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Abstract.-Sounds produced by spawning fishes in Pamlico Sound, North Carolina, have been recorded both under captive conditions and in hydrophone and sonobuoy field surveys. These sounds, produced by males, are species specific, are associated with spawning, and are most likely used for advertisement to attract females. Sounds can be discriminated by use of spectral analysis (oscillograms and spectrograms) of recordings, and the peak frequencies produced by each species can be correlated with species and fish size. Sonobuoys were used for passive acoustic surveys, which were ''sound truthed'' from recordings of captive fishes to determine the timing and location of spawning sites for four species in the family Sciaenidae: red drum Sciaenops ocellatus, spotted seatrout Cynoscion nebulosus, weakfish C. regalis, and silver perch Bairdiella chrysoura. During May-September 1998, sounds were first detected in the early evening, increased in loudness after sunset, and ended by sunrise. Weakfish and silver perch were heard predominantly at inlet locations in May and June, whereas spotted seatrout (peak drumming in July) and red drum (peak drumming in September) were heard predominantly at lower-salinity river mouth locations in western Pamlico Sound. Passive acoustic surveys can be used to determine critical spawning habitats of sciaenid fishes; such surveys have revealed interesting insights into fish behavior and should be integrated into ocean observing systems.

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In the coastal systems of the southeastern United States, populations of weakfish (Cynoscion regalis) and red drum (Sciaenops ocellatus) are in decline, and knowledge of their spawning areas is important for the for- mulation of fisheries management plans. Weakfish and red drum, both members of Family Sciaenidae, use their swim bladders to produce species-specific sounds associated with spawning activity. Large spawning aggregations of these fish can produce sound levels as high as 145 dB (re:1 μPa), and these sounds can be used to identify spawning areas. Recordings and spectrograms of spawning sounds will be presented for each species. Water depth, bottom type and contour, sound-speed gradient, and water current gradient all affect the propagation of the fish sounds through the water. Measurements of these factors and the sound level of the fish calls are used to obtain an approximate range to the spawning aggregation. [Work supported by North Carolina Division of Marine Fisheries and U.S. Fish and Wildlife Service.]

Fish produce species-specific sounds during courtship, during aggressive encounters with other fish of the same species, and as a response to threats from predators. Particular sounds are species-specific and have been recorded from fish during spawning in captivity. Such acoustical data may be used to identify and locate fish that are reproductive in the sea. In this paper, nocturnal sound production and planktonic egg production are correlated for weakfish (Cynoscion regalis) and red drum (Sciaenops ocellatus) (Family Sciaenidae), two species for which there are concerns over declining stocks. Recordings of underwater sounds and ichthyoplankton net tows were made after sunset at ten sites in Pamlico Sound, NC. Sites were relocated with a differentially corrected Global Positioning System receiver on a biweekly basis from May through October 1997. Based on laboratory studies, weakfish ‘‘purring’’ sounds and red drum ‘‘knocking’’ sounds only occur during spawning. ‘‘Purring’’ was recorded along with sciaenid eggs at stations near Ocracoke and Hatteras Inlets during May through July. ‘‘Knocking’’ was recorded in September and October at sites away from the inlets, also occurring with sciaenid eggs in one case. Mapping of sciaenid spawning areas may be possible using acoustical data alone, but may overestimate egg production.