Sonic muscles attached to the swim bladder contract rapidly, driving the gas-filled organ as a resonator. The result is a pulse concentrated below about 100 hertz, which travels well through water and is often described by divers as a percussive thud rather than a growl. Goliath grouper produce it during courtship and when a diver approaches too closely.
Because the call is species-typical and low frequency, hydrophones moored at a reef or wreck can log aggregation activity continuously over months, without any of the disturbance a diver survey introduces. That matters for a species whose spawning aggregations were the exact feature that made it easy to fish to collapse.
The Atlantic goliath grouper was placed under a US harvest moratorium in 1990 after severe depletion, and populations off Florida have recovered substantially since; a limited permitted harvest has since been reintroduced in Florida state waters. Recovery elsewhere in the range is far less clear, and the IUCN assessment remains cautious.