Abstracts: Acoustics Ecology
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Assessing the Impact of Pile Driving Upon Fish
Anthony Hawkins (Phone: 1224 86894, Email: email@example.com), Loughine Ltd., Kincraig, Blairs, Aberdeen AB12 5YT, United Kingdom
Pile driving associated with the removal and reconstruction of a jetty was monitored at a busy harbor in the North East of Scotland, adjacent to an important Atlantic salmon river. The main concern was with the impact of noise upon salmon migrating through the lower part of the river estuary. Pile driving was allowed to proceed subject to an agreed program of works to monitor sound levels and ensure least disturbance to salmon.
Both percussive and vibratory pile driving took place. Sound-pressure levels from both were measured. Percussive pile driving involved the repeated striking of the head of a steel pile by a double-acting hydraulic hammer, with a 5 tonne ram weight operated with a mean stroke of about 1 m. Vibratory pile driving was achieved by means of a variable eccentric vibrator attached to the head of the pile.
The majority of piles were initially driven into the substrate by vibration, over a period of several minutes. Each pile was then subsequently driven to its full depth with a sequence of repeated hammer blows. Steel facing piles were inserted adjacent to the quayside and subsequently backfilled to provide a new frontage to the quay. Diagonal-bearing piles were also inserted well behind the quay to strengthen the adjacent roadway.
Sound pressure levels generated by pile driving in water were measured using a calibrated hydrophone suspended 1 m above the bottom. The hydrophone was connected to a low-noise amplifier, which controlled the signal gain and bandwidth. The output was connected to a laptop PC by a digital audio interface. When recording at close range, where sound levels were especially high, a less-sensitive hydrophone transducer was used, connected directly to the audio interface. All sound recordings were made as 16-bit WAV files. For some of the piles, particle-velocity amplitudes were measured by means of an assembly of three orthogonally mounted, calibrated geophones placed on the seabed.
The sound-pressure levels (SPL) of the background noise and vibro-piling noise were measured as a root-mean-square (rms) level expressed in decibels relative to a reference level of one micro Pascal (dB re 1µPa). The shorter-duration impulsive sounds generated by the individual blows of the pile-driver hammer were measured in several different ways: the peak pressure reached during the impulse, the rms pressure measured over the time period that contained 90% of the sound energy (rms impulse), and as the sound-exposure level (SEL) expressed in dB re 1µPa2-s. The latter was defined as the constant sound level of 1s duration that would contain the same acoustic energy as the original sound. Sound levels were converted to source levels (SL), i.e., normalized to an equivalent noise level at a distance of 1 m. In all SL calculations, it was assumed that the spreading loss was represented by the expression 15 log R where R was the distance in meters.
Received sound level in water may be expressed in terms of sound pressure, particle velocity, or intensity, all of which can vary with time over the duration of the sound. In this study, the majority of measurements were expressed in terms of sound pressure. However, it was recognised that it was really necessary to determine the particle velocities as this is the stimulus which is received by the ear of a fish like the salmon. On a few occasions, the particle velocities were measured and the acoustic intensity calculated.
Background-noise levels within the harbor and even within the river itself were high, within the range 118 – 149 dB re1µPa rms over a bandwidth of 10 Hz-10 kHz. Much of the noise derived from manoeuvring and stationary ships. The sound-pressure levels generated in water by percussive pile driving were very high, but variable depending on the pile type, the substrate being penetrated, the distance from the source, and whether the bubble curtain was in operation. Within the harbor, they ranged from 142-176 dB re 1µPa peak, with sound exposure levels (SELs) of between 133-154 dB re 1µPa2-s, without the bubble curtain in operation. Estimated source levels ranged from 177-202 dB re 1µPa peak. Within the river, more than 220 meters away from the pile driver and separated from it by a spit of land, the soundpressure levels reaching the fish ranged from 162-168 dB re1µPa peak, with SELs of between 129-145 dB re 1µPa2-s. Sounds measured at a distance from the source within the harbor consisted of a low-frequency pre-pulse, followed by the main sound pulse. In this case, and in the river itself, the sound was propagated through the substrate, as well as the water, perhaps accompanied by flexural waves at interfaces between strata. Particle velocities within the harbor and in the river reached 110 dB re 1 nms-1, mainly in a vertical direction, and intensities of up to 0.023 Wm-2 were registered.
The main energy generated by the percussive pile driver extended up to and above 10 kHz close to the source, with most of the energy below 2 kHz. By the time the sound reached the river the higher frequencies had been removed and the predominant frequencies were below 1 kHz, still with considerable energy within the hearing range of salmon (which declines above 250 Hz).
Vibro-piling also generated high sound levels in water, with sound-pressure levels within the harbor ranging from 142-155 dB re1µPa rms and source levels between 173-185 dB re 1µPa rms. Levels in the river ranged from 140-143 dB re 1µPa rms.
A bubble curtain was successful in reducing the peak amplitude of the sound from the pile driver by up to 5 dB and in reducing the high-frequency content of the sound. The bubbles therefore reduced the likelihood of damage or injury to fish. However, they did not reduce energy at the lower frequencies to which fish are sensitive, especially at a distance from the source.
The principal purpose of monitoring the pile driving was to assess the impact upon salmon. There is some controversy and uncertainty about the actual levels of pile-driving sound which affect fish adversely. It is evident that sound affects different species to a differing degree. Thus, although in some instances a level of 180 db re1µPa has been adopted as a standard, above which sounds are likely to kill or cause damage to fish, this is a very uncertain figure which is open to question. It was concluded that the sound pressure levels (SPLs) and sound exposure levels (SELs) generated by percussive pile driving within the harbor were not likely to have killed fish, whether the fish were within the river or the harbor itself. However, the sound levels were high enough close to the pile driver to injure or induce hearing loss in some species of fish. The noise from pile driving in the harbor was certainly high enough to be detected by salmon in the river at considerable distances from the source. The levels of sound from both percussive and vibro-piling were well above the hearing thresholds of the fish. As salmon could not be observed during this exercise, it was not possible to determine whether salmon reacted adversely to the sounds. However, there was a risk that their upstream migration may have been delayed or prevented with consequent effects upon spawning populations. The measurements indicated that any pile driving within the river itself would have the potential to injure or induce hearing loss in salmon and might have adverse effects upon their behavior.
During this exercise, trains of low frequency 'thumping' sounds were recorded within the River Dee, similar to those made by fish. The sounds may be emitted by European eels, which are common at the location.
Barotrauma Injury of Physostomous and Physoclistous Fish by Non-Explosive Sound and Pressure Cycling
Thomas J. Carlson (Phone: 503-417-7562, Email: firstname.lastname@example.org), Battelle-Pacific Northwest National Laboratory, 620 SW 5th Ave, Portland, OR 97204-1423
Barotrauma injury has historically been a concern for fish exposed to underwater explosions and passage through hydroturbines. Recently this concern has been extended to include underwater sound generated by pile driving, particularly that generated during impact driving of larger-diameter steel casing. Description of the characteristics of sound impulses generated by impact pile driving that are a threat to fish is lacking and current protective criteria that rely on simple peak overpressure do not have a clear scientific basis and appear too restrictive. This paper considers the mechanisms for barotrauma injury to both physostomous and physoclistous fish as a function of acclimation depth and the criteria developed for protection of fish from barotrauma pressures generated by explosions and passage through hydroturbines. These mechanisms and criteria are discussed within the context of observations of impact pile driving generated pressure time histories and observations of barotrauma injury to fish made during pile driving projects on the West Coast of the United States. Also considered are the results of recent sound-mitigation efforts, including driving of steel casing pile in the dry, the use of both confined and unconfined bubble curtains, and the success of these mitigation efforts as measured by comparison with fish-protection criteria.
Pile Driving and Bioacoustic Impacts on Fish: How Did We Get Into This Mess? Where Do We Go From Here? (Status of Developing Best Available Science to Improve Decision-Making Processes)
Deborah C. McKee (Phone: 916-653-8566, Email: email@example.com), Senior Environmental Planner, Aquatic Resource Biologist for the California Department of Transportation (Caltrans), Sacramento, CA 94274
How did those of us in the transportation industry suddenly find ourselves in need of knowing about underwater pressure waves and fish barotrauma? On October 17, 1989, a portion of the East Span of the San Francisco Oakland Bay Bridge collapsed. That event was the catalyst for the State of California to institute a comprehensive seismic retrofit program for its bridge structures. The bridge is considered a "vital lifeline structure" to San Francisco. Therefore, the bridge was to be designed to withstand the maximum expected credible quake with a design-life of 150 years. The criticality of the structure, the design life, and the soil conditions in San Francisco Bay precipitated the need for an innovative foundation design that was the nexus to use steel piles as the preferred structural support material. Ultimately, there was no structural alternative. When we began driving the steel piles, we realized that underwater pressure waves were being generated that caused stunning and even death to fish near the pile.
Pressure waves are generated when the hammer strikes the pile, imparting a flexural wave that moves down the pile at approximately 5000 feet per second. As the wave does this, it interacts with the air, creating a localized pressure perturbance, resulting in airborne noise. It then moves through the water column creating compressional waves. This results in what we refer to as a hydroacoustic pulse. Finally, the energy moves down into the more-resistant substrate, where it is dissipated through the physical displacement of soil particles. A wave travels down, then back up, and it continues to reverberate until all of the energy has been dissipated, into the air, water, and soil.
Our efforts to develop a better understanding of the acoustic properties of pile driving and its effects on fish began with examining the findings from past research for their relevance and applicability while looking at a variety of wave forms. The U.S. Army Corp of Engineers, Canada's Department of Fisheries, the US Navy, and others have done many studies on the effects of explosive blasts on fish. There is a relatively small, but high-quality, body of literature that exists for effects of long-term continuous noise exposure on fish, such as that found in active sonar arrays. There is almost no information on pile driving impacts.
We have also been designing and testing various noise-attenuation technologies. The bubble-tree attenuation device used to surround piles being driven for the Benicia-Martinez Bridge Project successfully reduced peak noise levels to an approximate 20m radius around the pile. This equated to a 99.8% reduction in radiated energy compared to an unattenuated pile.
What are some of the lessons we have learned so far? First, one needs to understand the ramifications of permit terms and conditions for these types of projects. These have to be meaningful and measurable criteria. They need to be biologically relevant and technologically possible conditions. For instance, underwater noise-monitoring equipment needs to be able to measure the target frequencies committed to within the permit. Second, one needs to develop and follow monitoring protocols with specific objectives and study controls. In other words, don't go out and collect a bunch of data and then try and make something of it. Third, one needs to obtain incidental take authorization to avoid unanticipated work stoppages. Last and most important, avoid jeopardy and avoid and minimize the incidental effect of take to the extent practicable.
What else have we learned? This is a highly complex issue, and we need to be very careful to ensure we base decisions on credible and relevant information. Just because it is in print does not mean it is useful, credible, or relevant. As the Endangered Species Act (ESA) clearly states: "The best available information is to be used in the implementation of the ESA and this information must be reliable, credible, and represent the best scientific and commercial data available."
We soon realized other states and industries were struggling similarly with this issue and that by working together we could be more effective in our efforts. Therefore, two years ago we formed the Fisheries and Hydroacoustic Working Group. The three key goals of the Fisheries and Hydroacoustic Working Group are to summarize: 1) what we currently know (what is the best available science); 2) what we need to know (define future research needs); and, 3) what is the best application of current information for consistent interim standards. As new information is developed, the cycle repeats itself, and we will continue to update our summary of current understanding, re-evaluate further research needs, and re-evaluate and possibly modify noise-criteria standards based on what we have learned. In support of this effort, Caltrans funded preparation of the report titled "Effects of Sound on Fish" by Mardi C. Hastings, Ph.D., and Arthur N. Popper, Ph.D., that was completed in January 2005. The final report constitutes a comprehensive literature review and analysis of relevant research, recommendations for preliminary guidance, areas of uncertainty, and recommended research.
Caltrans also submitted a proposal to the Transportation Research Board, National Cooperative Highway Research Program to fund a national research study to evaluate hydroacoustic impacts on fish from pile installations. That proposal was accepted and is underway. It is Project 25-28, Hydroacoustic Impacts on Fish from Pile Installation.
The Federal Highway Administration has also sponsored a pooled-fund project titled "Structural Acoustic Analysis of Piles." The study's goals are to develop and validate models of sound fields and the effects of attenuation systems, to develop and validate acoustical source models of pile driving, to synthesize information from this project with other pertinent research, and to develop a guidance document for practitioners.
The three most recent efforts that Caltrans has underway are: 1) the development of an Interim Guidance Manual that identifies procedures for assessing and mitigating effects of pile driving sound on fish; 2) the development of an underwater sound-pressure compendium; and, 3) development of a methodology for measuring and reporting underwater sound pressure.
What Do We Know About Pile Driving and Fish?
Arthur N. Popper (Phone: 301-405-1940, Email: firstname.lastname@example.org) Department of Biology and Center for Comparative and Evolutionary Biology of Hearing, University of Maryland, College Park, MD 20742
There are growing concerns about the potential effects of in-water pile driving on aquatic organisms. These concerns arise from an increased awareness that high-intensity sounds have the potential to harm both terrestrial and aquatic vertebrates (e.g., Fletcher and Busnel 1978; Kryter 1984; Richardson et al. 1995; Popper 2003; Popper et al. 2004). The result of exposure to intense sounds may extend over a continuum running from little or no effects to the death of the ensonified organism. This paper is a brief review of what is known about the effects of pile driving on fish. It also provides some ideas about the design of future experiments that can be used to test these effects. The conclusions and recommendations presented here are explored in far more detail in a recent review on effects of pile driving on fish (Hastings and Popper 2005). In addition, a broader examination of the general effects of sound on fishes can be found in Popper (2003) and Popper et al. (2004).
It is widely believed that fish close to pile-driving activities may be killed by exposure to very intense sounds. There is also some evidence that fish at some greater (but undefined) distance may survive exposure to pile-driving activities. However, experimental data are very limited. Moreover, nothing is known about non-life-threatening effects on fish of some (undefined) distance from the pile-driving operation. Such effects may include (a) non-life threatening damage to body tissues, (b) physiological effects including changes in stress hormones or hearing capabilities, or (c) changes in behavior (discussed in Popper et al. 2004). These effects could be temporary (e.g., a temporary loss of hearing that recovers over time) or of sufficient length to lower long-term survival and/or reproductive potential of individual animals or communities. There are also no data on effects of cumulative exposure to pile-driving sounds.
The concerns about currently available pile-driving data arise because there is very little quantification and replication of experiments and because the investigators were not able to control the stimulus to which the fish were exposed. Thus, little is known about the stimulus actually received by fish during experiments. It therefore becomes difficult to evaluate the effects of pile driving on fish that are at different distances from the source. Moreover, there are no studies to date that included observations of the behavior of fish during exposure to pile-driving signals (but see paper by Hawkins in this volume).
Because of the dearth of data on effects of pile driving on fish, it has been suggested that data from other types of experiments involving intense signals be extrapolated to pile driving. A problem, however, is that the sounds used in other studies, such as the effects of sonar (Popper et al. 2005a), seismic air guns (Pearson et al. 1992; Engĺs et al. 1996; Wardle et al. 2001; McCauley et al. 2003; Popper et al. 2005b), and pure tones (Enger 1981; Hastings et al. 1996) differ greatly from sounds produced during pile-driving activities. Moreover, there are also concerns about extrapolating effects between species, and particularly between species that have different life styles, sound-detection capabilities, and responses to adverse stimuli (see Hastings et al. 1996; McCauley et al. 2003; Popper et al. 2005b). Furthermore, there is some evidence to suggest that it may not always be possible to generalize the effects of high-intensity sounds between different age classes of the same species (e.g., Popper et al. 2005b).
Since there are issues with the way pile-driving experiments have been done to date, it is worth considering how one might design an experiment that would provide the data needed to understand the effects of pile driving or, for that matter, any intense sound, on fish. One caveat with these suggestions, however, is that they require that fish be kept in a limited locale (e.g., a cage or tank) so that they can be observed before, during, and after the sound exposure, and that the fish can be retrieved for physiological and morphological analysis. Such requirements preclude direct observations on how fishes might behave if they were free from constraints or confinement during the exposure to pile driving, as has been done in one study on the effects of seismic air guns on fishes on a reef (Wardle et al. 2001).
Bioacoustic Profiles: Evaluating Potential Masking of Wildlife Vocal Communication by Highway Noise
Edward West (Phone: 916-737-3000, Email: email@example.com), Senior Environmental Scientist, Jones & Stokes, 2600 V Street, Sacramento, CA 95818
Highway noise can mask vocal communication and natural sounds important to wildlife for mate attraction, social cohesion, predator avoidance, prey detection, navigation, and other basic behaviors. This acoustic interference can potentially result in the reduced ability of individuals to acquire mates successfully, reproduce, raise young, and avoid predation. Because different species have evolved unique vocal repertoires, they are differentially susceptible to the masking effects of highway noise. No single noise-level criteria can be used to accurately define impact thresholds for all species. Here we show the utility of using bioacoustic profiles of bird vocal signals to identify and describe the range and variability of acoustic-masking thresholds. Variation in noise load, source amplitude, and signal frequency are modeled to illustrate the dynamic nature of each species' critical acoustic space.
Estimating Effects of Highway Noise on the Avian Auditory System
Robert J. Dooling (Phone: 301-405-5925, Email: firstname.lastname@example.org), Center for the Comparative and Evolutionary Biology of Hearing, University of Maryland, College Park, MD 20742
Our own common experience suggests that the adverse effects of noise on birds can be considered with regard to four potentially overlapping categories. First, noise might be annoying to birds. This may cause them to abandon a particular site that is otherwise ideal in terms of food availability, breeding opportunities, etc. Second, noise which lasts for very long periods of time can be stressful. Such noise levels can raise the level of stress hormones, interfere with sleep and other activities, etc. Thirdly, very intense noise (acoustic overexposure) can cause permanent injury to the auditory system. Finally, noise can interfere with acoustic communication by masking important sounds or sound components. The first two categories of investigation are probably best addressed by field experiments. The second two categories of effects are probably best addressed by laboratory experiments where precise control can be obtained. The results of some of these experiments are described in this paper.
Evaluating and Minimizing the Effects of Impact Pile Driving on the Marbled Murrelet (Brachyramphus Marmoratus), A Threatened Seabird
Emily Teachout (Phone: 360-753-9583, Email: email@example.com), U.S. Fish and Wildlife Service, Lacey, WA 98503, Fax: 858-974-3563
The purpose of this paper is to describe the methods used to evaluate the potential adverse effects of underwater sound from impact pile driving on the marbled murrelet (a seabird that is federally listed as threatened), and to introduce measures that have successfully minimized adverse effects. The U.S. Fish and Wildlife Service has evaluated the effects of pile driving on the marbled murrelet through several recent Endangered Species Act consultations. Over the past few years, there has been increased attention to the potential for impact pile driving to adversely affect fish species. When foraging, marbled murrelets dive in pursuit of prey and can be exposed to the same elevated sound pressure levels that adversely affect fish. Exposure to these sounds could result in mortality, injury, and/or modification of normal behaviors.
Marbled murrelets forage in the marine waters throughout Puget Sound. Recent transportation projects that have occurred in Puget Sound include replacement of the Hood Canal Floating Bridge and multiple Washington State Ferry terminal-maintenance and preservation projects. These projects typically use 36-inch and 24-inch hollow steel piles. Impact installation of these piles can produce sound pressure levels of 210 dB peak. Physical injury, including death, may occur in aquatic organisms at sound-pressure levels above 180 dB peak. Sound-pressure levels above 153 dBrms are expected to cause temporary behavioral changes that may negatively affect foraging efficiency.
These projects were evaluated by determining the area where sound pressure was expected to exceed the above levels and then estimating the potential for marbled murrelets to be exposed to those sound-pressure levels. When exposure was likely to occur, the U.S. Fish and Wildlife Service anticipated adverse effects in the form of harm (physical injury) and harassment (modification of normal behavior patterns). Minimization measures focused on reducing that potential exposure. Sound-attenuation devices (bubble curtains) were used to reduce the extent of the geographic area where adverse effects could occur. A hazing program was used to move murrelets out of the area where physical injury was expected.
We present the analysis used to evaluate adverse effects to marbled murrelets from pile driving, discuss the method used to estimate the extent of effects, and introduce measures to minimize adverse effects. Finally, we recommend future research needed to better understand and to reduce further these impacts.
Synthesis of Noise Effects on Wildlife Populations
Paul A. Kaseloo (Phone: 804-524-6991, Email: firstname.lastname@example.org), Department of Biology, Virginia State University, Petersburg VA 23806
This report contains a partial summary of a literature review dealing with the effect of noise on wildlife emphasizing the effects on birds. Beginning with studies in the Netherlands and, later, in the United States, a series of studies have indicated that road noise has a negative effect on bird populations (particularly during breeding) in a variety of species. These effects can be significant with ‘effect distances' (i.e., those within which the density of birds is reduced) of two to three thousand meters from the road. In these reports, the effect distances increase with the density of traffic on the road being greatest near large, multilane highways with high densities. A similar effect has been reported for both grassland and woodland species. It is important to note that 1) not all species have shown this effect and 2) some species show the opposite response, increasing in numbers near roads or utilizing rights-of-way. It is important to determine the cause of this effect and to utilize additional or alternative methods beyond population densities as the sole measure of effect distance, because the latter is susceptible to variation due to changes in overall population density. Recommendations for further study are given, including alternative measures of disturbance in birds.