Marine Bioacoustics Research Articles

Summer school for acoustics graduate students

In addition to subject mastery and the focused effort required to complete a thesis project, graduate students also need to develop a broad understanding of their field and cultivate a familiarity with the larger community of researchers and practitioners. The “summer school” format has been shown to enhance both subject-matter breadth and build community awareness in physical acoustics. Physical Acoustics Summer School (PASS) has been held in late-May, in even-numbered years, since 1992. The format for each day is usually two three-hour lectures followed by evening discussion groups to answer questions and explore extensions of the day’s lecture topics. One lecture session is typically dedicated to acoustics demonstrations. Attendance for the full week is required of all participants who also dine together three times each day. Venues are chosen to provide isolation that minimizes distraction and maximizes interactions among all participants. Typical enrollment has been 10 distinguished lecturers (including many Silver Medal winners in Physical Acoustics), 10 discussion leaders, and 30 graduate students. This format has been successfully extended to one other ASA Technical Committee: the marine bioacoustics community has held their summer school twice (SeaBASS). PASS has now been functioning long enough that former students have become lecturers.

Sound and biological models.

We consider the coupling of biological and acoustic models in the ocean (marine bioacoustics). A casual look at journal publications and meeting programs over the last 10 years shows the extraordinary growth in research. Consider these five examples: animats, which are virtual marine mammals, swim in simulated oceans, acting as acoustic dosimeters to simulate the exposure of real animals in the ocean. The animats themselves respond to the sound field, avoiding unpleasant noises or seeking out sounds that suggest feeding or reproductive opportunities. Meanwhile, the songs, whistles, clicks, rumbles, etc., of living mammals allow a listener to follow their paths, or even to coarsely image the ocean environment. As they move through the sound field they may also disrupt it, scattering energy. Thus we see an intimate coupling between the biological models and the sound field in both virtual and real worlds. This talk will present examples of each of these couplings.

Acoustic characterization of pingers on Queensland Shark Control nets.

Active acoustic applications in marine bioacoustics include the use of pingers to dissuade marine mammals. Pingers are most frequently used by the fishing industry to prevent depredation and entanglement. Pingers are also used by other marine industries to dissuade animals from potentially dangerous sites, e.g., underwater turbines. The Queensland Shark Control uses pingers to prevent marine mammal entanglement in shark control nets along public beaches. We have recorded and characterized some of the most common pingers off Queensland. Sound propagation and the potential detection of pinger sounds by marine mammals were modeled. Ambient noise was recorded in the vicinity of shark nets to estimate the contribution of pingers to ambient sound budgets. [Work supported by the Australian Department of the Environment, Water, Heritage and the Arts; Australian Antarctic Division.]

Methodology for environmental impact assessment of underwater noise on marine mammals

The oil and gas industry uses some exploration and production technologies that produce high levels of underwater sound, such as seismic surveys, underwater blasting for demolition and construction, and offshore piling. These underwater noise sources have the potential to impact marine species, which are usually reliant on sound instead of light as their primary sense for communication and sensing their environment. Regulatory interest in minimising the impacts of underwater noise on marine fauna is increasing. This paper presents a methodology for assessing these environmental impacts, with particular focus on cetaceans (whales and dolphins) and pinnipeds (seals and sea lions), although it can easily be adapted to other marine mammal species and fishes. It requires input from a variety of fields, such as: underwater acoustics for sound propagation modelling and source noise characterisation; marine bio-acoustics for determining the effects of sound on marine species’ hearing and communication; and marine ecology for identifying the marine species that may be affected and assessing the biological importance of noise-affected marine areas. These inputs are used in a risk assessment to assess the likely impacts of underwater noise on marine species, which is a collaborative effort by specialists in the fields of underwater acoustics, marine bio-acoustics and marine ecology.

Marine bioacoustics in a changing Arctic.

The retreat of summer ice in the Arctic during the past 5 years has been accompanied by a surge of alarm about iconic ice‐associated marine mammal species: polar bears, walrus, ringed seals, and others. Changes for subarctic species of mammals, fishes, and planktonic organisms have not received as much attention, but will also need to be monitored. The paucity of data about Arctic marine mammals is now more than ever a serious impediment to good decision making. One of the greatest sources of hope is the tremendous advance in marine bioacoustic sensing technology that has occurred within the past decade. Passive and active acoustic technologies offer new means of obtaining biological data in a summer Arctic Ocean where ice is less available as a platform for animals and scientists, and in a winter Arctic Ocean that will continue to be one of the most difficult research environments in the world.

Principles of Marine Bioacoustics by W.W. L. Au and M. C. Hastings

<scp>Principles of Marine Bioacoustics</scp> by W.W. L. Au and M. C. Hastings

Mathematics of pulsed vocalizations with application to killer whale biphonation

Formulas for the spectra of pulsed vocalizations for both the continuous and discrete cases are rigorously derived from basic formulas for Fourier analysis, a topic discussed qualitatively in Watkins' classic paper on "the harmonic interval" ["The harmonic interval: Fact or artifact in spectral analysis of pulse trains," in Marine Bioacoustics 2, edited by W. N. Tavogla (Pergamon, New York, 1967), pp. 15-43]. These formulas are summarized in a table for easy reference, along with most of the corresponding graphs. The case of a "pulse tone" is shown to involve multiplication of two temporal wave forms, corresponding to convolution in the frequency domain. This operation is discussed in detail and shown to be equivalent to a simpler approach using a trigonometric formula giving sum and difference frequencies. The presence of a dc component in the temporal wave form, which implies physically that there is a net positive pressure at the source, is discussed, and examples of the corresponding spectra are calculated and shown graphically. These have application to biphonation (two source signals) observed for some killer whale calls and implications for a source mechanism. A MATLAB program for synthesis of a similar signal is discussed and made available online.

Working group on ‘‘The effects of sound on fish and turtles’’: An update

In order to develop acoustic exposure criteria for fish and marine turtles based on scientific evidence, an ASA Standards Working Group was formed with a membership that includes basic scientists expert on fish and turtle bioacoustics, physical acousticians with special expertise in marine bioacoustics, and several individuals with expertise on effects of anthropogenic sound in the marine environment. This presentation is a summary of the group’s progress to date. One of the Working Group’s goals is to publish several papers, one on what is known about damage risks due to exposure to underwater noise (e.g., from pile driving, seismic exploration, sonar systems), and one assessing the efficacy of various measures to mitigate adverse effects of noise exposure. The working group has tentatively decided that the fish potentially affected should be categorized with respect to their hearing sensitivity (potential for auditory system damage) and whether the species is known to detect sound pressure or acoustic particle motion. Over the next year to 18 months, the Working Group will be evaluating the known effects of sound sources on fish and turtles, identifying areas in which further research is needed, and beginning to develop noise exposure criteria for both turtles and fish.

Thirty years of Australian marine bioacoustics and the Cummings connection

Marine bioacoustics research in Australian waters has developed for more than 30 years, and has revealed a wide diversity of sounds and acoustic environments. The number of researchers and the complexity of the experiments has increased over the years. In the early days we had little knowledge or experience, and so relied on advice and help from American researchers. Of those, Dr. William C. Cummings remains one of our greatest supporters. This paper reviews some of the main features of the Australian work and the Cummings influence. Some of the earliest work, on fish sounds, echoes his work of the 1960s. This has since developed substantially, and we are planning to apply methods developed by Cummings of combined video and acoustic observation to source identification. Humpback whale sounds have been studied continually for more than 20 years and have revealed the complex songs of similar overall structure to those of the northern hemisphere, but with some surprises. Recordings have been made of southern right whales and Antarctic seals, and this year we recorded a large set of diverse sounds from blue whales. This data set and visual / acoustic observations of humpback whales are being used in censusing.

Reduced interference distribution application and interpretation for transient acoustic events

Transient acoustic events often present difficulties when using conventional time-series or spectral methods. The Reduced Interference Distribution (RID) and its derivatives have been under development [W. J Williams and J. Jeong, Time-Frequency Signal Analysis, edited by B. Boashash (Longman Cheshire, New York, 1992)] for several years. The RID was specifically motivated by the need for a better analysis tool for transient acoustic events [ONR Grants N00014-90-J-1654, N00014-97-1-0072]. The deficiencies of the spectrogram for marine mammal sound analysis were early recognized [William Watkins, Marine Bioacoustics 2, 15–43 (1966)]. Watkins’ illustrations of spectrogram deficiencies and updated results obtained using the Wigner distribution (WD) and the RID will be presented. The RID represents an attempt to retain the desirable mathematical properties of the WD while reducing the often troublesome WD interference terms. Examples drawn from several acoustic transients such as marine mammal sounds, joint clicks and vortex formations in turbulent air flow will be used to illustrate the usefulness of the RID approach. The importance of retaining such properties as proper time and frequency marginals; time and frequency support along with proper group delay and instantaneous frequency will be discussed. The value of covariance with time and frequency shifts and scale changes will also be emphasized.

Evidence of hearing loss in an Atlantic bottlenose dolphin (Tursiops truncatus)

Auditory thresholds were behaviorally measured for two Atlantic bottlenose dolphins (Tursiops truncatus); a 14-year-old female, and a 33-year-old male. Stimuli were delivered directly to the lateral sides of the lower jaw via jawphones as opposed to free-field broadcasts. The female’s audiogram clearly reflects the standard for this species [C. S. Johnson, in Marine Bio-Acoustics, edited by W. N. Tavolga, pp. 247–260 (1967)]. Previous thresholds for the male measured at age 26 indicated a hearing loss in the left ear of approximately 2 to 3 dB [re: 1μPa] between 4 to 10 kHz, which were considered unremarkable. At age 33, the same male demonstrates distinctive losses. The right ear shows a 16–33-dB loss over 10–40 kHz, the range of best sensitivity. Above 55 kHz, the right ear is 2–3 dB more sensitive than the left. Both ears then decline to an upper frequency cutoff of approximately 70 kHz below the standard 120 kHz. Hearing losses due to age have been reported for this species [S. H. Ridgway and D. A. Carder, J. Acoust. Soc. Am. 101, 590–594 (1997)]. The data reported in this paper suggest both uni- and bilateral hearing losses in the male which may be the result of age, impairment of the auditory system, or both.

Bioacoustic research on cetaceans in the Mediterranean Sea

In recent years new impetus has been put into cetacean research in the Mediterranean Sea. From 1988 to 1994 research cruises were organized by our laboratory and the Tethys Research Institute within the seas surrounding the Italian peninsula and islands. Recordings of underwater sounds produced by cetaceans and other ethological and zoogeographical data were collected and analyzed with the use of instruments and techniques mainly developed by the Laboratory of Marine Bioacoustics, which was conceived by the University of Pavia and financed by the Inspectorate of Sea Defence of the Italian Ministry of the Environment. Specific instruments and software packages were developed, including a high‐quality towed array of hydrophones, with its own amplifier and filtering unit, a portable Digital Signal Processing Workstation (DSPW) with real time analysis and file processing capabilities and an Interactive Digital Sound Library (IDSL). Cetacean sounds were recorded in their natural environment from auxiliary sailing vessels up to 26 m long; sounds from six odontocete and one mysticete species were recorded, analyzed, catalogued and organized in a sound library in order to allow flexible and specific access to sound information for research and other purposes such as environmental monitoring, species identification, censusing activities and educational applications.

Bioacoustics: A tool for the conservation of cetaceans in the Mediterranean Sea

Massive human presence in the Mediterranean and inadequate management of marine resources have recently become a threat to marine mammal survival in this region. The main problems facing cetaceans in the Mediterranean include: by‐catch in fisheries competition with artisanal coastal gillnet fisheries, presence of noxious manmade, compounds in the trophic chains, and finally, a generalised degradation of environmental quality, particularly evident over the continental shelf, caused by loss of biodiversity, depletion of living resources, increased human disturbance, and changes in the physical and chemical properties of the environment. Conserving cetaceans in the Mediterranean is a modern challenge: appropriate management schemes and pollution control measures should enable marine mammals to coexist with intense human activities, and the Mediterranean could provide an excellent testing ground for such an enterprise. Recent developments in the field of marine bioacoustics could provide information highly relevant to the conservation of cetaceans in the Mediterranean Sea: acoustic surveys can be performed to monitor the distribution and relative abundance pelagic species, and to investigate habitat partitioning of coastal species. Analysis of distinctive vocalisations can indicate the likelihood of links between Mediterranean an Atlantic populations. Finally, acoustics can play a major role in solving problems posed by interactions between cetacean and fisheries, in monitoring the effects of high‐intensity acoustic deterrents, and to understand the possible negative effects of some manmade noise on cetacean populations.

Sound Fields within Aquaria

Small aquaria are generally convenient for bioacoustic experiments. Sound introduced into such tanks is often measured with pressure-sensitive hydrophones. Unfortunately, sound in a small tank never propagates in a plane wave, and therefore pressure measurements can be highly misleading. The sound field also fails to resemble the natural acoustic environemnt of the organisms. We have obtained further measurements of the effective wall impedance and, hence, estimates of the wave impedance within such tanks, using the technique described at the Second Symposium on Marine Bio-Acoustics (1966). The fields within the tanks are similar whether the sound source is located in the water or in the air nearby. Particle velocities in the water (and hence displacements) are orders of magnitude greater than has been sometimes assumed from uncritical use of pressure hydrophones. This suggests that animal behavior may be due to lateral-line response rather than to auditory system response. [Hudson Lab. of Columbia Univ. Informal Documentation No. 148. This work was supported by the U. S. Office of Naval Research.]

Animal Noises in the Sea

Marine Bio-acoustics Proceedings of a Symposium held at the Lerner Marine Laboratory, Bimini, Bahamas, April 11–13, 1963. Edited by William N. Tavolga. Pp. xii+413. (London and New York: Pergamon Press, 1964.) 100s.

Erratum: Marine Science

In the review of Marine Bio-Acoustics, W. N. Travolga, Ed. (24 July, p. 379), the American publisher of the book was erroneously given as John Wiley and Sons. Actually, the book is distributed in the United States by the Macmillan Co.