Smithsonian Marine Station at Fort Pierce

Website Search Box

Advanced Search


The Gag Grouper, Mycteroperca microlepis. Illustration by Diana Rome Peebles 1998. Courtesy of Florida Fish and Wildlife Conservation Commission, Division of Marine Fisheries.

Species Name: Mycteroperca microlepis Goode and Bean, 1880
Common Name: Gag
Gag grouper
Velvet rockfish
Charcoal belly
Synonymy: Trisotropis microlepis Goode and Bean, 1879
  1. TAXONOMY

    Kingdom Phylum/Division Class: Order: Family: Genus:
    Animalia Chordata Osteichthyes Perciformes Serranidae Mycteroperc

    Other Taxonomic Groupings

    Superclass: Osteichthyes
    Subclass: Neopterygii
    Infraclass: Teleostei
    Superorder: Acanthopterygii

    Species Description

    The gag, Mycteroperca microlepis is an oblong, robust grouper that may reach 96 cm (38 inches) total length (TL) and 23 kg (50 lbs). Body depth tends to be somewhat shallower than the length of the head, which is convex in profile. The lower jaw projects beyond the upper. Canine teeth are well developed on both the jaws and palatines. Scales are ctenoid and smooth, except for those on the pectoral fins. There are 88 - 89 lateral line scales. Fishes larger than 40 cm (15.7 inches) SL, develop a rounded lobe at the angle of the preopercule that bears large serrae. In adult fishes, the posterior nostrils are larger than anterior ones. There are 16 gill rakers on the lower limb of the gill arch. The dorsal fin is rounded and continuous, with 11 spines in the anterior portion and an interspinous membrane that is deeply incised. The soft dorsal has 16-18 soft rays. The rounded anal fin has 3 spines and 10 - 12 soft rays.

    Body color differs somewhat based on sex, age, and activity level. Adult females and juveniles are typically a pale gray to brown-gray with darker blotches and vermiculations that lend a marbled appearance to the dorsal surface and sides. The pelvic, anal and caudal fins have black-blue outer margins. In resting fishes, a camouflage pattern is often observed: 5 dark brown "saddles" separated by white bars below the dorsal fin. Large adult males are generally pale to medium gray in color, with faint reticulations below the dorsal fin. The ventral surface is darker gray or black, as is the margin of the soft dorsal fin, caudal fin, and posterior margins of the pectoral and pelvic fins. Some also exhibit a "black-back" phase in which the posterior body, dorsal caudal peduncle, and all of the soft dorsal and anal fins are black.

    Potentially Misidentified Species

    Juveniles under 40 cm (15.7 inches) standard length (SL) that have not yet developed the rounded lobe on the preopercule are often confused with a related species, the black grouper, Mycteroperca bonaci. However, the gag and black grouper are easily distinguished based on a scale count along the lateral line: M. bonaci has 78-83 lateral line scales, while M. microlepis has 88-89.

  2. HABITAT AND DISTRIBUTION

    Regional Distribution

    Gag groupers range from North Carolina south through Florida, the Gulf of Mexico, Yucatan Peninsula, as far south as Brazil. Juveniles have been observed as far north as Massachusetts and New York. Gag are rare in Bermuda, and are generally absent from the West Indies (Smith 1971; McGovern 1998).

    IRL Distribution

    Juvenile gag are common throughout the Indian River Lagoon in seagrass beds. Adults are more common in nearshore and offshore areas, but can be common in the vicinity of inlets.

  3. LIFE HISTORY AND POPULATION BIOLOGY

    Age, Size, Lifespan

    Gag are a long-lived, slow growing species that reach approximately 120 - 127 cm (50 inches) total length (TL) (Manooch and Haimovici 1978; Collins et al. 1987; IGFA 2001 ) and live 21 - 22 years. Gag grow 28 - 41 cm (11 - 16 inches) by age 1; approximately 79 cm (31 inches) by age 6; and 102 cm (40 inches) by age 10 (Manooch and Haimovici 1978; Hood and Schlieder 1992; Schirripa and Burns 1997). The International Game Fish Association (2001) reports that the largest gag grouper on record was a 145 cm (4.7 feet) male. Maximum reported weight for a gag was 36.5 kg (80.5 pounds) (IGFA, 2001).

    Abundance

    The gag is the most common grouper species on rocky ledges in the Gulf of Mexico. Beaumariage (1969) reported that after leaving seagrass nursery habitats, gag that take up residence on reefs and ledges and thereafter, show some degree of site specificity. Individuals may be solitary or can occur in groups numbering 50 or more individuals (Heemstra and Randall 1993).

    Gag dominate the seabass fishery on the Atlantic coast, and are second only to the red grouper (Epinephelus morio)in the Gulf of Mexico.

    Reproduction

    Gag are protogynous hermaphrodites that begin life as female. The ovary is a bilobed sac that is joined in the posterior to the oviduct. Mature females have oocytes arrayed in lamellae that surround a central lumen. Along the periphery of the lamellae is dormant spermatogenic tissue. After spawning as a female for one or more seasons, some gag change sex and function as males thereafter. When sex transition occurs, oocytes degenerate and spermatogonia become active, thus transforming the ovary into a testis (Heemstra and Randall 1993).

    Analysis of sex ratios of gag in the South Atlantic Bight from 1976-1982 revealed that 84% of the population was female, 15% was male, and 1% was transitional (Collins et al. 1987). However, in a subsequent study, McGovern et al. (1998) reported that the population of males in southern Florida waters has decreased to approximately 5.5%, most likely due to fishing pressures focused on large males, which are preferentially removed from the population. In the McGovern study (1998), the relative abundance of males was greater off Florida than any other southern state, with northern Florida accounting for the highest population of male gag.

    Female gag mature between Age 5 and 6, when they reach approximately 67 - 75 cm total length (TL). Fecundity of a 95 cm female gag was estimated at 1.5 million eggs (Collins et al. 1987). Sex transition in females can occur as early as Age 5, but typically takes place when females are 10 - 11 years old, and reach 95 - 100 cm TL. No males younger than ages 5 - 7 are present in most populations (Collins et al 1987; Hood and Schlieder 1992; Collins et al. 1998).

    In the South Atlantic Bight, annual migrations occur in late winter, bringing reproductive fishes to offshore spawning grounds where water depth is approximately 70 m (230 feet). Spawning occurs from December through May (Hood and Schlieder 1992), and peaks in late March and early April (Collins et al. 1987).

    Gag in spawning condition are observed at different times during the season, depending on location. In central and southern Florida, reproductive fishes are observed throughout the entire spawning period; In northern Florida waters, reproductive fishes are observed from January through May, while in South Carolina, most reproductive fishes are observed from January through April (McGovern et al 1998).

    In the eastern Gulf of Mexico, spawning, occurs from late December through April, peaking in February and April (Hood and Schlieder 1992, Bullock and Smith 1991; Collins et al. 1998).

    Following spawning, in May and June, females tend to move to shallower waters where water depth is less than 30 m. Conversely, large males become solitary and move into deeper waters of 50 - 90 m depths. (McGovern et al 1998).

    Embryology

    Fertilized eggs are pelagic and transparent, measuring approximately 0.70 - 1.20 mm (0.02 -0.07 inches) in diameter, with a smooth chorion and a single oil globule. Eggs hatch in approximately 45 hours under laboratory conditions where water temperature was held at 21°C (Roberts and Schlieder 1983). Larvae are kite-shaped, with the second dorsal spine and the pelvic spine greatly elongated. Larvae persist for 40 - 50 days (McErlean 1963), during which time they are transported to estuarine nursery habitats. Peak recruitment of postlarvae to seagrasses, mangrove creeks, oyster reefs and salt marshes in coastal lagoons and estuaries occurs in April and May (Ross and Moser 1995). Juveniles remain 3 - 5 months in seagrass nursery habitats before migrating to offshore reefs and ledges, typically by fall of the year (Ross and Moser 1995; McErlean 1963).

  4. PHYSICAL TOLERANCES

    No information is available at this time

  5. COMMUNITY ECOLOGY

    Trophic Mode

    Adult Mycteroperca microlepis feed primarily on fishes but are known to also prey upon crabs, shrimps and cephalopods. Of primary importance in the diet are fishes of the families Clupeidae, Carangidae, Sparidae, Sciaenidae, and Mugilidae. Juveniles measuring less than 20 cm (7.8 inches) in length feed on crustaceans that occur in seagrass, mangrove and oyster reef habitats (Naughton and Saloman 1985; Heemstra and Randall 1993)

    Habitats

    Eggs and early larval stages of Mycteroperca microlepis are pelagic. Postlarvae recruit to estuaries and coastal lagoons where they inhabit seagrasses, saltmarshes, oyster reefs and mangrove creeks for 3-5 months. Early juveniles utilize seagrasses, oyster beds and rock bottoms.

    (Ross and Moser 1995; McErlean 1963). As they grow, later juveniles migrate to offshore reefs and ledges (Bullock and Smith 1991). Adults are typically found in offshore reefs and hardbottom areas, shipwrecks, coral reefs, and rock ledges in depths of 40 -100 m (100 - 329 feet) (McErlean 1963; Bullock and Smith 1991; Heemstra and Randall 1993).

    Gag are the most common groupers on rocky ledges in the eastern Gulf of Mexico. Adults are either solitary or in groups of 5 to 50 individuals (Heemstra and Randall 1993).

  6. ADDITIONAL INFORMATION

    Fisheries Importance

    Commercial Fishery
    Mycteroperca microlepis is ranked among the most valuable finfishes in the southeastern United States (Heemstra and Randall 1993), both commercially and recreationally. Fishing pressure is intense on gag in all seasons, but populations may be especially vulnerable from late fall through early spring, when large numbers of gag aggregate offshore for spawning. Some evidence indicates that fishing pressures on spawning aggregations may adversely impact population size, sex ratio, genetic diversity and behavior due to the selective removal of large, aggressive males (Smith et al 1991; Gilmore and Jones 1992; Carter et al. 1994; Coleman et al 1996).

    Total landings of gag in Florida during 2001 were 7,815,061 pounds, with the recreational fishery accounting for 56%, or approximately 4.2 million pounds. From 1987 - 2001, the statewide commercial catch of gag in Florida totaled 28.3 million pounds, and was valued at over $64.4 million.

    Within the 5 county area encompassing the IRL (Volusia, Brevard, Indian River, St. Lucie and Martin Counties) the commercial catch of Mycteroperca microlepis accounts for only 7% of the statewide total, with a harvest of 1.9 million pounds, and a value of approximately $4.3 million. This ranks the gag sixteenth in commercial value within the IRL, and twenty-sixth in pounds harvested.

    Figure 1 below shows the dollar value of the gag grouper fishery to IRL counties by year. As shown, catch rates are relatively stable from year to year, but began to decrease slightly beginning in 1999. The commercial value of the gag harvest ranged from a low of $144,418 in 1988 to a high of over $460,516 in 1998
    (Table 1). Volusia and Brevard Counties account for the bulk of the commercial harvest, with 52% and 27% of the catch respectively (Figure 2). From 1987 - 2001, the annual dollar value to Volusia county ranged from $50,844 to $227,129, averaging $147,000. In Brevard County, the annual dollar amount ranged from $44,834 to $144,223, averaging $76,175. The remaining counties collectively account for the remaining 21% of the commercial harvest, with Indian River County taking in $155,637; St. Lucie County taking in $466,262, and Martin County taking in $300,703. Note, however, that the gag harvest in Martin County begins to increase after 1991, nearly tripling between 1990 and 1991. Indian River county follows a similar trend, with the commercial harvest doubling between 1991 - 1992, and doubling again between 1994 - 1995.


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

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

    VOLUSIA BREVARD INDIAN RIVER ST. LUCIE MARTIN TOTAL
    YEAR Value ($) Value ($) Value ($) Value ($) Value ($) Value to IRL
    1987 $93,659 $89,452 $5,350 $53,463 $377 $242,301
    1988 $50,844 $54,196 $1,759 $37,589 $30 $144,418
    1989 $132,451 $56,023 $108 $29,711 $2,710 $221,003
    1990 $187,377 $46,451 $1,226 $14,054 $4,124 $253,232
    1991 $178,609 $24,390 $2,171 $20,192 $3,386 $228,748
    1992 $227,129 $44,834 $4,868 $19,916 $11,837 $308,584
    1993 $175,136 $77,910 $5,346 $30,872 $27,274 $316,538
    1994 $128,226 $84,754 $7,099 $30,304 $38,744 $289,127
    1995 $224,742 $67,669 $15,380 $15,672 $19,739 $343,202
    1996 $151,198 $69,508 $19,720 $29,505 $38,955 $308,886
    1997 $155,148 $104,003 $21,332 $16,448 $37,234 $334,165
    1998 $160,536 $144,223 $33,152 $78,181 $44,424 $460,516
    1999 $83,886 $113,273 $9,737 $26,914 $21,832 $255,642
    2000 $137,334 $84,077 $12,047 $22,505 $22,226 $278,189
    2001 $120,330 $81,872 $16,378 $40,936 $27,811 $287,327
    Cumulative Totals: $2,206,605 $1,142,635 $155,673 $466,262 $300,703 $4,271,878
    Table 1. Total dollar value of IRL gag grouper, Mycteroperca microlepis between 1987 - 2001.


    VOLUSIA BREVARD INDIAN RIVER ST. LUCIE MARTIN
    YEAR % Total % Total % Total % Total % Total
    1987 38.65% 36.92% 2.21% 22.06% 0.16%
    1988 35.21% 37.53% 1.22% 26.03% 0.02%
    1989 59.93% 25.35% 0.05% 13.44% 1.23%
    1990 73.99% 18.34% 0.48% 5.55% 1.63%
    1991 78.08% 10.66% 0.95% 8.83% 1.48%
    1992 73.60% 14.53% 1.58% 6.45% 3.84%
    1993 55.33% 24.61% 1.69% 9.75% 8.62%
    1994 44.35% 29.31% 2.46% 10.48% 13.40%
    1995 65.48% 19.72% 4.48% 4.57% 5.75%
    1996 48.95% 22.50% 6.38% 9.55% 12.61%
    1997 46.43% 31.12% 6.38% 4.92% 11.14%
    1998 34.86% 31.32% 7.20% 16.98% 9.65%
    1999 32.81% 44.31% 3.81% 10.53% 8.54%
    2000 49.37% 30.22% 4.33% 8.09% 7.99%
    2001 41.88% 28.49% 5.70% 14.25% 9.68%
    Table 2. By-county annual and cumulative percentages of the gag grouper harvest for the years 1987-2001.


    Volusia Brevard Indian River St. Lucie Martin
    Dollars $2,206,605 $1,142,635 $155,673 $466,262 $300,703
    % 51.7% 26.7% 3.6% 10.9% 7.0%
    Table 3. By-county cumulative dollar value and percentage of total for the gag grouper harvest from 1987 - 2001.


    Recreational Fishery
    The recreational fishery for gag accounted for 56% of statewide landings in 2001. Of this, approximately 89% of recreational landings were made on the Gulf coast of Florida. Within the 5-county area of the Indian River Lagoon, recreational anglers captured more than 166,000 gag. Figure 3 and Table 4 below show annual recreational landings of gag between 1997 - 2004. The bulk of the recreational catch (73.3%) is taken in waters 3 - 200 miles offshore. Approximately 15.5% 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 6% of the recreational harvest, and other East Florida inland waters accounted for 5.2% of the harvest.


    Figure 3. Survey data for the gag recreational fishery showing the number of fishes harvested in East Florida waters from 1997 - 2004.

    Figure 4. Summary of the gag recreational harvest and percentage of total by area from 1997 - 2004.

    To 3 Miles To 200 Miles Other Inland IRL TOTAL
    1997 6,752 3,398 3,267 1,593 15,010
    1998 881 16,912 1,319 19,112
    1999 5,215 27,420 2,505 686 35,826
    2000 2,710 11,747 2,711 17,168
    2001 862 22,157 121 2,841 25,981
    2002 1,074 10,693 1,263 13,030
    2003 3,030 18,229 1,785 23,044
    2004 5,296 11,353 425 17,074
    Total: 25,820 121,909 8,604 9,912 166,245
    Table 4. Summary data for recreational fishery in Eastern Florida waters for the gag, Mycteroperca microlepis, from 1997 - 2004. Data provided by National Marine Fisheries Service, Fisheries Statistics Division, NOAA.


    To 3 Miles To 200 Miles Other Inland IRL
    % Total % Total % Total % Total
    1997 44.98% 22.64% 21.77% 10.61%
    1998 4.61% 88.49% 0.00% 6.90%
    1999 14.56% 76.54% 6.99% 1.91%
    2000 15.79% 68.42% 15.79% 0.00%
    2001 3.32% 85.28% 0.47% 10.93%
    2002 8.24% 82.06% 0.00% 9.69%
    2003 13.15% 79.11% 0.00% 7.75%
    2004 31.02% 66.49% 0.00% 2.49%
    Table 5. By-county annual and cumulative percentages of the gag harvest for the years 1997 - 2001. Data provided by National Marine Fisheries Service, Fisheries Statistics Division, NOAA.


    To 3 Miles To 200 Miles Other Inland IRL
    No. Fish 25,820 121,909 8,604 9,912
    % 15.53% 73.33% 5.18% 5.96%
    Table 6. Summary of the gag recreational harvest and percentage of total fish captured in each area from 1997 - 2004. Data provided by National Marine Fisheries Service, Fisheries Statistics Division, NOAA.
  7. REFERENCES

    Adams, S.M., 1976. Feeding ecology of eelgrass fish communities.. Trans. Am. Fish. Soc. (4):514-519.

    Beaumariage, D.S. 1969. Returns of the 1965 Schlitz tagging program including a cumulative analysis of previous results. Fla. Board Conserv. Mar. Res. Lab. Tech. Ser. 59, 38 p.

    Beaumariage, D.S., and L.H. Bullock. 1976. Biological research on snappers and groupers as related to fishery management requirements. Fla. Sea Grant Prog. Rep. No. 17:86-94.

    Bullock, L.H., and G.B. Smith. 1991. Sea Basses (Pisces: Serranidae). Memoirs of the Hourglass Cruises. Marine Research Laboratory, Florida Dept. of Natural Resources, St. Petersburg, Florida. Vol. 8, Pt. 2. Pps. 1-205.

    Coleman, F.C., C.C. Koenig, and L.A. Collins. 1996. Reproductive styles of shallow-water groupers (Pisces: Serranidae) in the eastern Gulf of Mexico and the consequences of fishing spawning aggregations. Environ. Biol. Fishes 47:129 -141.

    Collins, L.A., A.G. Johnson, C.C. Koenig and M.S. Baker, Jr., 1998. Reproductive patterns, sex ratio, and fecundity in gag, Mycteroperca microlepis (Serranidae), a protogynous grouper from the northeastern Gulf of Mexico. Fish. Bull. 96:415-427

    Collins, M.R., C.W. Waltz, W.A. Roumillat, and D.L. Stubbs. 1987. Contribution to the life history and reproductive biology of gag, Mycteroperca microlepis (Serranidae), in the South Atlantic Bight. Fish. Bull. (U.S.) 85(3):648-653.

    Gilmore, R.G., and R.S. Jones. 1992. Color variation and associated behavior in the Epinepheline groupers, Mycteroperca microlepis (Goode and Bean) and M. phenax Jordan and Swain. Bull. Mar Sci., 51(1):83-103.

    Heemstra, P.C. and J.E. Randall, 1993. FAO species catalogue. Vol. 16. Groupers of the world (family Serranidae, subfamily Epinephelinae). An annotated and illustrated catalogue of the grouper, rockcod, hind, coral grouper and lyretail species known to date.. FAO Fish. Synop. 125(16):382 p.

    Hood, P.B. and R.A. Schlieder, 1992 Age, growth, and reproduction of gag, Mycteroperca microlepis (Pisces: Serranidae), in the eastern Gulf of Mexico. Bull. Mar. Sci. 51(3):337-352.

    IGFA, 2001 Database of IGFA angling records until 2001. IGFA, Fort Lauderdale, USA.

    Johnson, A.G., L.A. Collins and J.J. Isley. 1993. Age-size structure of gag, Mycteroperca microlepis, from the northeastern Gulf of Mexico. Northeast Gulf Science. 13(1)59-63.

    Keener, P., G.D. Johnson, B.W. Stender, E.B. Brothers, and H.R. Beatty. 1988. Ingress of postlarval gag, Mycteroperca microlepis (Pisces: Serranidae), through a South Carolina Barrier Island inlet. Bull. Mar. Sci., 42(3):376-396.

    Koenig, C.C. and F.C. Coleman. 1998. Absolute abundance and survival of juvenile gags in seagrass beds of the northeastern Gulf of Mexico. Trans. Am. Fish. Soc. 127:44-55.

    Lindberg, W., D.M. Mason, and D. Murie. 2002. Habitat-Mediated Predator-Prey Interactions: Implications for Sustainable Production of Gag Grouper in the Eastern Gulf of Mexico. Final Report to Florida Sea Grant. R/LR-B-49.

    Manooch, C.S. III. 1984. Fisherman's Guide. Fishes of the southeastern United States. North Carolina State Museum of Natural History Raleigh, North Carolina. Pp. 224-239.

    Manooch, C.S., and M. Haimovici. 1978. Age and growth of the gag, Mycteroperca microlepis, and size-age composition of the recreational catch off the southeastern United States. Trans. Am. Fish. Soc.,107:234-240.

    McErlean, A.J. 1963. A study of the age and growth of the gag, Mycteroperca microlepis Goode and Bean (Pisces: Serranidae) on the west coast of Florida. Florida Bd. Conserv., Mar. Lab. Tech. Ser., 41:1-29.

    McErlean, A.J., and C.L. Smith. 1964. The age of sexual succession in the protogynous hermaphrodite, Mycteroperca microlepis. Trans. Am. Fish. Soc., 93:301-302.

    McGovern, J.C., D.M. Wyanski, O. Pahuk, C.S. Manooch III, G.R. Sedberry. 1998. Changes in the sex ratio and size at maturity of gag, Mycteroperca microlepis, from the Atlantic coast of the southeastern United States during 1976 - 1995. Fish. Bull. 96:797-807.

    Mullaney, M.D., Jr. 1994. Ontogenetic shifts in the diet of gag, Mycteroperca microlepis (Goode and Bean) (Pisces: Serranidae). Proc. Gulf Caribb. Fish. Inst. 43:432-445.

    Naughton, S.P., and C.H. Saloman. 1985. Food of gag (Mycteroperca microlepis) from North Carolina and three areas of Florida. U.S. Dep. Commer. NOAA Tech. Memo. NMFS-SEFC-160, 36 p.

    Roberts, D.E., and R.A. Schlieder. 1983. Induced sex inversion, maturation, spawning and embryogeny of the protogynous grouper, Mycteroperca microlepis. J. World Maricult. Soc., 14:639-649.

    Ross, S.W., and M.L. Moser. 1995. Life history of juvenile gag, Mycteroperca microlepis, in North Carolina estuaries. Bull. Mar. Sci. 56(1):222-237.

    Smith, C.L. 1971. A revision of the American groupers: Epinephelus and allied genera. Bull. Am Mus. Nat. Hist., 146:1-241.

Report by: K. Hill, Smithsonian Marine Station
Submit additional information, photos or comments to
irl_webmaster@si.edu
Page last updated: June15, 2004

[ TOP ]