Description of Periodicity and Location of Red Drum (Sciaenops ocellatus) Spawning in Charleston Harbor, South Carolina
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No published literature exists regarding the location, daily and seasonal periodicity of red drum spawning in South Carolina. Studies from North Carolina and Georgia report that red drum typically spawn in aggregations during afternoon or evening hours in late summer and early fall, at water temperatures between approximately 25 and 30°C. The objective of this study was to describe the location, timing, and physical and environmental cues associated with red drum spawning in South Carolina. Acoustic observations at the entrance to Charleston Harbor during August and September of 2008 indicated an aggregation of drumming male red drum at a previously suspected spawning site. Acoustic recordings showed that aggregated drumming was underway as of August 28 and continued every day through a peak water temperature of approximately 30°C until September 23, when water temperature dropped below 25.5°C. Drumming began daily around noon, peaking in volume between 1430 and 1700 hours, and ending by around 2000 hours (dusk). Plankton sampling captured red drum eggs from August 7 to September 26, 2008. Early-staged eggs were captured every sampling date from August 12 through September 11, confirming that spawning had occurred less than two hours previously. The influence of decreasing temperature and day length on cessation of spawning in Charleston Harbor was corroborated by conducting laboratory trials on red drum held in captivity. Captive fish in three tanks were exposed to the same photoperiods and water temperatures which occurred in Charleston Harbor during the month of September, 2008 while monitoring spawning occurrence. During laboratory trials, 97% of spawning events took place between 29.9 and 25.5°C, confirming that captive spawning ceased at a temperature similar to the observed 25.5°C which marked the last spawning in Charleston Harbor. This study therefore presents new data on the location and timing of red drum spawning in South Carolina.