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Species Name:    Paralichthys dentatus
Common Name:            (Summer Flounder)



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

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


Species Name:
Paralichthys dentatus (Linnaeus, 1766)

Common Name:
The preferred common name for this species is summer flounder; however, there are many other common names used in reference to this species: fluke, plaice fish, plaice, plaise, splaice, chicken halibut, brail, turbot, flatfish, long-toothed flounder, flounder of New York and common flounder.

Species Description:
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).


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



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.



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).

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

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.

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).



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).

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
(Brown and Pancirov 1979; Rogers and Van Den Avyle 1983).



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.

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).



Special Status:

Fisheries Importance:
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
  Value Value Value Value Value Value 
YEAR ($) ($) ($) ($) ($) 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.
  % % % % %
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


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.



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
To 200 Miles Other 
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
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 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.





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