Distribution of red drum spawning sites identified by a towed hydrophone array

Knowledge about fish spawning habits and habitats is an essential component of fisheries management. This paper reports on a survey of potential spawning sites for red drum Sciaenops ocellatus in the nearshore western Gulf of Mexico conducted using a towed hydrophone array. Two classes of red drum sounds could be distinguished. One was a low-frequency rumble with a prominent energy peak at approximately 150 Hz. ne other was a clearly distinguishable call made by individual or small groups of red drum. Calls of individual red drum were detected along most sections of all transects. There were extensive areas along each transect where no close drumming was heard and where drumming rates were primarily low (< 16 calls/min). Calls were detected in both extensive clusters and isolated occurrences along the transects. The distribution of drumming fish suggests that some, if not most, spawning takes place among widely dispersed individuals as opposed to highly aggregated groups. Only 7% of the 1-min summaries recorded high drumming rates (>= 16 calls/min), and even these typically were produced by only a few individuals. Most low drumming rates were produced by a single fish. Based on the distribution of sound production, red drum apparently spawn all along the nearshore region of the central Texas coast. This survey was not spatially comprehensive enough to fully delineate the spawning area, but it made clear that spawning activity is widespread and not concentrated at inlets, as has been suggested by earlier authors. The use of towed hydrophone arrays offers promise of an efficient means to determine the full extent of red drum spawning areas and their reproductive strategies.