Abstract

Diel and seasonal periodicities of a resident Tampa Bay spotted seatrout (Cynoscion nebulosus) spawning aggregation were determined using passive acoustics during the 2004 spawning season. This was possible because spotted seatrout males make courtship sounds or calls associated with spawning. Data were collected by two long-term acoustic recording systems (LARS) between February and early October 2004. The LARS recorded ten continuous seconds of sound every ten minutes. Sounds were categorized based on the estimated number of fish calling: 0, 1-2 males, 3-5 males, small aggregation, and large aggregation. Sounds from large aggregations were first recorded in mid-March and were detected daily from mid-May to mid-September (except during July, when the LARS was not functioning). Spotted seatrout typically begin spawning in mid to late March or early April in Tampa Bay, but the LARS data indicated that large aggregation sound did not occur daily until the month of May. Daily large-aggregation sounds ceased in mid-September, which is when previous studies have reported that the spawning season ends. Duration of aggregation sounds during the prime spawning season varied daily and seasonally, with peaks in sound coinciding with new and full lunar phases. Longer durations of aggregation sounds were recorded daily during the second half of the prime spawning season (August-September) than during the first half (May - June).

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