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The Nassau Grouper, Epinephelus striatus.  Illustration by Diana Rome Peebles 1998.  Courtesy of Florida Fish and Wildlife Conservation Commission, Division of Marine Fisheries.

Species Name: 
Epinephelus striatus (Bloch, 1792)

Common Name:
Nassau grouper, grouper, rockfish, hamlet.

Species Description:
Overall body color of Epinephelus striatus varies from tawny to pinkish red, with five dark vertical bars. The third and fourth bars branch above the lateral line and form a "W".  E. striatus can be distinguished from its congeners by several characteristics:  1) the third spire of the dorsal fin is longer than the second;  2) the interspinous membrane is slightly indented; and 3) the caudal fin is slightly emarginated (Jory and Iversen 1989). Although Nassau and red grouper are similar in overall appearance, Nassau grouper possesses a black saddle on top of the caudal peduncle, black spots around the eye and a distinctive tuning-fork shaped marking on top of the head.

Potentially Misidentified Species:
Epinephelus morio (Red grouper)

II.  HABITAT AND DISTRIBUTION 

Regional Occurrence:
Nassau grouper, along with black and red grouper, occur from New England to southeastern Brazil, throughout the Bahamas, Caribbean and Gulf of Mexico.  Occurrences of this species north of the Carolinas are probably the result of larval transport (Jory and Iversen 1989).  In Florida, Nassau grouper are most common in south Florida.  In east central Florida, they are not common. 

IRL Distribution:
Epinephelus striatus has been infrequently observed (Gilmore 1977) in the IRL.  Juveniles may sometimes be found in grass beds, inlet areas, and in nearshore habitats; while adult fish are typically observed in rocky reefs offshore to 100 meter depths.

III. LIFE HISTORY AND POPULATION BIOLOGY

Age, Size, Lifespan:
Epinephelus striatus first matures at or before about 48 cm total length (TL) and approximately 180 g (Thompson and Munro 1978). It is estimated that Nassau Grouper can grow between 1.92 - 4.55 mm per month, depending on initial size, with smaller size fish (175 - 200 mm) growing faster than larger size fish (326 - 451 mm) (Randall 1962 as cited in Jory and Iversen 1989).

When reared from eggs, larval Nassau grouper began transformation to the juvenile stage at 42 days post-hatching, and had finished the transformation as early as 46 days post-hatching and as late as 70 days post-hatching. After 98 days, juvenile Nassau grouper measured 49 - 95 mm TL and weighed 1.7 - 12.8 g.  After 243 days post-hatching, total lengths were 81 - 203 mm, and weights ranged from 7.0 - 143.1 g (Tucker and Woodward 1993).

Abundance:
Epinephelus striatus is an infrequently observed species in the Indian River Lagoon;  however, it is common throughout much of its range, especially in Bermuda and the Bahamas.

Locomotion:
Transport of settlement-stage Epinephelus striatus was studied in Exuma Sound, Bahamas. Transport of fish took place in tidal passes between islands during flood tides on moonless nights. Most recruitment of Nassau grouper during this particular study took place during a 4 day storm which resulted in considerable cross-shelf transport of water. It was suggested that the unpredictable nature of this transport could be an underlying factor in the interannual recruitment variability of fish (Shenker et al 1993). Another study at Lee Stocking Island, Exumas, Bahamas in January 1989 and 1990, showed that ingress of pelagic Nassau Grouper though tidal channels lasted about one week and occurred during nocturnal flood tides. By back calculating from otolith incrementation, spawning was estimated to have taken place at the time of the full moon in December. A larval life of 37 - 45 days was also estimated (Colin et al 1997).

Reproduction:
Spawning aggregations in Nassau grouper have been known for some time throughout the tropical western Atlantic and can be as large as 100,000 individuals (Smith 1972). Aggregations of Nassau grouper are often exploited by local fishermen (Tucker et al 1993). Spawning aggregations have been documented in Bimini and southern Berry Islands, Bahamas as well as in Belize, all during the full moon in January (Smith 1972; Bannerot 1984 and Miller 1984 as cited in Jory and Iversen 1989); and off Bermuda (Burnett-Herkes 1975 as cited in Jory and Iversen 1989); and the Virgin Islands (Olsen and LaPlace 1978). Water temperatures of 25 - 26 °C appear to be the one environmental factor common to ripe and spawning Nassau grouper throughout its range (Colin 1992; Tucker et al. 1993). 

An aggregation of Nassau grouper was described at the eastern ends of the Cayman Islands, but spawning activity was not observed. The aggregation occurred around the time of the full moon in January when Nassau grouper migrated upcurrent to the eastern ends of the islands. The full moon was considered to be a superior spawning cue primarily for migrating and spawning adults to coordinate their activities. It was suggested that Cayman Island populations of Nassau grouper could be self-recruiting (Colin et al 1987). In a later study, Colin (1992) described reproductive behavior in Nassau Grouper on Long Island, Bahamas, during the winters of 1987 - 1988 and 1988 - 1989: Groupers (~500 individuals per site) aggregated at two sites in December and January shortly before or at the time of the full moon. Water temperature was 25.0 - 25.5 °C. There was no size difference between males and females between months or years. Female to male sex ratios were approximately 5:1 and 3:1. Courtship took place in late afternoon and spawning began before sunset. Distinct coloration patterns of males and females representing spawning subgroups of 3 - 25 fish were described. A bicolor pattern was displayed by both female and male fish thought to be submissive. A dark phase is displayed by female Nassau grouper that are followed by bicolor fish in courtship. These dark phase females take the lead in spawning events. Release of gametes (noted by presence of sperm clouds) takes place well above the bottom, at 3 - 15 meters.  At these study sites, drogue releases indicated that larvae would be retained nearshore for about one week.  The larval period lasts for 35 - 40 days (Colin 1992).

Nassau groupers are considered an excellent candidate for development as an aquaculture species.  Human chorionic gonadotropin (HCG) has been used successfully to induce spawning in Nassau grouper (Tucker et al 1991).

When reared from captive fish, hatching of planktonic eggs took place one day after fertilization and juveniles settled 46 - 70 days later (Tucker and Woodward 1993). Nassau groupers 445 mm standard length (SL) can produce over 785,000 planktonic eggs, 0.90 - 1.02 mm in diameter (Smith 1961and Manday and Fernandez 1966 as cited in Jory and Iversen 1989). Egg and larval stages have been described (Manday and Fernandez 1966; Powell and Tucker 1992). 

Embryology:
Egg and larval phase are described by Powell and Tucker (1992). They report egg diameters from laboratory reared specimens of Nassau grouper averaging 0.92 mm and ranging from 0.86 - 0.97 mm in diameter.  A single oil globule, 0.24 mm in diameter was present.  Planktonic eggs hatched at 27 - 29 hours post fertilization at 25 °C and 23 - 25 hours at 28 °C.  Newly hatched larvae were 1.7 - 1.8 mm in notochord length (Powell and Tucker 1992).   

A hatchery study indicated that a temperature of 26 °C was preferable to higher temperatures for both incubating eggs and  rearing first-feeding larvae. Eggs were spawned from captive adult Nassau grouper and reared at three temperatures, 26, 28 and 30 °C at 37 ppt salinity on a 12:12 hour photoperiod.  Although hatching success did not vary, incubation time to hatching decreased with increasing temperature, from 24.9 hours at 26 °C to 20.4 hours at 30 °C.  Development time to first feeding stage also decreased as temperatures increased, from 86 hours at 26 °C to 71 hours at 30°C. However, survival of pre-feeding larvae declined at elevated temperatures. Lower temperatures were also shown to delay starvation of first-feeding stage fish (Watanabe et al 1995). A larval life of 37 - 45 days was estimated (Colin et al 1997).

 Johnson and Keener (1984) published a guide for differentiating larvae of American grouper, including the Nassau grouper.

IV.  PHYSICAL TOLERANCES

Salinity: 
Nassau grouper are euryhaline. It has been reported that Nassau grouper lived for an extended period in the old New York Aquarium where water was occasionally fresh (Townsend 1905 as cited in Jory and Iversen 1989).

V.  COMMUNITY ECOLOGY

Trophic Mode:
The diet of larger grouper over  300 mm  Standard Length (SL) vs. smaller Nassau grouper consisted of proportionately more fish (53 %) than crustaceans (39 %). Gut content analyses of 150 Nassau grouper revealed parrot-fishes, wrasses, damselfish, squirrelfish snapper and grunts. Crustaceans included crabs, stomatopods, hermit crabs, panulirid lobsters, and both caridean and penaid shrimp (Randall 1965).

In a feeding ecology study of recruitment in early-juvenile Nassau grouper (20.2 - 27.8 mm S L), gut content analysis revealed evidence of filter and particulate feeding as well as piscivory. Food items ranged from dinoflagellates (80 um in length) to larval fish as large as 9.4 mm SL, thus indicating substantial trophic plasticity during this transitional phase (Grover 1993), which takes place over the period of approximately one week (Grover et al 1998).  When Nassau groupers were in the transition phase from pelagic (pre-settlement) to demersal (post-settlement), it was found that pelagic fish consumed calanoid and poecilostomatoid copepods as well as decapod larvae. The diet of demersal  Nassau groupers consisted of gammaridean amphipods and harpacticoid copepods. Six months post-settlement, the diet of these juvenile groupers was comprised mainly of gammaridean amphipods, but mysids and isopods increased in importance.  

In a hatchery based study, survival of larval Nassau grouper was greater when larvae were fed smaller sized (117 um) as opposed to larger sized (161 um) rotifers (Watanabe et al 1996). 

Predation: 
Predation in groupers is not well documented, but small sized grouper are probably preyed upon by moray eels as well as by larger grouper (Smith 1961 as cited in Jory and Iversen 1989).  Sandbar sharks and the great hammerhead shark have been reported to prey on large grouper (Thompson and Munro 1978 as cited in Jory and Iversen 1989). Yellowtail snapper were seen preying on freshly released Nassau grouper eggs in the Bahamas (Colin 1992).

Competitors:
Because of habitat overlap in groupers, interspecific competition for food and space is probably common (Thompson and Munro 1978). Jacks, snappers, barracudas and shark are also considered likely competitors for food (Jory and Iversen 1989).

Habitat:
Nassau grouper (like other grouper) are considered cryptic, occupying crevices and caves along ledges and reefs as well as shipwrecks (Smith 1961 as cited in Jory and Iversen 1989).

Juvenile Nassau grouper are common in seagrass beds of south Florida (Jory and Iversen 1989). Nassau grouper has been documented in the Indian River Lagoon, FL (Gilmore 1977). 

Activity Time:
While grouper are known to feed during the day as well as at night, they are more likely to be actively feeding at dawn and at  dusk (Randall 1967 as cited in Thompson and Munro 1978).

Associated Species:
Nassau grouper on coral reefs take advantage of the symbiotic cleaning behavior of gobies and shrimp, allowing these animals to remove parasitic isopods from their bodies, fins, mouths and gill chambers (Bohlke and McCosker 1973; Darcey et al 1974; Sargent and Wagenbach 1975).

VI. SPECIAL STATUS

Special Status:
Fisheries

Fisheries Importance:
Nassau grouper is the most economically important fish in the Bahamas (Colin 1992). In Florida, however, Nassau grouper are not frequently observed, and thus are not considered a viable fishery species.  However, groupers as a whole are economically important in Florida, and accounted for approximately $18 million in revenues from tourism and recreational fishing activities in 1999.  They are also considered excellent candidates for development as an aquaculture species. 

The statewide commercial catch of Nassau grouper, Epinephelus striatus, between the years 1987 - 2001 was $42,123 pounds, with a dollar value of $70,044.  Within the 5 county area encompassing the IRL (Volusia, Brevard, Indian River, St. Lucie and Martin Counties) the commercial catch of Nassau grouper during this time period accounts for only 6% of the statewide total, with a harvest of 2,784 pounds, and a value of $4,275.   This ranks the Nassau grouper ninety-second  in commercial value within IRL counties, and ninety-fifth in pounds harvested.   

Figure 1 below shows the dollar value of the Nassau grouper to IRL counties by year.  As shown, the commercial fishery for this species essentially ended in 1993.  Before 1993, Nassau grouper accounted for only a small fraction of the commercial catch across all species, barely averaging a value of $800 per year. 

Figure 1.   Annual dollar value of the commercial catch of Nassau grouper to the 5-county
        area of the Indian River Lagoon. 
 

Figure 2.  Total Nassau grouper dollar value and percentage by county for the years
     1987 - 2001.

Table 1.  Total dollar value of the IRL harvest of Nassau grouper, Epinephelus striatus,
     between 1987 -2001.

Table 2.  By-county annual and cumulative percentages of the Nassau grouper harvest for the
     years 1987-2001.