Red grouper, Epinephelus morio, are dark reddish brown graded to pink in color with occasional white spots or blotches on their bodies. They can be distinguished by their large dorsal fin, which has dark edges (as does their anal and caudal fins). Image credit: NOAA.
The red grouper, Epinephelus morio, is non-migratory, bottom-dwelling fish that is found in the Western Atlantic Ocean from Massachusetts to southern Brazil, including the Gulf of Mexico. It is a thick-bodied fish, with a head and body colored reddish brown shading to pink with occasional white spots or blotches on the sides. They are distinguished by this body coloring, their large, dark edged dorsal fin, and their large mouths. Red grouper feed on a variety of other marine fishes and invertebrates including snapper, parrotfish, crabs, shrimp, and squid. Young fish (1-6 years of age) occupy seagrass beds, rock formations, and reefs in shallow, nearshore waters. Older juveniles and adults are traditionally found around offshore ledges, crevices, and caverns of rocky reefs.
Red grouper produce sounds throughout the day and night, mostly at sunrise and sunset. Red grouper produce two types of low-frequency (with a peak near 180 Hz), pulsed vocalizations. The first consists of 1 to 4 brief (0.15 second) pulses immediately followed by a 0.5-2 second short call, or growl. Produced less frequently, the second vocalization is the short call followed by a burst of 10 to 50 pulses. Behaviors associated with red grouper sound production include males patrolling, male and female fish swimming together, and/or direct physical contact between male and female fish while rapidly swimming. These observations, in addition to red grouper producing sound during a known peak-spawning month (May), indicate that sound production in red grouper is likely related to spawning activity.
Understanding red grouper spawning activity and defining spawning areas is key to fisheries management of the species. Red grouper are a commercial important fishery. Since they are long-lived and grow slowly, they are vulnerableto fishing pressure. Fisheries managers are looking to designate marine reserves to protect red grouper stocks. Passive acoustics can be used to monitor red grouper behavior, map their and define critical habitat. Passive acoustic platforms, such as underwater gliders, have been used to detect and map red grouper sound production in the Gulf of Mexico.