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Listening to Fish: Proceedings of the International Workshop on the Applications of Passive Acoustics to Fisheries


By Rodney Rountree1, Cliff Goudey2, and Tony Hawkins3

1School for Marine Science and Technology, UMASS Dartmouth, 706 South Rodney French Blvd, New Bedford, MA 02744

2 Center for Fisheries Engineering Research, MIT Sea Grant College Program, MIT Bldg. NE20-376, 3 Cambridge Center, Cambridge, MA 02139

3 Kincraig, Blairs, Aberdeen, Scotland AB12 5YT

Workshop Objectives

  1. Convene an international conference to assess the potential of passive acoustics as a tool with applications in fisheries and marine conservation in estuarine, coastal and oceanic ecosystems.
  2. To promote the use of passive acoustics for exploring the oceans, surveying marine biodiversity, and assessing the impact of man’s activities upon the oceans.
  3. Develop an international research initiative to explore and extend the use of passive acoustics in the marine sciences in both applied and non-applied fields, and to develop potential research theme areas for future funding.


On April 8-10, 2002, MIT Sea Grant hosted an international workshop on the application of passive acoustics in fisheries in Dedham, Massachusetts. The 'hands-on' workshop drew over 40 European and North American experts from fisheries, fish biology, acoustics, signal processing, underwater technology and other related fields. The workshop was divided into 4 sessions and 2 working groups with a total of 29 presentations delivered. The first session entitled: "Passive Listening for fishes — what has been done?" reviewed past and current research activities, while the second session "Future developments and applications" examined recommendations for future research and examples where existing programs could be enhanced by passive acoustic technology. The third session "Acoustic technology" reviewed the state of the art and future developments for underwater acoustic and related technologies. A special session included demonstrations of hardware and software. The workshop was capped off by a working group on the biological and ecological aspects of passive acoustic research, moderated by Joe Luczkovich of East Carolina University, and a working group on technology and software issues moderated by David Mann of the University of Southern Florida in St. Petersburg. A web page was constructed to document the findings of the workshop (

The workshop was a great success at bringing together an outstanding group of international researchers to exchange research results, knowledge and ideas related to the application of passive acoustics to fisheries, census of marine life and related issues. The workshop demonstrated the high potential of passive acoustics as a research tool for fisheries and related fields through the presentation of the results of a number of successful research projects. One of the important outcomes of the workshop was the exchange of information about ongoing and past research projects that have successfully used passive acoustics. Previously, many of these scientists had been working in isolation with little interaction with their colleagues working across North America and overseas. The fisheries biologists participating in the workshop also gained valuable insight from exchange of information with scientists with well-established backgrounds in the use of passive acoustics to study marine cetaceans (see Clark, Jarvis and Moretti, herein). Another important result was the exchange of hardware and software technologies among the participants. The workshop has already fostered renewed enthusiasm among the participants for this field of research and has resulted in new domestic and international collaborations. In addition, the workshop brought researchers together with administrators, staff and scientists from several funding agencies and with the media (e.g., NURP, National Geographic, etc.). Finally, extensive discussion of the future research priorities for passive acoustics, and development of both domestic and international collaborations, are expected to go a long way towards promoting the application of passive acoustic technology to fisheries and related fields. Some of the most important research initiatives identified by the workshop participants were: 1) the importance of developing a national database of historic underwater sound archives (see Bradbury and Bloomgarden, herein), 2) the importance of establishing a National/International Reference Library of fish sounds, which would be guided by an international panel of scientists drawn in part from the workshop participants, 3) the importance of establishing an international research and training center for passive acoustics applications to fisheries and marine census (potentially at Grant Gilmore’s Laboratory at the Kennedy Space Center), and 4) the importance of active promotion of the technology through publications of the workshop proceedings and related articles. Many more specific research needs in biology and technology were addressed and are presented throughout these proceedings.



Fish are difficult to see and study in the ocean. SCUBA techniques can help in shallow waters and a range of active acoustic and optical techniques can assist in deep water, but we are still largely ignorant of the distribution and behavior of the great majority of marine fish. Possibly one of the greatest challenges to researchers attempting to study the behavioral ecology of fishes is that of finding the fish in the first place. Often a scientist must go to great lengths conducting expensive and time consuming biological surveys simply to determine the locations or habitats where a fish can be found, before any attempt to study its biotic and abiotic interactions can be made. After all, you can't study something you can't find. Any tool that can help scientists to locate fish is therefore valuable. Fish too face the problem of assessing their environment, navigating through it, and communicating with others of their kind. A surprisingly large number use sound to overcome the problem of living in a visually opaque medium.

Over 800 species of fishes from 109 families worldwide are known to be vocal, though this is likely to be a great underestimate. Of these, over 150 species are found in the northwest Atlantic (Fish and Mowbray 1970). Amongst the vocal fishes are some of the most abundant and important commercial fish species, including cod, haddock and the drum fishes (sciaenidae).

Passive acoustics offers a unique tool to study these fishes, which often live in dark and turbid waters and are difficult to observe by other means. Passive acoustic techniques can be used to locate concentrations of particular species, especially during their vulnerable spawning stage. This in turn allows spawning habitat to be identified, mapped, and protected. It can allow the numbers of fish to be assessed. And it can be used to gain a better understanding of fish behaviour, including fish migrations. Passive acoustics can also be used to simultaneously monitor sources of noise pollution, and to study the impact of man’s activities on marine communities. Anthropogenic sources include noise generated by boating activity, seismic surveys, sonars, fish-finders, depth finders, drilling for oil and gas, and military activities. These all have an unknown but potential important impact on marine fauna. We believe that passive acoustic technologies hold special promise and will become important tools in the coming years. However, it has been largely ignored in the northwest Atlantic in the study of fishes important in the marine food chain. It is also a technique that is amenable to cooperative research with commercial fishermen, who can bring their own knowledge to such studies.


Applications to Fisheries

Sounds travel much farther in water than light and underwater sounds, including fish calls, can often be heard over much greater distances than fish can be seen. Listening to fish can contribute a great deal to our knowledge of their abundance, distribution and behavior. Passive acoustics studies using relatively simple techniques have been successful in locating concentrations of important fish species, opening the way for further, more detailed studies of their behavior, distribution and habitat use. As reflected in the various research programs described within this proceedings, already significant strides have been taken in the application of passive acoustics to fisheries:

  • in an Arctic fjord in northern Norway, workers from the FRS Marine Laboratory, Aberdeen and the University of Tromsø have located a spawning ground of haddock, Melanogrammus aeglefinus. Passive listening has revealed that this species, previously thought to spawn offshore in deep water, can also form large spawning concentrations close to shore (see Hawkins).

  • Norwegian researchers are using passive acoustics to study spawning behavior of Atlantic cod and other gadids (see Nordeide and Finstad, Svellingen et al.).
  • a number of studies in the estuaries of the eastern United States have helped to localize the spawning areas of drum fishes and demonstrating the usefulness of passive acoustics as a tool for identification of essential fish habitat requirements, as well as a tool to provide fisheries managers with information of sciaenid reproductive biology (see Collins et al., Gilmore, Holt, Luczkovich and Sprague, Roumillat and Brower).
  • for the first time in the United States passive acoustics are being explored as a tool to census marine fishes on the continental shelf. In one study, a towed hydrophone array is being used to identify spawning sites of red drum in the western Gulf of Mexico (see Holt). In another study, passive acoustics are being used to catalogue soniferous fishes in the Stellwagen Bank National Marine Sanctuary (see Rountree et al., Rountree and Juanes). One goal of the study is to determine the feasibility of using passive acoustics as a supplemental tool in the census of fish diversity and habitat use patterns in the sanctuary.
  • an ongoing survey of soniferous fishes of Massachusetts has resulted in a significant range extension for the cryptic estuarine and inshore fish the striped cusk-eel, Ophidion marginatum (see Rountree and Juanes). Extensive sampling over many decades with conventional gears in the region had failed to recognize the importance of striped cusk-eel to the fauna, while passive acoustics revealed it to be widespread and abundant. This study demonstrates that even a low-budget, low-tech, approach to passive acoustics can contribute significantly to the census of marine life.

New Technology

Studies described at the workshop have pushed technology to new levels that will allow researchers to expand the frontiers of fisheries science and ocean exploration:

  • the potential for combining hydrophone arrays with other underwater census technologies is being explored, including ROVs (see Rountree et al., Luczkovich and Sprague), underwater video (see Svellingen et al., Lobel, Barans et al.) and active acoustics (Fudge and Rose). Lobel has pioneered the use of advanced SCUBA technologies for studies of fish vocal behavior.
  • researchers are beginning to look towards existing acoustic arrays maintained by the Navy and other agencies for applications to fishes (see Jarvis and Moretti).
  • Advances are being made in the development of modeling tools and software for tracking vocal fish (see Forsythe) and identifying individual fish (see Wood).
  • New technologies for detecting and recording underwater sounds are rapidly evolving (see Mann).
  • Historic archives of fish sounds are being assembled and rescued from deterioration and will be made available to researchers and the public through the internet (see Bradbury and Bloomgarden). The establishment of internet access to libraries of fish sounds is an important step to more widespread use of passive acoustics in fisheries science and related fields.


The Future of Passive Acoustics

Although studies described during the workshop reflect the rapid growth of research on passive acoustics applications to fisheries and marine census, there are many areas where technical developments are needed to promote future research:


  • the development of sound recognition systems, based on wavelet analysis and other new techniques to enable the automatic discrimination of different species. For a north Atlantic species, the haddock, it has already proved possible to distinguish the voices of individual male fish (see Wood).
  • automatic event detection/analysis software to quantify temporal patterns of sounds over long time periods.
  • localization/tracking software (see Forsythe).
  • software allowing simultaneous analysis of video and audio data in behavior studies (i.e., click on the sound wave of a fish call and view the corresponding video frame in a second window). This capability would allow rapid correlations of individual sounds and sound components with behavior and functional morphology.
  • the improvement of passive listening technology for systematically detecting and recording sounds at sea, including:
  • ship based listening systems, with dangling and towed hydrophones.
  • bottom mounted listening systems based on underwater vehicles and pop-up buoys.
  • drifting sonobuoy systems, either storing the data, or telemetering data to ships or shore-based listening stations.
  • large hydrophone arrays, capable of localizing sound sources.
  • measurement of source levels, and calibration techniques for measuring the distance of sound sources.


-back-yard science: Perhaps of equal importance to passive acoustics systems for use in the open ocean is the development of technology to aid in small scale, low budget studies of marine fishes in estuarine and inshore habitats. We feel that passive acoustics have a great potential as a tool to provide basic information on essential fish habitat use patterns, as it becomes more widely used in classrooms and State and Federal sampling programs. Several studies presented at the workshop demonstrate the usefulness of this type of research to fisheries. A good example of this is the discovery, using passive acoustics, that striped cusk-eels are abundant in Massachusetts estuaries, where despite a long history of conventional sampling in the region, the species was thought to be a very rare straggler. Technologies to aid this type of research include:

  • archival acoustic recorders - unmanned recorders for use on ships of opportunity in many types of habitats.
  • homing devices to locate sound sources (see Forsythe, Rountree et al.).
  • devices that allow simultaneous recording of both audio and video data.
  • hand-held devices for shore based, or small boat surveys in shallow water.
  • miniature ROV designed for both video and audio recording of fish behavior from small boats and from shore.


-application of passive acoustics in a wider range of habitats where fish may aggregate to spawn. For example:

  • mangrove areas, which are especially difficult to survey by conventional means, but where the diversity of fishes may be especially high.
  • coral reefs and rocky reefs, where again many species aggregate.
  • oceanic and inshore banks, where the mass spawning of sound producing species, like cod and haddock, takes place.
  • the deep sea, where many species like the morids and macrourids are suspected to be vocal from anatomical evidence.
  • estuaries - the primary spawning grounds for many economically important fishes.
  • development of local, regional, national and international networks of "listening posts" especially in estuarine and inshore waters. Incorporation of listening posts into local and regional environmental data networks like GoMOOS and the NOAA/OCRM/NERR's System Wide Monitoring Program.


The Benefits of Passive Acoustics

  • non-invasive, non-destructive census of marine life.
  • works at night without bias (versus video and other techniques that require lights).
  • can provide continuous monitoring of fishes.
  • provides remote census capabilities.
  • determine the daily and seasonal activity patterns of fishes including determination of discrete daily spawning times.
  • a better foundation for the management of exploited species by mapping their distribution and pinpointing their spawning grounds.
  • a better understanding of the habitat preferences of key fish species (e.g., Essential Fish Habitat "EFH" assessment in the US), giving a better focus for their conservation.
  • establishment of baselines for the abundance and distribution of key fish species, allowing examination of the effects of future environmental change.
  • obtaining a wider knowledge of the behavior of those fish that cannot readily be studied by any other method.
  • can be used to monitor environmental noise and determine their sources.
  • can be used to examine the impact of anthropogenic noise on fish, especially on spawning behaviors.
  • networks of listening posts can provide synoptic data on the occurrence of fishes and spawning activities on local, regional, national and global scales.


Closing Comments

Research presented at this workshop underscores the great strides that have been made in the application of passive acoustics to fisheries and related issues in the last two decades. It is clear from this body of work, that although passive acoustics is currently largely overlooked as a research tool, it is a rapidly "up-and-coming" field of research that holds great promise for the future. It is our hope that publication of this proceeding will stimulate the growth of this field, and will encourage funding agencies to support passive acoustics research.



This workshop and the publication of the proceedings benefited by contributions from many individuals. Grace Lee set up the web page and did much of the text and graphics layout for the proceedings. The staff of the Endicott House and Brooks Center provided outstanding conference facilities and support for the workshop. The workshop and publication of the workshop proceedings received major funding from MIT Sea Grant, the Office of Naval Research, and from the Northeast-Great Lakes Center of the National Undersea Research Program. Travel for some workshop participants was funded in-whole, or in-part by: Connecticut Sea Grant, Florida Sea Grant, Hawaii Sea Grant, Louisiana Sea Grant, North Carolina Sea Grant, the South Carolina Sea Grant Consortium, Texas Sea Grant, and the Woods Hole Sea Grant Programs.

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