Use of passive acoustics to determine red drum spawning in Georgia waters

Passive acoustic sampling to locate spawning sites of red drum Sciaenops ocellatus was conducted along the Georgia coast during July-October 1995-1997. Spawning red drum were observed in captivity to determine the level of sound associated with spawning. In 1997, a known red drum spawning site was sampled weekly with a mobile hydrophone and continuously with a remote hydrophone deployed from 23 September to 2 October 1997. Both field and tank observations indicated that red drum males make calls with four or fewer pulses per call without associated spawning. However, calls consisting of at least 8 pulses/call occurred only prior to spawning. In 1995 and 1996, a total of 372 hydrophone observations were made at regularly sampled stations in Doboy, Altamaha, St. Simon's, and St. Andrew sounds and at supplemental locations along the Georgia coast. Only one nearshore spawning site was located; it was found in St. Mary's channel at the mouth of Cumberland Sound. Duration of peak red drum sound production at this site varied from 1 to 4 h but generally occurred from 1600 to 1900 hours. The Cumberland Sound site was characterized by deep water (> 13.7 m) and relatively high salinity (>30 parts per thousand). Red drum spawning activity at this site was estimated to occur during August through mid-October based on calls.