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Summer flounder, Paralichthys dentatus. Image courtesy NOAA, Chesapeake Bay Office of Fisheries.

Species Name: Paralichthys dentatus Linnaeus, 1766
Common Name: Summer flounder
Synonymy: None
  1. TAXONOMY

    Kingdom Phylum/Division Class: Order: Family: Genus:
    Animalia Chordata Actinopterygii Pleuronectiformes Paralichthyidae Paralichthys

    Other Taxonomic Groupings

    Subphylum: Vertebrata
    Superclass: Osteichthyes
    Subclass: Neopterygii
    Infraclass: Teleostei
    Superorder: Acanthopterygii
    Suborder: Pleuronectoideii

    P. dentatus is one member of a large family of distinctive benthic flatfishes that inhabit continental shore waters in the tropical and temperate zones of the Atlantic, Pacific and Indian oceans. Flatfishes such as the flounders are unlike most other fishes in that they begin life as bilateral animals, having equal right and left side, and swim as do other fishes. However, toward the end of the larval period, flatfishes settle to the benthos and take up a cryptic, somewhat sedentary lifestyle, lying on one side of the body, and swimming laterally to the substratum. Metamorphosis to the juvenile stage involves complex modification of the skeletal structure of the head, and rearrangement of the nervous system and muscle tissues. Additionally, the eye on the side that faces the substratum (termed the blind-side eye) begins to migrate to the upper side of the body. P. dentatus is a left-eye flounder, thus it lies on its right side, and at metamorphosis, the right eye migrates to the left side of the head. Lefteye flounders sometimes exhibit sexual dimorphism, with females having eyes that are closer together than in males, and males having somewhat longer pectoral fins (Rogers and Van Den Avyle 1983).

  2. HABITAT AND DISTRIBUTION

    Regional Occurrence

    Recorded range for this species is from Maine to Cape Canaveral, Florida (Powell and Henley 1995).

    IRL Distribution

    P. dentatus can be common throughout the Indian River Lagoon, however, it is most common north of Cape Canaveral.

  3. LIFE HISTORY AND POPULATION BIOLOGY

    Age, Size, Lifespan

    Powell (1974) showed that the annual growth cycle in P. dentatus begins in the spring and ends in the fall as the water temperature reached approximately 7 °C threshold. Flounder in North Carolina were 111 - 219 mm (4.4 - 8.6 inches) TL at the end of their first season. Maximum sizes of males collected from New York were about 600 mm (23.6 inches) TL and 2200 g (5.9 pounds), while females reached 800 mm (31.5 inches) and 5500 g (14.7 pounds) (Powell 1974).

    Summer flounder may live about 10 years (Rogers and Van Den Avyle 1983).

    Growth rates published for flounder collected outside the South Atlantic Bight were summarized by Smith et al. (1981).

    Abundance

    P. dentatus is one of the largest and most commercially valuable flounders in the western North Atlantic (Burke et al. 1991).

    Reproduction

    Adults migrate to offshore spawning grounds during the fall and winter, though some remain in estuaries year-round. Summer flounder begin a spawning migration as they near peak gonadal development. Often the oldest, largest fish migrate first each year (Morse 1981). P. dentatus spawns during late fall, winter, or early spring on or near the bottom in shelf waters ranging from 30 - 200 m deep (Rogers and Van Den Avyle 1983). Evidence indicates that P. dentatus is a serial spawner, continuously releasing mature eggs throughout the spawning season (Morse 1981; Rogers and Van Den Avyle 1983). Evidence from Wilk et al. (1980) shows that summer flounder from Middle Atlantic stocks tend to use the same spawning grounds and wintering areas each year. This pattern has not been proven for stocks in the South Atlantic Bight.

    In the Middle Atlantic Bight, the spawning cycle is strongly correlated with the cooling of coastal waters throughout fall and winter. Thus, spawning along the Atlantic coast begins along a North-South gradient, with summer flounder in the northernmost region beginning to spawn in September, and those in the southern region spawning in early spring. In the area between Virginia and North Carolina, the major spawning period for P. dentatus is from November to late January and early February (Smith 1973). From Cape Hatteras through Florida, P. dentatus begin spawning in late November to early December, and are spent by early spring.

    Embryology

    Larvae spawned offshore make their return to estuarine habitats by passive transport on nearshore and tidal currents from November through April in North Carolina, with a peak in recruitment occurring in February (Burke et al. 1991).

  4. PHYSICAL TOLERANCES

    Temperature

    Data for the Middle Atlantic Bight and Cape Hatteras areas indicate that adults spawn when bottom water temperatures are 12 - 19 °C. However, most eggs are collected when temperatures are between 18 - 19 °C. Temperatures between 5-21 °C promoted faster development of embryos and yolk-sac larvae. During development, temperatures below 11 °C were lethal to larvae, but at higher temperatures, all larvae were approximately the same length by the time the yolk-sac had been absorbed (Grimes et al. 1989).

    Temperature has a pronounced effect on growth efficiency feeding rate, and assimilation efficiency of juveniles held under laboratory conditions (Grimes et al 1989).

    Salinity

    Laboratory studies show that growth rates in P. dentatus increase with increasing salinity. Maximum growth rate occurred at salinities greater than 10, which correlates with typical environmental salinity levels during the period when young summer flounder are most abundant in estuaries (Rogers and Van Den Avyle 1983).

    Summer flounder eggs and larvae from wild populations develop in offshore waters, with late stage, premetamorphic larvae (stage 4b to 5), likely returning to estuarine habitats via passive transport on nearshore and tidal currents. Once returned to estuaries, larvae settle on the substratum and metamorphose into juveniles. In one North Carolina study, data from Burke et al. (1991) suggest that settlement in P. dentatus is influenced by substratum type. In a comparison with larvae of P. lethostigma, the southern flounder, the authors reported that though larvae of summer flounder and southern flounder both recruit into estuaries during the same period, southern flounder larvae concentrate on tidal flats near the heads of estuaries where salinity ranges from 9 - 25, and the substratum has a low sand content (4 - 50%). Conversely, summer flounder larvae settle more downstream, in the low to middle reaches of estuaries where salinity ranges from 24 - 35 and the substratum has a much higher sand content (53 - 95%). Burke et al. (1991) concluded that southern flounder settlement was more highly correlated with salinity, while summer flounder settlement was more highly correlated with substratum type.

    Other Physical Tolerances

    Dissolved Oxygen
    Effects of dissolved oxygen concentration on P. dentatus has not been investigated, but studies of the southern flounder, P. lethostigma, a close relative to P. dentatus, indicate that this species is likely to prefer water with dissolved oxygen concentrations exceeding 5.3 mg/l (Deubler and Posner 1963; Rogers and Van Den Avyle 1983).

    Environmental Contaminants
    Toxic levels of most contaminants to summer flounder have not been quantified (Rogers and Van Den Avyle 1983). However, Hall et al. (1978) showed that arsenic, copper, and zinc residues were somewhat high in summer flounder collected in the South Atlantic Bight. Mean and maximum values for mercury concentrations were below U.S. Food and Drug Administration action levels. Low levels of some polynuclear aromatic hydrocarbons were detected in summer flounder collected from the Baltimore Canyon in the Middle Atlantic Bight (Brown and Pancirov 1979; Rogers and Van Den Avyle 1983).

  5. COMMUNITY ECOLOGY

    Trophic Mode

    Adult P. dentatus are visual feeders that are adept at feeding on the bottom or in the water column (Olla et al. 1972). They are generally regarded as top or near-top predators. Though the feeding ecology of this species is not fully documented, larvae and postlarvae are thought to initially feed on zooplankton. In a Pamlico Sound study, juveniles longer than 80 mm were found to initially consume mysid shrimp. As they grew, they fed on progressively larger prey items, shifting their diets from mysids to small fish and other crustaceans. As these fish reached adulthood, the diet was again shifted toward larger fish (Rogers and Van Den Avyle 1983). Data from the South Atlantic Bight indicate that adults in estuaries and shelf waters north of Cape Hatteras feed primarily on fish and large invertebrates (Rogers and Van Den Avyle 1983).

    Burke (1995), based on differences in morphology and behavior between summer flounder and southern flounder in North Carolina, compared prey distribution and feeding ecology between the 2 species following metamorphosis to the juvenile stage. Summer flounder juveniles have generally smaller mouths, smaller, teeth, and lighter, more numerous gill rakers than do southern flounder. Feeding in the summer flounder was always preceded by active searching behavior (Burke 1995), while southern flounder tended to remain still on the bottom and wait for prey to come within striking distance (Minello et al. 1987; Burke 1995). In this study, summer flounder 20 - 60 mm SL consumed spionid polychaete worms, followed by clam siphons, mysid shrimp, calanoid copepods, the blue crab, Callinectes sapidus, and small fishes. In contrast, southern flounder primarily consumed amphipods and mysid shrimp, followed by copepods, insects, fish and invertebrate parts. Burke concluded that post-settlement differences in feeding habits developed between the 2 species, with southern flounder shifting to more mobile prey which could be attacked from below, while summer flounder continued to feed upon benthic prey organisms.

    Habitats

    Adult summer flounder spend the warmer months in nearshore shelf waters and coastal embayments (Rogers and Van Den Avyle 1983). Summer flounder eggs and larvae from wild populations develop in offshore waters, with late stage, premetamorphic larvae (stage 4b to 5), likely returning to estuarine habitats via passive transport on nearshore and tidal currents. Once returned to estuaries, larvae settle to the substratum and metamorphose into juveniles.

    In a comparative study, Burke et al. (1991) reported that larvae of both summer flounder and southern flounder recruit into estuaries during the same period, and for a time, show considerable overlap in distribution within an estuary (Burke 1995). However, segregation occurs quickly (Burke et al. 1991; Burke 1995). Premetamorphic larvae of southern flounder tend to concentrate on tidal flats in the upper reaches of estuaries where salinity ranges from 9 - 25, and the substratum consists of 4 - 45 % sand. Premetamorphic larvae from summer flounder generally move into the silt and mudflat areas in the lower and middle reaches of estuaries where salinity ranges from 24 - 35 and the substratum consists of 50 - 95 % sand (Burke et al. 1991). Burke et al. (1991) concluded that settlement in P. dentatus is most likely influenced by substratum type, while that of P. lethostigma is influenced by salinity. Capture data following segregation of the 2 species within the Newport River Estuary, North Carolina showed that summer flounder were most common on sand flats vs. mudflats in the lower estuary, while there was little difference in capture rates among southern flounder in sandy vs. muddy substrates in the upper reaches of the estuary. Data from Rogers and Van Den Avyle 1983 are in agreement with Burke et al. (1991) study, showing that juvenile summer flounder occur more frequently over sandy substrata than mud or silt bottoms in Pamlico Sound, North Carolina. They further reported that during daylight hours, summer flounder tended to occupy areas in estuaries that have submerged vegetation.

    Activity Time

    Laboratory studies and field collections indicate that summer flounder are active primarily during daylight hours (Rogers and Van Den Avyle 1983).

  6. ADDITIONAL INFORMATION

    Special Status

    Fisheries.

    Fisheries Importance

    Commercial Fishery
    P. dentatus is an important commercial and recreational fish along much of the Atlantic seaboard, but the commercial fishery is not substantial in the southernmost extent of its range (between Cape Hatteras, North Carolina and Florida). The estuaries of Pamlico Sound, North Carolina are believed to be a major nursery ground for juvenile summer flounder from the Middle Atlantic Bight (Cape Hatteras northward to Cape Cod) and South Atlantic stocks, but this is uncertain because dispersal patterns are not well understood (Rogers and Van Den Avyle 1983).

    In 1982 the Atlantic States Marine Fisheries Commission prepared a Fishery Management Plan for summer flounder which included recommendations for the best management practices for this species. Beneficial practices included regulating the annual catch and setting size limits for harvest; regulating commercial gear types; maintaining and protecting wetland habitat areas; controlling sedimentation; and controlling sources of thermal, chemical and physical pollution (Rogers and Van Den Avyle 1983). Among the adverse management practices cited in this plan were draining wetlands, marshes, ponds and lakes; dredging; wastewater assimilation and disposal; flow withdrawal of water supply; shoreline development; and construction of migration barriers (Atlantic States Marine Fisheries Commission 1987).

    Flounders of all species are harvested annually from waters in and around the Indian River Lagoon, and are especially prized by recreational anglers. However, the commercial fishery is not of particularly high value. For the years 1987 - 2001, 1.7 million pounds of flounders were harvested, with a dollar value of over 3.1 million reported in the 5 county area encompassing the IRL (Volusia, Brevard, Indian River, St. Lucie and Martin Counties). This ranks flounders nineteenth in commercial value within the IRL, and twenty-ninth in pounds harvested.

    Figure 1 below shows the dollar value of the flounder fishery to IRL counties by year. Note that all species of flounders were combined in the data presented. As shown, commercial catch ranged from a low of $77,149 in 1987 to a high of over $350,927 in 1999. Volusia County annually accounts for the largest percentage of the flounder catch with 83% in total (Figure 2), followed distantly by Brevard County, which accounts for 8% of the total. Indian River, St. Lucie and Martin Counties account for 3%, 4% and 2% of the total respectively. Note that the fishery's value brings in $125,000 - $300,000 annually to Volusia County businesses, while in all other IRL counties, the dollar value is typically less than $25,000.


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


    Figure 2. Breakdown of total flounder dollar value 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 $52,332 $16,478 $462 $4,740 $3,137 $77,149
    1988 $125,679 $24,502 $773 $4,896 $6,499 $162,349
    1989 $159,271 $0 $0 $5,312 $0 $164,583
    1990 $135,210 $20,461 $1,113 $10,947 $5,396 $173,127
    1991 $168,724 $20,692 $2,446 $22,654 $6,410 $220,926
    1992 $117,085 $16,988 $2,813 $15,816 $4,620 $157,322
    1993 $182,403 $20,647 $1,574 $11,826 $7,469 $223,919
    1994 $202,828 $15,739 $6,091 $5,041 $5,984 $235,683
    1995 $238,435 $14,654 $6,773 $5,227 $4,412 $269,501
    1996 $137,805 $7,207 $7,347 $638 $2,625 $155,622
    1997 $194,655 $20,528 $19,640 $7,254 $2,787 $244,864
    1998 $145,311 $16,449 $13,133 $14,215 $5,855 $194,963
    1999 $306,281 $25,090 $9,182 $8,772 $1,602 $350,927
    2000 $265,389 $19,629 $3,097 $13,248 $3,244 $304,607
    2001 $148,233 $14,655 $9,103 $4,789 $1,256 $178,036
    Cumulative Totals: $2,579,641 $253,719 $83,547 $135,375 $61,296 $3,113,578
    Table 1. Total dollar value of flounders to IRL counties between 1987 -2001


    Volusia Brevard Indian River St. Lucie Martin
    YEAR % Total % Total % Total % Total % Total
    1987 67.8% 21.4% 0.6% 6.1% 4.1%
    1988 77.4% 15.1% 0.5% 3.0% 4.0%
    1989 96.8% 0.0% 0.0% 3.2% 0.0%
    1990 78.1% 11.8% 0.6% 6.3% 3.1%
    1991 76.4% 9.4% 1.1% 10.3% 2.9%
    1992 74.4% 10.8% 1.8% 10.1% 2.9%
    1993 81.5% 9.2% 0.7% 5.3% 3.3%
    1994 86.1% 6.7% 2.6% 2.1% 2.5%
    1995 88.5% 5.4% 2.5% 1.9% 1.6%
    1996 88.6% 4.6% 4.7% 0.4% 1.7%
    1997 79.5% 8.4% 8.0% 3.0% 1.1%
    1998 74.5% 8.4% 6.7% 7.3% 3.0%
    1999 87.3% 7.1% 2.6% 2.5% 0.5%
    2000 87.1% 6.4% 1.0% 4.3% 1.1%
    2001 83.3% 8.2% 5.1% 2.7% 0.7%
    Table 2. By-county annual and cumulative percentages of the flounder harvest for the years 1987-2001.


    Volusia Brevard Indian River St. Lucie Martin
    Dollars $2,579,641 $253,719 $83,547 $135,375 $61,296
    % 82.9% 8.1% 2.7% 4.3% 2.0%
    Table 3. By county cumulative dollar value and percentage of total for the IRL flounders harvested from 1987 - 2001.

    Recreational Fishery
    The recreational flounder fishery in Florida accounts for 65 - 70% of the annual state-wide harvest (Florida Fish and Wildlife Conservation Commission 2004). Landings on the Gulf coast of Florida are somewhat lower than those on the East coast, averaging approximately 198,015 pounds per year. On the Atlantic coast, landings have averaged less than 300,000 pounds per year since 2001. However, catch rates on both coasts are apparently stable, and have remained so since the early 1990s. The recreational fishery was first regulated beginning in 1996, when a 10-fish bag limit and 12-inch minimum size limit was implemented.

    Based on angler survey data provided by the national Marine Fisheries Service, summer flounder are not of particular importance as a fishery within the Indian River Lagoon, with most fishes harvested in nearshore and offshore waters (Figure 4). Since 1997, the recreational harvest in the 5-county area encompassing the Indian River Lagoon has remained fairly insignificant in inland waters and the IRL, with the bulk of the catch (80.4%) being taken from nearshore waters to 3 miles offshore, and in offshore waters to 200 miles. Inland waters other than the IRL accounted for nearly 19% of the catch, while the IRL itself accounted for only 0.8% of the harvest. The entire catch of summer flounder within waters of the IRL was only 360 fishes, all of which were taken in 1999.

    The total catch of summer flounder between 1997 - 2004 was 43,001 fishes. Of note is that much of the total harvest in eastern Florida was taken in 2 anomalous years: 1998 and 2001. The 1998 catch accounts for 37% of the total harvest, with over 16,000 fishes captured in nearshore waters to 3 miles. In 2001, the bulk of the catch, 9,800 fishes, was taken in offshore waters to 200 miles. The lowest harvest was recorded in 2002, when just 352 summer flounder were reported captured. The highest harvest occurred in 1998 when 22,114 summer flounder were taken. No data were available for 2004.


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


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


    To 3 Miles To 200 Miles Other Inland IRL TOTAL
    1997 - - 808 - 808
    1998 16,032 1,729 4,353 - 22,114
    1999 - 1,866 350 360 2,576
    2000 4,441 - 995 - 5,436
    2001 690 9,804 524 11,018
    2002 - 352 - 352
    2003 - - 697 - 697
    2004 - - - - -
    Total: 21,163 13,399 8,079 360 43,001
    Table 4. Summary data for the summer flounder, Paralichthys dentatus, recreational fishery in Eastern Florida waters 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 0.0% 0.0% 100.0% 0.0%
    1998 72.5% 7.8% 19.7% 0.0%
    1999 0.0% 72.4% 13.6% 14.0%
    2000 81.7% 0.0% 18.3% 0.0%
    2001 6.3% 89.0% 4.8% 0.0%
    2002 0.0% 0.0% 100.0% 0.0%
    2003 0.0% 0.0% 100.0% 0.0%
    2004 0.0% 0.0% 0.0% 0.0%
    Table 5. By-county annual and cumulative percentages of the summer flounder 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 21,163 13,399 8,079 360
    % 49.22% 31.16% 18.79% 0.84%
    Table 6. Summary of the summer flounder 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

    Atlantic States Marine Fisheries Commission. 1987. Summer flounder. Available online: http://www.asmfc.org/species/summer-flounder. Accessed: 4 July 2016.

    Brown RA, Pancirov RJ. 1979. Polynuclear aromatic hydrocarbons in Baltimore Canyon fish. Environ Sci Technol 13: 878-879.

    Burke JS. 1995. Role of feeding and prey distribution of summer and southern flounder in selection of estuarine nursery habitats. J Fish Biol 47: 355-366.

    Burke JS, Miller JM, Hoss DE. 1991. Immigration and settlement pattern of Paralichthys dentatus and P. lethostigma in an estuarine nursery ground, North Carolina, USA. Netherlands J Sea Res 27: 393-405.

    Deubler Jr EE, Posner GS. 1963. Response of postlarval flounders, Paralicthys lethostigma, to water of low oxygen concentrations. Copeia 1963: 312-317.

    Florida Fish and Wildlife Conservation Commission. Recreational fisheries landings. Available online: http://myfwc.com/research/saltwater/fishstats/recreational-fisheries/landings. Accessed: 4 July 2016.

    Grimes BH, Huish MT, Kerby JH, Moran D. 1989. Species profiles: life histories and environmental requirements of coastal fishes and invertebrates (mid-Atlantic): summer and winter flounder. Fish and Wildlife Service. Arlington (VA).

    Minello TJ, Zimmerman RJ, Klima EF. 1987. Creation of fishery habitat in estuaries. In: Beneficial uses of dredged material: proceedings of the first interagency workshop, 7-9 October 1986, Pensacola, Florida. Final Report. 106-120.

    Morse WW. 1981. Reproduction of the summer flounder, Paralichthys dentatus (L.). J Fish Biol 19: 189-203.

    Olla BL, Samet CE, Studholme AL. 1972. Activity and feeding behavior of the summer flounder (Paralichthys dentatus) under controlled laboratory conditions. Fish Bull 70: 1127-1136.

    Powell AB. 1974. Biology of the summer flounder, Paralichthys dentatus. Pamlico Sound and adjacent waters, with comments on f. lethostigma and f. albigutta. MS Thesis. University of North Carolina, Chapel Hill (NC).

    Powell AB, Henley T. 1995. Egg and larval development of laboratory-reared gulf flounder, Paralichthys albigutta, and southern flounder, P. lethostigma (Pisces, Paralichthyidae). Fish Bull 93: 504-515.

    Rogers SG, Van Den Avyle MJ. 1983. Species profiles: life histories and environmental requirements of coastal fishes and invertebrates (South Atlantic). Atlantic Menhaden (No. FWS/OBS-82/11.11). Georgia Univ., Athens (USA). School of Forest Resources.

    Smith WG. 1973. The distribution of summer flounder, Paralichthys dentatus, eggs and larvae on the continental shelf between Cape Cod and Cape Lookout, 1965 - 66. Fish Bull 71: 527-548.

    Wilk SJ, Smith WG, Ralph DE, Sibunka J. 1980. Population structure of summer flounder between New York and Florida based on linear discriminant analysis. Trans Amer Fish Soc 109: 265-271.

Report by: K. Hill, Smithsonian Marine Station
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Page last updated: July 9, 2005

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