An International Workshop on the Application of Passive Acoustics in Fisheries
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Over 800 species of fishes worldwide are known to be vocal, though this is likely to be a great underestimate. Of these, over 150 are found in the northwest Atlantic. Amongst these families are some of the most abundant and commercial fish species, including the herring, cod and haddock. 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.

Listening to Fish
cusk-eel photoFish 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 behaviour of the great majority of marine fish. Possibly one of the greatest challenges to researchers attempting to study the behavioural 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.

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 behaviour. Already significant strides have been taken:

  • in the northern Adriatic, workers at the WWF’s Miramare Nature Reserve have searched for spawning concentrations of the corvina Sciaena umbra. Passive listening from a sailing boat has revealed that large number of this threatened species are associated with harbours and marinas (many of them newly constructed) along the coasts of Italy, Slovenia and Croatia. (Bonacito, Costantini, Picciulin, Ferrero & Hawkins, 2001).
  • 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 — thought to spawn offshore in deep water — can form large spawning concentrations close to shore. (Hawkins, Casaretto & Picciulin, 2001).
  • a number of studies in the estuaries of the eastern United States have helped to localise the spawning areas of drum fishes. (Saucier and Baltz 1993; Connaughton, Fine & Taylor, 2001; Luczkovich & Sprague, 2001).
  • for the first time in the United States passive acoustics are being explored as a tool to census marine fishes on the continental shelf. A two-year study to catalogue soniferous fishes in the Stellwagen Bank National Marine Sanctuary was begun in October 2001 (Rountree, 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 Cape Cod, Massachusetts has resulted in a significant range extension for the cryptic estuarine and inshore fish the striped cusk-eel, Ophidion marginatum. Extensive sampling over many decades with conventional gears in the region had failed to recognise 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.

These studies, using relatively simple techniques, have confirmed that passive listening can locate concentrations of important fish species, opening the way for further, more detailed studies of their behaviour, distribution and habitat use.

Future Proposals

Necessary technical developments for further research to take place are:

  • the preparation of descriptive catalogues of the sounds produced by the fish faunas of given areas, taking account of seasonal changes, to be based on both field and aquarium studies. A start has been made in the eastern North Atlantic by Rodney Rountree of the School for Marine Science and Technology, UMASS Dartmouth, together with the establishment of a National Archive of Fish Sounds at Cornell University.
  • software
  • 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. (Wood, Casaretto, Horgan & Hawkins, 2001)
  • automatic event detection/analysis software to quantify temporal patterns of sounds over long time periods
  • localisation/tracking software
  • software allowing simultaneous analysis of video and audio data in behaviour 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 behaviour 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 localising 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, including:
  • archival acoustic recorders - unmanned recorders for use on ships of opportunity in many types of habitats
  • homing devices to locate sound sources (research underway)
  • 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 behaviour from small boats and from shore
  • application of these techniques in a 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

  • 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 behaviour of those fish that cannot readily be studied by any other method.
  • 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
  • determine the daily and seasonal activity patterns of fishes including determination of discrete daily spawning times
  • provides remote census capabilities
  • 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

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