Mark W. Sprague - spraguem@mail.ecu.edu
Joseph J. Luczkovich and Stephen Johnson
Department of Physics
East Carolina University
Greenville, NC 27858
Popular version of paper 4pAO6
Presented Thursday afternoon,
June 25, 1998
135th ASA Meeting, Seattle, WA
Using a boat, a hydrophone and a tape recorder, we have been able to make acoustic recordings of Pamlico Sound weakfish (Cynoscion regalis) and red drum (Sciaenops ocellatus) during their spawning periods and correlate the distinctive spectrographs for each species with their egg presence. The sounds recorded in nature are analyzed to obtain species-specific patterns of the component sound frequencies, which are compared with sound recordings from captive fishes of the same species. The importance of this research, as described in our earlier ASA paper (see Luczkovich et al., 4pAO5), is our improved ability to efficiently prepare spawning maps for use by fishery managers for protection of these overfished species.
The "purring" calls of weakfish (audio sample 1) or the "knocking" calls of the red drum (audio sample 2) are made during courtship by the males with the fish's swimbladder and surrounding musculature. Although some researchers have published spectrographs and descriptions of the calls of sciaenid fishes, to date no calls have been published of these fish North Carolina waters, a region thought to be the most important along the Atlantic coast for reproduction in these migratory fishes. Here we report the first recorded spectrographs of weakfish (image 1) and red drum (image 2) in Pamlico Sound during their respective spawning periods. We are able to use information from "loudness" of the sound to predict the distance to the spawning fish. The "loudness" of the sound recorded during choruses of weakfish "purring" (audio sample 3) can be as high as 145 dB in water (equivalent to 120 dB in air). This sound pressure level produced by these spawning aggregations is approximately the same level as that at a rock concert. Using a mathematical model of sound spreading, we can estimate transmission loss in the signal and calculate the maximum distance between the spawning fish and the hydrophone. These valid and reliable passive acoustical measures of spawning activity are economical, time-saving and of great importance to the formulation of fishery management policy.
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