Goliath grouper Epinephelus itajara sound production and movement patterns on aggregation sites

Abstract

Sound production by goliath grouper Epinephelus itajara was characterized on 2 aggre- gation sites in the Gulf of Mexico off the southwest coast of Florida, which are likely to be spawning sites, based on the presence of fish with ripe gonads. Goliath grouper produced predominately low- frequency single-pulse sounds with dominant frequencies around 60 Hz. Long-term acoustic record- ings documented that sounds were most frequently produced between 01:00 and 03:00 h. Sound pro- duction had a lunar periodicity, with reduced levels occurring for several days around the full moon. A single goliath grouper was implanted with an acoustic telemetry transmitter that indicated the depth of the fish. This fish remained on the aggregation site for all but 1 d of the 2 mo record and was located near the bottom (46 m) for the majority of the time. Several forays to shallower depths were detected, most of which occurred near midnight and 03:00 h. These short-duration shallow-water forays could possibly indicate spawning ascents. The combination of passive acoustics and active acoustic telemetry indicates that efforts to document spawning should be concentrated around mid- night. The prolific sound production of goliath grouper will allow large spatial and temporal scale mapping and monitoring of aggregation sites.