species of cetaceans, including both lower frequency calls and higher frequency echolocation clicks.
Related Paper: Review of 40 Years of Acoustic Playback Experiments
Deecke, V.B. Studying marine mammal cognition in the wild - a review of four decades of playback experiments. 2006. Aquatic Mammals 32(4):461-482 [DOWNLOAD PAPER(pdf)]
Since 1964, biologists have been using playback of sounds to assess behavioral responses in marine mammals. The purposes of these studies have ranged from learning more about the response of animals to sounds of their predators, investigating kin recognition or other communication questions, and determining responses to human noise. The author found 47 such studies: 17 prior to 1990, and 30 in the past ten years. This paper summarizes the historical trends and purposes of such research, and looks at procedural and design improvements that could be warranted.
Manatees Avoid Noisy Grassbed Feeding Grounds
Miksis-Olds, Donaghay, Miller, Tyack, Nystuen. Noise level correlates with manatee use of foraging habitats. J. Acoust. Soc. Am., Vol. 121, No. 5, May 2007, 3011-3020.
This study explores the possible effects of boat noise on manatee feeding behavior. After analyzing noise levels, presence of boats, and manatee preference of feeding location, the authors conclude that manatees are especially affected by low frequency boat noise in the morning hours, when a concentration of boats (likely fishermen heading out). In the morning, manatees seem to seek out quieter grassbeds to graze on, and avoid the louder areas (average sound levels differed by as much as 30dB); no such pattern emerges later in the day. Among other observations, the authors point out that manatee vocalizations are "not particularly loud, registering only 10 12 dB above the background noise at 3 4 m in a vegetation-choked canal. Increases in ambient noise levels on the order of 10 12 dB are not uncommon, but could have drastic repercussions for the manatee in terms of effective range of communication."
5-Minute Hearing Protocol Proposed for Use in Beached Cetaceans
Michel André, Eric Deloy, Eduard Degollada, Josep-Maria Alonso, Joaquin del Rio, Mike van der Schaar, Joan V. Castell, and Maria Morell. Identifying cetacean hearing impairment at stranding sites. Aquatic Mammals 2007, 33(1), 100-109.
This research team proposes a 5-minute AEP protocol for use in determining whether hearing impairment has taken place in stranded dolphins or whales. This study also substantiates the potential usefulness of such an approach by comparing the AEP results in a rehabilitated dolphin with results of a post-mortem necropsy, which revealed that the hearing loss was related to abnormal dilation of ventricles that prevented healthy acoustic reception (it was not possible to tell whether the dilation and associated lesions were caused by acoustic trauma or not). The researchers note that this dolphin appeared otherwise healthy, and that the profound hearing loss, approaching deafness, was the deciding factor in not releasing it back into the wild. They also note that, since few stranded cetaceans survive to be released, similar opportunities to compare AEP measurements and later necropsies could shed light on any possible patterns in hearing loss in stranded animals.
(Ed. note: Michel André and various research associates have been looking closely at possible noise-induced hearing loss in cetaceans in recent years. An incident that has been reported in the media and presented at conferences, but that has not has yet appeared in the literature, involved sperm whales struck by ferries, which, based on necropsies, were probably deaf or nearly so, at the same frequencies as shipping noise. Source: Powerboat World, 10/31/07 [READ ARTICLE] )
Evoked Potential and Behavioral Thresholds (Mostly) Not as Different as Previously Believed
Schlundt, Dear, Green, Houser, Finneran. Simultaneously measured behavioral and electrophysiological hearing thresholds in a bottlenose dolphin (Tursiops truncatus). J. Acoust. Soc. Am. 122 (1) , July 2007. p. 615-622.
Auditory Evoked Potential instrumentation measures brainwave patterns via electrodes placed on the outside of the skull of animals. AEP has been used in recent years as a way of doing relatively quick and easy testing of hearing sensitivity; a beached or captive animal is exposed to sound (at various frequencies and intensities) while the electrodes measure changes in brain activity, with increased activity is assumed to indicate that the sound was audible. Previous studies have observed differences in measured hearing sensitivity between behavioral observations and Auditory Evoked Potential thresholds, with dolphins appearing to react behaviorally to sounds as much as 20dB quieter than those that AEP indicate they can hear. It has been suggested that differences in the test environment, sound source, stimulus wave form, duration, or presentation of sound could account for these differences, so this study measured behavioral and AEP thresholds while holding these parameters constant. The results show a much closer fit between behavioral and AEP thresholds, mostly within 5dB, with some frequencies ranging somewhat higher (ed. note: including frequencies commonly used by dolphins for social whistles: a 12dB difference at 10kHz and 8dB at 20kHz). There was not a consistent pattern of behavioral thresholds being lower (ie responding to lower sound levels), as at some higher frequencies behavioral reactions occurred only with slightly louder sounds and at several frequencies there was almost no difference; it was at the lowest (10kHz and 20kHz) and highest (150kHz) frequencies measured that there was the most difference, in all cases more sensitivity shown in behavioral responses. The current researchers suggest that the difference at lower frequencies could be caused by the nature of the analysis system being used to measure the AEP threshold ("envelope following response", or EFR), which are not as effectively generated a lower frequencies, thus creating a higher threshold in the AEP results; they also note that some other studies have suggested that at the high ends of hearing sensitivity, perceptual magnification can take place, which may explain the more sensitive behavioral response to the high frequency sounds.
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. The researchers note that "mean hourly RLs exceeded 116 dB nearly every day surveyed, indicating bottlenose dolphins in the ICW near Wilmington, North Carolina could be at risk for noise exposure on a daily basis. High mean RLs were often recorded over consecutive hours, making high sound levels the rule in this area during the summer, not the exception." Further, they note that since bottlenose dolphins feed mainly on soniferous fishes (fish that make noise), and that fish vocalizations are primarily below 1kHz, the range most dominated by boat sounds, dolphins may well find it more difficult to hear and find prey.
Near-Surface Beaked Whale Sounds Recorded in Mid-frequency Range
Rankin, Barlow. Sounds recorded in the presence of Blainville's beaked whales, Mesoplodon densirostris, near Hawai'i. J. Acoust. Soc. Am. 122 (1) , July 2007, p. 42-45.
Recorded vocalizations near the surface, from three cow/calf pairs of Blainville's beaked whales. While foraging clicks are high-frequency, these frequency-modulated calls, somewhat similar to dolphin calls, were in lower frequencies. Four calls were recorded, and were in the frequency ranges of 6 and 16 kHz. This study extends our understanding of beaked whale calls; a recent study by Johnson et al did not detect any sounds with significant energy below 20kHz, and detected no calls when the animals were within 200m of the surface. Acoustic detection of beaked whales will be enhanced with this new information. In addition, as the researchers note, "The pulsed sounds presented in this paper provide verification that beaked whales do, indeed, use midrange frequencies which overlap in frequency with some naval sonar applications."
Current Marine Mammal Population Monitoring Effort Is Very Unlikely to Detect Even Precipitous Declines
Barbara L. Taylor, Melissa Martinez, Tim Gerrodette, Jay Barlow, Yvana N. Hrovat. Lessons from monitoring trends in abundance of marine mammals. Marine Mammal Science, 23(1): 157175 (January 2007)
Marine mammals are notoriously hard to count, since they spend so much of their time underwater. Scientists, policy makers, and industrial and military planners all need to have accurate assessment of populations and population trends. However, many populations are not surveyed often enough or comprehensively enough to really know how many animals there are. Using statistical analysis, the researchers looked at a hypothetical situation in which populations were declining 50% over a 15 year period (the rate at which a stock can be legally classified as "depleted"). The percentage of precipitous declines that would not be detected as declines by current survey techniques and frequency was 72% for large whales, 90% for beaked whales, and 78% for dolphins/porpoises, 5% for pinnipeds on land, 100% for pinnipeds on ice, and 55% for polar bears/sea otters (based on a one-tailed t-test, ? = 0.05; this number measures the statistical significance of the results, or in lay terms, how confident we can be in the results--more on this key factor below). "Fundamentally, we cannot reliably detect even precipitous declines in most whale, dolphin, porpoise, and ice-hauling pinniped populations with present levels of investment in surveys and current survey technology and design," the researchers stressed. They recommended several alternatives to improve performance, including (to list a few) more diligent focus on indicator species, increase in survey frequency, and most fundamentally, a change in the "decision criteria." This last suggestion involves a shift in the balance of risk between over-protection and under-protection: the current standard of statistical significance of ? = 0.05 means that we will over-protect (perceive a decline where none actually exists) only 5% of the time; meanwhile, this standard, as suggested by the results above, leads us to MISS a decline up to 50-90% of the time. Softening our standard of significance to ? = 0.2 would detect a decline 80% of the time that one existed, while also over-protect 20% of the time (equal over and under). They also suggested possible changes to the math used in analyzing trends, development of better models, and designing surveys to more specifically detect trends than absolute abundance (though noted the drawback that, especially during declines, it is common for distributional shifts to occur. In many cases, for animals that range widely, repeated survey cannot be sure that they are observing the same animals/population; thus, researchers suggest that changing the decision criterion is a "more reliable" solution.
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.
Pingers Used to Lower Dolphin By-Catch May Be Partially Effective
Leeney, Ruth H. et al. “Effects of pingers on the behaviour of bottlenose dolphins.” Journal of the Marine Biological Association of the United Kingdom 87 (2007): 129-133.
Pingers have been tested in the past few years for their usefulness in the mitigation of cetacean by-catch by fishing trawlers. In this study, Leeney et al. have conducted the first tests of this equipment on wild bottlenose dolphins. The study took place in the Shannon Estuary off the west coast of Ireland. Both constant pingers (CPs) and responsive pingers (RPs) were tested, the former making a sound every 5-20 seconds and the latter activating only when it senses dolphin clicks at close range. T-PODs, underwater recording submersibles, were moored both to the sea floor and to ships to record the dolphins’ vocal response to the pingers. Corresponding pingers were moved daily to prevent habituation of local dolphin populations to the sound. From the immobile locations, T-PODs recorded notably fewer clicks around active CPs than inactive, indicating avoidance behavior. The discrepancy was lower for RPs, which should be expected, as these only activate well within audial range. From the boats, both pingers had mixed effects. Sometimes dolphins would actively evade the sounds, and sometimes they would seem unaffected. It is unknown whether a pinger malfunction may have caused these differing reactions. The authors wish to emphasize that their results only apply to bottlenose dolphins, significantly different results having been found in previous studies on harbor porpoises.
Changes in Cetacean Abundance During Seismic Surveys in Brazil: Possible Long-term Monitoring Approach?
Parenti, JP de Araujo, ME de Araujo. Diversity of cetaceans as a tool in monitoring environmental impacts of seismic surveys. Biota Neotrop. Jan/Apr 2007 vol. 7, no.1
[DOWNLOAD PAPER (pdf)]
In this study, Brazilian researchers analyzed existing data on cetacean abundance (as monitored by the Brazilian government and reported to the IWC, and as monitored by seismic survey vessels), on seismic surveys (from Brazilian oil and gas agencies), and on oceanographic parameters; the period analyzed was from 1999 to 2004. The results suggest a decrease in the diversity of species in the face of an increase in the number of seismic surveys during the years 2000 and 2001, even though there was no significant change in oceanographic patterns in this period, and that a relationship exists between diversity of cetaceans and intensity of seismic surveys between 1999 and 2004. Most of the differences in diversity were caused by fewer dolphin species being observed. While more detailed and ongoing data collection (including more species and a broader array of other possible causes for changes in species diversity) will be needed to evaluate this seeming connection, the results suggest that species diversity may be a useful indicator of the long-term impacts of seismic surveys on cetaceans.
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 WindKey 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, 275291
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.
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): 690699 (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.