Using fish sounds to identify spawning activity of weakfish (Cynoscion regalis) and red drum (Sciaenops ocellatus) in nature

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.]