Freeway noise can be much louder than expected over 300m in some atmospheric conditions
Ovenden, Shaffer, Frenando. Impact of meteorological conditions on noise propagation from freeway corridors. J. Acous. Soc. Am. 126 (1), July 2009, 25-35.
This study combined field recordings and new acoustic modeling to describe the effects of wind shear and temperature differentials on the distance over which road noise exceeds regulatory limits. The particular concern here is whether reducing the height of barrier walls (which is sometimes allowed when quiet road surfaces are used) will lead to increased noise at a distance. This study could offer important additional information for use in recent US National Park Service efforts to understand the ways that road noise affects the "effective listening distance" of animals nearby. The results MAY also have applicability to some wind farm noise issues, though extrapolation from these results must be made with extreme caution.
The essence of this study's results is that sound may bounce off a layer boundary that is caused by wind shear or temperature layers at 30-50 meters high (a wind shear is a situation in which wind speed increases substantially with height, especially when there is a relatively sharp boundary between low and higher wind speeds). Most sound propagation models assume relative uniformity in the atmosphere; this study aimed to see how propagation differs from traditional models when the atmosphere is more varied. In some conditions, the researchers here found that while sound levels remain close to what traditional sound models would suggest at ranges of 200-300 meters, noise levels can actually increase at ranges of 300 meters and beyond, creating conditions in which regulatory limits are exceeded at these greater distances. In some conditions, increases occur in chaotic patterns at closer ranges, as well. The difference between traditonal sound models and the results here were as high as 15-20dB, and quite commonly occurred at 5-10dB.
While there is much interest in what may be causing reports of excessive noise from wind farms, and this work may inform these inquiries, it should be noted that the wind shears studied here may not apply to many industrial wind farms. Most notably, the hub heights of turbines may well be above the level of the wind shears addressed here (especially in problematic situations in which night time wind shears trigger turbines into action), so that the noise is not reflected downward in patterns similar to those of ground-based noise such as traffic. However, there clearly are some atmospheric conditions in which wind farm noise is higher than expected, sometimes at surprisingly large distances, so consideration of these effects would be a very useful topic for further study. It is quite possible that the turbine sound that does project down toward the ground during wind shear conditions is subject to the same factors that create chaotic and at times surprisingly high levels at larger distances; this could partially account for unusually high noise levels reported by some neighbors at certain times.
Exciting new models for assessing and visualizing extent of noise impacts in the ocean
Clark, Ellison, Southall, Hatch, Van Parijs, Frankel, Ponirakis. Acoustic masking in marine ecosystems: intuitions, analysis, and implication. Mar Ecol Prog Ser, Vol. 395: 201-222, 2009. [DOWNLOAD (pdf)]
This has to be one of the most exciting papers I've seen this year; reading it was downright joyous, especially in contrast to decidedly unsatisfying previous attempts to address cumulative impacts of ocean noise (mostly undertaken by large committees and resulting in vague and complex conceptual approaches that are nearly impossible to implement). By contrast, here we have, at last, a clear and strikingly rigorous approach to assessing the impacts of ocean noise sources on the communication of whales. As promised in the introduction, the authors "present an analytical paradigm to quantify changes in an animal's acoustic communication space" and "a metric to quantify the potential for communication masking." While of course, much uncertainty remains, both in some of the specific terms used in these metrics and in assessing the biological impact of reduced communication space, the tools provided here will open a vast and exceedingly useful new doorway for biologists and ocean managers.
Researchers will find much to work with in the suite of new metrics and relatively simple functions used to calculate them, including factors that reflect "ancient ambient" conditions as well as "present ambient" and "present noise sources", a more nuanced twist on signal-to-noise ration called the "recognition differential", acknowledgement of subtle biological inputs such as "signal processing gain", and "potential communication space" for a sender, and for a receiver hearing multiple other animal senders….this is just a hint of the power of these combined metrics, and surprisingly, most of the functions are really quite simple, though they do of course interact in complex ways. The present examples focus on the effects of low-frequency shipping noise on low-frequency communication by large whales, and incorporate differences in the specific frequency ranges used by the three species addressed; the model can easily be used to address mid- or high-frequency noise sources and higher frequency animal sounds such as those used for echolocation.
For the rest of us who are not designing new studies, though, the power of this approach is equally clear, and can readily inform both public awareness and policy-making. Extending the nascent idea of "communication space" (which has recently been introduced in terrestrial ecosystems by researchers at the National Park Service and Colorado State) into ocean habitats, we are presented with an intuitively obvious way to both imagine and assess the effects of ocean noise – measuring the area in which an animal can hear or be heard by others of its species. As its first application, this paper presents data from ongoing work at Stellwagen Bank National Marine Sanctuary offshore from Boston Harbor. There, a network of hydrophones is collecting soundscape data that allows researchers to both pinpoint and track the locations of whales and ships, along with the actual received sound levels throughout an extended area. By plugging this data into their new equations, the researchers are able to, for the first time, quantify the effects of shipping noise on local populations of fin, humpback, and right whales.
The results are both fascinating and sobering. Thanks to slightly different frequency bands used by each species, and the lower source level of right whale calls, the impacts of shipping noise on these three species vary substantially. On the day used for this initial analysis, two ships passed through the region (an average of six ships has been noted here). On a low-traffic day with two ships, the Communication Space for humpbacks were reduced by an average of 11%, fins by 33%, and right whales by a staggering 84%. For most of the day (from 5am until 5pm), right whale Communication Space was diminished by 88-98%. While we do not know how this vastly shrunken communication range affected the whales, the authors note that "we do know that these whales counter-call and use these episodes of calling to find each other and to aggregate, so one immediate cost is the loss of opportunities to form social groups. Right whales form aggregations during mating and during feeding, so one likely cost is the loss of mating and feeding opportunities."
Back to the science-advancement side of things, the authors stress that this metric provides "a critical missing link to the major current dilemma of assessing noise impacts" that can, for the first time, "quantify biological cost within an ecological framework." They note that this model is a key step toward giving some practical form to the previous PCAD (Population Consequences of Acoustic Disturbance) model proposed by the National Research Council in 2005. There is still uncertainty in some key variables. Most strikingly, we don't know how far these species actually communicate; while we know they can be heard for tens to hundreds of kilometers, limited studies have only confirmed communication exchanges in the range of 20km, which is used in this model for now (if actual communication ranges are longer, as is entirely possible, then reductions in Communication Space would be much greater, especially for the fin and humpback whales). The authors note it was 1971 when Payne and Webb first raised the question of whether shipping might reduce long-range communication for some large whales, and that "that hypothesis was ignored for a quarter of a century." They conclude: "As the planet's dominant species, humans have choices to make. In the case of the ocean's acoustic ecological habitat, the choices we are making now have profound implications for the future of marine mammals. It is our opinion that the right choice cannot wait another 3 decades."
Summary of human and natural noise in the sea
John A. Hildebrand. Anthropogenic and natural sources of ambient noise in the ocean. Mar Ecol Prog Ser, Vol. 395: 5-20, 2009. [DOWNLOAD]
This is a good current overview of the known sources of both human and natural sounds that contribute to the cumulative background ambient noise level of the seas. For each noise source, the author includes frequency bands and source levels, as well as a sense of how widespread the source is. Some lesser-considered noise sources are included, such as acoustic modems used to transmit data from industrial and scientific sites at sea. The key omissions are sources that are still relatively rare, though increasing in number: undersea mining and oil and gas subsea processing installations. Unlike a similar presentation to the IWC a few years ago, the author does not attempt the much harder challenge of calculating the total sound energy that each noise source contributes to the global ambient noise budget (that paper ruffled some feathers by suggesting that seismic surveys may contribute nearly as much as shipping; it is likely that there is not enough solid data to assess how much air gun sound actually moves from continental shelves and slopes into the ocean basins). The paper also includes a good basic summary of sound measurement systems, and is a good starting place for those wishing to get up to speed on the diversity of ocean noise sources.
The main take-away is familiar: at low frequencies, shipping is the dominant noise source (with some indications that seismic surveys are contributing more as they move to deeper water) and has impacts at ocean-basin scales; in mid-frequencies, sounds travel tens of kilometers, with wave and wind sounds dominant (with mid-frequency sonars from 300 ships, operating up to 10% of the time each, also significant); at high frequencies, sounds travel only tens to hundreds of meters, and the main source of noise is actually thermal noise of water molecules (with depth-sounder sonars on many to most ships also a factor).
Specific data that may be worth holding in mind includes source levels of two important low-frequency sounds. Pile driving (increasingly used for siting offshore wind turbines) can be close to 200dB at 100m, with repetition every 2 to 4 seconds; since this takes place in relatively shallow waters, the impact is fairly local despite being low-frequency. Shipping noise varies from 195dB re uPa2/Hz for fast-moving supertankers to 140dB for small fishing vessels and 150-180dB re 1uPa for small private motorboats. Also of note is that wind turbines, after installation, are relatively quiet: the highest tonal component yet measured is 151dB re 1uPa at 180Hz, and broadband low frequency noise at four different wind farms was just 100-120dB re 1uPa.
Parks and Sanctuaries: Collaborative noise management in protected areas
Leila T. Hatch, Kurt M. Fristrup. No barrier at the boundaries: implementing regional frameworks for noise management in protected areas. Mar Ecol Prog, Vol. 395: 223-244, 2009. [DOWNLOAD]
Yet another excellent and ground-breaking synthesis, this one highlighting the similar challenges and opportunities present in managing protected areas on land and in the sea. The authors, one of whom works for the National Park Service, and the other a National Marine Sanctuary, have both been active in focusing on the noise intrusions and impacts relevant to their respective jurisdictions. This paper addresses several important themes and calls for a more integrated and dynamic approach to managing the acoustic resources in protected areas.
It's well worth reading the entire paper, which includes many useful insights, ideas, and case studies, including cogent discussions of the various management challenges that need to be overcome (including different cultures and priorities within agencies that need to collaborate, and a natural resistance to bringing more detailed and expensive-to-collect data requirements into EIS processes that have been sufficient in the past). Here, I'll highlight a few of the key passages. This excerpt frames the impacts of noise in a concise and new way:
"Hearing extends animal awareness under all conditions, and is essential when vision is compromised."
"Noise presents at least 4 threats: diversion of attention and disruption of behavior, habituation or ‘learned deafness’, masking of important signals, and spurious physiological stimulation. These threats present several costs: compromised physiological function, diversion of time and energy, failure to detect important cues, impaired acoustical advertisement and communication, and reduced utilization of important habitats or resources. All of these costs have consequences for fitness."
"Terrestrial noise management is informed and encumbered by the history of community noise management. Historical noise studies and regulations focused on maximum tolerable conditions for humans, in terms of health effects or annoyance. The concept of preserving a high quality acoustic environment has been largely ignored until very recently….An enormous gulf separates the outstanding acoustical conditions that the NPS is required to protect and the noise exposures that result in health effects or high levels of annoyance." However, "In the marine realm, emerging noise management practices are not burdened by the history of community noise management….The broad mandate of the National Marine Sanctuaries Act provides a unique opportunity to create noise management practices and regulations that represent today’s best available science."
"Parks and sanctuaries should be afforded heightened levels of noise protection. Sanctuaries should become quiet refugia for species, as well as enhanced environments for the development of science and technology that promote the research and management objectives throughout the regions they occupy."
The authors note that current regulatory responses to noise are focused on the impacts of discrete sound sources on individual animals; they encourage a broader view that would take into account the ways that effects on species ripple through an ecosystem (e.g., effects on prey species will have an indirect but crucial impact on predators). They summarize several leading-edge computer models that are capable of ever more accurate and dynamic modeling of multiple sound sources and entire populations of animals in a region (though note that even these cannot yet take into account inter-relationships between species). There is also a time-scale limitation on most current impact analyses: the five-year span of most permits.
As examples of noise in protected areas, the authors discuss both data and management approaches taken in Grand Canyon National Park and Stellwagen Bank National Marine Sanctuary (in each case, the protected unit with the longest history of acoustic monitoring). In the Grand Canyon, aircraft are audible for a third or more of the day in the entire park: "If a visitor does not want to hear aircraft at Grand Canyon, they need to be in a busy parking lot or near one of the rapids on the Colorado River." In Stellwagen, low frequency noise in the shipping lanes "were >82 dB 50% of the day and as high as 110 dB 5% of the day."
The paper concludes with for elements of a "common ground" that these case studies suggest as cornerstones of a constructive forward motion in managing noise impacts:
- Investment in expanded and continued acoustic monitoring, especially for "evaluating which sanctuaries contain relatively quiet versus relatively noisy conditions."
- Development of new impact assessment tools, such as visual representations of acoustic data, and effective metrics with which to summarize and compare results. They stress that these metrics are most useful when they relate directly to "functional consequences" for animals that are easy for managers to interpret and for the public to understand (such as the newly emerging metric of reduced listening area). New modeling techniques offer several advantages, including "a rigorous framework for spatial interpolation, when acoustical monitoring data are sparsely distributed." The authors stress that the degree of uncertainty in the models' results needs to be emphasized, and that "in the face of considerable scientific uncertainty, the precautionary principle should be applied to ensure that areas of designated national importance fulfill their protective mandates."
- Enhanced interagency coordination. In particular, "Noise should be addressed by emerging regional management frameworks (i.e. The Gulf of Mexico Program, West Coast Governors’ Agreement on Ocean Health, Northeast Regional Ocean Council), and during the design, implementation and evaluation of protected areas."
- Public engagement and education regarding the benefits of quieting natural areas.
Humpbacks avoid boat noise at nearly 5 miles
Sousa-Lima and Clark. Whale sound recording technology as a tool for assessing the effects of boat noise in a Brazilian marine park. Park Science 26:59-63. [DOWNLOAD]
Using an array of pop-up recorders, this study was able to track eleven individual singing humpback whales and monitor their movements in response to four separate approaches by a tourist boats in the Abrolhos Marine National Park off Brazil, in the main humpback breeding grounds in the southwest Atlantic. Nine of the eleven whales moved away from the boat; of these, four continued singing and five stopped singing (these did not resume singing for at least 20 minutes). Six of the nine began moving away while the boat was more than 4km (2.5mi) away; this distance was chosen as the onset of the "exposure" period, since it had been previously shown to be the median distance at which humpbacks respond to boats. In fact, the mean distance at which the nine whales began moving away was 7.5km (4.7mi); previous studies have suggested that 8km is the greatest distance at which humpbacks would exhibit avoidance, with some studies suggesting they would not move until boats were within 300 meters. The authors note that earlier studies suggesting whales would only move when boats are closer "could be a reflection of smaller sampling areas or specific close-range analytical designs, it could also be a bias toward less sensitive whales."
Earlier, the authors point out that other research had proposed that "individuals that are most sensitive to boat approaches would abandon preferred areas because of increased boat disturbance. Assuming this is true, only the individuals less sensitive to boat disturbances would remain in the area." This is a proposition that is gaining increasing credence within the research community (see Bejder et all 2009, below). The present authors continue, "The effect this selection for boat noise–habituated males could have on the population structure is unknown; it could affect female choice and consequently the distribution of breeding success among the males of this population."
Importantly, the authors note that "during the post-exposure period, singers were still moving away from the boat, which suggests a residual avoidance of the disturbance area."
Overview of new autonomous ocean noise recorders for use in small and large areas
Van Parijs SM, Clark CW, Sousa-Lima RS, Parks SE, Rankin S, Risch D, Van Opzeeland IC. Management and research applications of real-time and archival passive acoustic sensors over varying temporal and spatial scales. Mar Ecol Prog Ser, Vol. 395: 21-36, 2009. [DOWNLOAD]
Very good overview of the range of recent research using acoustic recorders, including both archival systems (deployed for weeks to years, with data downloaded periodically) and real-time systems (in which data is available on an ongoing basis remotely). Includes discussion of acoustic systems deployed in Brazil, Antarctica, the US, and Norway, as well as a series of studies using towed hydrophone arrays in the Pacific. The authors stress the importance of the different research designs and baseline information necessary to effectively study behavior that takes place on different scales, and suggest adaptation of long-standing terminology used in other fields to discuss relevant oceanic scales (synoptic scales for regional marine areas of >2000 km2, mesoscale as areas between 1 and ~2000 km2 in size and microscales as areas <1 km2).
The importance and the flexibility of these new technologies is well expressed in the paper's conclusion: "Archival and real-time passive acoustic arrays are now among the lowest cost approaches for mesoscale monitoring of marine areas and can be used to monitor vocal marine life in areas difficult to survey by traditional visual methods. Fixed autonomous passive acoustic arrays sample continuously for prolonged periods of time, allowing assessment of seasonal changes in distribution and acoustic behavior of individuals without introducing into the environment the types of disturbances generated by the presence of survey vessels or aircrafts. Unlike more traditional visual methods, passive acoustic technologies can survey in darkness and remain active during adverse weather conditions. Further, the ability to retrieve and redeploy archival ARUs provides a level of flexibility in data acquisition that is not available with other fixed long- term monitoring systems."
Whale watching boat noise and impacts on dolphins – including some key new findings on high levels of masking and sound peaks during frequent gear-shifting
Jensen, Bejder, Wahlberg, Aguilar Soto, Johnson, Madsen. Vessel noise effects on delphinid communication. Mar Ecol Prog Ser, Vol. 395:161-175, 2009. [DOWNLOAD]
This study was designed to determine how much the sounds of motorboats (whale watching or private recreation) reduce the communication ranges of dolphins and pilot whales. The researchers assessed natural background ambient noise in shallow (dolphin) and deep water (pilot whale) environments, as well as doing field measurements of the noise from two outboard motorboats, then deployed D-tags on pilot whales to assess received levels. The results reinforce some standard whale-watching guidelines, and highlighted some previously un-noticed impacts.
Engine noise at 5 knots and 50m (typical limits for whalewatching) did reduce communication ranges significantly: by 26% in dolphins and 58% in pilot whales (living in quieter deepwater habitats). Slower speeds of 2.5 knots produced virtually no masking noise, suggesting that at the closest ranges, slower speeds are important (the authors take special note of the need for research vessels using "close follow" techniques to be aware of this, so as not to change behavior by their presence). Speeds of 10 knots produced dramatic reductions in communication range, even at 100 and 200 meters, though the researchers note more uncertainty about these results.
In the tagging experiments, the pilot whales experienced often extreme masking noise levels within pilot whale whistle frequencies, up to 55dB above the levels that would begin to obscure communication; which the authors note that this "suggest(s) that vessel noise may be an important factor in determining range of communication signals in this deep-water environment with significant whale-watching and commercial marine traffic activities."
In addition, whale watching boats shift shift gears quite often in order to remain in proximity of the dolphins or whales they are observing (as often as 2 or 3 times a minute); this study found that gear shifting creates pulses of much louder sound (up to 200dB re 1 uPa peak-peak) containing a much broader range of frequencies, especially higher frequencies. Since such unpredictable bursts of sound tend to elicit more powerful short-term behavioral responses, "steps taken to lessen the erratic movement and number of gear shifts of vessels…would lessen the impact." Finally, the authors note that this study only addresses communications masking, and that, while not investigated here, some higher frequency noises created by cavitation (especially at higher speeds) "has the potential to impact foraging toothed whales by masking weak echoes from their echolocation signals."
Acknowledging differing underlying values as a key to breakthroughs in conservation conflicts
Raphael D. Sangarin and Larry B. Crowder. Breaking through the Crisis in Marine Conservation Management: Insights from the Philosophies of Ed Ricketts. Conservation Biology, Volume 23, No. 1, 24-30. [DOWNLOAD]
This short paper is well worth a read by all who have been frustrated by the lack of constructive progress in moving beyond contentious conflict in addressing environmental challenges. Here, two contemporary researchers (one with a focus on policy, and the other on marine conservation) sketch the three-part approach of Ed Ricketts, a mid-20th century marine ecologist (immortalized as "Doc" in Steinbeck's Cannery Row). In addition to his scientific work, Ricketts articulated an approach to science and policy that drew from Taoism, Buddhism, and his friendships with Steinbeck and Joseph Campbell. While the three aspects of Rickett's approach are far more philosophical than practical, they bear consideration in light of the seeming inability of the best intentions of both scientists and policy-makers to effectively turn the tide of ocean ecosystem collapse. At its heart, Ricketts' approach contains two key aspects. First, a clear and ongoing commitment to observing what is, rather than a focus on what should be – with a related emphasis on shifting relationships rather than facile attempts to assess simple cause and effect in what are always complex, holistic systems. Central to this approach is a conscious intent to avoid neatly preconceived ideas about who or what is to blame for the problem under consideration. Second, and most resonant for me, Ricketts emphasizes that most intractable conflicts over policy are, at root, reflective of differing underlying priorities, worldviews, or "sacred values." The key factor that drives "breakthroughs" is a shared commitment to be forthcoming about each party's underlying values. Sharing the diverse "core needs" is, in Ricketts' view, the foundation of a constructive search for mutually favorable solutions, rather than a mutually damaging fight to chip away at two widely different, predetermined positions. The authors suggest that today's rapidly expanding toolbox of monitoring technologies provides us opportunities to initiate the sorts of ongoing observations that underlay Ricketts' approach, and that developments over the last generation in policy and public engagement support an attempt to be more explicit about the underlying values that are too often unspoken as competing advocates argue their sides in a fight to "win" in policy decisions which have turned unwittingly into battles, thanks to a simplistic focus on particular causes and effects within systems that are spinning out of control due to countless inter-related factors. As in his time, it is not altogether obvious how to apply Ricketts' ideas in practice, but reading this brief overview of his thoughts, along with the context provided in relation to current attempts to define and enact Ecosystem Based Management in the oceans, is bound to spur some new perspectives among reflective policy players today.
Related: A key paper cited by Sangarin and Crowder is another short essay perspectives piece, which suggests that the repeated failure of worldwide fisheries management might be ameliorated by inverting the traditional "trophic pyramid" that places humans at the top, and instead using a model that puts humans at the bottom, or at the tipping point of a circle which explicitly includes consideration of three key factors: ethics, corporate responsibility, and social justice.
Bundy, Chuenpagdee, Jentoft, Mahon. If science is not the answer, what is? An alternative governance model for the world's fisheries. Front Ecol Environ 2008; 6(3): 152-155. [DOWNLOAD]
Moderate seismic survey noise linked to increase in blue whale calling
L. Di Lorio and C.W. Clark. Exposure to seismic survey alters blue whale acoustic communication. Biology Letters doi:10.1098/rsbl.2009.0651 [DOWNLOAD]
This study found that a seismic survey in wide bay at the mouth of the St. Lawrence Seaway caused blue whales feeding and socializing nearby to double or triple their call rates. The calls were near-range communication signals, rather than the long, loud songs that are heard over hundreds of miles. The research was meant to simply learn more about these social calls, but during the study, their recordings began to pick up the pulses from a seismic survey. “The whales made more calls on days when the testing was happening. It seems they are having to repeat themselves in order to not lose information,” said lead researcher Lucia Di Lorio. During the four days in which survey sounds were heard, the whales also increased their call rates when the sparkers were audible than when they were not, and tended to rapidly increase call rates when the sounds appeared.
The results were especially surprising, since the survey in question was using a much lower-power sound source (sparkers) than the airguns used in most surveys. The electronic sparkers top out at only 190dB, rather than the 230-240dB of airguns. Sparkers are slightly higher frequency as well, but still solidly centered in low-frequency bands of 30-450Hz, primarily 60-250Hz, very similar to airguns, and matching key blue whale communication frequencies.
The study notes that “Our results clearly show that blue whales change their calling behaviour in response to a low-medium power technology that is presumed to have minor environmental impact. In fact, the mean sound pressure impinging on the (study) area, and thus probably on the whales present there, was relatively low, 131 dB re 1 uPa (peak to peak, 30 – 500 Hz) with a mean sound exposure level (SEL) of 114 dB re 1 mPa2 s. The increase in calls was a contrast to some other studies, which have found call rates reduced near seismic surveys, perhaps in part due to animals moving away; in some cases, animals call louder or change the pitch of their calls to cope with noise intrusions. This is the first study to find a marked increase in call rates, or repeating themselves, which Di Lorio suspects may be due to the key role of this area in socializing and feeding (i.e., the communication is time- and place-dependent, and cannot easily be postponed until a quieter time).
The study concludes by noting that the St. Lawrence Estuary “is an important feeding area where blue whales acquire energy and also a place where this wide-roaming, highly dispersed population congregates to engage in social interactions. Reducing an individual’s ability to detect socially relevant signals could therefore affect biologically important processes. This study suggests careful reconsideration of the potential behavioural impacts of even low source level seismic survey sounds on large whales. This is particularly relevant when the species is at high risk of extinction as is the blue whale.”
UPDATE: A skeptical note received by email from a longtime correspondent: “To me, given a detectable new sound, mammals tend to decrease vocalization if it induces fear, or increase vocalization if it stimulates interest. How a sparker could block communications rather eludes me, but whales responding to a pulse—be it noncoherent noise stimulates noise, or actual whale talk directed at the pulse—comes to mind….Sperm whales in the GOM seemed to alter click patterns and perhaps anticipated a pulse once they got the beat. That was a casual observation by one of the acoustic team - always thought that would have been a great add-on study but we were already at overload working on acoustic tracking for tagging purposes. More at home, my grey parrot, who talks quite a bit, of course becomes completely silent when visitors ask ‘if he talks?’ - his reaction to seeing new people is silence. Now, if you go into another room and play classical music, the next question is ‘how do you stop him?’ I think there is a complexity to animal behavior and acoustic responses and the reasons blue whales would increase calls could be many.”
What do beaked whales hear?
Finneran, Houser, Base-Guthrie, Ewing, Lingenfelser. Auditory evoked potentials in a stranded Gervais' beaked whale (Mesophlodon europaeus). J.Acous.Soc.Am 126(1), July 2009. 484-490.
This study took place with a stranded beaked whale that was euthanized after three days in captivity; it was very ill (organ failure due to bacterial infection) throughout. Since beaked whales seem to be more affected by Naval mid-frequency active sonar, the study was designed to see whether beaked whale hearing is more sensitive than other closely related families of cetaceans. The results find a hearing sensitivity curve that is similar to those of dolphins and orcas, with no indication of greater hearing acuity. The highest frequency that could be heard was 80kHz (though this could be limited by hearing impairment in this individual, as one earlier study of this species found good sensitivity than at 80kHz , and did not test higher). Highest sensitivity was found at 40kHz (i.e. the animal can hear sounds at this frequency when they are relatively faint--higher and lower frequency sounds must be louder to be heard) No tests were done using frequencies below 20kHz; mid-frequency active sonar ranges from 2-10kHz.
Some breeding birds avoid areas within 500-800m of wind turbines
Pearce-Higgins, Stephen, Langston, Bainbridge, Bullman. The distribution of breeding birds around upland wind farms. Journal of Applied Ecology, doi: 10.1111/j.1365-2664.2009.01715.x [DOWNLOAD]
This comprehensive survey of breeding birds in non-agricultural British uplands (moors and grassland) included weekly surveys during the breeding season at 12 different wind farm sites, along with comparable nearby landscapes without turbines. Half the wind farms were from the previous generation (WAY back in the '90s), with hub heights of 40m and less; the other half had hub heights of 60-70m. Of the twelve species that were observed often enough to provide good data, five seemed relatively unaffected by turbines (including kestrel, lapwing, grouse, skylark, and stonechat), while 7 species were less likely to nest within 500m of turbines, with smaller (i.e., not statistically significant) effects extending to 800m, or roughly half a mile. For six of the species (buzzard, hen harrier, plover, snipe, curlew, and wheatear), numbers were reduced by 39-52%.
The authors note that there is a pressing need for examination of the reasons for the depressed numbers: "we do not know whether our observations of avoidance of turbines reflect a behavioural displacement, the local population consequences of collision mortality or reduced productivity, or both. The distinction is important. If there is high mortality of birds breeding close to the turbines associated with collision (ed. note: or reduced productivity), then a wind farm may become a population sink if repeatedly colonized by naive birds. If, however, the birds simply avoid breeding close to the turbines, then…displaced birds may settle elsewhere with little cost." They also note that "Whether wind farms result in meaningful population-level effects at a regional and national scale depends both upon the mechanisms involved, and the overlap between bird distribution and wind farm development," and encourage new development to avoid high densities of open country species, until these factors can be more clearly understood.
They note the contrast between these findings and those of Devereux et al (2008), which "may suggest that species occupying remote semi-natural habitats are more sensitive to wind farm development than species occupying intensive production landscapes." (Ed. note: The earlier study looked at wintering birds in farmland, rather than breeding birds in uplands.)
Habituation often misused or wrongly assumed in impact assessments
Bejder, Samuels, Whitehead, Finn, Allen. Impact assessment research: use and misuse of habituation, sensitization and tolerance in describing wildlife responses to anthropogenic stimuli. Mar Ecol Prog Ser, Vol. 395:177-185, 2009. [DOWNLOAD]
This paper serves as an excellent review of an important line of reasoning that is skeptical of facile claims that animals readily habituate to human disturbances such as noise. While the paper may be seen by some as little more than a set of "what if" propositions designed to undermine the simple observation of animals not being affected by a disturbance (and in this way, proposing an extreme precautionary view that supposes the worst in situations where we do not have complete information), the underlying intent is more serious than this: when policy decisions are being made based on a simplistic assessment of the situation, then we should at least be aware of the limitations of our terms and our study designs. This paper adds clarity to these issues in important ways.
The authors distinguish between true habituation (which is a learning process that occurs over time) and tolerance (which can be measured instantaneously), and suggest that most impact studies are designed in ways that can only confirm tolerance, since they do not track the responses of individual animals over time. Further, they point out that even studies of tolerance can be easily distorted if the most sensitive animals leave at the first disturbance, leaving more tolerant individuals as the "study group." Another key – and often ignored – factor is that any behavioral response is influenced by many factors, not just the invasive human disruption being studied; for example, increased human noise may be one factor in an animal's decision about moving away, but this decision is also dependent on other key factors, such as the quality of the site where the animal current is (e.g. for feeding, mating, resting), the distance to and quality of other suitable sites, the relative risk of predation or density of competitors in other sites, and any investment the individual or group has made to the site (e.g., establishing a territory, gaining dominant status, or acquiring environmental information). It is commonly assumed that avoidance or lack of avoidance of a human sound source is a good indicator of whether that sound has a negative impact; the authors stress that this is an unwarranted and often incorrect assumption, and point out that the few studies that have assessed both behavioral responses and physiological measures (heart rate, stress hormones) have often found physiological markers of a negative response even when animals exhibited little or no behavioral reaction, i.e., when they appeared to tolerate the intrusion.
This paper serves as a good starting point for examining previous research that has raised similar questions about the design of behavioral response studies, and the use of these studies in making policy decisions (In particular, previous work by JA Gill and L Bejder). The core message here is that managers should be very cautious in assessing claims of habituation (since few studies truly are designed to prove habituation), and likewise that habituation or tolerance do not necessarily imply the lack of negative impacts on individuals or populations. As they conclude, "Most studies are restricted to monitoring short-term, observable, behavioral responses, (which) limits the scope of conclusions that can be drawn…The conclusion is likely to be specific only to the response variable that has been monitored…(while) animals may become habituated in one modality but not in another….The most effective course of action in impact studies would therefore be to complement behavioral assessment with monitoring of physical condition and physiological measures such as heart rate, body temperature and/or hormonal levels."
"Worst case" wind turbine noise can occur 30% of summer/fall nights
Clifford P. Schneider. Measuring background noise with an attended, mobile survey during nights with stable atmospheric conditions. Internoise 2009. [DOWNLOAD PAPER(pdf)]
This well-designed study, by a retired New York State Department of the Environment staffer, sheds light on several key questions surrounding standard noise assessments of wind farms. Most strikingly, it quantifies the extent of one of the key atmospheric components of excessive wind farm noise, finding that stable night time atmospheres may occur two-thirds of the time in the summer and fall, with wind high enough at turbine height to trigger them into action on 30% of nights, increasing to 40% in June and July. On these "worst case" nights, turbine noise is likely to be significantly louder than local background ambient noise from late evening until the beginning of the pre-dawn bird chorus. Schneider's study also included a brief but useful test of whether a quick but systematic mobile sound survey can be used instead of set of arbitrarily-chosen monitoring sites (addressing questions about whether arbitrary site selection accurately measures local averages) – he did 10-minute recordings at 21 sites, one every mile along two rural roads, and compared the results to 5 baseline sites chosen arbitrarily around the same town.
This study took place in the township of Cape Vincent, New York, which sits at the confluence of the St. Lawrence River and Lake Ontario, where two wind farm proposals would place 200 turbines in town, covering the majority of its land area. Local and state ordinances require sound to be within 5dB of average ambient noise levels; the wind developer's sound level report based their projected compliance on a day-night average of 45dBA. By contrast, Schneider's study focused in on the times when other wind farms have generated the most problematic noise impacts: nights when wind is low at ground level but high enough at hub height to trigger turbines to turn on. In these conditions, night-time background ambient sound levels are very very low, and turbine noise can dominate the nighttime soundscape. The results are striking, to say the least.
Night-time sound levels were at or below the lowest that the researcher's meters could record, 25dBA, for most of the late-night hours at 4 of the 5 locations, and under 30dB from 9pm-4:30am at three; one site received shore waves and dropped below 35dB for just a few hours in the middle of the night. Average readings along the mobile monitoring route (which was traversed over the course of three nights) were similar, and generally ranged from 25-32dB, with one site at 36dB. By contrast, measurements near a wind farm in the region, also measured at several (10) locations, showed the quietest times of night (L90) ranged from 35-43dB, and the average (LEQ) from 36-45dB. Bottom line: wind turbine sounds are likely to be 10-15dB louder than background ambient sound on these "worst case" nights in Cape Vincent.
But how often do such nights occur? In what is likely to be the section of the study with them farthest-reaching impact, the results suggest that turbines could be operating (hub height winds >4 m/s) on nights with very still, quite ground conditions (ground wind <1.5 m/s) for 42% of nights in June and July, and for a total of 30% of nights from June through October. This lines up well with the only other study that I know of that specifically addressed stable night air conditions, the van den Berg study that found such conditions occur about a third of the time in the Netherlands, with similar levels suspected in many temperate zones. Using New York State DEC standards for predicting human reaction to noise, which is based on increasing levels of industrial noise above background ambient, this study suggests that (counter to the developer's prediction that no residents will experience noise more than 5dB above ambient, i.e., loud enough to trigger complaints), the vast majority of households in town will find the noise "very noticeable" (9-14dB above ambient) on these nights, with 34% finding it "objectionable" (84 homes at 14-19db above ambient) and a further 19% finding it "very objectionable to intolerable" (48 homes at 19-25dB above ambient).
It is important to note that these levels of audibility and possibly objectionable sleep disruption will occur on a minority of nights; indeed, on an annual basis, probably around 15% of nights. And, on those nights, just a portion of the population will be affected. This perspective is part of what has led to our current acceptance of relatively small setbacks from homes (often 1000-1500 feet). Our social decisions about wind farm siting will need to grapple with the question of how much disturbance we consider acceptable – in this case, a third to half of the residents of Cape Vincent may be looking at troubling noise levels for a third to half of summer and autumn nights. To protect most residents from most of the noise intrusions (keeping noise levels to 5-10dB above ambient) would require setbacks of 1km or so, which would likely mean more like 30-50 turbines in Cape Vincent, rather than the planned 200.
Two other results are worth mentioning. As mentioned above, the systematic mobile sound assessments matched closely with those made at arbitrary locations, suggesting that either method is reliable. The author notes that the arbitrary locations that he chose were well away from buildings, while a systematic mobile survey with a random start avoids possible problems of subjectivity in site selection. He notes: "I could have increased the measures SPL (at the arbitrary locations) if I had located equipment closer to homes, barns, and roads, and if I had picked nights with moderate winds." Further, he notes that the attended metering used in the mobile survey allows identification and documentation of noise intrusions, some of which might be of interest in assessing either true ambient or noise conditions with turbines operating (i.e., a site with many cars passing will show elevated sound levels, compared to one with fewer; this increased noise could either lead to over-estimate of quiet times at these sites, or improperly suggest that turbines are the primary source elevating sound levels at a site.) Finally, this study's measurements of dBC (low frequency sound) found substantial variability at different sites, more variable than audible sound, including several sites where the difference between dBA and dBC approached 20dB; this suggests that later measurements with turbines operating may not necessarily suggest that the turbines are the source of such variability.
Animal listening area and alerting distance reduced substantially by moderate human noise
Barber, Crooks, Fristrup. The costs of chronic noise exposure for terrestrial organisms. Trends in Ecology and Evolution, 2010. [ARTICLE IN PRESS AVAILABLE HERE]
This is one of the most important and interesting papers published this year. It emerges from the partnership between the National Park Service's Natural Sounds Program and researchers at Colorado State University, who have been working together for several years to create metrics that are more useful for assessing the biological impacts of moderate human noise on wildlife. The assessments presented here, along with the paper's review of recent studies documenting changes in foraging, anti-predator behavior, reproductive success, density and community structure in response to noise, form the basis for a much more cogent assessment of noise impacts on wildlife.
The focus of this research is the ways that moderate increases in background noise can affect animals. The authors note that both air and road traffic in the US has tripled in recent decades; even in National Parks, noise is audible 25% of the time in more than half of sites assessed. Over 80% of US land area is close enough to roads for some low-frequency masking to occur, with passing trucks and motorcycles increasing the sound levels at 1km to 40dB(A).
One of the new proposed metrics is the effective "listening area." Changes in listening area has impacts involving both communication and what the authors term "adventitious" sounds (sound made largely by movement, which are important in predator/prey awareness). For predators, the listening area is the area over which they might hear the rustling of their prey, and for prey, it is the area in which they are alerted to approaching predators, whether wingbeats or footsteps; in each case, the most important sounds are those right at the edge of audibility. Social groups rely on hearing each other's alarm calls or songs inviting mating; reduced listening areas for these calls result in effectively reducing the number of individuals in any given communication network. Each animal has its own auditory acuity, so can hear at different distances; but for all animals, increasing background noise will reduce their natural listening area in predictable ways. The authors note analyses of transportation noise impacts often assert that a 3dB increase in noise – a barely perceptual change – has "negligible" effects, whereas in fact this increased noise reduces the listening area of animals by 30%. A 10dB increase in background noise (Ed. note: likely within a few hundred meters of a road or as a private plane passes nearby) reduces listening area by 90%.
Throughout, the authors stress the difficulties in separating noise-related effects of traffic from other related forces, such as habitat fragmentation or threat responses; there is also a fascinating short section citing studies showing behavioral changes in response to quiet recreation, sometimes even more dramatic than those caused by vehicles. Though only a few studies have directly addressed this ambiguity, many studies cited here provide strong indications that acoustic masking is a significant factor in behavioral changes near roads. Among the findings that caught my eye/ear:
- Masking affects not only audibility, but understanding: "thresholds for discrimination between calls of the same species were consistently higher than were detection thresholds for the same calls." Not surprising, but easy to forget: background sound often obscures the words being said, though we can still hear the voice.
- Bats that listen for ground movements of their prey hunt more in quiet areas than noisy ones; similarly insect-eating birds are more likely to avoid noisy areas than other birds.
Masking can also make it more difficult for animals to tell what direction a call (such as a mating call) is coming from
- Pronghorn antelope showed a marked shift in proportion of time spent foraging and in vigilance (looking around) when closer to roads: foraging dropped from 45% of the time to 35%, while vigilance increased from 40% to over 50%.
- Two key studies of increased vigilance in clearly noise-triggered contexts: Ground squirrels showed a marked increase in vigilance behavior when hearing squirrel alarm calls at a site in a wind farm than in a quiet site (including a slightly less "relaxed" non-vigilance baseline state), and a lab study with chaffinches found that the mean time spent pecking (eating) between times scanning the area decreased when noise was introduced.
The authors conclude by stressing: "Chronic noise exposure is widespread. Taken individually, many of the papers cited here offer suggestive but inconclusive evidence that masking is substantially altering many ecosystems. Taken collectively, the preponderance of evidence argues for immediate action to manage noise in protected natural areas….The costs of noise must be understood in relation to other anthropogenic forces, to ensure effective mitigation and efficient realization of environmental goals. Noise pollution exacerbates the problems posed by habitat fragmentation and wildlife responses to human presence; therefore, highly fragmented or heavily visited locations are priority candidates for noise management. Noise management might also offer a relatively rapid tool to improve the resilience of protected lands to some of the stresses imposed by climate change."
Bias in Military (or Conservation) Funded Ocean Noise Research
Wade, Whitehead, Weilgart. Conflict of interest in research on anthropogenic noise and marine mammals: Does funding bias conclusions? Marine Policy 34 (2010) 320-327.
(Ed. note: This lay summary includes more analysis and interpretation by AEI than we generally include; some of this commentary questions the conclusions of the paper, and some of it addresses the underlying controversies surrounding ocean noise issues. I have attempted to be clear about which statements are simple summations of the report's data and findings, and which are AEI's reflections or perspectives. It is a long read, but the issues that triggered this study are important ones. Though the clear-cut results reported here are difficult to take at face value, it is well worth considering the underlying forces that drive tensions between environmental groups and Navy/industry actions in the seas.)
In the United States, the US Navy funds about half of the research into the effects of ocean noise on wildlife. For many years, conservation groups have questioned whether this preponderance of funding is skewing research results, whether by constraining the types of questions being studied, or by leading researchers to downplay negative impacts of noise in order to continue receiving funding. This paper investigates the latter possibility, by comparing five recent reviews of the effects of ocean noise on wildlife, one funded by a leading environmental group, three that received substantial Navy funding, and two funded by organizations with no particular stake in the debate. The researchers compared the number of citations in each that showed an effect of noise, or not, or that showed both an effect and lack of effect. They also attempted to identify funding sources of the primary papers cited in each of these secondary reports, and to correlate the funding source with the same three parameters (noise shown to have an effect, noise causing no effect, or aspects of the primary research showing both effects and no effect).
Using both simple citation counts and G-test statistical analysis to test for a null hypothesis of random connection between funding sources and outcomes, the authors report a significant correlation between funding source and proportion of citations reporting "no effect" of noise. The five review papers certainly show a trend, though it appears to AEI that three papers that form the anchors of that trend each may be somewhat shaped by its original intention.
Reviews: Proportion of citations of each stance
The authors recognize that the one conservation-funded paper ("Oceans of Noise", WDCS) drew almost only on studies that did show an effect of noise, and re-analyzed the trend with that one excluded; a significant effect remained, though it was half as strong. However, one of the "independent" papers, a chapter in a book on the ocean environment (Hildebrand), was perhaps similarly constrained by its purpose; it was titled "Impacts of Anthropogenic Noise," and was not necessarily intended as a comprehensive assessment of what does and does not cause an effect. On the other end of the spectrum of the five surveys, the only Navy-funded survey that diverged notably from the other independent paper (from ICES), was the third National Research Council report, which addressed the difficulties in determining when repeated behavioral disruptions of a portion of a population accumulates to the point of becoming "biologically significant." Thus, this survey could be expected to include more papers that were exploring the edges of impacts, and so it is not surprising that to do so, more citations would appear that show no effect. Given these underlying intentions of the two reports showing the fewest "no effect" citations, and the one showing the most "no effect" citations, it appears that the five papers being compared are not quite on the same playing field. The other three papers (ICES and the first two NRC reports on noise and marine mammals) showed no marked differences in balance between citations, with the Navy-funded reports actually having a lower proportion of "no effect" papers and higher proportion of "effect" papers than the ICES survey.
Primary papers: funding sources and results reported
Turning to the primary papers, the situation is not muddied by the variable intentions of the reviews. Here, there is a clearer trend of increasing conclusions of "no effect" as funding moves from conservation to no-agenda to industry and military funding. Again, the 19 conservation-funded papers nearly all reported an effect, with just one showing both effect and no effect to separate questions being investigated. The 67 military-funded papers, by contrast, were far more likely (2.3 times as likely) to come to a no-effect conclusion than papers funded by other (non-conservation and non-industry) sources. However, and significantly, less than 30% of military-funded papers came to that conclusion, while about 50% did report an effect of noise, and 20% showed both effects and lack of effects. Likewise, in the first two NRC reviews, about 20% of citations showed "no effect," while over 60% showed an effect; even the most "extreme" review had more citations showing an effect than not.
Of special note is that the authors did not find any strong trend toward bias of results reported by independent, academic researchers receiving Navy funding for research studies - these studies showed a similar proportion of effect and no effect results as studies funded by neither the military nor conservation groups (though when comparing military-funded studies with all the others, including consevation-funded, a non-statisticially significant trend of 1.64 times more "no effect" findings was observed). As the authors stress in consideration of the possible bias of conservation-funded primary studies, conflicts of interest would be dangerous if scientists "orient(ed) their goals, methods, analysis or interpretation towards the perceived interests of the….community that funded them." The authors conclude that "much of the bias in military-funded research was in work carried out at military institutions, rather than in studies funded by the military but carried out at universities and other institutions." This seems to suggest that the concern about bias in funding alone is negligible, thus diffusing concerns that cash-strapped academic researchers are "cooking the books" to retain Navy funding. Research coming directly out of military offices is likely to remain less reliable as representing "the whole picture," as may research entirely funded by conservation groups. Still, by integrating and considering the full range of studies reported in all of these reviews, the public can get a pretty decent picture of current state of our understanding of the effects of ocean noise.
Of note, though, is that the proportion of "no effect" to "effect" findings is slightly lower in military-funded studies. In addition, military-funded studies are more likely to report BOTH effects and lack of effects in a single paper; this could indicate either a more careful assessment of the margins where effects are just noticeable, or a tendency to split the difference in order to either underplay the effects or accentuate the non-effects to assuage funders.
Overall, at both layers of analysis, it seems clear to AEI that the conservation-funded papers and survey report showed the most obvious "bias." However, this is not necessarily problematic (unless used as a baseline to suggest bias in others). As the authors note, "conservation groups do not fund research unless they have previously identified a potentially damaging effect," and since conservation groups' focus on precautionary approaches, and their mandate to "publicize activities that are potentially damaging to the environment" is quite transparent, it "should not be problematic unless threats are 'hyped' where there are none." (Note: while non-existent threats are rarely hyped by conservation groups, a more difficult question arises when moderate or minor threats are presented to the public as more dramatic than they may be.) The authors note that while these results could suggest that conservation funding may be considered problematic, "the argument can be made that their role as a preventative authority is necessary."
Indeed, while primary research and even survey reviews funded by the military are evidently not overly biased toward finding no effect (since in both cases, they include far more results showing effects than not), it also appears to AEI that in practical terms, the EIS's generated by the Navy and the mitigation measures imposed by regulators on both military and oil and gas activities are largely grounded in the belief – and regulatory determination – that any effects of these activities are "negligible," to use the formal term. Thus the focus of the conservation community on funding research and publishing overviews that emphasize credible studies outlining observed negative effects is understandable, given these groups' role in raising public awareness and balancing the singular interpretation of the more nuanced research by the military and industry. It might be more fruitful to explore ways that the "balance" of Navy-funded studies and reviews serve as a fig leaf for actions that nearly always presume no harm. Another key question not yet considered with the rigor brought to this study is whether Navy-funded research is oriented toward studies that, by the questions being asked, may be more likely to come up with "no effect" findings, as apparently the investigations that conservationists tend to fund ask questions that lean toward those that are likely to show an effect. Similarly, the questions being asked can color the perceived importance of changing our ways of using sound in the sea. For example, a study might seek to identify "recoverable thresholds" of exposure (the maximum sound can an animal experience, causing temporary hearing shifts, but with their hearing returning to normal after a few minutes or hours), while another study may be looking for "behavioral thresholds" (the sound exposure that triggers behavioral changes). Implicit in the first question is the thought that as long as the effect is not permanent, it's acceptable; conversely, the second question implies a desire to minimize disturbance of animals. Indeed, the first question seeks the maximum sound level we can feel comfortable imposing, while the second inquires as to the minimal sound that the animal might be affected by.
More to the point, though, many or most of the studies that do show effects are somewhat ambiguous (e.g., only a proportion of the population shows the effect, or the practical import of the change or effect is difficult or impossible to determine), while a finding of "no effect" is more clear-cut. It is not outlandish on the face of it for the Navy to say, as it does, that their actions are not likely to cause any major disruption of animal life: the only clear-cut evidence we have is that extremely loud sounds at very close range (tens of meters) can injure animals, while the rest of the research really is shades of grey. Nearly all of the controversy over military and oil and gas noise today boils down to differing interpretations of how important moderate behavioral changes are, and whether they should be avoided or not. And science is nearly incapable of shedding any definitive light on how important behavioral changes are, thus leaving the two sides largely reliant on their divergent faith: the Navy and oil industry's faith that the behavioral changes are transient and negligible, and environmentalists' faith that chronic behavioral disruption by human noise is bound to have negative consequences. Meanwhile, ethical questions about humanity's relationship to the natural world are outside the bounds of discussion on one side, and central to the whole discussion, on the other. In the end, studies like this – and indeed, reviews such as those considered here – are largely diligent exercises in quantifying an issue that has become, for all practical purposes, an exercise in divergent world views talking at and past each other.
Two Pinger Studies: Harbour Porpoise Bycatch Reduced, Common Dolphins Show Little Response
Palka, D.L., M.C. Rossman, A.S. VanAtten, and C.D. Orphanides. 2008. Effect of pingers on harbour porpoise (Phocoena phocoena) bycatch in the US Northeast gillnet fishery. Journal of Cetacean Research and Management 10(3):217-226.
Berrow, S., R. Cosgrove, R.H. Leeney, J. O'Brien, D. McGrath, J. Dalgard, and Y. Le Gall. 2008. Effect of acoustic deterrents on the behaviour of common dolphins (Delphinus delphis). Journal of Cetacean Research and Management 10(3):227-233.
Two studies of the use of pingers on gillnets came up with starkly different results for two key species of dolphins. The first, a long-term study of actual by-catch off the northeast coast of the US from 1999-2007, found that harbour porpoise bycatch was reduced 50-70% in fisheries that used pingers, with no bycatch at all in nets using 15cm mesh. Most importantly, there were no long-term increases in by-catch, which offers strong evidence that the porpoises are not habituating to the pinger sounds. However, the second study found that pingers that caused evasive responses in bottlenose dolphins had no effect on common dolphin behavior. A pinger source that allowed several types of signals to be tested also elicited no response in the common dolphins; the researchers conclude that “pinger, at their current state of development, may not provide a consistently effective deterrent signal for common dolphins.”
Treefrogs Call More when Human noise intrudes
Kaiser, K & JL Hammers (2009) The effect of anthropogenic noise on male advertisement call rate in the neotropical treefrog, Dendropsophus triangulum. Behaviour 146: 1053-1069.
This detailed study of treefrog calls in an Amazonian neotropical forest showed a near-doubling of call rates when frogs were exposed to recordings of a variety of human noises. Engine noise, music, and intermittent engine noise were all tested. Call rates increased by roughly 75% in the presence of motor noise and music, and nearly tripled when motor noise was presented intermittently. The response of this species of frog, to increase call rates, matched their response to increased presence of other frogs of this species; a chorus of treefrog calls produced the same change as the same volume of anthropogenic noise. While other species were not studied, the researchers note that their observations suggest that other chorusing frogs responded similarly to the anthropogenic noise, also increasing their call rates, while solitary-calling frogs ceased their calls during noise, and resumed when the noise stopped.
The researchers note that road construction and traffic are extending into ever more pristine habitats in neotropical forests worldwide. Unlike birds, frogs are considered incapable of short-term changes in call frequency (e.g., many birds have been shown to shift their calls to a higher pitch to be better heard in noisy urban environments); increasing call rates imposes a fairly substantial energetic cost on the calling males. The impact of increased noise on the effective call distance for males (or audibility distance for females), and the resultant difficulty of females to hear the calls was not studied, but is mentioned as another likely impact of increasing road noise in neotropical forests.
Reef Fish Hearing Measured
Parmenter, Colleye, Mann. Hearing ability in three clownfish species. Journal of Experimental Biology 212, 2023-2026 (2009)
Recent years have seen increasing interest in the question of whether and how reef fish may use sound for communication or orientation; however, while it was known that fish make sounds, their hearing capacities have not been widely measured. This study used AEP to measure the auditory response of clownfish to various frequencies of sound. Clownfish were found to detect sound from 75Hz to 1.8kHz, and to be most sensitive to sounds below 200Hz. It’s long been known that the sounds made by fish are closely related to their size, with lower frequency sounds made by larger fish. Interestingly, younger (i.e. smaller) fish have best hearing sensitivity at frequencies lower than the sounds they make, but close to the dominant frequencies of larger fish calls. It is suggested that this allows juvenile fish to hear and localize the position of adults, which may be useful as juveniles return to their home reefs.
Offshore wind farms: impact area on porpoises is small during operation, but potentially over 20km during construction
These two papers, from related research teams, assessed the impacts of construction and operation of wind farms in Europe on local populations of harbor porposeis and harbor seals.
Tougaard, Henriksen, Miller. Underwater noise from three types of offshore wind turbines: Estimation of impact zones for harbor porpoises and harbor seals. J. Acoust. Soc. Am. 125 (6), June 2009. 3766-3773.
Underwater noise was recorded from three different types of wind turbines in Denmark and Sweden. The authors note that virtually all airborne noise from the turbine blades is reflected off the surface of the water, while vibrations from the machinery are transmitted through the tower and into the foundation, from where it radiates out into the water column and seabed. In general, turbine noise was only measurable above ambient noise at frequencies below 500Hz, with total SPLs of 109-127db re 1uPa rms, measured at 14-20m from the turbines’ foundations. By comparing measured sound levels with audiograms of harbor seals and harbor porpoises, the researchers determined that the sounds were only slightly audible for the porpoises at ranges of 20-70m, whereas harbor seals may hear the sounds at ranges of 100m to several kilometers. As a bottom line, researchers suggest that behavioral changes are very unlikely in harbor porpoises except at very close ranges, while seals may have some behavioral reaction out to a few hundred meters. For both species, masking is predicted here to be low to non-existent (due to differences between vocalization frequency patterns and the predominantly low-frequency turbine noise), and the sound is too low to cause physical injury, no matter how close the animals are.
Tougaard, Carstensen, Teilmann, Skov, Rasmussun. Pile driving zone of responsiveness extends beyond 20km for harbor porpoises (Phocoena phocoena (L.)) (L). J.Acous.Soc.Am. 126(1), July 2009. 11-14.
This study took place during construction of an offshore wind farm in the North Sea. Acoustic T-PODs were placed in the wind farm and in two locations outside the wind farm, at 7 and 20km away. During pile driving operations, which generate high-intensity impulsive sounds (235dB peak-peak), detections of harbour porpoises declined at all listening stations. (The baseline was detections during construction, but without pile driving activity taking place) The declines were not dramatic (within the 95% confidence bars in most cases, barely beyond them in some cases), but were consistently found. There was no clear difference in detection rates at 7 and 20km, which implies that the displacement effect extends well beyond 20km. The differences inside the wind farm were minimal when pile driving was occurring, though total detections were lower inside the farm than outside at all times, suggesting that animals inside the construction zone were individuals who were more acclimated or tolerant of the ongoing construction noise.
A Summary of Recent Studies of Wind Farm Noise Annoyance and Possible Health Effects
The take-away from these new reports appears to be that while significant proportions of the population are affected by moderate wind farm noise, neither increasing wind farm noise nor even annoyance to it lead inevitably to health effects. There is an entire separate body of research investigating various attitudinal aspects related to stress and health, which only muddy the waters as we try to interpret these direct studies on wind farm noise. Some studies indicate that attitudes toward a noise source can affect both annoyance and stress responses, and that a subjective sense of being threatened can likewise increase physiological responses to noise; however, once again, these correlations are far from universal, so they cannot be used to "explain away" either annoyance or health impacts that do take place, any more than annoyance can be used as a clear indication of eventual health effects.
There is far more gray than black and white in these reports. Still, they provide a concrete picture of annoyance and sleep deprivation increasing as turbine noise increases, along with a better sense of the proportion of affected neighbors who will experience these impacts at various distances and received sound levels. Clearly, 35-45dB is a range at which impacts on neighbors become far more widespread. The social question that will need to addressed is what proportion of nearby neighbors we will accept causing sleep deprivation or annoyance in: 10%? 20%? Where will we draw the line, beyond which we consider turbine placement too close?
Minnesota Dept of Health
Minnesota Department of Health, Environmental Health Division. Public Health Impacts of Wind Turbines. May 2009. [DOWNLOAD REPORT HERE]
This state agency report provides a good overview of the current state of knowledge regarding wind farm noise propagation, with particular attention given to possible low frequency noise impacts. The report makes no dramatic recommendations, though the data presented suggests that audible and low-frequency noise could affect neighbors within a half mile to mile. Among the key pieces of information contained in this report, gleaned from previous research studies:
- A reminder that the 2007 report on wind farms and human health from the National Academies of Science concluded that "noise produced by wind farms is generally not a major concern beyond a half mile" (i.e., under a half mile can be problematic).
- Some individuals have extraordinary sensitivity to low frequency sound, up to 25dB more sensitive than presumed (average) thresholds at some frequencies
- Some people can dismiss and ignore repetitive but low intensity noise, while for others, the signal will grow and become more apparent and unpleasant over time. These reactions may have little relationship to will or intent, and more to do with previous exposure history and personality.
- The difference, in dB, between soft (acceptable) and loud (annoying) noise is much less at low frequencies, due to the our perceptual compression of the full audible range.
- Compiled data from two recent Swedish studies (summarized below) suggest that wind farm noise levels of over 40dB(A) lead to annoyance in about half the population, while slightly lower sound levels of 35-40dB(A) leads to annoyance in about a quarter of the population.
- A surprising study from New Zealand found that over half of household 2-2.5km AND 5-9.5km from wind farms could hear them at times (fewer in between heard them); these wind farms were in mountainous terrain, which likely explains the great distances at which they could be heard.
- Two charts from a 2006 report by the UK Department of Transport and Industry suggest that low frequency noise (LFN) from wind turbines can be well above audible levels, and above the UK's night noise LFN criterion, at frequencies of 50-200Hz.
Summary of Three European Studies
Eja Pederson. Effects of wind turbine noise on humans. Third International Meeting on Wind Turbine Noise, Aalborg, Denmark, June 2009.
This review by one of the leading researchers of wind turbine noise, annoyance, and health, compiles data from three studies, two in Sweden and one in Holland. The results, while indicating clear thresholds for annoyance and sleep disruption at sound levels often experienced by wind farm neighbors, also illustrate the subtleties inherent in making generalizations based on ambiguous data. The author makes a key introductory point: that wind farms "often are placed in rural settings considered places with low exposure (to) environmental stressors….in such a setting, even when the levels are comparably low, (wind farm noise could) be perceived as a potential health risk."
The heart of the studies shows a correlation between increasing noise levels and annoyance. This effect was clearly stronger in the two flat, rural areas, than in a study that took place in a more suburban, rolling landscape that had more other noises present. A dramatic increase in proportion of people annoyed by turbine noise took place when the noise was over 40dB(A); here, 25-45% reported annoyance in rural settings, and 10% in the suburban area. At 35-40dB, annoyance ranged from 16-20% in rural settings but was only 5% in suburban; at 30-35dB, annoyance hovered around 10% in rural areas.
The studies showed no direct correlation between noise levels and health effects related to stress (including headaches, tiredness, tenseness, and irritability); this is not surprising, since at all noise levels, a majority of the population was not annoyed, so also not likely to be stressed. Among those experiencing annoyance, there was a correlation with stress effects, but it was far from universal (correlations generally in the 1.25 range).
Sleep disruption from any source was reported by 15-20% of rural respondents even at sound levels under 30db; some may interpret this as evidence of impact from wind turbines at very low sound levels, but it could as well be considered a baseline of sleep disturbance from non-wind farm causes. At sound levels of 30-40dB, 5-8% more rural residents reported sleep disruption, and as levels rose above 40dB, a total of 30-40% of rural residents reported being awakened.
More Insight into Noise Perception and Annoyance
Kerstin Persson Waye. Perception and environmental impact of wind turbine noise. Presentation at Inter-noise 2009.
This is another paper that re-analyzes results from the several previous studies, including the Swedish and Dutch ones cited above (Waye and Pederson were co-authors of one of these earlier studies), and adds several interesting and important points to the discussion.
First, she cites studies that suggest that the swishing nature of turbine noise is especially problematic, leading to a much higher correlation with annoyance than simple dB level measurements. Indeed, even at sound levels of only 35-40dB(A), when swishing was present, 45% of respondents reported being "rather" or "very" annoyed; over 20% were similarly annoyed at 30-35dB.
Waye delves too-briefly into studies addressing the connection between SEEING turbines and being annoyed by them. This is an especially difficult question, but she cites studies suggesting very high correlations between visibility and annoyance, much higher than the related correlation between visibility and audibility. This ties into other studies suggesting that those who don't like seeing turbines, also don't like hearing them; again, though, it's important to remember that even these strong correlations are not universal, and many who experience noise issues are content to see turbines, if they are far enough away to not create audible disruptions to their recreational, work, and sleep life.
In parsing the data from the three studies also addressed by Pederson, above, Waye adds two key pieces of information: first, all these wind farms consist of relatively small turbines, by current standards: 500-800kW. Second, our consideration of annoyance thresholds at various dB levels is greatly enhanced by also including a graph showing that, in addition to those annoyed at each sound level, another 40-70% of the population could HEAR the turbines, but did not report annoyance. For example, at 30-35dB, over half of rural residents reported hearing the turbines, while only 8-12% were annoyed; at 35-40dB (within most global regulatory limits), 85% heard them, while just under 20% were annoyed; and at 40-45dB (within common US regulatory limits), 95% heard them, while 45% were annoyed.
Finally, Waye addresses a commonly reported finding: that annoyance levels are higher for wind turbines than for noise from less dynamic industrial sources, such as factories. She cites a study that shows that annoyance when indoors is pretty much the same, but that outdoors in rural settings, annoyance is significantly higher at sound levels above 35dB (annoyance at the one suburban wind farm was nearly identical to that from factory noise, again suggesting that expectations in rural setting plays a key role). Waye suggests that in rural settings, recreational and "restorative" aspects of outdoor experiences are impinged upon by wind farm noise. A final fascinating tidbit in her paper is that people who move from cities to the country are significantly more sensitive to noise than people who had always lived in the country; that is, those who actively chose to relocate to the country are more attached to the quiet nature of the landscape, while those who grew up there are more accepting of changes. (Ed. note: As with so many statistics in these studies, though, this should not be over-emphasized; surely many long-time locals also struggle with noise impacts. Indeed, the difference in sensitivity to noise, while an interesting finding, is just 15%)
Low-Frequency Active Sonar Annual Report to NMFS
Annual Report No. 1: Operation of the Surveillance Towed Array Sensor System Low Frequency Active (SURTASS LFA) Sonar Aboard the R/V Cory Chouest and USNS Impeccable (T-AGOS 23) Under the National Marine Fisheries Service Letters of Authorization of 15 August 2007. Department of the Navy, Chief of Naval Operations, September 2008. [DOWNLOAD (pdf)]
This report details the actual operations of the US Navy's two LFAS-equipped ships, from mid-August 2007 to mid-August 2008. Both ships remained close to the Asian Pacific coast, near China, the Philippines, and Japan. The Letter of Authorization issued by NMFS, allows the Navy to use LFAS for up to 432 hours per vessel each year. During this year, the Cory Chouest used the system for 25 days, totaling 71 hours of transmissions, and the Impeccable used it on 24 days for a total of 65 hours of transmissions. During these missions, both passive acoustic detection and an active "whale-finder" high frequency sonar were used to supplement visual marine mammal observers; no whales were heard via passive listening, one group of whales was spotted visually, and on 19 occasions, whales or turtles were spotted by the whale-finder sonar. Operations were suspended 43 times, including the 20 encounters just noted, and 23 times when the whale-finder sonar was not working correctly. Such shut-downs occur when whales may move within 1km of the ship; the whale-finder sonar reliably detects whales out to 2km away. Based on current population studies of whales in the region, the report estimates that LFAS operations injured no animals, and created possible behavioral reactions (received levels of 120dB or more) in less than 1% of most cetacean species, with no more than 3% of any species affected.
The report notes that the LFAS source transmitter send out sound in a full 360 degrees, at a source level of 215dB or less, using a variety of signal types at 100-500Hz. The document provides a good overview of the Navy's EIS process since it began in 1996, along with court challenges and rulings from 2002-2008.
Safety Thresholds for Ocean Noise Should Address Character of Signal, Not Just Loudness
Michael Stocker. The importance of incorporating signal characteristics in the evaluation of noise exposure impacts on marine life. Acoustical Society of America presentation, May 2009.
This paper is a literature review that presents evidence suggesting that our current reliance on simple amplitude (dB level) limits as the foundation of noise-exposure guideline for sonar and other ocean noise sources may not provide the assumed protection for animals. The author proposes several other characteristics of sound signals that may have biologically relevant effects that contribute significantly to possible injury or behavioral responses to human sound.
Current safety thresholds are largely based on hearing tests with captive dolphins. A striking graphic in this paper shows the wide variability in these lab-based results from one species, with reported hearing thresholds varying by up to 50dB. This could well be due to large individual variations in hearing health among captive dolphins; the author stresses as well that the simple sine-wave-based signals used in most hearing tests may not be especially relevant to cetacean hearing. He notes that predominant natural ocean noises (waves, rain, etc.) are relatively simple sine-like sounds, so that ocean species may in fact be adapted to NOT hear them as well as sounds important to communication or which are threats. He concludes his overview of existing hearing studies: "It is clear that animal hearing systems are not just 'auditory frequency bins' but include complex ways of discriminating the characteristic differences between biologically useful signals, 'safe sounds,' and 'pernicious sounds.'" He then cites studies from Holland that have used various non-sinusoid signals to determine discomfort levels, and associated "discomfort zones" related to various signal differences; and, studies indicating that signals with high "kurtosis" (variability in sound levels and harmonic content) produce greater physiological damage than similarly-loud sounds with low kurtosis.
The author concludes by noting that current regulations are based on simple lab auditory threshold tests that are favored because they are easily replicable, but which "only demonstrate the subject's sensitivity to the test signal and do not necessarily reflect the subject's auditory thresholds to the range of signals that they might encounter in their own habitat." He suggests that exposure criteria should be modified to reflect characteristics known to enhance behavioral responses or increase the risk of physiological injury; he proposes evaluation of the following signal characteristics:
- Rise time of impulse signals
- Periodicity of intermittent signals
- Kurtosis, evaluated three ways: FFT of spectral distribution, amplitude variability, and spectral variability.
Measuring Air Gun Propagation from New NSF Research Ship R/V Langseth
Tolstoy, Diebold, Doermann, Nooner, Webb, Bohnenstiehl, Crone, Holmes. Broadband calibration of the R/V Marcus G. Langseth four-string seismic sources. Geochemistry Geophysics Geosysytems, Vol. 10, Number 8. August 2009. [DOWNLOAD (pdf)]
This study marks the primary calibration of the new seismic survey vessel managed by Columbia University's Lamont-Doherty Earth Observatory (LDEO) and often chartered by the National Science Foundation for academic surveys. The Langseth's air gun arrays are different than those on the previous vessel, the R/V Ewing, as it uses four identical 9-gun linear arrays of somewhat smaller air guns, rather than up to 20 separately towed and larger air guns. Tests were run in a deep water site and a shallow water site, since sound propagation varies considerably with depth. Sound levels were calculated using both 90% RMS (re 1uPa) and SEL (re:1uPa2s). The resulting exposure radii (safety zones to prevent exposure at the given level) are as follows:
|dB threshold RMS
|dB threshold SEL
Interestingly, actual received levels at distances over 3km at the deep site were below the slope of the statistical "line" the data created at closer ranges; thus the very distant exposure radii are likely over-estimates. As has been widely noted in recent years, sound energy was concentrated in the 10-300Hz range (120-150dB energy spectral density at 1km), but continued to have significant energy up to 1kHz (100-120db shallow, 90-110dB deep) and 20kHz (60-80dB shallow, 20-60 ESL deep). Of special note in this study is the further clarification that, contrary to previous assumptions, differences between RMS and SEL are not consistent, but rather vary greatly with water depth. Reverberations in shallow environments create a smaller difference (about 8dB) than in deep water (about 14dB).
Fin Whales Seem to Avoid Seismic Survey
Castellote, Clark, Esteban. Mediterranean fin whale migration movements altered by seismic exploration noise. Presentation at Acoustical Society of America, May 2009.
This study took place in the western Mediterranean, off the coasts of Spain, France, and northwestern Italy; its main purpose was to simply identify seasonal patterns of fin whales and better understand their migratory movements, using the now-common Cornell Marine Autonomous Recording Units (MARU), which are deployed for weeks or months, and then "pop up" for recovery. By chance, an medium-sized academic seismic survey took place in the vicinity of the recorders for ten days, from 8-17 December 2006, using 5 typical air guns and 4 small "sleeve" guns, totaling 1555 cubic inches. The resulting changes and in fin whale call rates strongly suggest that they shifted their migratory path, though given the limited "perspective" offered by two MARUs deployed near each other, and the fact that understanding of normal migratory pattern is limited, the study is not conclusive.
During the ten days before the survey began, whale calls were heard fairly regularly; during the first three days of the survey, it appears that whales vocalized more, while moving to a different position relative to the recorders. The call rate was most dramatically higher on the 2nd day of the survey: whale calls were heard for over 20 hours, rather than the 6-8 hours that was more typical before and after the survey (some non-survey days peaked at 12-14 hours). The researchers note a dramatic change in bearing (angle at which most of the calls came from) during this peak early in the survey, which was followed by a dramatic drop in calls, to zero on the 4th day of the survey, and continuing at zero or close to it for two weeks after the survey was completed; presumably the whales moved out of range of the recorders (the peak in call rates may represent more whales being temporarily closer as their route shifted). By the beginning of January, whale calls sporadically rose again to near the levels before the survey, and, by January 7th, became more consistent, and back to the bearing that had been noted before. The researchers cite a few other studies that have shown displacement or changed vocalizing patterns near surveys, to bolster their sense that this study should be added to that emerging body of research suggesting behavioral effects that are not fully accepted yet by the scientific and industrial communities.
Ocean Acidification Not Likely to Increase Ambient Background Noise
Reeder, Chiu. Ocean acidification and its impact on ocean noise level: An analysis using empirical and physical models of acoustic transmission loss. Presented at ASA October 2009 meeting.
Udovydchenkov, Duda. Ocean noise level change in response to ocean acidification. Presented at ASA October 2009.
These two papers take a closer look at the widely-noted ocean noise implications of increasing ocean acidification (a combination of factors related to global warming is triggering a steady increase in the ocean’s pH, which decreases sound absorption). When the acidification results were first released there was much speculation that shipping noise would propagate farther, resulting in cumulative ambient noise increases throughout the oceans. These two papers, presented at this fall’s Acoustical Society of America meeting, both come to the same conclusion: low frequency noise will not be significantly increased due to ocean acidification; rather, the primary changes will occur at mid-frequencies. This calms concerns about shipping noise, but may (over time) lead to slightly larger areas being impacted by mid-frequency active sonar, some acoustic harassment devices used by fish farms, noise from recreational boating, and other mid-frequency noise.
Rather than simply looking at the effects of sound absorption, both papers assessed the combined effects of many factors in sound propagation: seabed attenuation and boundary effects, waveguide physics, and the distribution of pH and absorption through different depths of water. The first paper looked at shallow water, a surface duct, and deep ocean, and found that the maximum change in noise transmission occurs at about 2kHz, with no significant change below 800Hz. The second paper notes that at low frequency, little sound is absorbed anyway, so pH-related absorption effects are much smaller than all the other effects, and that at high frequencies, sound does not propagate very far, also minimizing effects of decreased absorption; the authors note that effects can be sizable at middle frequencies. (Ed. note: for both papers, pre-conference abstracts do not quantify the mid-frequency effects; details will follow after the presentations and with later publication of results.)
Sleep "Arousal" and Awakening Could be Cause of Wind Farm Health Woes
Christopher Hanning. Sleep disturbance and wind turbine noise. June 2009 [DOWNLOAD REPORT]
(Ed. note: this is not a peer-reviewed paper; it was written for an anti-wind group in Swinford, UK. However, Dr. Hanning, unlike some other physicians wading into industrial wind noise issues, is not writing outside his area of expertise. He's a renowned sleep disturbance expert: his school hospital named their sleep lab after him.)
This report by a UK MD whose specialty is sleep disorders takes a comprehensive look at factors affecting sleep disturbance caused by nearby wind farms, and is highly recommended reading for anyone working to develop regulations at the local or state level. Hanning’s primary point is that external noise need not wake a sleeper to cause problems, and the repeated “arousals” can break the most restful periods of sleep. He notes that “The sleep, because it is broken, is unrefreshing, resulting in sleepiness, fatigue, headaches and poor memory and concentration.” These are precisely the symptoms often reported by people living near wind farms.
He stresses that arousals are also associated with “physiological changes, an increase in heart rate and blood pressure, which are thought to be responsible for the increase in cardiovascular risk. Arousals occur naturally during sleep and increase with age (Boselli 1998) which may make the elderly more vulnerable to wind turbine noise. Arousals may be caused by sound events as low as 32 dBA and awakenings with events of 42dBA (Muzet and Miedema 2005), well within the measured noise levels of current wind farms” and the levels permitted by most jurisdictions.
The report also summarizes other studies suggesting that night-time noise levels are often higher than sound models predict, as well as one that suggests that wind farms cause high levels of annoyance at lower sound levels than other common noise sources. He concludes that “While it may be possible to produce a reasonable acoustically based theoretical approach to calculating set back distances (Kamperman and James 2008b), it makes more sense to rely on recommendations from observations of the effects on real people at established wind farms.”
Some Birds Choose Noisy Areas For Nests
Francis, C.D., Ortega, C.P., and A. Cruz. 2009. Noise pollution changes avian communities and species interactions. Current Biology DOI: 10.1016/j.cub.2009.06.052
A new study surveyed nesting birds in New Mexico woodlands with oil and gas compressors, and came up with a surprising result. While, as expected, most birds were more numerous in areas farther from the compressors, two species seemed to prefer these areas. Black-chinned hummingbirds and house finches had more than 90 percent of their nests at the noisy sites. The researchers dug a bit deeper, and found that nests in the quiet areas were more likely to be attacked by predators, with predator birds significantly less abundant around noisy sites. It is suggested that the noise may mask their calls or make it harder for them to find their prey.
Increase in Noise Levels Leads to More Annoyance Than Similar Noise in Steady State
Brown, Kamp. Response to a change in transport noise exposure: Competing explanations of change effects. J. Acoust. Soc. Am. 125 (2), February 2009
This literature review addresses an interesting question, and one that may be relevant to concerns about noise from wind farms. A long history of studies of human annoyance responses to traffic noise seems to suggest that a change in noise levels (for example, traffic noise increasing from 50dB to 60dB) triggers more annoyance than occurs when exposure is steady at the higher level (in this case, a steady 60dB). This paper reviews many proposed explanations for this affect; while no single explanation is identified as most likely, several common ones are shown to be unlikely, and a set of plausible explanations remains. Among the explanations that are rejected is the common assumption that the annoyance after an increase is transient, and over time will dissipate as people adapt to the new noise level; in fact, evidence suggests that annoyance remains for years after a change. Also of note is that the one study that looked closely at whether attitudes toward a noise source is related to annoyance after an increase in noise found that neither prior attitude nor changes in attitude could account for the increased annoyance. This paper, and its many citations, are highly recommended for anyone addressing community responses to new or increased noise sources.
Harbor Porpoise TTS, Behavioral Response at Moderate Noise Levels in Lab Tests
Lucke, Seibert, Lepper, Blanchet. Temporary shift in masked hearing thresholds in a harbor porpoise (Phocoena phocoena) after exposure to seismic airgun stimuli. J. Acoust. Soc. Am. 125 (6), June 2009.
Field researchers have observed for years that harbor porpoises appear more sensitive to noise than most other cetacean species, moving away from noise sources at greater distances than typically considered problematic (belugas and bowhead whale mothers are also more behaviorally sensitive to noise). This study was the first that measured harbor porpoise auditory sensitivity in the lab, using Auditory Evoked Potential measurements (brain-wave scanners that note auditory brain activity), and the results confirm that this species' avoidance behavior occurs at relatively low sound levels, and may be linked to a similarly low threshold of TTS (temporary hearing loss). The test animal was a wild-born ten-year old porpoise who has lived in captivity in Denmark for most of his life; the testing facility is open to the sea, so background noise (ranging roughly from 60-80dB pressure spectral density) is dominated by local shipping sounds. A single small (20 cubic inches) airgun was used as the sound source, gradually moving closer until a TTS was observed at one of the 3 tested hearing frequencies (4, 32, and 100kHz). The airgun source sound was, as is typical, loudest at low frequencies (max of 150dB SPL at 300Hz), but had significant energy at higher frequencies as well (100-110dB SPL from 2kHz to 5kHz), at the relatively close range used in this test (14-150m).
The key finding was that the airgun sounds caused TTS in the 4kHz hearing range at received levels of 165.5dB SEL (202.1dB peak to peak); perhaps more importantly, recovery was quite slow, with reduced sensitivity (i.e., sound had to be louder than normal to be heard) still measured at 29 hours post-exposure. Based on the pattern of recovery, the researchers estimate that the animal's hearing returned to normal at about 55 hours. Also striking was the clear avoidance of the airgun sounds exhibited by Eigil, the test animal. While there was no apparent avoidance during initial exposures at 145dB SEL (174dB peak to peak), at levels above this, he tried to move away, and eventually resisted being placed in the exposure station (a small part of the pool where he was constrained during the actual tests, and where received level from the airguns was highest). This avoidance of the testing location continued for the rest of the 4.5 months that the tests continued.
Current US regulatory measures, while still evolving, have zeroed in on a proposed TTS threshold of 198Db (SEL) for both single impulses and multiple impulses; this is based on earlier TTS studies of bottlenose dolphins and belugas. The authors of this paper point out that these "mid-frequency" cetaceans may well have different hearing sensitivity thresholds than "high-frequency cetaceans" such as the harbor porpoise; thus, this study provides new information that could inform regulatory thresholds for seismic surveys and pile-driving (during construction of wind farms, bridges, or piers) in harbor porpoise habitat. The US Navy, in estimating the numbers of animals that will be behaviorally affected by sonar training, has been singling harbor porpoises out as more sensitive to disruption, and assuming that any animal exposed to 120dB will potentially change its behavior to some degree.
SEL Metric Does Not Simplify TTS Assessment
Mooney, Nachtigall, Breese, Vlachos, Au. Predicting temporary threshold shifts in a bottlenose dolphin (Tursiops truncatus): The effects of noise level and duration. J. Acoust. Soc. Am. 125 (3), March 2009.
This study, from one of the leading researchers investigating Temporary Threshold Shift (TTS; temporary decline in hearing sensitivity) after exposure to loud noise in dolphins, calls into question one of the key advantages of the Sound Exposure Level metric. SEL measurements are designed to measure total sound exposure over a given period of time; simply stated, SEL remains constant when sound intensity increases while duration decreases (e.g., twice as loud for half as long should result in "equal energy", or the same SEL). The assumption was that SEL offered an "equal energy" metric that could allow biologists and ocean regulators to set a SEL threshold that would apply to many types of noise exposure. However, this study indicates that a given SEL dB level (arrived at via a mathematical equation combining sound energy from many noise pulses over time) did not seem to induce TTS in the single captive dolphin used in this study. As with other metrics, higher SELs were required to induce TTS with shorter duration sounds. By extension, the hypothesis that TTS is caused by a given level of sound energy (the "equal energy" hypothesis) is called into question. The relationship appears to be logarithmic, rather than linear. In this study, the sound source was short (20ms) digitally generated tone bursts.
Related: Mid-Frequency Sonar Must Be Very Loud/Close to Trigger TTS
Mooney, Nachtigall, Vlachos. Sonar-induced temporary hearing loss in dolphins. Biology Letters, doi: 10.1098/rsbl.2009.0099
The same team more recently found the same difficulty with using SEL to predict TTS when using a recording of a US naval mid-frequency active sonar; short duration MFA "pings" had to be ramped up to a SEL of 214dB (equivalent to 203dB SPL rms) to induce a modest TTS of 6dB, which faded rapidly back to normal hearing levels in 20-40 minutes, a higher SEL than had induced TTS using longer duration sounds in the above study. This was the first hearing test on dolphins to use actual mid-frequency active sonar signals; previous studies had used sonar simulations or tones at similar frequencies. Ed. note: The usual caveats are in order here, as a long-time captive dolphin may not hear as well as his wild relatives; it is often assumed that captive dolphins are less sensitive both physiologically (hearing loss from living in noisy pens) and behaviorally (habituated to noise, and given food to remain in the test area), though the relative lack of clear studies on wild animals makes this assumption difficult to confirm.
Wind Turbines Do Not Seem to Displace Wintering Farmland Birds
Devereaux, Denny, Whittingham. Minimal effects of wind turbines on the distribution of wintering farmland birds. Journal of Applied Ecology 2008, 45, 1689-1694.
In what be the first study examining whether wind farms displace birds, this team studied bird distributions around two small wind farms in England (each had 8 2MW 60m hub-height turbines in two rows). Birds of four different functional groups (seed-eaters, corvids, gamebirds, and skylarks) were counted at five distances (multiples of 150m, out to 750m). After controlling for crop types and boundary effects, there was no overall significant difference in distribution by distance. One species was an exception to the overall findings: the largest and least maneuverable bird, the common pheasant, was more common as distance increased. Two other species not included in the overall study of functional groups were also less abundant within 150m: the mallard and the wood pigeon, also both less maneuverable than most of the other birds in the area (the authors note that counts were low enough for these that the pattern may have been skewed by a few large flocks). In some cases (skylarks and corvids), the data showed statistically significant increases in bird numbers closer to the turbines. The authors make a point of noting that this winter study needs to be complemented by similar investigations of distribution during the breeding season, when birds may be affected differently. This study did NOT study noise, but just the presence of the turbines.
Related: Compressor Station Noise Can Reduce Forest Bird Abundance
Bayne, Habib, Boutin. Impacts of Chronic Anthropogenic Noise form Energy-Sector Activity on Abundance of Songbirds in the Boreal Forest. Conservation Biology, Volume 22, No. 5, 1186-1193, 2008.
This study used an innovative study design to separate the effect of noise from the also-important effects of habitat disruption and edge effects caused by energy development. The authors compared bird distributions around (quiet) well pads and (constantly noise-producing) coalbed methane compressor stations in the forest of Alberta. They found that areas near well pads had a passerine density of 1.5 times higher than areas near compressor stations; one-third of the species studied showed this affect. The noise levels produced by the compressor stations is typically 75-95 dB(A) at the source, sometimes reaching 105dB(A) at large facilities; compressor noise is commonly heard at distances of well over 1km in the boreal forest; with 5000 compressor stations in boreal Alberta, the question of noise-related displacement is potentially significant. In addition to the overall tendency for passerines to be found in greater numbers near quiet energy installations than noisy ones (with three species especially affected), seven other species showed less dramatic but still noticeable differences, while eleven other species showed no difference. Red-eyed Vireos, White-throated sparrows, and Yellow-rumped warblers were particularly affected, with chickadees, jays, and wrens showing little effect.
Right Whales Experience Dramatic Variations in Noise During Annual Movements Along North American Coast
Parks, Urazghildiiev, Clark. Variability in ambient noise levels and call parameters of North Atlantic right whales in three habitat areas. J. Acous. Soc. Am. 125 (2), February 2009.
This study used pop-up recorders to examine ambient noise conditions and right whale calls in three of the species' annual habitats: The Bay of Fundy, Cape Cod Bay, and the coast of Georgia. While the variability of calls was subtle, there was some indication that louder call patterns were in response to the peak sound in an area, rather than the overall noise level. However, the seasonal variability of noise experienced by this population is the key finding here. Overall sound levels were highest during the summer season spent in the Bay of Fundy, and lowest in the winter off Georgia. Likewise, the percentage of time that the habitat was "loud" (ambient noise over 105dB re 1uPa in the 50-350Hz frequency range of right whale contact calls) varied dramatically: in the Bay of Fundy, it was loud 85-95% of the time, in Cape Cod Bay it was loud 53-63% of the time, and off Georgia it was loud only 20-30% of the time. While the quiet is surely appreciated during calving time in Georgia, the high proportion of noisy times in the Bay of Fundy could impede summer social interaction, perhaps including mating. The population of North Atlantic right whales is precarious, and slowly decreasing; the researchers conclude with the urgent observation that "Locating the mating grounds for right whales and quantifying the noise occurring in their breeding areas may be crucial in understanding how increases in ambient noise may limit the range of communication signals that are vital for successful reproduction."
Orcas Increase Volume of Calls in Synch With Increasing Boat Noise
Holt, Noren, V. Veirs, Emmons, S. Veirs. Speaking up: Killer whales (Orcinus orca) increase their call amplitude in response to vessel noise. J. Acous. Soc. Am. 125(1), January 2009.
This study found that Southern Resident killer whales, who are nearly always within earshot of boat traffic, increase their call amplitude by 1dB for every 1dB increase in background noise levels. Call amplitudes ranged from 133-174dB re 1uPa (mean 155dB), while background noise (measured in the 1-40kHz band) ranged from 98-123dB (mean 110dB), as nearby boat counts ranged from 1-46. Of course, source levels of calls vary, based on the type of call; still, there was a significant correlation between call source level and background noise for all call types. The detailed analysis was restricted to the one call type with the largest sample size. It appeared that call amplitude was relatively unaffected until background noise reached 105dB, though the researchers note a small sample size below that level, and suggest further investigation to see whether there is a threshold at some point. Above 105dB, calls increased 1dB for each 1dB of increased boat noise. Interestingly, they found no increase in duration of calls; an earlier study had found that calls were longer in noisy conditions. The researchers suggest that this difference may be due to differences in study design, or due to the fact that the current study site did not provide any "no boat noise" conditions (i.e., perhaps call duration increases at the first appearance of background noise, with call amplitude increasing with the noise).
Boats Reduce Foraging Time in Orcas
Lusseau, Bain, Williams, Smith. Vessel traffic disrupts the foraging behavior of southern resident killer whales Orcinus orca. Endangered Species Research, Vol. 6: 211-221, 2009.
This recent paper continues a line of research undertaken by this team throughout this decade, which investigates the ways that boat traffic changes orca behavior, with a special focus on foraging activity (a 2004 paper by these researchers suggests that reduced foraging is the most significant impact on an animals' energy budget; ie, the extra energy used in, e.g., avoidance is much less significant than the much larger decrease in energy received when foraging is reduced). As in their study of the northern orcas of BC, and in line with studies by others of delphinid species in other parts of the world, this study found that orcas around San Juan Island reduced their time spent foraging by about 21% when boats were within 400m (from 76% of the time to 60% of the time). They had hoped to identify behavior patterns when 100m, 400m, and 1000m or more from boats; unfortunately, in the San Juan Islands, boat traffic is nearly constant, and there were very few opportunities to observe orcas with boats more than 1000m away. In the end, the authors show a clear affect with boats within 100m and 400m, as well as an apparently smaller affect when boats were within 1000m. The authors note that it is possible that the 400m affect is mainly caused by boats not far beyond 100m (a study with finer spatial analysis would be needed to clarify this). Nonetheless, they show that the current whale watching standard of remaining 100m away is not sufficient to avoid disrupting the key foraging behaviors of orcas.
Related: Number of Vessels May Play Larger Role than Proximity of Vessels
Williams, Bain, Smith, Lusseau. Effects of vessels on behavior patterns of individual southern resident killer whales Orcinus orca. Endangered Species Research, Vol. 6: 199-209, 2009.
This companion paper by the same research team does not address foraging, but rather looks at overall behavioral effects of the same boat traffic measured in the above study. They find that behavioral changes such as swimming speed and directness of travel path changed slightly in response to boats, and in general, they found that changes were more correlated to the number of boats within 400 yards than by the proximity of the boats, whereas current whale watching standards address only how close each boat is, rather than total numbers of boats. They also note that, given the difficulties in finding clear patterns within this noisy environment, it may be hard for managers to feel that the data is solid enough to warrant additional protections. However, the authors conclude with the observation that it appears that this population is food-limited (many researchers consider declining salmon runs to be a primary factor in population stagnation and sometimes dips), and suggest that reducing the ambient noise levels would improve the whales' ability to find the limited food that remains in the region. Ed. note: This paper's focus on numbers of vessels corresponds well with the Holt paper directly above, which finds overall ambient noise is closely tied to the number of boats in the vicinity.
Soundscapes, Acoustic Daylight, and Fish Hearing
Richard Fay. Soundscapes and the sense of hearing in fishes. Integrative Zoology 2009; 4: 26-32.
This fascinating review offers a wide-ranging consideration of the implications of a simple observation: goldfish have an acute sense of hearing, though they do not vocalize or engage in any known sound communication. What are they listening to? Fay introduces several key lines of research into fish hearing, some dating from the 80s, and some from the past decade. His own research, along with that of several others, has demonstrated that fish can isolate multiple sound sources (though studies cited are limited to two distinct sounds, rather than much more complex mixes of sound). From there, Fay suggests that fishes' sensitivity to particle motion in water, via their lateral lines, provides them the ability to engage in what in human perception is termed "auditory scene analysis," or the perception of a complex environment by distinguishing the many sound sources and their motion through the soundscape. The most intriguing suggestion in the paper is less solidly fleshed out: that fish make use of reflections of ambient sound to build this "auditory scene." That is, ambient noise can act as "acoustic daylight," with subtle differences in the echoes of the overall ambient sound bouncing off specific objects being a source of perception (as light reflects off objects to create visual perception). Fay mentions one study in which goldfish were shown to be able to perceive a single point source of delayed (as if echoed) signal in a noise field; this was apparently done with artificial noise sources, though the researchers (and Fay) propose that it represents an ability of goldfish to perceive the fish bladder of another fish re-radiating ambient noise. This may well be true, though this (and one other related study that showed fish using echoes from self-produced sound) do not yet cross the chasm of showing that fish process complex acoustic scenes by using reflections of ambient noise. Yet the point of this review is not to "make a case" for these higher order perceptual abilities, but rather to open our minds to the likely fact that fish listen to much more than simply communication signals, which have been overlooked due to our "profound ignorance of the other possible sounds and sources that probably have biological significance to fish," and to suggest that "environmental soundscapes (are) most probably important sources of information." This more modest first step is clearly successful here, opening the way to future studies of the undoubtedly subtle and complex sensory world of fishes.
IUCN Report Highlights Noise Impact of Shipping in Mediterranean, Calls for MPAs to Provide "Acoustic Comfort"
Ameer Abdulla, Olof London (editors). 2008. Maritime traffic effects on biodiversity in the Mediterranean Sea: Review of impacts, priority areas and mitigation measures. Malaga, Spain: IUCN Centre for Mediterranean Cooperation. 184 pp. [DOWNLOAD(pdf)] [WEBSITE]
This comprehensive look at Mediterranean shipping, from the International Union for the Conservation of Nature and Natural Resources, includes a long section in the early pages on noise impacts. Due to the concentration of shipping in the Mediterranean, ambient noise is 40dB higher than in relatively shipping-free seas such as the Sea of Cortez. Among the recommendations made in regards to noise are that "Much effort should be devoted to developing a legal framework within which underwater noise is recognized and regulated as a threat," and the advocacy of MPAs that are designed to provide acoustic protection to critical and productive habitats, where "noise levels should not be allowed to exceed ambient by more than a given value, including noise from sources located outside the MPA." In addition, the report stresses the importance of moving rapidly to develop regional hydrophone networks with which to monitor noise and develop current "noise budgets," as well as the need for expanded research with Auditory Brainstem Response techniques to examine hearing sensitivity and changes due to noise exposure, and analysis of stress hormones in response to noise. The authors of the report forge important new ground as they summarize:
"In addition to defining which impacts should be avoided or mitigated, we also need to draw up a model of 'acoustic comfort' that we should guarantee to animals, at least over sufficiently extensive protected areas. This is a novel concept. It means we should define the (near to) zero-impact noise level that a habitat should have for each type of marine life."
Yet Another Study Shows Dramatic Decrease in Dolphin Foraging Near Boats
Antonella Arcangeli and Robert Crosti. The short-term impact of dolphin-watching on the behaviour of bottlenose dolphins (Tursiops truncatus) in western Australia. Journal of Marine Animals and Their Ecology. Vol 2, No. 1. 2009. [DOWNLOAD PAPER]
Over the past few years, a steady trickle of new studies have indicated that many species may decrease foraging activity in the presence of boats. In many situations, it can be difficult to have enough sightings without boats to create a data set large enough to have statistically significant results (e.g., orcas in the Pacific northwest, or dolphins in the Mediterranean). Also, the presence of the observation boat can confound results. This study took place in a bay near Bunbury, 200km south of Perth, western Australia, a location where these limitations could be overcome. The weather conditions in summer are generally calm, allowing excellent observing conditions, with the observation inflatable's motor often shut down; observations were only made in quite calm seas (Beaufort 2 or lower). A large local population of dolphins offered plenty of data, and the population is generally stable in place, engaging in a series of regular behaviors over relatively prolonged timeframes. Behavior "without" boats present was noted when no boats (other than the observation inflatable) were within 350m; behavior "with" boats present was noted when tour boats came within 150m. (Ed. note: it would be interesting to consider the data when tour boats were 150-350m distant, to assess whether the observed effects extend to greater distances). Over the course of 65 hours of observation by a single observer, 1028 3-minute behavioral samples were taken, 781 with no boat (average duration 69 min.), and 247 with a tour boat present (average duration 47 min.). As usual with such studies, several behavioral states were analyzed: Traveling, Socializing, Resting, Milling, Feeding, and Diving. All showed some change in the presence of boats, with Traveling, Milling, and Diving all increasing in the presence of boats, and Socializing, Feeding, and Resting decreasing. Of these, the most relevant to an animal's energy budget all were negatively affected: Traveling increased from 27% of the time to 46%, Resting decreased from 31% to 20%, and by far the largest energetic impact was seen in Feeding, which reduced from 20% of the time to just 7.6% of the time. This is the most dramatic decrease in feeding seen in such studies (others have tended to find a 25-35% decrease in foraging). This may indicate that the relatively localized population had plenty of time to eat when the boats were not present, and chose to either leave or play with the boats when they were present. The study did look at attraction/deterrence, finding that in in 20% of cases, dolphins moved closer to the boats, while in 28% of encounters, they moved away (about half the time, there was no spatial difference, though behaviors may still have changed). The Discussion section of this paper includes an unusually detailed comparison of the findings and the contexts of this and several similar studies, as well as consideration of the ways that in other settings, were human activity is more prevalent, these behavioral changes could have longer-term, population-level impacts.
Excellent Review of the Effects of Human-Generated Sound on Fish
Popper and Hastings. The effects of human-generated sound on fish. Integrative Zoology 2009; 4: 43-52
This recent review is a great place to get up to speed on the current state of our knowledge regarding the effects of human sound on fish. It begins by sketching a sense of the "natural" and 21st-century aquatic world's acoustic nature, and proceeds to review various possible physiological and behavioral effects of human sounds ranging from sonars to pile-driving, seismic surveys, shipping, and even research vessels themselves. The authors note that a significant challenge to improving our understanding of the behavioral effects of noise sources is our inability to observe wild fish over large enough areas (fish-finding sonars can only see fish out to a few hundred meters, not enough to observe possible avoidance of noise sources). As is usually the case with ocean noise issues, the concerns about noise and fish far exceed the ability of our limited data to discern possible effects. As the authors note, "Because of a striking paucity of well-designed and controlled experimental data, very little is actually known...Human-generated sounds, even from very high intensity sources, might have no effect in some cases or might result in effects that range from small and temporary shifts in behavior all the way to immediate death."
Following are some highlights of the 2008 Research Summaries;
see archive pages linked above for more entries
Pinger Study Illustrates Extreme Variability of Real-world Sound Propagation
Shapiro, Tougaard, Jorgensen, Kyne, Balle, Bernardez, Fjalling, Karlsen, Wahlberg. Transmission loss patterns from acoustic harassment and deterrent devices do not always follow geometrical spreading predictions. Marine Mammal Science, 25(1): 53067 (January 2009)
This study was designed to investigate why acoustic harassment devices, or pingers, on fishing nets do not always succeed in keeping dolphins away. The researchers did a series of recordings around pingers of several different styles, and found that the received sound levels did not simply increase as they came closer, but fluctuated dramatically; thus, animals approaching the nets may not have clear sense of how far away they are. While the results here are somewhat mixed for pingers (overall, the average sound level DOES go up as the animals approach, albeit mixed with large variations), the study offers a fascinating glimpse into the real-world factors that will often confound simple geometric or spherical-spreading models generally used to predict sound exposure levels around any sound source. The researchers suggest that many factors likely contribute to the variation: changes in directivity of the source, subtle differences in source level for each ping, and, most influentially, as a result of the constructive and destructive interference of direct, surface-reflected, and bottom-reflected sound waves.
Ed. note: This graph is a great picture of the degree of variation seen. Note a routine variation of 10-15dB, with some more dramatic shifts: at 400m, the sound shifted from around 127dB to over 150dB; and again, at just under 200m, from just above 130dB to over 160dB (around a general average at that distance of perhaps 150db). Given the increasing concern among biologists about behavioral disruptions triggered by noise, it is extremely important to acknowledge that real-world exposures can vary to this degree; many more animals respond behaviorally at 150dB and above, than down at 120-140dB.
Related: Beaked Whales Very Sensitive to Pingers; By-Catch Reduced to Zero over 11 Years
Carretta, Barlow, Enriquez. Acoustic pingers eliminate beaked whale bycatch in a gill net fishery. Marine Mammal Science, 24(4):956-961 (October 2008).
This study documents a dramatic shift in beaked whale bycatch by gill nets set for sharks and swordfish in the California Current. Over the first 6 years of data, 1990-1996, 33 beaked whales died in the nets; after installation of pingers in 1996, NO beaked whales were caught by the nets over the succeeding 11 years, though 260 cetaceans of 11 other species did drown in the nets. Ed. note: this result seems to dovetail well with observed reactions of beaked whales to other sounds; it appears they are especially sensitive to noise, perhaps at a wide range of frequencies.
Passive Acoustic Detection of Beaked Whales: Easy Within 1km, Nearly Impossible Beyond 4km
Zimmer, Harwood, Tyack, Johnson, Madsen. Passive acoustic detection of deep-diving beaked whales. The Journal of the Acoustical Society of America, November 2008, Volume 124, Issue 5, pp. 2823-2832.
Beaked whales spend very little time at the surface, with foraging dives that last an hour or more, including about 30 minutes of active echolocation at the feeding depth. Visual detection is very difficult, so the possibility of using Passive Acoustic Detection (PAD) is an attractive complement to visual spotting. However, these high-frequency clicks attenuate rapidly. According to this paper, acoustic modeling suggests that in "good conditions,"e.g. wind speed of 2 m/s, a hydrophone close to the surface should detect beaked whales with a high probability within .7km. At the other end of the detection range, no whales would be detected at distances greater than 4km, except in very low ambient noise or unusually good propagation conditions. The detection curve generated by the models, drops steeply as distance increases, with a relative leveling off that suggest roughly 50% detection when whales are 1.5-3.5km distant. Additionally, the researchers substituted some actual dive profile data obtained in D-Tag studies, and found that in these instances, detection probability may rise somewhat, with 80% detection being possible at distances of 1.5-2.5 km. Actual detection of real whales is complicated by the fact that the sound of the clicks is highly directional; only clicks directed nearly directly toward the receiver will be heard at the modeled distances, but echolocating whales do scan in many directions, so at least some clicks from any whale should be detected. Finally, the relatively quiet interval between deep foraging dives can be as long as 110 minutes, meaning that listening time should be roughly 140 minutes to have a high probability of detecting if beaked whales are present. This, in turn, suggests that a slow-moving vessel (such as gliders or drifting buoys) will be more successful than a fast-moving active sonar vessel. (That is, if detections are only going to occur within roughly 4km, the listening platform should not move out of a relatively similar area during the 2-hour-plus PAD session.) Ed. note: While it has still not been confirmed to all observers' satisfaction, there is some evidence that beaked whales affected by mid-frequency active sonar may well have been tens of km from sonar vessels. Thus, PAD may be useful for avoiding nearby exposure, but may not fully mitigate for effects that could occur at greater distances, including fleeing in ways that disrupt the whales' post-dive recovery and oxygen/nitrogen rebalancing.
Detailed Review of Sound Exposure Impacts on Puget Sound Orcas Released by NOAA
Marla Holt, Sound Exposure and Southern Resident Killer Whales (Orcinus orca): A Review of Current Knowledge and Data Gaps. NOAA Technical Memorandum NMFS-NWFSC-89, February 2008. 77pp. [DOWNLOAD REPORT(pdf)]
This review includes summaries of most of the studies of ambient and shipping noise in the range of the southern resident orca pods of the Pacific Northwest. Topics covered include ambient sound patterns, shipping noise, whale watching noise, orca auditory capabilities and auditory effects of sound exposure, including masking and hearing loss, and behavioral changes in the presence of excess sound. An important section looks at the emerging concept of "zones of influence" of sound: the zones of audibility, response, masking, and hearing loss or injury. The report concludes with a section that assesses the likelihood of acoustic impacts and suggestions for future research.
The report is a treasure-trove of clear information on noise/sound impacts. Among the points that stood out in my reading are the following. Ambient noise is generally elevated at least 10-15dB by small boats, and 20-25dB by large ships (another study indicates increases more in the range of 50-70dB in the presence of various boats). The section on hearing sensitivity makes a point about captive animal testing that is rarely noted: when animals receive negative reinforcement for reporting a "false positive" (i.e. responding as if hearing a sound, when no sound was played), they may well become conditioned to be conservative in their response to faint sounds, and so the results can easily underestimate the hearing sensitivity of the species (for orcas, only two studies have been done on captive whales to assess hearing sensitivity curves). Tentative measurements of the critical ratios for orcas (tentative because, again, there are few test subjects) suggest that they are more affected by masking than many other toothed whales: to hear a target sound in noise, the target sound must be 20dB louder than ambient at 10kHz, and 20dB louder than the noise levels at 80kHz. There are some indications that orcas spend less time feeding and more time traveling or resting when boats are nearby (within 100m or 400m); likewise, they may travel in less direct paths in the presence of boats within 1000m (though interestingly, one study suggests that when there are many boats present, paths are more direct; perhaps there is little use in trying to avoid boats in this instance). An interesting study (based on models, not measured/observed results in the field) suggest that the presence of boats can significantly decrease the detection range for an orca echolocating on a salmon: boats at 400m decreased the detection range by roughly 35-90%, and boats at 100m decreased the detection range to as little as 0-20m, or 90-100%.
European Cetacean Society Workshop Addresses Offshore Wind Turbine Impacts on Marine Mammals
Evans, P.G., Ed. ASCOBANS/ECS Workshop: Offshore Wind Farms and Marine Mammals: Impacts and Methodologies for Assessing Impacts. ECS Special Publication Series No. 49, February 2008. 70pp. [DOWNLOAD REPORT]
Prospect of Widespread Offshore Development Requires Cumulative Impact Analysis
Simmonds, Dolman. All at sea: renewable energy production in the context of marine nature conservation.
This survey of potential conservation impacts of offshore wind development quotes several previous studies that address specific concerns. Madsen et al. (2006) comment that “if the very large offshore wind farms are realised... this could involve construction activities at several locations in the area [of the German Bight] simultaneously every summer for the next decade.”
Madsen, P.T., Wahlberg, M., Tougaard, J., Lucke, K. and Tyack, P. 2006. Wind turbine underwater noise and marine mammals: implications of current knowledge and data needs. Mar Ecol Prog Ser., 309: 279-295. Wahlberg and Westerberg (2005) concluded that fish behaviour could be affected at ranges of several kilometres. Wahlberg, M. and Westerberg, H. 2005. Hearing in fish and their reactions to sounds from offshore wind farms. Mar Ecol Prog Ser., 288: 295-309. Carstensen et al. (2007) commented that ‘given the extensive plans for expanding the offshore wind energy sector, it is important to know the effect of single wind farms and well as the cumulative affects of several wind farms within the range of each marine mammal species”. Indeed, it would make good sense to consider the cumulative impact of all new developments on
populations and yet, in our experience, this rarely seems to happen. Carstensen, J., Henriksen, O.D. and Teilmann, J. 2007. Impacts on harbour porpoises from offshore wind farm construction: acoustic monitoring of echolocation activity using porpoise detectors (T-PODs). Marine Ecology Progress Series 321: 295–308.
UK Offshore Development Scaling Rapidly to Much Larger Facilities
Prior, McMath. Marine mammals and noise form offshore renewable energy projects—UK developments.
This paper notes that offshore wind farm development in the UK has taken place in licensing "rounds," with rapid increases in the size of wind farms being built. Round 1 was an initial demonstration phase, with eleven projects permitted so far (and five in operation), each relatively small in scale (less than 30 turbines) and relatively short construction phases (as short as one month). Fifteen Round 2 projects have been proposed (with four approved so far); these are larger developments often including hundreds of turbines. Round 2 construction will likely take place over a number of seasons, so construction disturbance will be longer and the impacts could be different than those seen in Round 1. In addition, piles of up to 6 feet in diameter have been proposed to support larger turbines; this will lead to substantially increased noise during construction, with disturbance impacts extending over tens of kilometers. Proposals for Round 3 are currently undergoing Strategic Environmental Assessment; however, the proposed capacity of development may be as much as four times the eventual level built out under Rounds 1 and 2 combined. Concern over cumulative impacts may be prominent during the consenting process, particularly if construction operations on adjacent sites takes place concurrently, giving rise to the potential for longer term and geographically widespread increases in underwater noise.
Porpoises Numbers in Wind Farms Can Vary Dramatically
Teilmann, Tougaard, Carstensen. Effects from offshore wind farms on harbour porpoises in Denmark. Included in:
In a paper summarizing the results from acoustic monitoring at two Danish offshore wind farms, results clearly show a dramatic difference in harbour porpoise responses. At one wind farm, Horns Reef, porpoises numbers decreased modestly during construction (both inside the farm in in monitoring sites 10km away), and decreased a bit more during early start-up, when maintenance activity was highest, but rebounded to baseline (pre-construction) levels early in the first year of normal operations. However, at the Nysted wind farm, the decrease in porpoise numbers that likewise began during construction was not reversed during the first two years of operations: porpoises mostly avoid the wind farm (though numbers were slowly increasing by the end of the second year), while they returned to the areas 10km away once construction ended. The authors note two possible explanations for the different long-term impacts of the wind farms. The area around Horns Reef is an important harbour porpoise habitat, with a larger natural population density; it is possible that the "the porpoises around Nysted are not particularly interested in the area and will simply avoid it if disturbed." In addition, the area around Nysted is relatively sheltered, whereas Horns Reef has higher wind and waves, and thus a higher background natural ambient noise level, so that "the relative noise level from the turbines is higher and audible to the porpoises at greater distances at Nysted than at Horns Reef." The authors conclude that "it can be concluded that the same species may react differently to similar types of disturbance (wind farms) in different localities. This is an important conclusion for future monitoring programmes of wind farms and other offshore installations."
Orcas Avoid Mid-frequency Sonar Signals, but not LFAS; Herring Unaffected
Kvadsheim, Benders, Miller, Doksaeter, Knudsen, Tyack, Nordlund, Lam, Samarra, Kleivane, Godo. Herring (slid), killer whales (spekknogger) and sonar - the 3S-2006 cruise report with preliminary results. Norwegian Defence Research Establishment (FFI). 30 April 2007
This paper reports preliminary results from an ambitious multi-national Controlled Exposure Experiment using acoustic D-tags, which allow researchers to record received sound levels while charting dive patterns. Six orcas were tagged, with 17 hours of data collected, with one animal exposed to LFAS signals, two to mid-frequency active sonar signals, and one used as a control, fewer samples than hoped. The whale exposed to LFAS signal did not change its behavior, nor did its companions. However, the group exposed to mid-frequency sonar signals ceased feeding and moved rapidly away; in addition, they exhibited an unusual dive pattern, diving roughly twice as deep (over 60m) as normal (20-45m), including a highly unusual reversal of their ascent (coming up to 15m from the surface, then retreating again to 60m). [Ed. note, not part of the report narrative, based on observation of included diagrams: Four other dives during the 35-minute sonar transmission were within the normal range of depth (the deep dive was the third of five dives during sonar transmission), with three longer than normal rest periods at the surface during the hour after sonar transmission ceased.] Received levels did not exceed 150dB re 1uPa. Looking at longer-term responses, while the experimental use of sonar in the herring trials did not seem to deter orcas from the general area, by contrast, no orcas were seen during three days of a planned Navy exercise in the area that included mid-frequency sonar use. The herring trials used bottom-mounted sensors to chart the mean depth of a school of herring as a sonar vessels passed nearby. Herring at shallow depths (25-50m) tended to show a minor downward reaction as the sonar source ship passed overhead, while herring located deeper, or in less dense schools, showed no detectable reaction; no horizontal avoidance was seen. While herring hearing curves suggest they should be able to clearly hear LFAS signals, but not mid-frequency signals, the responses were the same for all signals (including ship-only, no sonar), suggesting that the herring may have been responding to the sound of the ship, rather than the sonar signal; such reactions to ships have been seen for many fish species. A related trial using orca echolocation signals on the herring showed more of a response, suggesting that the herring could distinguish between the mid-frequency sonar and the orca sounds, but the three trials all produced slightly different response patterns, suggesting the need for further study.
Review of Possible Ways that Increasing Ocean Noise May Affect Marine Mammals
Peter L. Tyack. Implications for marine mammals of large-scale changes in the marine acoustic environment. Journal of Mammalogy, 89(3): 549-558, 2008. [DOWNLOAD PAPER(pdf)]
In this wide-ranging literature review, Peter Tyack of Woods Hole Oceanographic Institute sketches the history of research into the effects of noise on marine life, with some references as well to effects seen in terrestrial creatures. He begins by noting that while acute disturbance of individuals attracts the most attention, the likely more profound effects of chronic disturbance on population vitality (success in foraging and mating) are much harder to discern. Several examples are presented of studies that documented both temporary and long-term abandonment of key habitat when loud noise was present (including gray whales abandoning a birthing lagoon for several years, then returning when the salt production facility was abandoned, and dolphins moving away from foraging habitat when shipping traffic is heavy).
Next, Tyack turns to a detailed examination of the question of whether global shipping may be dramatically decreasing the area within which whales can hear each other's calls, beginning with the thought that the unintentional consequences of increased shipping noise may be creating unexpected problems analogous to those created by the introduction of industrial-waste gasses into the atmosphere, which went unnoticed for decades. Following on models created in the 1970s, updated to take into account the hundred-fold increase in shipping noise since then, he notes that "the increase in ambient noise from shipping seems to have reduced the detectable range of low frequency whale calls from many hundreds of kilometers in the prepropeller ocean down to tens of kilometers in many settings today." (For example, the finback whale range shrank from at least 400km in the pre-engine ocean to 90km in the 1960s, down to 32km today.) He notes that, as populations of great whales fall, the separation between them may increase, with these increases in shipping noise compounding the challenge of finding mates or sharing information about active feeding grounds. However, he then goes on to point out that there is, so far, no clear evidence that the great whales do indeed communicate over long distances; clear responses to the calls of other whales have been seen only at ranges of 10km or less; the fact that a human acoustic sensor can detect a signal at 400km does not necessarily mean that the whales themselves rely on hearing signals at such distances. He suggests that acoustic tags may help to clarify whether distant, faint signals from conspecifics (whales of the same species) do in fact trigger any discernable reaction (calling in response, or moving toward the distant whale).
While noting that it may be impossible to design scientifically valid studies to uncover the possible cost of "lost opportunities" when communication is drowned out by shipping noise, an indirect way to get at this question is within reach of researchers: if animals alter their calls in noisy conditions, we can infer that the noise is disrupting their normal communication channels. And indeed, Tyack notes a long list of studies that show such changes, such as beluga whales and manatees increasing the volume of their calls in noisy conditions, and an apparently dramatic increase in the frequency (pitch) of right whale calls in sections of the ocean where low-frequency shipping noise is more intense. While noting that these and other studies "suggest that vessel noise clearly does interfere with communication in marine mammals," Tyack also notes that we do not know how costly these adaptations are, or what noise level would preclude such compensation. Also, he asks, "When does noise so degrade the usefulness of a habitat that animals leave? Can this level be predicted by the compensation behavior?" As of yet, these are unanswered, and difficult to answer, questions.
Finally, Tyack turns to research that show clear disturbance reactions to ocean noise, including killer whales staying 4km away from acoustic harassment signals near fish farms, dolphin numbers dropping to 8% of normal within 3.5 km of similar noise-makers on other fish farms (with those small numbers implying that the avoidance distance was far greater). He notes that the degree of displacement or behavioral response is not necessarily a direct indicator of the severity of impact, suggesting that "if an animal is in bad enough condition that the risk of altering behavior is high, then it may be less likely to show a disturbance response." For example, hungry animals will linger in a feeding area the longest. He also notes that some responses to noise may be caused by noise sources that resemble a predator's call (as in recent modeling Tyack has done that suggests beaked whale decompression sickness may result from a long series of near-surface dives as the whales flee sonar signals that they mistake for orca calls). He cites some compelling studies on terrestrial animals showing that repeated disturbance exacts high costs in reproductive success and overall health (including a study of geese that showed that when undisturbed, geese increased their body mass and had a 46% breeding success, whereas in nearby areas where farmers scared them off their fields, they did not gain mass and had a breeding success of only 17%).
To conclude, Tyack suggests that there are several lines of research that have so far received little attention, which could help to move key understanding of noise impacts forward, including: focusing on the most vulnerable animals as subject of study into the effects of disturbance, further study of the possibility that predator responses underlay key behavioral impacts (including fleeing, increased vigilance, and avoiding habitats), and following up on the recent theory of allostasis (behavioral changes that allow an animal to maintain equilibrium in the face of external environmental changes or stressors) as a way of understanding the costs and benefits of changing behavior in the face of noise.
Workshop Report: Encouraging Establishment of Noise-Free Zones in and Around Marine Protected Areas
Agardy, Aguilar, Canadas, Engel, Frantzis, Hatch, Hoyt, Kashner, LaBrecque, Martin, Notarbartolo di Sciara, Pavan, Servidio, Smith, Want, Weilgart, Wintle, Wright. 2007. A Global Scientific Workshop on Spatio-Temporal Management of Noise. Report of the Scientific Workshop. 44 pages. [DOWNLOAD(pdf)]
In June 2007, a workshop was held in the Canary Islands to consider the potentials for extending the management principles used in Marine Protected Areas to provide some protection from anthropogenic noise. Fundamental to the purpose and effectiveness of MPAs are "spatio-temporal restrictions" (STRs) of specific human activities: for example, excluding fishing, from a specific area (spatial restriction), or sometimes at times of special biological importance, such as spawning (temporal restriction). Few of today's MPAs are large enough to provide protection from "elevated levels of ensonification:" buffers of tens of kilometers would be necessary for protection from mid-frequency sound, and a hundred or more kilometers from low-frequency sound. Of today's 350 MPAs that include some cetacean habitat, 64 are large enough to provide some mid-frequency protection, 20 are large enough to provide at least some low-frequency protection (e.g. shipping), and only the 6 largest are probably sufficient to protect from shipping noise. (of course, shipping is not generally excluded from MPAs: this is merely a hint at the scale of noise STRs that would be useful.) The Workshop report includes several key sections:
- Descriptions of some existing attempts to provide STRs focused on noise: In 2003, Brazil established a large buffer zone around a small existing MPA, to exclude the sounds of seismic survey airguns from entering the MPA (the buffer was withdrawn by a court due to jurisdictional issues; attempts are underway to re-establish it). In the Canary Islands, a 50 nautical mile buffer zone has been established around the islands, in which active sonar is not allowed (there have been some subsequent strandings that raise questions whether this is large enough a buffer).
- Recommendations for MPA managers, centered on a framework for making management decisions regarding possible noise-related STRs.
- Recommendation that noise-producers provide more information, and longer lead times prior to operations near MPAs, to allow for analysis of effects of proposed noise. A far-reaching element of this is a call for use of "detectability curves" to reflect how easy it is to find various species of whales, and to insure that more effort is made to find hard-to-detect whales, rather than assuming that they are not present if none are found using standard observational techniques.
- Recommended measures that could reduce the noise impacts of the primary noise producing activities.
- Suggested MPAs or proposed MPAs where noise-oriented STRs could be introduced, as case studies for future MPA management protocols. These include the PELAGOS Sanctuary in the northwestern Mediterranean, off France, Italy, and Monaco, the Alborian Sea/Strait of Gibraltar, the Bay of Bengal, and East Asian waters off Japan, China, and the Philippines.
Ocean Fish Vary Widely in Startle Response to Noise
Kastelein, van der Heul, Verboom, Jennings, van der Veen, de Haan. Startle response of captive North Sea fish species to underwater tones between 0.1 and 64kHz. Marine Environmental Research 65 (2008) 369-377.
This study exposed eight marine fish species to pure tones ranging from 100Hz to 64kHz. The tests took place in specially designed quiet tanks; species were chosen in part due to their economic importance to fisheries. Some species did not respond to the sound at all, even at the highest dB levels that could be produced, while others exhibited very clear startle responses to a relatively narrow range of frequencies (generally 100-700Hz), at received levels of about 100dB (re 1uPa, rms) for the lowest frequencies, with the startle threshold increasing to the range of 160dB as frequency increased to 700Hz. Only one species responded to higher frequencies than this: Horse mackerel responses extended up to 2kHz. The species that did not startle at all were Atlantic cod, Pollack, Common eel, and Atlantic herring. Horse mackerel startled to the widest range of frequencies, with Sea bass also quite responsive; Thicklip mullet and Pout both startled to a narrower range of frequencies. Interestingly, for fish that have established audiograms, it appears that the startle response does not begin until the noise is 10-30dB above the hearing threshold; and, again, some fish showed no startle even at levels up to 45dB above their presumed hearing threshold. The researchers note that these results on captive fish to pure tones can not be reliably extrapolated to wild fish in varied contexts or to more complicated sounds, but suggest that the extreme variability seen here is an important consideration in more natural situations as well. They suggest further study using "sounds more similar to anthropogenic noise, to more complicated sounds, such as sweeps, and to the actual broad-band noise of, for instance, wind turbines and shipping..."
Related research: Some Fish Affected by Sound of Pingers
R.A. Kastelein et al. Effects of acoustic alarms, designed to reduce small cetacean bycatch in gillnet fisheries, on the behavior of North Sea fish species. Marine Environmental Research 64 (2007) 160180
Pingers are used in large fishing nets, to alert dolphins so they avoid entanglement and drowning. This study found that some pinger signals seem to affect he behavior of Sea bass, mullet, and herring (increased swimming speeds and/or movement toward or away from surface). The researchers note that "Pingers developed to reduce odontocete bycatch should not deter the fisheries’ target species from the gillnets, and should not deter target or non-target fish from ecologically important areas such as feeding and breeding grounds, or mask their communication sounds"