Species Description: Black grouper, Mycteroperca bonaci, is a robust, oblong grouper that grows to a total length (TL) of approximately 133 cm (4.4 feet). Body depth is less than the length of the head, which is convex in profile. The lower jaw projects beyond the upper. The jaws have well developed canine teeth anteriorly, with teeth also on the palatine bones. Scales are large and ctenoid. The preopercule is evenly rounded with no notch or lobe at the angle. The nostrils are subequal. There are 8-12 gill rakers on the lower limb of the gill arch. The dorsal fin has 11 spines, with 15-17 soft rays. The interspinous membrane is deeply incised. The anal fin has 3 spines and 11 - 13 soft rays. The pectoral fins have 16-17 rays. Both the dorsal and anal fins are somewhat rounded at the margins, but the caudal fin is truncate. There are 78-83 lateral line scales (Heemstra and Randall 1993).
Body color varies greatly depending on hormonal levels and activity of the fish (Bohlke and Chaplin 1964; Fischer 1978) but is typically light tan or olive to gray or dark brown marked with irregular brassy/bronze, somewhat rectangular blotches and spots. Reticulations are separated by slightly bluish markings. Spots may join to form horizontal streaks along the sides. The soft dorsal, anal, and leading edge of pelvic fin all have dark margins, while the pectoral fin has a narrow orange margin.
Potentially Misidentified Species: Black grouper, Mycteropera bonaci, are easily confused with 2 related species: the gag, M. microlepis, and the yellowfin grouper, M. veneosa. Black grouper are more easily distinguished from yellowfin grouper due to their having a straighter caudal fin and rows of rectangular spots and blotches, which tend to be larger and more defined than in the yellowfin grouper. Black grouper also have a narrow, orange outer margin on the pectoral fins, while the yellowfin grouper has a wide, yellow pectoral margin (Bohlke and Chaplin 1964; Fischer 1978).
Small black grouper are difficult to distinguish from gag less than 40 cm because gag at that size are similar in overall coloration and marking pattern and have not yet developed the characteristic notch and rounded lobe at the angle of the preopercule. Scale counts separate the black grouper from the gag; the black grouper having 78-83 lateral line scales, while the gag has 88-96.
Regional Occurrence: Mycteroperca bonaci ranges from New England south through Bermuda, Florida, the Gulf of Mexico, the Bahamas, and the Caribbean, to southeastern Brazil (Bohlke and Chaplin 1968, Fischer 1978). However, occurrences of this species north of the Carolinas are thought to be due to larval transport in the Gulf Stream current rather than from immigration of adults (Thompson and Munro 1978).
Black grouper are abundant in south Florida, the Florida Keys, Cuba and the Bahamas, but are somewhat less common in the eastern Gulf of Mexico (Randall 1968; Smith et al. 1975; Jory and Iversen 1989).
IRL Distribution: Juvenile black grouper are found infrequently in seagrasses and oyster reefs within the IRL, but can be common in seagrasses in south Florida. Adults are not generally found within the confines of the IRL, but can be common in offshore hard bottom and reef areas 10 - 30m (32 - 98 feet) or more in depth.
Age, Size, Lifespan: Mycteroperca bonaci attains a maximum size of approximately 133 cm (4.4 feet) TL and 81 kg (178.6 pounds) (Mowbray 1950). However, most are caught at less than 70 cm (2.3 feet) TL and weigh less than 26 kg (57 pounds). They may live 33 years or longer (Crabtree and Bullock 1998).
Crabtree and Bullock (1998) reported that black grouper in south Florida grow rapidly throughout the first 10 years, with growth slowing thereafter. Manooch and Mason (1987) back-calculated total lengths for black groupers, and reported that growth in length is greatest in the first 3-4 years, gradually slowing as fish age. The following table summarizes their calculations:
|Age (years)||Total Length (cm)||Total Length (inches)|
Reproduction: Black grouper, like most serranid fishes, are protogynous hermaphrodites, beginning life as females, with some later transforming into males. Brule et al. (1993) examined reproduction of black grouper in Campeche Bay, Mexico.
Fish collected from inshore waters tended to be entirely female, while those collected offshore were 75.1% female, 24.3% male and 0.6% transitional. Females ranged in size from 57 - 123.5 cm (22.4 - 48.6 inches), males from 86.0 - 132.0 cm (33.9 - 52 inches), and transitional fish from 99.0 - 121.5 cm (39 - 47.8 inches). The overall sex ratio was 1 male for every 4 females.
The size at which 50% of females were sexually mature was 72.1 cm (28.4 inches), lower than for black grouper in Florida, which matured at 82.6 cm (32.5 inches) or those in Cuba, which matured at 84.4-108.7 cm (33.2 - 42.8 inches) (Brule et al. 1993). Sexual transition occurred when females reached 85.5 - 125.0 cm (33.7 - 49.2 inches) in length, with a 50% transition to male at a length of 111.4 cm (43.9 inches) fork length (FL). This figure is lower than has been reported for black grouper in Florida waters, where 50% of females have transitioned to male at a length of 119.9 cm (47.2 inches) (Brule et al. 1993).
Reproduction in Mycteroperca bonaci is seasonal in south Florida, peaking in December - March, though females with vitellogenic eggs are present in all months (Crabtree and Bullock 1998). In Puerto Rico, spawning has been reported to occur as early as February (Erdman 1956). In Bermuda, the spawning season extends from May through August (Smith 1971).
Estimated fecundity of an 80.5 cm (31.6 inches) female black grouper was reported by Smith (1961) as 503,534 eggs.
Embryology: Eggs are pelagic and hatch into larvae having greatly elongated, serrate spines. In groupers, the second dorsal fin spine as well a pelvic fin spine extend outward to discourage predation on larvae.
Temperature: Black grouper have been reported to depths of 151m (495 feet) (Moe 1969) where bottom temperatures ranged from 16 - 28 °C (60.8 - 82.4 °F).
Physical Tolerances: Stout (1980) reported black grouper from the southeastern United States had an average of 0.009 ppm DDT in their tissues, and up to 0.059 ppm PCB's compared to other fishes.
Trophic Mode: All groupers are unspecialized and opportunistic in their feeding behaviors. Black grouper are among the top predators in reef community food webs and may control some aspects of community balance in reef systems (May et al. 1979). Adults prey primarily on other fishes, while juveniles prey tend to prey more on various crustaceans.
Randall (1968) reported that body conformation and the level of development of the canine teeth in black grouper suggested a more piscivorous diet in comparison to other groupers. Analysis of stomach contents of black grouper revealed the presence of clupeoid fishes, grunts, cornetfish, and pink shrimp (Costello and Allen 1970).
Competitors: Groupers likely compete interspecifically due to overlapping food habits, space, and habitat requirements (Thompson and Munro 1978). Groupers are also likely to compete for prey with other large species such as jacks, snappers, barracuda, and sharks.
Predators: Predators of smaller groupers include other groupers and moray eels. Larger groupers are likely preyed upon by sharks, among them the sandbar shark, Carcharhinus plumbeus; and the great hammerhead, Sphryna mokarran (Compagno 1984).
Parasites: Groupers are susceptible to a number of parasites, including trematodes, cestodes, and nematodes (Manter 1947; Overstreet 1968) which affect the stomach and intestines. Major parasites include the digenetic trematodes of the genera Lecithochirium, Postporus, and Prosorhynchus (Overstreet 1968).
Habitats: Adult Mycteroperca bonaci prefer rock bottoms, drop-off walls, and coral reefs to depths of 10-30 m (32 - 98 feet) (Fischer 1978; Heemstra and Randall 1993). In the eastern Gulf of Mexico, Bullock and Smith (1991) found that black groupers tend to be found in waters deeper than 30m (98 feet). Smaller black grouper tend to be found in shallower waters then are adults. Young juveniles are commonly encountered in seagrass beds in south Florida. Springer and McErlean (1962) reported collecting juvenile black grouper less than 24 cm (9.4 inches) standard length (SL) in seagrasses in the Florida Keys. Most grouper species move to progressively deeper waters as they age (Jory and Iversen 1989), but can remain site-specific for long periods of time (Beaumariage and Bullock 1976). Moe (1969) reported black grouper to depths of 151 m (495 feet).
Activity Time: Randall (1967) reported black groupers to feed actively at both dawn and dusk.
Fisheries Importance: Commercial Fishery
Though not as important a fishery in east central Florida as it is further to the south, black grouper have comprised a significant percentage of the grouper fishery in some years within the Indian River Lagoon. From 1987 - 2001, 11.4 million pounds of black grouper with a commercial value of $23.6 million were commercially harvested in Florida waters. Of this, the 5 county area encompassing the IRL (Volusia, Brevard, Indian River, St. Lucie and Martin Counties) accounted for 557,735 pounds of black grouper, only 4% of the statewide total. However, even this small percentage of the total harvest was commercially valued at $1.05 million. This ranks the black grouper thirty-seventh in commercial value, and forty-sixth in pounds harvested.
Figure 1 below shows the dollar value of the black grouper fishery to IRL counties by year. The commercial black grouper fishery ranged in value from a high of $345,120 in 1987 to a low of $7,529 in 2001. As shown in Figure 1 below, the only years with a commercial harvest that exceeded $100,000 were 1987 - 1988. Volusia County accounted for more than half of the total catch in both of those years, with Indian River County accounting for almost 30% in 1987. Note, however, that catch rates drop dramatically from 1988 - 1992, and then fall off again to less than $20,000 per year for the remainder of the study period.
Volusia County accounted for nearly half of the commercial harvest, followed by Brevard, with 64% and 21% of the catch respectively (Figure 2). From 1987 - 2001, the annual dollar value to Volusia county ranged from $591 to $214,210, averaging $34,028. In Brevard County, the annual dollar amount ranged from $0 to $70,653, averaging $14,488. The remaining counties collectively account for the remaining 15% of the commercial harvest, with Indian River County taking in $112,054; St. Lucie County taking in $189,678, and Martin County taking in $25,238.
|VOLUSIA||BREVARD||INDIAN RIVER||ST. LUCIE||MARTIN||TOTAL|
|YEAR||Value ($)||Value ($)||Value ($)||Value ($)||Value ($)||Value to IRL|
|VOLUSIA||BREVARD||INDIAN RIVER||ST. LUCIE||MARTIN|
|YEAR||% Total||% Total||% Total||% Total||% Total|
|Volusia||Brevard||Indian River||St. Lucie||Martin|
Within the 5-county area of the Indian River Lagoon, recreational anglers captured more than 37,600 black grouper (Table 4). Figure 3 below shows the annual recreational landings of black grouper between 1997 - 2004. The bulk of the recreational catch (62.2%) is taken in waters 3 - 200 miles offshore. Approximately 32.3% of the recreational catch is harvested from the shoreline to 3 miles offshore. Anglers fishing within the confines of the Indian River Lagoon accounted for 3.7% of the recreational harvest, and other East Florida inland waters accounted for 1.7% of the harvest.
|To 3 Miles||To 200 Miles||Other Inland||IRL||TOTAL|
|To 3 Miles||To 200 Miles||Other E. FL Inland||IRL|
|% Total||% Total||% Total||% Total|
|To 3 Miles||To 200 Miles||Other Inland||IRL|
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