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Submitted August 31^st 1999.

Title: Development of a portable hydrophone array system for passive localization, census, and tracking of vocalizing fishes in estuarine and shelf habitats.

Principal Investigator: James H. Miller, Associate Professor of Ocean Engineering, University of Rhode Island.

Co-Principal Investigators: Rodney A. Rountree, Adjunct Assistant Professor, Dept. Forestry and Wildlife Management, UMASS-Amherst; and Francis Juanes, Assistant Professor, Dept. Forestry and Wildlife Management, UMASS-Amherst.

Introduction: Although over 150 species of fish from 36 families are known to vocalize (Fish and Mowbray 1970), this likely represents a small fraction of the species capable of some type of vocal communication. Recent advances in acoustic technologies and acoustic tomography theory have led to increased interest in their use for in situ studies of animal behavior (Lobel et al. 1995,Mann and Lobel 1995, 1997). Studies of fish sounds can provide a wealth of data on temporal and spatial distribution patterns, habitat use, and spawning, feeding, and predator avoidance behaviors. However, few in situ studies of behaviors associated with fish sounds have been attempted (Tavolga 1980). Long-term studies of sounds recorded at specific sites have been used to suggest temporal patterns in spawning events and seasonal movements (Fish et al. 1952,Breder 1968). Alternatively, investigators have attempted to locate spawning aggregations by listening for fish sounds along transects. For example, sounds produced by spotted seatrout, Cynoscion nebulosus, and black drum, Pogonias cromis, during spawning have been used to locate spawning aggregations and identify critical estuarine spawning habitats for these species (Saucer and Baltz 1993). More recently, sophisticated passive acoustic arrays have been used to obtain more detailed information on spawning behavior of coral reef fishes (Mann and Lobel1995a,b). It has long been recognized that triangulation methods might be used to determine the location of calling animals and the method has been pioneered in studies of marine mammals (Walker 1963; Watkins and Schevill 1972, Clark 1980). Spiesberger and Fristrup (1990) present are view of acoustic tomography theory and its application for the passive localization of calling animals and suggest, based on computer simulations, that the technique has a great potential to allow researchers to collect detailed data on animal movements and behavior, and could even be used to collect passive abundance data in certain situations. The P.I. recently conducted successful trials of an acoustic array for passive tracking of echolocating harbor porpoise, Phocoena phocoena (Miller, Langlais and Gampert, unpublished). We intend to use similar technology and methods to localize calling fishes. To our knowledge the use of advanced acoustic technology to passively locate and monitor fish movements has not yet been attempted.

Objectives: We propose to develop a prototype for a Portable Hydrophone Array System (PHAS) which can be deployed in a variety of estuarine and shelf habitats to passively monitor the behavior of calling fishes. Specific objectives are: 1) construct a working model of a PHAS, 2) develop software to allow automatic tracking of calling fishes, 3) conduct a series of system tests both in the laboratory and in situ within the Jacques Cousteau NERR, 4) conduct a pilot study of the behavioral ecology of the striped cusk-eel, Ophidion marginatum, within the Jacques Cousteau NERR, and 5) collect occurrence and behavioral data on weakfish, Cynoscion regalis, American eel, Anguilla rostrata, striped searobin, Prionotus evolans, and other calling species likely to be encountered during the pilot study and test deployments with the NERR and LEO-15 sites (Table1). We anticipate that the PHAS can provide the following minimum ecological information: 1) real-time data on marine sounds produced by fishes and invertebrates within specific habitats, 2) temporal (diel and tidal) occurrence data on species with known vocal patterns, and 3) temporal occurrence data on specific behavioral activities (e.g., spawning) for species with known behavioral vocal patterns. In addition, we expect to develop a system capable of providing: 4) spatial location and fine-scale movements patterns of individuals and/or aggregations of calling fishes, and 5) abundance estimates of calling fishes located in the array vicinity.  

Prototype PHAS development- We will use five buoyed hydrophones set along five points of a circle of 100 m diameter (Figure 1). Each buoyed hydrophone will include a Differential Global Positioning System and radio transmitter to continuously provide positional information and transmit data to a central computer located up to 5 km away.  The computer will monitor sounds and compute directions and locations of sound sources and display sound characteristics and source locations to a computer screen. Sound source locations will be overlain onto an area map showing depth and temperature (JIM can this be done real-time or during post-processing?). Initial field trials will be conducted during June 2000 in the Jacques Cousteau NERR at the Rutgers Marine Field Station and at LEO-15 to fine-tune the system's hardware and software and to develop deployment methodologies. During these trials, tests will be conducted in various depths from 2-20 m using known sound sources to determine the depth limitations of the technique in shallow estuarine and shelf waters. Once the system is ready it will be used in a pilot study of the behavior of cusk-eels, weakfish, and other estuarine species within the Jacques Cousteau NERR at a site located 5 km from the Rutgers Marine Field Station  (Figure 1).

Pilot study- In order to fully evaluate and test the system, we propose to conduct a full-scale pilot study of the behavioral ecology of the striped cusk-eel within the Jacques Cousteau NERR. Striped cusk-eels are an important component of estuarine fish communities on the east coast, but because of their cryptic nocturnal behavior, are poorly studied (Fahay 1992, Schwartz 1997). Although they have long been known to produce sounds based on anecdotal accounts and the presence of strong sonic muscles (Courtenay 1971), their sound characteristics have only recently been described by the co-P.I. Rountree and his colleagues (Mann et al 1997). This species makes an ideal test subject for the passive acoustic tracking system for several reasons: 1) it is one of the one most abundant species in the study site with a well described vocal pattern, 2) males set up choruses each night between 1800-2030 h at least from July-September (Mann et al 1997, pers. Observ.), 3) the time of the beginning of the chorus is highly predictable on any given night (shortly after sunset), and 4) males tend to remain partially buried during early stages of the chorus, while the females search them out. Because the time of cusk-eel choruses are so predictable, they will serve as a highly reliable test species. In addition, the tendency for males to remain sedentary during early stages of the chorus increases the likelihood that an accurate census of cusk-eel abundance and densities can be obtained with the acoustic technology. These behavioral characteristics make cusk-eels an ideal test subject to develop the PHAS system.  The occurrence, timing and abundance of other species in the area are less predictable, and are thus less desirable for the initial pilot study.  However, other highly vocal species such as the weakfish, do occur regularly in the specific site for the pilot study (Rountree and Able 1992, 1993, 1997,Rountree and Juanes, unpublished data) and we anticipate collecting significant behavioral information on these species incidental to the cusk-eel study.  Cusk-eels captured this summer by the co-P.I.s Rountree and Juanes will be held under laboratory conditions at URI to collect additional data on sound characteristics and to be used in laboratory tests. Three field trials of five days duration will be conducted between July and September of 2000, during the peak spawning period of cusk-eels. The specific site for the PHAS deployment will be determined by surveying the study area with a hydrophone to locate concentrations of calling cusk-eels.  Once the cusk-eels are located, they will be fully or partially surrounded by five buoyed hydrophones set along a 100 m diameter circle.  The PHAS will then be used to monitor cusk-eel and other fish sounds over a 4-5 day period.  The PHAS will collect data on the intensity and timing of calls over the diel and tidal cycles throughout the trail.  It will also be used to calculate an index of abundance based on the number of unique calls monitored during any given time interval.  Most interestingly, it will provide data on the spatial location and density distribution of calling individuals (Figure 2).  If laboratory observations of cusk-eel behavior reflect natural behavior, then we can expect individual males to call for several minutes while still fully or partially buried in the sediment.  This behavior would allow us to map burrow locations of individuals and compare their distributions each night to determine if individuals set up permanent or temporary territories.  Tracking data on individuals calling as they move can provide data on spawning behavior and territorial interactions.  Further, it may be possible to estimate the length frequency distribution of calling individuals and to examine size related spatial distribution patterns based on the correlation between sound frequency and body size as has been demonstrated for damselfishes (Lobel and Mann 1995).  It may even be possible to identify specific individuals based on unique characteristics of their calls as has been done with quail in terrestrial applications of this technology (Magyar et al. 1978) These capabilities would provide an extremely valuable tool to study fish behavior.

Densities of cusk-eels will be determined by three independent methods for comparison with data derived from the acoustic system. In shallow areas (<3m) a large 6m by 15 m box net will be used to capture cusk-eels using methodologies being developed by the co-P.I.s Rountree and Juanes in a current study of marsh nekton funded by the Marsh Ecology Research Program. All individuals captured will be sexed (based on external characteristics) measured, tagged and released. Cusk-eel densities will also be estimated by using a shore-based ROV to count cusk-eels along transects running perpendicular to the shoreline. The ROV should be equipped with infrared or red lights to allow night observations as red lighting appeared to have no effect on cusk-eel vocalization or spawning behavior in laboratory studies (Rountree, pers. Observ.). If possible, the position along the transect of partially buried cusk-eels will be marked with a colored weight dropped by the ROV and microhabitat characteristics recorded (e.g. temperature, DO, turbidity, sediment type, etc.). Alternatively, sonic transducers could be dropped at the burrows of several individuals to allow re-location on subsequent days and analysis of fish movements over several days time for comparison with data derived by passive tracking with the PHAS.  Finally, divers will be used to search for cusk-eels in order to observe and film their behaviors.  At least two methods will be used to help in calibration of the model system: 1) transducers with known sound characteristics and positions will be placed within the circle formed by the buoyed hydrophones, as well as at various distances away from the hydrophones, 2) positional information obtained from the PHAS will be used to guide a ROV to calling cusk-eels to obtain visual observations of behavior and verify position data. Visual verification of the sound source is a critical component of the study, but has rarely been available in previous studies of vocalizing fishes (Tavolga 1980). We anticipate that the pilot study will be valuable in its own right and will result in publication of a detailed description of cusk-eel nocturnal behavior, movements, and microhabitat use (i.e., identification of essential fish habitat).  The latter method will also be used to determine the source of unknown sounds recorded by the system (i.e., other species vocalizing in the study area, or new sounds produced by cusk-eels which are associated with other behaviors).

Conclusion: This project represents an exciting opportunity to make an outstanding contribution to marine ecology. We feel that this technology has many applications within estuarine, shelf and deep sea environments.  Future efforts would be directed at using the PHAS to study spawning behavior of soniferous commercial species such as Atlantic cod and haddock on the shelf, and at establishing long-term acoustic listening stations within the NERR and at Leo-15. We feel the latter application would constitute a major addition to the LEO program and would likely become a highly popular source of real-time data for educational programs through Internet links. We feel that our proposal is highly suited to the goals of the MABNURC program as it addresses four of the six research priorities (LEOs, Characteristics of essential fish habitat, Undersea technology development, and NERR studies). The investigators intend to use the results from this study to support proposals to other agencies to fund the establishment of permanent listening stations at the NERR and Leo-15 sites, as well as to conduct studies of vocal behavior of estuarine and shelf fishes such as weakfish, Atlantic cod and haddock.

Literature cited

Breder, C.M., Jr. 1968. Seasonal and diurnal occurrences of fish  sounds in a small Florida Bay. Bull. Am. Mus. Nat. Hist. 138(6):329-278.

Clark, C.W. 1980. A real-time direction finding device for determining the bearing to the underwater sounds of southern right whales Eubalaena australis. J. Acoust. Soc. Am. 68:508-511.

Courtenay, W.R. 1971. Sexual dimorphism of the sound producing  mechanism of the striped cusk-eel, Rissola marginata (Pisces: Ophidiidae). Copeia 1971:259-268.

Fahay, M.P. 1992. Development and distribution of cusk eel eggs  and larvae in the middle Atlantic Bight with a description of Ophidion robinsi n.sp. (Teleostei: Ophidiidae). Copeia 1992(3):799-819.

Fish, M.P., A.S. Kelsey, Jr., and W.H. Mowbray. 1952. Studies on  the production of underwater sound by North Atlantic coastal fishes. J. Mar. Res. 11:180-193.

Fish, M.P., and W.H. Mowbray. 1970. Sounds of Western North  Atlantic fishes. Johns Hopkins Press, Baltimore, MD. 205 p.

Hawkins, A.D., and K.J. Rasmussen. 1978. The calls of gadoid  fish. J. Mar. Biol. Ass. U.K.58:891-911.

Lobel, P.S., and D.A. Mann. 1995. Spawning sounds of the damselfish, Dascyllus albisella (Pomacentridae), and relationship to male size. Bioacoustics 6(3):187-198.

Magyar, I., W.M. Schleidt, and D. Miller. 1978. Localization of  sound producing animals using the arrival time differences of their signals at an array of microphones. Experientia 34:676-677.

Mann, D.A., J. Bowers-Altman, and R.A. Rountree. 1997. Sounds  produced by the striped cusk-eel Ophidion marginatum (Ophidiidae) during courtship and spawning. Copeia 1997(3):610-612.

Mann, D.A., and P.S. Lobel. 1995a. Passive acoustic detection of  fish sound production associated with courtship and spawning. Bull. Mar. Sci. 57(3):705-706.

Mann, D.A., and P.S. Lobel. 1995b. Passive acoustic detection of  sounds produced by the damselfish, Dascyllus albisella (Pomacentridae). Bioacoustics 6:199-213.

Mann, D.A., and P.S. Lobel. 1997. Propagation of damselfish (Pomacentridae) courtship sounds. J. of the Acoustical Society of America 101(6):3783-3791.

Rountree, R.A., and K.W. Able. 1992. Fauna of polyhaline  subtidal marsh creeks in southern New Jersey: composition, abundance and biomass.  Estuaries 15(2):171-185.

Rountree, R.A., and K.W. Able. 1993. Diel variation in  decapod crustacean and fish assemblages in New Jersey marsh creeks.  Estuarine, Coastal and Shelf Science 37:181-201.

Rountree, R.A., and K.W. Able. 1997.  Nocturnal fish use  of New Jersey marsh creek and adjacent bay habitats. Estuarine, Coastal and Shelf Science 44:703-711.

Saucier, M.H., and D.M. Baltz. 1993. Spawning site selection by  spotted seatrout, Cynoscion nebulosus, and black drum, Pogonias cromis, in Louisiana. Env. Biol. Fish. 36:257-272.

Schwartz, F.J. 1997. Biology of the striped cusk-eel, Ophidion marginatum, from North Carolina. Bull. Mar. Sci. 61(2):327-342.

Spiesberger, J.L., and K.M. Fristrup. 1990. Passive localization  of calling animals and sensing of their acoustic environment using acoustic tomography. Am. Nat. 135:107-153.

Tavolga, W.N. 1980. Hearing and sound production in fishes in  relation to fisheries management.P.102-123, In: Bardach, J.E., J.J. Magnuson, R.C. May, and J.M. Reinhart (eds.). Fish Behavior and its use in the capture and culture of fishes. ICLARM Conference Proceedings 5, 512 p. International Center for Living Aquatic Resources Management, Manila, Philippines.

Walker, R.A. 1963. Some intense, low-frequency, underwater sounds of wide geographic distribution, apparently of biological origin. J. Acoust. Soc. Am. 35:1816-1824.

Watkins, W.A., and W.E. Schevill. 1972. Sound source location by  arrival times on a non-rigid three-dimensional hydrophone array. Deep-Sea Res. 19:691-706.

Table 1. Partial list of species known to be capable of sound production based on field and/or laboratory studies, and which occur at least seasonally in New Jersey estuarine and/or shelf waters (Fish et al. 1952, Fish and Mowbray 1970, Hawkins and Rasmussen 1978, Tavolga 1980, Mannet al. 1997).  *Sound production capability assumed based on the presence of anatomical structures usually associated with vocalization.

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